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Cable Heating - How


  1. No Title)
    by George Booth <> (Mon, 30 Nov 92)
  2. [F] Modern Aquascaping - Part 9 (Final)
    by david-at-vlsisj.uucp (David Hsu) (Tue, 27 Apr 93)
  3. [F] Modern Aquascaping - Part 9 (Final)
    by david-at-vlsisj.uucp (David Hsu) (3 May 93)
  4. Undergravel Heaters??
    by booth-at-hplvec.LVLD.HP.COM (George Booth) (Wed, 9 Jun 1993)
  5. [F][Plants] Heating coil effects - discussion
    by (Uwe Behle) (Mon, 18 Oct 1993)
  6. Re: [F] Subsstrate heating
    by (Uwe Behle) (Fri, 14 Jan 1994)
  7. [F] New plant tank
    by () (26 Apr 1994)
  8. Heating coil temperatures
    by () (31 May 1994)
  9. DIY Substrate Heater
    by vaanderi-at-benji.Colorado.EDU (Eric Vaandering) (19 Aug 1994)
  10. DIY Substrate Heater
    by (Glen W Osterhout) (Fri, 19 Aug 1994)
  11. Help needed with heating cables
    by (Shiao Y. Wang) (30 Aug 1994)
  12. [F] DIY Substrate Heating Coil Details
    by (George Booth) (7 Nov 1994)
  13. DIY Heating System Question?
    by (Glen W Osterhout) (Fri, 11 Nov 1994)
  14. [F] DIY Substrate Heating Coil Details
    by (Patrick White) (Wed, 16 Nov 94)
  15. Aquatic Plants Digest V1 #23
    by (Glen Osterhout) (Tue, 18 Apr 95)
  16. re: substrate heating
    by "Wehde, Mark B." <> (Mon, 24 Apr 1995)
  17. RE: Aquatic Plants Digest V1 #294
    by MORRISON-at-FNALV.FNAL.GOV (Thu, 7 Sep 1995)
  18. RE: Aquatic Plants Digest V2 #5
    by "Williams, Rochelle - DCSPIM" <> (Tue, 11 Jun 1996)
  19. Re:90 gallon plant tank, suggestions?
    by Don Hutton/Omnipoint <> (22 Nov 96)
  20. poor man's heating cables
    by Jim Spencer <jimsp/> (Mon, 9 Mar 1998)
  21. Need 24v Power Supply for Dupla 500 Cables
    by George Booth <booth/> (Thu, 2 Apr 1998)
  22. Substrate longevity
    by krandall/ (Tue, 20 Oct 1998)
  23. Heat gradients
    by George Booth <booth/> (Wed, 06 Jan 1999)
  24. Dupla heating cables
    by Don Hutton <dhutton/> (Wed, 23 Dec 1998)
  25. Heat gradients and UGH
    by Neil Frank <nfrank/> (Thu, 07 Jan 1999)
  26. Dupla Cables
    by "Christopher Coleman" <christopher.coleman/> (Tue, 5 Jan 1999)
  27. Cheap 24v transformers for DIY heating cables
    by BOLLING37/ (Sat, 13 Mar 1999)
  28. "Transformers" at IKEA
    by "Torsten Tiedtke" <ttiedtke/> (Wed, 24 Feb 1999)
  29. re:"Transformers" at IKEA
    by cwells <cdwells/> (Sun, 24 Jan 1999)
  30. Cables, RFUG's & flourite
    by "Thomas Barr" <tcbiii/> (Mon, 10 Jul 2000)
  31. re: Heating cables & plant growth
    by George Booth <booth/> (Thu, 6 Jul 2000)
  32. UGH Cables
    by "Schenck, Lyndle" <lschenck/> (Tue, 2 Jan 2001)
  33. Substrate cables
    by Dave Gomberg <gomberg/> (Tue, 02 Jan 2001)
  34. heating cable sources
    by Bill Wichers <billw/> (Mon, 01 Jan 2001)
  35. Thick coated wire
    by Bill Wichers <billw/> (Mon, 01 Jan 2001)
  36. RE: Duplamat 300w transformer replacement
    by "Charles Kuehnl" <ckuehnl/> (Mon, 7 May 2001)
  37. (No Title)
    by ()
  38. heating cable sources
    by Dan Resler <resler/> (Mon, 1 Jan 2001)

(No Title)

by George Booth <>
Date: Mon, 30 Nov 92


> So, what I'm interested in knowing is exactly what's IN the Dupla cables...
> How long are they?  What's the insulation made of?  Are they stiff like
> nichrome wire?  I know they use a 42v transformer... Do you know the current
> rating?  You are the only person on the net who's talked about using
> undergravel heating cables, so any info would be greatly appreciated.

Well, I didn't take the cables apart, but ...

I have a 250 watt cable in the SST and it's approx. 60 feet long.  As
far as I can tell, the insulation is silicon (I think Dupla mentions
this in the book or instruction sheet).  They aren't stiff - they are
kind of like the thick, flexible leads you find on voltmeters.  For
the U.S. systems, they use a 24 V transformer, not 42 V.  The
transformer was around 10 A (you know, like 250 W / 24 V :-).

> My plan at the moment would be to get a high-current 42v or similar surplus
> transformer, a large length of nichrome wire sheathed in silicone tubing (or
> "real" cables), controlled by one of those $15 radio shack digital
> thermometers.

Yeah, I would use the Dupla cables and set up your own controller and
transformer.  The cables use banana plugs to connect to the
transformer, so there is no problem hooking them up.  The cables are
the cheapest part of the system (~$100 depending on heat rating).
If you get some weird cables and need to replace them, you have to
completely tear the aquarium down.  Not a pleasent prospect. 

The most bizarre part of the Dupla system (cost-wise) is the "cable
anchors".  They are suction cups with little plastic arms that hold
the cables, sort of like:
     /  ______________   _____________  \     
     \O/        ______|_|_______      \O/         <-- O = cable
               /                \                 <-- suction cup
    ===========================================   <-- bottom of tank

They sell for about $2.00 each and you need around 60 for a 75 gallon
tank.  Yup, $120 for suction cups and bits of plastic!  I would think
a clever person could come up with some kind of DIY solution. 

One thing to keep in mind is the dynamics of the heating coil system.
We keep our tank at 82 F.  The coils keep the bottom of the gravel at
92 F (the top of the gravel is the same as the water temp) so there is
a good temperature gradient.  There is a lot of hysterisis in the
system.  We found that, for example, the coils will keep the water at
the set point (82 F) most of the day.  Once the MH lights come on,
they will raise the temperature 0.5 F by the evening and the coils
will turn off.  This allows the thermal mass of the gravel and tank
bottom (1/2" glass) to cool down some.  When the lights turn off, the
temperature will drop for a while until it gets below 82 F (the
controller has a 0.1 F hysterisis).  Once the coils come on, it takes
a long time for the thermal mass to heat up again, so we found that
the water temperature will continue to drop.  There is a 1 degree drop
at night due to this effect.

> Thanks for all the articles that initially got me into the hobby!
>    Erik Olson  (member, AGA.  Volunteer, Seattle Aquarium.  Member, Seattle
> Aquarium Society.  member, International Society of People who Spend over
> 1/3 their Income on Fish... darn, still doesn't even come close to the
> impressiveness you have in that new sig :) )
> ---
> Erik Olson                               (e-mail)
> University of Washington                      (e-mail)
> Cosmic Ray Lab, Phys. 405

Well, the "new sig" was actually kind of a joke - but if it works,
what the heck ...

George L. Booth                                Author, Aquarium Fish Magazine                      Member, Rainbowfish Study Group
Software Development Engineer               Member, Colorado Aquarium Society
Manufacturing Test Division            Member, Aquatic Gardener's Association
Hewlett-Packard Company                Author, Aquatic Gardener's Association
Loveland, Colorado                Founding Member, The Colorado Aquarium, Inc
         /\                     Member, The Colorado Aquarium Plant Committee
    /\  /  \/\           Chairman, The Colorado Aquarium Filtration Committee
___/  \/   /  \___  Member, The Colorado Aquarium S.E. Asia Exhibit Committee

[F] Modern Aquascaping - Part 9 (Final)

by david-at-vlsisj.uucp (David Hsu)
Date: Tue, 27 Apr 93

George Booth's excellent series of articles was extremely timely,
as we're setting up our 55g plant tank again 9 months after moving.
George's opinion on the importance of heating cables reinforces
my decision to use them, but in a different implementation ($600-
$700 mail order for cable, Duplamat and Tunze controller was just
too steep):

In article <2800334-at-hplvec.LVLD.HP.COM>, booth-at-hplvec.LVLD.HP.COM
(George Booth) writes:
|> I haven't worked out the costs yet, but I think you can get substrate
|> heating for a lot less than the cost of a pure Dupla setup.  I would
|> recommend the Dupla heating coils, since they are not that costly by
|> themselves and are very high quality.  If a heating coil should go bad,
|> you have to tear down the entire aquarium to fix it.  Not a very appealing
|> thought.  

Definitely agree--I got the 100W Dupla (7 meters) at a fish store for $45.

|> The 24v step-sown transformer can be had for a lot less than the DuplaMat
|> transformer.  This will be a big cost saving.  

Appropriately sized surplus transformer was $5, but I bought a new 10 amp,
24V Magnetek for $34--it's still 1/10 the cost of a Duplamat...

|> I have seen various temperature controllers offering in the magazines,
|> all for a lot less than the Dupla or Tunze controllers.  Extreme
|> accuracy and rapid response aren't very important since the substrate
|> coils are very slow acting (slow to warm up, slow to cool down).

Radio Shack temperature module ($19) offers hi-lo setpoints, alarm and
flasher outputs, hi-lo temp. memory.  Output can be fed into an
RS flip-flop for control with hysteresis.  I will probably get a solid
state relay for the actual power switching.

|> The last component of the Dupla setup is the cable anchors.  They
|> offer suction cups with little plastic cable holders for $2 each and
|> you need 60 or so of them.  I would think there must be some kind of
|> home-made approach that would work just a well, if not better.

I'm going to make plexiglass standoffs with notches to hold and separate
the cable (the stuff is very twisty and uncooperative).

Adding a nice box, buttons and jacks, the total cost shouldn't go over
$200.  Funny, though, I called 4 or 5 Radio Shacks before I found one
with one remaining temp. controller--they all said that demand is
extremely heavy, and that the warehouses were out of stock.  Hmmm.

[F] Modern Aquascaping - Part 9 (Final)

by david-at-vlsisj.uucp (David Hsu)
Date: 3 May 93


Some clarification on the (almost) non-Dupla cable heating system
I'm working on...

- >5A transformer:  This was hard to find--no mail order sources I have
  listed one.  Luckily, a local source (Quement Elect., San Jose) has
  the entire Magnetek line.

- Switching a 10A transformer (inductive surges frying relays, etc.):
  I want a heater, not a light show.  Will be using optoisolaters where
  applicable, and probably a Gordos G120D25 solid state relay to switch
  the power (140V, 25A, rated for "severe inductive loads".  In the
  Active Electronics catalog, 800-677-8899).  If I'm really paranoid,
  I might get an inrush limiter...

- Cable anchoring/standoffs (or, how not to mess up an obscenely
  expensive hunk of wire and electrify your tank):  My standoffs
  are 1/2"X10"X1/8" (fits 55g tank) plex. strips, glued on edge
  to a 1.25"X10"X1/8" base.  I notched the strips with a 3/16"
  router bit.  The Dupla cable is roughly 1/8" in diameter, and I
  used 1/2" chunks of slit silicon airline wrapped around the cable
  to hold the cable in the standoff notch.  Made for a nice snug
  fit, and the silicon airline should be tough enough to stand
  abrasion.  (Notes:  I made 7 standoffs, 6 notches per standoff,
  plexiglas from the $1/lb. scrap bin at TAP Plastics.  Notch
  *before* cutting the strips...

Dave Hsu

Undergravel Heaters??

by booth-at-hplvec.LVLD.HP.COM (George Booth)
Date: Wed, 9 Jun 1993

In alt.aquaria, () writes:

    Does anyone out there use substrate heating for their
    plant tanks?

Yes, we have been quite successful with a Dupla system.

    I can build the thermostat and low voltage DC supply myself, 
    but need the cables.  Where can I find them?

Daleco Master Breeder Products in Indiana carries the full Dupla line.

Daleco Master Breeder Products
3340 Land Drive
Fort Wayne, IN

phone (219) 747-7376
FAX   (219) 747-7376

I've been corresponding with a German aquarist with a lot of knowledge
on matters such as this and he suggests 10 watts per 10 liters of water
for the main heating and 1-2 watts per 10 liters for the substrate. 
This would mean a 200w heater (or a pair of 100w) for a 55 gallon tank 
with 20-40w of heating cable under the gravel. 


[F][Plants] Heating coil effects - discussion

by (Uwe Behle)
Date: Mon, 18 Oct 1993

There seems to be a lot of misconceptions about the safety of home-built
heating coils. Here are the complete instructions. Because of the trans-
former and the low voltage it is absolutely safe.

        How to construct a cheap under-gravel heater

Recently more and more reports have surfaced claiming that superior plant 
growing conditions and good algae control in an aquarium can be achieved if 
under-gravel heating coils are used.
  There are basically two competing systems on the market which both
promise good results. The first method uses a high-wattage heating coil
(0.5W/l = 100 Watt coil for 200 l tank) and is marketed mainly by Dupla.
This method requires a temperature regulator in order to limit the heat
build-up in the gravel. The coil functions as the basic source of heat.

  The other method, used by Dennerle, proposes low-wattage coils (0.1 - 0.2W/l
= 20 - 40 Watt coil for 200 l tank). In this case, additional heating by
a submersible heater is required to maintain tropical water temperatures 
(unless the room temperature is relatively high and stable). 
While Dennerle suggests and sells a temperature controller that controls 
both the main heater and the low wattage heating cable (the cable is treated 
with priority and will stay switched on as long as possible), it is not 
strictly necessary.  The low wattage makes it possible to leave the coil 
on permanently for most applications. (One exception might be non-air-
conditioned rooms, which get very hot in the summer; in that case one would 
probably need a chiller anyway).

  Anybody with some basic knowledge of electrical wiring can set up an 
under-gravel heating system, which is relatively inexpensive. Just follow 
the steps outlined below. 

WARNING: If you are not sure about your capabilities in electrical
wiring, have some knowledgeable person help you or don't do this!

1) First determine the wattage and the length of cable that you need.
A rule of thumb is 1-2W per 10 liters of water (0.4W/gal - 0.8W/gal).
For a tank of 100cm x 50cm x 50cm we have 10x5x5 = 250 l gross volume. 
Let's say we deduct 20 l for thickness of the glass and another 50 l
for substrate volume. That leaves 180 l water. We choose 2W/10 l and
thus the required heating power is 18*2 = 36 Watts.
You also need to determine the approximate length of the cable. Normally
the cable is meandered on the tank bottom like this:

------------------------------------------------------------------------   ^
|A                                                                     |   |
|++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++\   |
|                                                                   )  |
| /++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++/   |   |
|(                                                                     |
| \++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++\   |   D
|                                                                   )  |
| /++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++/   |   |
|(                                                                     |
| \+++++++++++++++++++++++++++++++++^++++++++++++++++++++++++++++++\   |   |
|                                   X                               )  |
|+++++++++++++++++++++++++++++++++++v++++++++++++++++++++++++++++++/   |   |
|B                                                                     |
------------------------------------------------------------------------   v
< -  -   -   -   -   -   -  W -   -   -   -   -   -   -   -   -   -   ->

The feeding cable to the transformer is connected at points A and B.
Of course you can choose a slightly different arrangement: have point B end 
up at the same location as point A, for example. 
The important things to watch are:

     - have your cable go the entire length of the tank.
     - make sure the spacing X between the parallel lengths of cable is
       between 5 - 10 cm (2 - 4"), not any closer or wider.
     - try to avoid having one part of the heating cable touch another part.
       Although a short under the gravel is harmless (you won't get
       zapped) is is impossible to repair without re-doing your tank.
       Only if you can't get the right size wire would I suggest
       folding the wire in half so that you effectively double the
       wire length. That should rarely ever be necessary.

The length is obviously D + n*W. n is defined as  D/X.  {(D-X)/X + 1} 
Example: tank has bottom surface area of 100cm x 50 cm. Spacing X is 7 cm;
it follows that n=50/7 = 7, length = 50 cm + 7*100 cm = 750 cm = 7.5m

2) The commonly available voltages for transformers are 6V, 9V, 12V, 15V and 
24V. Since P*R = V*V, we have the following table (P is 36W from the above
          R = V^2/P                           |for 7.5m:
   V            V^2     R/Ohms          I/A   | Ohms/m
                                              |             wire gets thinner
   6            36      1               6     | 0.133           |
   9            81      2.25            4     | 0.300           |
   12           144     4               3     | 0.533           v
In the last column we calculated the resistance/length value a wire would 
need to have if it was 7.5m long (as in our example). We did that by dividing
column 3 (R/Ohms) by 7.5 (length of cable).
Now we need to find out which AWG wire size has the appropriate resistance
per meter. The following table helps:

   AWG          Dia/mm          Ohms/m          Ohms/1000ft
   26           0.405           0.136           41.62        <--- 6V
   27           0.361           0.172           52.48
   28           0.321           0.217           66.17
   29           0.286           0.274           83.44      \
   30           0.255           0.345           105.2      / ++++++ 9V
   31           0.227           0.435           132.7
   32           0.202           0.548           167.3        <---- 12V
   33           0.180           0.692           211
   34           0.160           0.873           266

As you can see the 6V transformer would require AWG 26 wire (7.5m) and
the 12V transformer AWG 32 wire. For 9V there is not really a suitable
wire size. Keep in mind that we can tolerate some variation here. A 
value within 20% of that calculated would be fine. (Our initial rule of 
thumb called for 1 - 2W for 10 l, which is 1.5W +/- 30%.)
  It is always desirable to achieve the heating power with a low current
(= high voltage). In our 6V example 6 Amps of current were needed for 
the 36 Watts. This would require the feeding cables from the transformer 
to the heating cable to be relatively thick. For up to 10 Amps you can 
safely use AWG 13 or AWG 12.  Use a sufficient length of wire to reach 
from your aquarium substrate to the transformer.
For 12V only 3 Amps are needed. That would be the better solution IF 
AWG 32 wire is available. 
The cable insulation should be PVC or silicon and be able to withstand at 
least 80 C, better 100 C (most cables do that anyway). The cables 
(heating and feeding) must be spliced and soldered together and then 
insulated with heat shrink tubing. Silicon aquarium sealer could also be
used to insulate the bare metal from water contact. 

3) Select the transformer. There are three requirements for this.
First and most importantly the transformer must provide insulation
between the primary and secondary windings. The best type is the one that 
uses separate bobbins for primary and secondary windings. In that case there 
is no way that they could accidentally touch. 

  >> The transformer is the part your safety depends on! <<

Second, make sure the transformer will be able to handle the needed power
(36 Watts in our case). Buy a transformer that will handle a
20-30% higher wattage than you need. Otherwise it will get relatively warm.
Third, the current rating of the secondary winding must be equal to or higher 
than the current you calculated.
  Don't forget to put a fuse (slow blow) into the primary side when you wire 
everything up. The value of the fuse can be calculated: 
   I = P/120V (In our case 36W/120V = 0.3A = 300mA). 
Use a fuse with approximately twice that calculated value.

Here are examples of some prices based on German electronics mail order 
catalogs; they should be equivalent elsewhere:

AWG32 wire:             $2 for 10m
AWG12 wire:             $2.50 for 6m
heat shrink tubing:     $2 for a large assortment of all sizes
transformer 12V/4.17A:  $17
plastic enclosure       $6
small items (fuse etc.) $2
Total:                 $31.50

Under-gravel heating shows the best results if used with a substrate
like clay or tropical laterite (I have heard clay works quite well).
DON'T use anything organic (potting soil or peat).
  If you are using the low heat method you should also provide adequate
insulation for the bottom of your tank. Especially if you use a glass
tank the heat loss can be substantial. Take a 1cm thick sheet of styrofoam,
cut it to size and put it underneath the tank. This will also help eliminate
any mechanical tensions caused by an uneven surface of your tank support.

*   Bei Risiken und Nebenwirkungen essen Sie die Packungsbeilage und          
*             fressen Ihren Arzt oder Apotheker                               

NAME    Uwe Behle, HP Boeblingen Instruments Division
EMAIL (internet)\ (packet radio)
SNAIL   Hewlett-Packard GmbH, BID R&D, Herrenberger Str. 130,\
        D-71034 Boeblingen, Germany
PHONE   011-49-7031-142016 (work)
FAX     011-49-7031-143883 (work)

Re: [F] Subsstrate heating

by (Uwe Behle)
Date: Fri, 14 Jan 1994

Niels M. Sampath ( wrote:
: In article <>

: > ("Niels M. Sampath") writes:
: >
: >>re: BioPlast substrate heater
: >
: >>I did stick my finger tip over the exhaust end of the substrate tubing
: >>and it was -quite- warm when the heater was on. I dare say it is
: >
: >It would be nice if someone could actually *measure* the temperature
: >differential here.

:         Well.... how about the Dupla/Dennerle?  Anyone stick a temp. probe
:         into the gravel yet?

I changed my substrate heating from low wattage (Dennerle) to high wattage,
just to try it out. I used 100 Watt cables (for about $45) and a 24V trans-
former that I had around anyway. If I put the coils on full power (100W)
my substrate heats up to about 34 C, while my water is initially 25 C. After
a while the heat of the substrate raises the water temperature to 27 C.
I have about 190 litres of water in my tank (100x50x50 cm - glass, gravel).
The plants don't seem to mind the high substrate temperature, some Echinodorus
actually took it for a signal to start blossoming. I have to add that after
I made the change, I had problems with plant growth and some algae. I don't
know whether the difference in heating is responsible for this or not, but I
believe that the difference between high level of substrate heat (Dupla) and
low heat level (Dennerle) is very small. Before installing the 100W, I had 
used 25W cables and the tank did quite well.


NAME    Uwe Behle, HP Boeblingen Instruments Division
EMAIL (internet), (packet radio)

[F] New plant tank

by ()
Date: 26 Apr 1994
Newsgroup: rec.aquaria,alt.aquaria,sci.aquaria

Keith is having some net.trouble and asked me to post this for him ...


For the past few weeks (and possibly the next several) a crossover to a
new Usenet server system has prevented me from posting, though I can
still read the postings of others.  I like your ideas for the new tank,
and thought I might make a couple of comments (not necessarily
suggestions for your system, but just FYI).

>  We will use substrate heating but will lean more towards the Dennerle
>  school of thought - lower wattage than Dupla-style heating.  We will
>  set up the heating coils like Dan Resler and Erik Olson have done - a
>  100 w Dupla coil controlled by a light timer or variable transformer.

I have been playing with the *really* cheap version of the substrate
heating coils.  The ~30-gauge wire seems to work, but I didn't care for
idea of brackets or stand-offs holding the wire above the tank bottom.
I went to a craft store and bought a sheet of "plastic canvas", which is
a fairly stiff nylon(?) screen with mesh holes of about 1/8 inch.  You
might have seen tacky little home-made ornaments made by weaving yarn
through this stuff.  Anyway, I got a 12"x17" sheet (<$1.50) of it and
wove about 25 feet of the ~30-gauge wire though it in a comb pattern.  I
hooked up a big transformer and got 30 watts or so cooking.  The idea
was to ensure that the mesh wouldn't be adversely affected by the heat.
Well, everything went fine.  The wires got warm to the touch, but not
what I would call hot, and the mesh seemed to be completely unaffected.
This was done in open air, BTW, with very closely-spaced wires.

So, I will probably take four of the mesh sheets, sew them together with
nylon monofilament fishing line, and place the resulting mat in my 90
gallon tank over a layer of gravel.  Much more gravel will cover the
mat, of course, and laterite will be used in the lower third.  The wire
will be spaced out in an appropriate pattern to give me good coverage
and 30 to 40 watts of heat.  The wire, BTW, I got from a factory, but it
looks remarkably similar to the 30-gauge wire-wrapping stuff that is
sold in several colors (mine's yellow) by Radio Shack (I think they call
it silver-plated wire with "Kynar" insulation).  A piece of plain brown
lamp (or "zip") cord will be affixed to one corner of the mesh and
soldered to the ends of the heating coil wire.  Generous blobs of
silicone sealer should insulate the connections.  The zip cord will go
to a box containing the transformer and some fuses.  The whole system
should me cost less than $20 since I have a few transformers laying

>  What will be different about this tank will be an attempt to provide
>  more natural filtration.  ...
>  What we will do is set up the now extra 55 next to the 120 and run
>  them in parallel, like an Adey algae turf scrubber except with Real
>  Plants in lieu of problematic algae.  ...
>  The 55 would be lit at night when the main tank is off, allowing
>  plants to utilize ammonium 24 hours per day and providing high levels
>  of oxygen continuously.  ...

Like you, the idea of intentional algae propagation gives me a creepy
feeling, so I'm considering filling a large portion of a 20-30 gallon
sump with duckweed or similar to help control nitrates and/or other
wastes.  Like you, I'll probably light it at night, out of sync with the
main tank.  A small, cheap fluorescent fixture ought to keep duckweed
happy.  My only concern is the duckweed competing with the "real" plants
for fertilizer and trace elements.

If you have the time, would you mind forwarding this to the net?  I'd
like to solicit comments from the masses in case I'm overlooking
something obvious and detrimental.

Thanks much, and please keep us posted as to the progress of your new

-- Keith

| W. Keith Brummett           (614) 860-3187          AT&T, Room 3B202 |
| or,    FAX: (614) 868-4021       6200 E. Broad St. |
| attmail!wbrummett             R,DW,HAHB!          Columbus, OH 43213 |

Heating coil temperatures

by ()
Date: 31 May 1994
Newsgroup: rec.aquaria,alt.aquaria,sci.aquaria

We made some measurements on some substrate heating coil setups
recently and thought the net may be interested.  

We used a heat sensing IC, an LM344.  This device gives an output
voltage equal to the temperature in degrees Kelvin: 0 degrees C equals
273 degrees K.  Room temperature, 77 F or 25 C, is 298 K.  There is
another device, an LM34, which is proportional to degrees C, but I
couldn't find one locally.  Digikey and other electronic suppliers
carry them.

The LM34 is better since you will have better resolution with a cheap
digital voltmeter; I had to use an expensive 4 1/2 digit HP voltmeter
to make the following measurements.  With the LM344, room temp is 2.98
volts and you need a precise voltmeter to resolve tenths of a degree
(2.981, 2.983, etc).  With the LM34, I conjecture room temp is a
reading of 2.50 volts and a cheap voltmeter can easily resolve tenths
of a degree.

Thanks to Lawrence Smith ( for giving me the
details on these devices. 


We recently renovated out 100 gallon discus tank and added heating
coils to it.  We did the Dan Resler thing; used 100 watt Dupla coils
run by a commercial transformer and controlled by a light timer.

We first set the coils up with a 18v 4a transformer instead of 24v
since that's what I had laying around.  This gave us just over 50
watts of heat.  The 100 watt Dupla coil is about 22 feet long and gave
us 4 transversals of the tank with the coils spaced 3 1/2 inches
apart.  For reference, the Dupla coil anchors dictate a spacing of 
1 3/4".

The timer was set to turn on and off every hour (1 hour on, 1 off).
This caused the water temperature to rise just a tad over the setting
of the Ebo-Jaeger heaters, creating the situation of having the
substrate coils supplying most of the heat to the water and the
Ebo-Jaeger heaters being used for backup.

We measured the temperature in the 3" deep substrate after the coils
were on for 1 hour.  This is what we found:

   Water temperature                 :     29.0 C
   Top of gravel, 2 1/2" from cable  :     29.2 
   Middle of gravel, 1" from cable   :     29.5
   At the cable                      :     30.1
   At the bottom, 1/2" below cable   :     29.9
   At the bottom, between cables     :     28.6

With 50 watts of heat and 3 1/2" between cables, there is a 0.9 degree
C temperature difference from the top of the gravel to the cable and a
1.5 degree temperature gradient between cables, giving rise to
hot/cold zones.  I suppose this will create some convection currents
but it's hard to measure.


Once the 24v 5a transformer arrived, we remeasured the temperatures.
With the higher heat, we had the coils on for 1 hour and off for 2
hours.  This seemed to maintain the temperature as before.  With a 50%
duty cycle, we noticed the water temperature was getting to 29.5 C.
We need to set the Ebo-Jaegers at a lower temp and watch what the 
coils will do on their own. 

Anyway, with the 100w coils on for 1 hour, this is what we found:

   Water temperature                 :     29.2 C
   Top of gravel, 2 1/2" from cable  :     29.4 
   Middle of gravel, 1" from cable   :     30.1
   At the cable                      :     31.5
   At the bottom, 1/2" below cable   :     30.8
   At the bottom, between cables     :     28.5

With 100 watts of heat and 3 1/2" between cables, there is a 2.1
degree C temperature difference from the top of the gravel to the
cable and a 3.0 degree temperature gradient between cables, giving
rise to hot/cold zones.  I suppose this will create some convection
currents but it's hard to measure.


The 90 gallon tank we set up over 2 1/2 years ago has a complete 250
watt Dupla cable setup with a Dupla transformer and controller.  The
250 watt coil is about 60 feet long and gave us 14 transversals of the
tank with the coils spaced 1 1/4" apart.  For reference, the Dupla
coil anchors dictate a spacing of 1 3/4".  We felt the extra wattage
was needed due to a glass tank with an open top with a water temp of
82 C in a cooler room.  We didn't realize the cable would be so long. 
It still requires an extra 250 watt Ebo-Jaeger heater to maintain the 
temperature on cold winter days. 

With the 250w coils on for 1 hour, this is what we found:

   Water temperature                 :     28.0 C
   Top of gravel, 3" from cable      :     28.0 
   Top 1/3 of gravel, 2" from cable  :     38.6
   Bot. 1/3 of gravel, 1" from cable :     30.4
   Bottom, at the cable              :     33.3
   Bottom, between cables            :     33.2

With 250 watts of heat and 1 1/4" between cables, there is a 5.3
degree C temperature difference from top to bottom, but no temperature
gradient between cables (no hot/cold zones).  I suppose this will
create some convection currents but it's hard to measure.


The lower wattage setup is based on Dennerle recommendations and the
higher wattage setup is based on Dupla (sort of :-).  We know the high
substrate heat setup produces excellent results (long term stability).
We will have to wait for awhile to assess the lower wattage results.

George Booth                 | Specialist in Freshwater Plant Tank Technology     | Keeper of Discus, Angelfish and Rainbowfish

DIY Substrate Heater

by vaanderi-at-benji.Colorado.EDU (Eric Vaandering)
Date: 19 Aug 1994
Newsgroup: rec.aquaria

>I've been trying to figure a good way to keep the wire in place - I guess 
>weaving it into a grill/grate will work pretty good.  But what about that 
>chrome on your typical grill/grate could it cause toxic water ?  I suppose 
>rust might also be a problem ?  Or is that where the egg-create light grills 
>come in ? (sounds like something you would find on a chicken farm)
>George is correct - I am looking for someone with experience using regular old 
>wire for DIY substrate heater.   If anyone knows who East Coast Matt is or is 
>email address I would like to contact him

I'm just using standard 22 gauge wire.  I simply siliconed it to the 
bottom of the tank. Probably not the most efficient way, but it seems to 


 Eric Vaandering       Physics Department      University of Colorado          
                       Boulder CO 80302 
 One atom bomb can really ruin your day.                                       

DIY Substrate Heater

by (Glen W Osterhout)
Date: Fri, 19 Aug 1994
Newsgroup: rec.aquaria

In article <3308jh$>,
George Booth <> wrote:
>Erik Olson ((e-mail)) wrote:
>> Yes.  Uwe Behle, Dan Resler, myself, and now George Booth all have tried this
>> (although I think only Uwe used zip cord cables... the rest used Dupla
>> cables).
>Scott was asking about using regular ol' wire to keep costs down, which
>is what Uwe wrote about.  Most of us use the Dupla cables.  I think
>I remember one of the East Coast "Matt"s using regular wire woven 
>into egg-create light grills.  
>George Booth                         "The power of accurate observation is 
>              commonly called cynicism by those who 
>Freshwater Plant Tank Technology      have not got it" - George Bernard Shaw.

I used wire-wrap wire,  threaded through an undergravel filter,  driven by a 
12v DC switching power supply.

Help needed with heating cables

by (Shiao Y. Wang)
Date: 30 Aug 1994
Newsgroup: rec.aquaria

Mark Shewell ( wrote:
: 2.  I am going to have trouble obtaining the Dupla cables where I live. (Perth
: Australia).  Thus I will probably try to ring up a mail order company in the US
: and get them by mail order. (If they will deliver to Australia that is).  What I
: need to know is what mail order companies will sell me just the Dupla cables and
: what there address/phone number is.  It would be even better if anyone in
: Australia knows of a place I can get them through (Sydney or whatever).

In the U.S. Daleco Master Breeder Products sells Duplafrex Heat Cables.
Their address is 3340 Land Drive, Fort Wayne, Indiana 46809-1531.
219-747-7376 (phone). If you can't find a distributor in Australia, I can
call Daleco and see if they would ship overseas.

Another possibility is heating tapes sold by scientific supply houses. I
just checked in the VWR catalog and they sell heating tapes of various
types, length and width. I'm thinking about the 8 ft, 0.5 inch tape that
is completely embedded in high temp, high strength silicone rubber. It is
designed for use at 120 V. Now here is my question: if you use a lower
voltage transformer (something like 12 or 24 V), would this simply mean
less heat generated? That would be desirable since we want steady but low
level heating. 

The price of this cable, $75.00 list, seems pretty reasonable. A 150W
Duplaflex cable is $80.36. Does anyone know the length of a 150W Dupla
cable? I'm trying to get a picture of how this heater coil would be set up.

Shiao Wang
University of Southern Mississippi

[F] DIY Substrate Heating Coil Details

by (George Booth)
Date: 7 Nov 1994
Newsgroup: rec.aquaria,alt.aquaria,sci.aquaria

I have been using DIY heating coils for some months now and I thought
the net might be interested in the parts I used.  The coils are in a
100g Discus tank and a 120g Rainbow tank, both heavily planted.

This is based on the excellent DIY Heating Coil posting by Dan Resler
and Uwe Behle some months ago.

The cost for this "high quality" DIY heating coil setup is about $250.
If you use a simple light timer to control the coils instead of the
fancy controller, the cost can be reduced by $80.  Plain old wire can
also be used instead of the Dupla coils, making the "bargain basement"
cost around $50.


I purchased the Duplaflex "300" (100 watt) heating coils from Daleco
Master Breeder Products (219) 747-7376.  The cost was $116.00 and
included 30 suction-cup cable anchors.  There seems to be some
confusion at Daleco whether or not the cable come with anchors, but I
received two sets (drop shipped from J.P.Burleson) in July and they
came with anchors.  The 100 watt cable is 22' long and fits nicely in
the 100g (60"x18") and the 120g (48"x24") tanks with about a 3"
spacing between the coils.  Since the Dupla anchors are designed for a
higher heat density (closer cable spacing), I didn't use them as
directed but simply connected the cable to the anchors with nylon
cable ties.

Power Supply

The coils are designed for use with a 24v step down transformer for
safety.  This is my version of a 100 watt substrate heating coil power
supply.  No big deal, but for the electrically challenged, it's nice
to have a plan.  

Here is the parts list:

  24V 4A transformer       24.70   Signal Transformer p/n 241-8-24
                                   Inwood, NY  (516) 239-5777
  3"x3"x5" case           $ 6.99   Radio Shack  (aluminum with vents)
  panel mount fuse holder   1.99   Radio Shack
  2 amp slo-blo fuses  4-at-   1.19   Radio Shack
  LED holder           2-at-   1.99   Radio Shack
  banana jacks         2-at-   1.79   Radio Shack
  6' extension cord         1.39   Ace Hardware
  red LED                     ??   parts box
  4.3k 1/4w resistor          ??   parts box
  18 ga wire                  ??   parts box
  22 ga wire                  ??   parts box
  heat shrink tubing          ??   parts box
  grommet                     ??   ??

I made holes in one side of the chassis for the fuse-holder, the grommet
(to protect the cord) and the LED holder.  The other side had two holes 
spaced 3/4" apart for the banana jacks.  The transformer was mounted inside 
with the lugs for the primary and secondaries facing the fuseholder side. 

The extension cord was cut down to 2', saving just the plug end.
After threading it through the grommet, one lead was connected to one
primary.  The other lead was connected to one lug of the fuseholder.
The other lug was connected to the other transformer primary lug.  All
110V connections were soldered and covered by heat shrink tubing.  A
fuse was put in the fuseholder. 
One of the secondary lugs was connected to one of the banana jacks
with 18 ga wire and to one lead of the LED with 22 ga wire.  The other
secondary lug was connected to the other banana jack with 18 ga wire
and to one lead of the resistor with 22 ga wire.  The other lead of
the resistor was connected to the other LED lead with 22 ga wire.  All
connections were soldered, covered with heat shrink tubing and neatly
dressed ("arranged in a pleasing fashion").  The center tap of the 
transformer was not used. 

The result looks very professional since the case has a nice black
crackle finish.  The LED glows when the transformer is on, giving
positive feedback that something is happening.

Temperature Controller

We were using a WalMart light timer (heavy duty, 24 programming steps,
$8.97) to control the coils at first.  The discus tank (kept at 83 F)
was set for 1 hour on and 1 hour off.  The Rainbow tank (kept at 78 F)
was set for 1 hour on and 2 hours off.  We didn't feel that this was
optimum, so we purchased two UltraReef Temperature controllers from
Pet Warehouse for $89.95 each.  These are very nice units capable of
controlling 3000 watts and have a titanium ground wire on the
temperature probe (used to eliminate induced electric fields in the
tank).  It displays both the set temperature and the actual
temperatureand indicates when the heating is on.

We have the controller set to the desired temperature in the tank.  We
have two 100 watt Ebo-Jaeger heaters in each tank as a backup.  They
are set to about 1 degree F below the desired temperature.  The idea
is to have the coils on as much as possible.  If the coils can't
maintain the desired temperature, the Ebo-Jaegers will kick on and
maintain the tank to within a degree of what is desired.  To get this
effect, the control on the auxilliary heaters must be very good; I
think only the Ebo-Jaegers would work in this application.

We have found that the coils are usually on all night with the
Ebo-Jaegers occasionally coming on.  The coils are on and off most of
the day.  The lights will usually push the temperature to a few tenths
above the set point causing the coils to go off towards the end of the 
light cycle.  Since we have the lights on for five hours in the morning, 
off the four hours then on for another five hours, the coils aren't off
all the much.  

Plant growth is, of course, fantastic. 

George Booth                     "Nothing in the world is more dangerous than             than sincere ignorance and conscientious
Freshwater Plant Tank Technology         stupidity" - Martin Luther King, Jr. 

From: (George Booth)
Newsgroups: rec.aquaria,alt.aquaria,sci.aquaria
Subject: Re: [F] DIY Substrate Heating Coil Details
Followup-To: rec.aquaria,alt.aquaria,sci.aquaria
Date: 8 Nov 1994 16:56:52 GMT
Organization: Hewlett-Packard Co., Loveland, CO
Lines: 49
Message-ID: <39oakk$>
References: <39m5cr$> <39mnt0$>
X-Newsreader: TIN [version 1.2 PL1.4]
Xref: rec.aquaria:47188 alt.aquaria:30437 sci.aquaria:10828

Erik Olson ((e-mail)) wrote:
> Mine were shipped directly from J.P. Burleson about a year and some
> change ago, and they did not have anchors.  It'd be nice if they've
> just changed policy now.

I talked to Burleson about 2 months ago and he said they are including 
anchors now.  The cost of the coils+anchors when up, but the anchors' 
"cost" is now quite reasonable (at least to rich people like me).  However, 
a neophyte I am helping just ordered some from Daleco and they were
quite sure the anchors did NOT come with the coils.  They should be here
in a day or two, so we'll see. 

> >Temperature Controller
> >---------------------

> I'm a little curious about this, because I seem to have been the only
> one to NOT rig up my cable system with a timer.  Could you perhaps
> expound on what you felt was not optimum (as, of course, opposed to
> Not Optimum(tm), referring to "not costing enough to be Dupla" :).
> ie, were the cables getting too hot for the tank if left on full-blast?
> Was the 1-hour time slice just too big to be healthy for the cables?

The Dennerle book indicates that the coils should be on as much as possible
to provide as close to continuous circulation as possible.  We are at
the high end of the recommeded Dennerele range (0.1 to 0.3 watt/liter).
The timer was set to keep the water temperature from rising too much 
with the house at daytime temps and the lights on.  At night, with the
house cooler and the lights off, we felt the coils should be on longer
but didn't want to stay up all night to find the perfect timing.  And, 
besides, the house temp will change with different seasons and the whole 
concept of trying to get the right timing was just too much work.  We
have more money than time, so we sprung for the controllers. 

The coils are not hot enough to raise the temperature of the substrate
all that much.  We measured something like 2 or 3 degrees difference 
right at the cable.  In the tank with the Dupla setup (just about enough 
cable wattage to keep the tank at temperature), the gravel around the
coils will get 10 degrees warmer than the water temp. 

> It sounds like your new setup is closer to a Dupla (high heat w/controller)
> than Dennerle (low heat w/the Ebo Jaegers supplying most of the wattage).

Based on the Dennerle book, we are doing exactly what they recommend. 

George Booth                     "Nothing in the world is more dangerous than             than sincere ignorance and conscientious
Freshwater Plant Tank Technology         stupidity" - Martin Luther King, Jr. 

DIY Heating System Question?

by (Glen W Osterhout)
Date: Fri, 11 Nov 1994
Newsgroup: rec.aquaria

In article <10NOV94.12341907-at-admin3>,  <carrutherst-at-admin3> wrote:
>I have just finished building a 100 g tank with a DIY trickle filter and the
>next step in this fresh water planted tank was to be an DIY undergravel heat
>system.  I decided to go with a low wattage (24-30 watt) system so that I can
>utilize readily available 12v 3amp transformers and initially will try leaving
>it on all the time.  Will add a timer if necessary.  The problem I have run in
>to is finding suitable wire for the heater element.  I need approximately 9 m o
>of wire and a total resistance of about 5 ohms to yield the desired power and
>current with the above transformer.  AWG 32 works but the only wire in this size
>that I can find is the kind used for wrapping coils or magnets. It has a very
>thin, clear insulating coat.  Is this wire suitable?  Will it stand up t
>constant submersion?  Suggestions as to alternate wire type and source would
>be appreciated.  I have checked with local electrical and electronics suppliers
>and with the Engineering College's shop.  The smallest silicone or PVC coated
>wire they handle is 25 gauge. TIA.

If you want my advice,  I would say don't use a gauge smaller than 30.  Any
lighter gauge wire is just too fragile,  and you don't want to have to do
repairs once the tank is set up.  If the length is too much,  double it
up by twisting it.  I used 10m of 30 gauge with a 12v DC switching power
supply to generate 40 watts.  It has been operating flawlessly for about a
year now.

[F] DIY Substrate Heating Coil Details

by (Patrick White)
Date: Wed, 16 Nov 94
Newsgroup: rec.aquaria,alt.aquaria,sci.aquaria

In article <39usli$>,
Erik Olson (e-mail) wrote:
>Dan Resler writes:
>>(Erik Olson)
>>>For comparison, I've been using a variable transformer (variac) to
>>>adjust the voltage of my cables, and run it at 70-80% all the time (50-60%
>>This is a nice system and would have been my first choice except that
>>variacs are quite expensive compared to good timers. (As I recall,
>>Erik, you didn't have to buy yours, right? <grin>)

	Thinking about control, one should be able to use an ordinary heater as
a thermostat -- use it to turn a 5V signal on and off, use the 5V signal
(buffered, of course) to control a relay, use the relay to control the power
(110VAC or 12VAC) to the cable.
	If use a low-current draw signal sink (eg. FET), then the resistance
of the element in the heater could probably be ignored.

	Something like thus:

 +5V ---heater----FET---relay--- 5Vgnd
110VAC ---transformer---relay--- neutral

	I don't have time to try this, but if someone else does, I'd
be willing to give (uneducated) suggestions as to what to try if it
doesn't work right off.

>Mike Carter:
>>The timer method may be cheap, but I would think it would not provide uniform 
>>tank temperature. Why not install a simple thermostat?
>I'm guessing because a simple thermostat is still more expensive.

	I'd say a thermostat, even as simple as I have described above, is more
expensive than a simple timer.. of course, it also takes a lot less time
to regulate.

Pat White (work:, (503) 578-3463)
hang 2

Aquatic Plants Digest V1 #23

by (Glen Osterhout)
Date: Tue, 18 Apr 95

>Hmm.  I still think the wire-wrap wire is too fragile and brittle for 
>such a task, and the amount of work it's going to take you to wrap 200 
>feet of wire around the core (I assume this is some sort of rack?)
>is probably worth more than it'll cost to buy the Dupla cable.
>But I want to hear how this comes out because I haven't 
>heard any "after" stories with 100% DIY setups yet.  I wonder how 
>hard it'd be to find out where dupla gets their flexible resistive wire,
>and just invest in a spool of 100 or 1000 feet...  Or if we could 
>somehow insulate nichrome wire, it only costs a few pennies a foot at the 
>Chem supply.
>    - Erik

Here's my after story:  after more than a year my DIY UGH (12v with 10 
meters of 30 gauge wire) is still going strong.  The insulation on that
stuff is actually very tough, and as long as you are careful not to
put kinks in the wire it is not all that fragile either.

- -Glen

re: substrate heating

by "Wehde, Mark B." <>
Date: Mon, 24 Apr 1995

>I've decided on a 24V, 2A transformer, and 30 gauge wire-wrapping
>wire, both from Radio Shack.  The only major problem is that I need
>200 feet of wire to get 30 watts of power.  I'm going to do this using
>4 reels of 50-foot wire, wound in parallel on a frame built of solid
>steel-core, vinyl-insulated clothesline from my local hardware store.
>The ends of the reels will them be soldered together to connect the
>four reels in series.  The frame will be glued to a 46" x 16" piece of
>plastic carpet backing and placed at the bottom of my tank.  Add
>gravel, and I should be all set.

Wire wrap wire is a single strand and is easy to break.  It would be better 
use stranded wire ( several small strands wrapped together in an insulated
jacket).  I used stranded 150 ft of stranded 30 gauge wire, doubled it , 
it and placed it onto an eggcrate frame.

To twist wire, have someone hold the middle, place the two ends in the chuck 
a drill and turn it on.  It will take a while to twist.  Be careful when you 
release it or
it will all wrap up on you.

The two ends should be brought out of the aquarium and soldered directly to 
the transformer ( or first to a fuse).  The 30 gauge wire will get warm but 
not get too hot with 1.2 amps flowing through it.  No matter how well you 
try to seal wire ends which are in water, water will eventually leak and the 
junction will corrode.

>    As an alternative, where might we find some high-resistance, thickly-
>   insulated cable like that used by Dupla and Dennerle, but without the
>    price associated with the (100% pure unobtainium, hand-crafted by
>    Bavarian elves) german products?

I believe the wire Dupla sells is similiar to a wire we use for medical 
applications.  It is silicon coated and very flexible.  It is used for 
electrode wire for ecg, etc.  The price is $1 or $2 per foot, which makes 
the dupla wire fairly similiar in price.  It is more flex resistant than 
ordinary wire, but I don't believe it is any stronger.  If anybody cares, I 
can find the name of the company that makes it.

>Hmm.  I still think the wire-wrap wire is too fragile and brittle for
>such a task, and the amount of work it's going to take you to wrap 200
>feet of wire around the core (I assume this is some sort of rack?)
>is probably worth more than it'll cost to buy the Dupla cable.
>But I want to hear how this comes out because I haven't
>heard any "after" stories with 100% DIY setups yet.  I wonder how
>hard it'd be to find out where dupla gets their flexible resistive wire,
>and just invest in a spool of 100 or 1000 feet...  Or if we could
>somehow insulate nichrome wire, it only costs a few pennies a foot at the
>Chem supply.

I believe nichrome would have far too high of a resistance to be practical. 

If I recall it is about 1 ohm per foot.

>The only problem there might be (not sure) would be corrosion and
>the lead in the solder. The wire is probably copper too so it needs to
>be sealed up. You could use silver solder to replace the lead solder
>but this is overkill. Sealing the connection in epoxy would do it.
>Electrical tape just won't seal. Corrosion would happen where

Even epoxy will leak over time because it makes a mechanical seal only.
A better choice would be to use an acrylic cement because it will weld to 
PVC insulation jacket on the wire.  ( don't use teflon insulated wire, 
nothing will
stick to teflon)  An even better choice if you are not heating the wire too 
much is
to run the ends of the wire out of the tank.  This way you can avoid 
corrosion entirely.

RE: Aquatic Plants Digest V1 #294

Date: Thu, 7 Sep 1995

STEVEN R AMOR asked about cable for ugh with a specific resistance per unit
length.  Here is a chart for nichrome wire that I got from the mailing list
some time ago.


Gauge     ohms per cm
- ---------------------
10       .0021281
12       .0033751
14       .0054054
16       .0085116
18       .0138383
20       .0216210
22       .0346040
24       .0548088
26       .0875760
28       .1394328
30       .2214000

When I built my DIY cables for a 20gal tank I used 12 feet of 22 guage
nicrome wire enclosed in airline tubing for insulation. I attached about
6 feet of 18 guage regular wire to each end for feeders. Two feet of each
feeder wire is inside the airline tubing also.

The cable has a resistance of about 12.6 ohms and my transformer puts out
21 volts for a ugh of 35 watts (v^2/r).  

With a mechanical timer set for 1 hour on / 2 hours off, the tank has been
a steady 82-83 degrees all summer. Probably should have used a little less

Steven, did  you build your digital temperature controller?  If so do you 
have plans or drawing you could post?

Stephen Morrison

RE: Aquatic Plants Digest V2 #5

by "Williams, Rochelle - DCSPIM" <>
Date: Tue, 11 Jun 1996

Alok asked, " What are the differences between the cable convective system 
and the
cable heating system? Just the wattage? What about the price difference?
Is there one? What is Sandpoint's phone number so that I can find out
this information first hand?"

The major difference in convective vs. heating system is you must have 
supplemental heating to maintain the water at the correct temperature and 
there is no adjusting the system.  You lay the cables, cover with substrate, 
and plug it in.  Honestly, that's all there is to it!  I have no experience 
nor have even seen a tank with the Dupla, old Sandpoint, or a DIY system. 
 The price I paid was $129 plus tax at my local freshwater specialty fish 
store (The Fish Store & More in Atlanta).  I was talking to the freshwater 
plant guy who said they were doing a full techno plant show tank.  He 
offered to order an additional system for me.  I said yes since I was going 
to call Sandpoint later that week and order one.  Sandpoint has a brochure 
with all their products.  The AT&T 800 weblist site gives 800-682-6699 as 
their number.  I couldn't find the brochure last night so give them a call. 
 They were very friendly and helpful when I called back in March.

Rochelle Williams
Where it's 40-something days and counting until the 

Re:90 gallon plant tank, suggestions?

by Don Hutton/Omnipoint <>
Date: 22 Nov 96

David Cooke enquired about a source of transformers for the Dupla heating 
cables.  For my Dupla cable I used an industrial control transformer that I 
purchased from Allied, 1-800-433-5700.  The part numbers etc. are as follows:

Stock no. VA rating Price
917-1030 180  38.57
917-1040 225  49.00
917-1050 275  63.21
917-1060 320  66.79

These transfomers are 120/240 volt primary and 24 volt secondary.  The VA 
rating is roughly the same as watts for this application.  These transformers 
come with screw type terminals which makes them a little easier to use.  Note 
that there are two links which need to be changed for 120 vs. 240 volt 
operation.  I used the 320VA unit and it has been running for roughly one week 
with no problems with a 250 watt cable.  These transformers are heavy duty and 
use alot of steel to improve efficiency.

Allied will ship UPS and they take credit cards.

Don Hutton

poor man's heating cables

by Jim Spencer <jimsp/>
Date: Mon, 9 Mar 1998

Susan wrote,
>For all the DIYers:

Has anyone out there tried using the heat tape made for de-icing the
edges of house roofs in place of heating cables?  I wondered if it
might work if attached to the outside of the bottom and  used with a
rheostat.  It might help if the top of the stand had an open top, if
any maintenance was needed. 
Is this a really off the wall idea, or has anyone tried it?  
- -hoping I could learn by your experience/mistakes

While there are many schemes for heating the bottom of the aquarium,
they are not going to have the same effect as heating cables in the
substrate. In theory the heating cables create microcurrents which
help move nutrients throughout the substrate.

DIY heating cables using ordinary wire are very easy to build and are
inexpensive. I put mine in a year ago and it is still working fine.
The following is the post I made at that time describing my system.

For about $25 I recently installed a simple DIY substrate heating
system in my 55g tank based on the article by Dan Resler and Uwe
Behle.  Without the cable on my substrate runs 1 to 2F lower than the
water temperature.  With the cables on 50% of the time the substrate
midway between the cables runs 1F higher than the water temperature.
At 100% it is about 2-3 F higher

I used a 5amp, 12 volt transformer that I bought from All Electronics
( for $11.  If you are uncomfortable with
wiring a transformer you could use a power supply for 12V outdoor
lighting which you can buy for about $40.  Just make sure it is rated
for 50W or more.

For wire I used #30 single strand WW wire which you can buy at Radio
Shack for about $3.  One post  on DIY heating systems suggest that
this wire would be too fragile to use - that is simply not true.  This
wire is very ductile and is designed to be wrapped tightly around a
.1" square post.  There is no way you are going to kink and
accidentally break this wire.

For a support system I used 1/2" pvc pipe cut into 1/2" lengths.  Half
way up on these I cut slots about halfway through.  Using a silicon
glue I tacked these on end on the bottom of the tank in 4 rows of  8
supports.  I alternated the slots facing towards the front of the tank
and then the back of the tank.  The slots on the end posts faced the
ends of the tank.  If you get the slots facing right you can create a 
continuous weaving pattern as long as you have an even number of posts
in each row.  Starting in the back of the tank go along the row
weaving the wire around the posts.  When you reach the last post in
the front row simply go around it and retrace you path to the

The ends of this wire are soldered to a heavier lead-in wire.  I made
this connection so it would be inside the tank.  I sealed the
connection first with heat shrink tubing and then with two coats of a
silicon sealant.  The wire doesn't get real hot so you could make the
connection outside the tank.  I put connectors on the lead-in wires so
I could disconnect them from the power supply.  I used a simple timing
circuit and relay to cycle the cables off and on(10min on--  0 to
10min off).  You could use a timer with 24 off or on cycles as Resler
and Behle did.  

I ended up with a resistance of 3.8 ohms or 38 watts for the system.
My wire length  was about 32' long.  As long as you keep the total
length somewhere in that ball park you should be OK.

Jim Spencer
Sayre, PA

Need 24v Power Supply for Dupla 500 Cables

by George Booth <booth/>
Date: Thu, 2 Apr 1998

>Date: Thu, 2 Apr 1998 10:44:37 -0500
>From: "Tom Brennan" <>
>I am setting up a new 90g tank and will be purchasing the DUPLAFLEX 500
>HEATING CABLE 150 WATT 24 VOLT. Does anyone have a good source for a 24v
>power supply to be used with Dupla 500 cables ? I do not want to pay the
>outrageous price for the Duplamat 250w/24v power supply.
>George B. are you still assembling them ? If so let me know.

Nope, sorry, that was too much work for too little money.  I charged $70 for a 
100w supply and $100 for a 200w supply.  Here are the ingredients:

4A 24V transformer  (Use 2 in parallel for 200w) 
Part Num 241-8-24  $24.70      
Signal Transformer Co.
500 Bayview Ave. 
Inwood, NY 11696
(516) 239-5777

Note: you have to lie and pretend you are a "business" to buy from them, so the 
ethically pure will have to look elsewhere. This is a good transformer that 
seems under rated for current. It runs much cooler than a "5A" transformer from 
All Electronics ($15). Allied Electronics also has a broad range of 

Perforated metal case, 6"x4"x5"  $18.01  
P/N L176-ND $18.01
(800) 344-4539

Banana jacks, fuse, fuseholder, power indicator LED, LED holder, 2.4k ohm 
resistor, rubber feet, power cord - Radio Shack, ~$15

Drills, reamer, soldering iron, solder, wire, heat shrink tubing and bandaids 
supplied by the assembler. 

Good luck,

Substrate longevity

by krandall/
Date: Tue, 20 Oct 1998

Bill Lynn wrote:

>For what it's worth, I set up my first Dupla tank about 88-89, the tank
(350L) has
>been set up in it's current position since August 1990 with Dupla cables,
>transformer and controller. I have not had any substrate problems ever. I
>George mentioned he vaccuums his substrate ( the top layer)
>is something I do not do. The only time a disturbance occurs is thinning the
>plants (especially eh giant Val.)

I wasn't in any way suggesting that a tank with Dupla cables WASN'T stable
long term... I would expect it to be.  It's just that I've seen excellent
long term stability in tanks without cables as well.  The limiting factor
in my experience has been the substrate becoming root bound.  If you're
growing a lot of plants in a confined space, it's going to happen sooner or
later.  There have been times when I've found that I can no longer even
work my fingers into the substrate of a tank through the root mass.

IMO. there are two ways of handling it.  You can get the whole thing
completely root bound, in which case, you make such a huge mess pulling
everything up for division that you might as well start over (been there,
done that<g>) or you can periodically pull up and divide just a section of
the tank at a time.  Claus Christensen suggests gravel vac'ing the area at
that time.  He says that plenty of laterite gets left behind.  But even if
you don't just pulling stuff out by the roots decompacts that area.  I
suspect that the root parts that get left behind just rot and turn into
plant food.

I may be wrong, and, George, please correct me if I am!<g>  But my
impression from watching George's video is that he does a fair amount of
uprooting when he does his regular maintenance.  I suspect this is how he
avoids the problem of root bound substrates.

Karen Randall
Aquatic Gardeners Association

Heat gradients

by George Booth <booth/>
Date: Wed, 06 Jan 1999

>From: "James Purchase" <> 
>Date: Wed, 6 Jan 1999 12:21:11 -0500 
>Mr. Booth, please get your thermometer out and let us know what kind of
>heating gradient is being produced in the substrates of your tanks by the
>Dupla cables.

Mr. Booth?? Well, my Dad doesn't know jack about heating cables but perhaps
I, humble George, can be of some assistance. 

I was surprised to find a wealth of information about heating coils in The
Krib! ;-)

[url deleted - editor]

Here is one of many archived articles that I found, reproduced for
your convenience. I've also added a bit at the end to bring closure 
to the information.

Heating coil temperatures
by George Booth 
Date: 31 May 1994 

[... body deleted - it's <a href="#7">elsewhere</a> in this file -- editor]

Back to the present (1/6/99). The "lower wattage" results were NOT very 
impressive. We had algae and growth problems in the lower wattage tanks
after about 1 year, just as we had in the "Almost Optimum Aquarium" a few 
years before (plain gravel and laterite, NO heating coils).
We had to tear down all the aquariums in May of 1996 for home remodeling and 
redid them all with "high wattage" cables. The two 100 gallon tanks got 150w 
coils (Rainbowfish tank kept at 76F) and 200w coils (Discus tank kept at 82F).
We scrapped the 90 gallon SST and picked the best equipment to set up the 
120 gallon Rainbowfish tank. It received the 250w coils and is kept at 76F.   

All the tanks have been doing great since they were redone. I would recommend 
the higher wattage scheme over the lower wattage scheme based on our non-
scientific observations.

George Booth, Ft. Collins, Colorado (

Dupla heating cables

by Don Hutton <dhutton/>
Date: Wed, 23 Dec 1998

Justin Collins aka Mortimer Snerd asked about the anchors for Dupla
heating cables.  The anchors come with the cables now.  They starting
including them a couple of years ago.


Heat gradients and UGH

by Neil Frank <nfrank/>
Date: Thu, 07 Jan 1999

For the last 10 years, I have listened to the discussions about heating
cables, convective currents and the problems of "cold feet" of plants.
(those discussions even precede the APD<g>).  Several times I have
considered installing cables in one of my tanks. The closest I came was a
40 gallon tank using the Randall/Christensen UG plate, lift tubes and 7.5
watt heaters. After a year, I tore that tank down because I did not see a
noticeable difference. (anyone want 2 goldfish bowl heaters?) <g>. I still
would love to try heating cables -- to see if my plant growth can be
improved (hard to believe, but possible<g>). It could also help with
long-term tank stability and algae avoidance, but I am not disciplined
enough to use daily fertilizer, so my occasional screwups and neglect would
interfere with any such long-term experiment. I even have a brand new
commercial set with a transformer for a 40-50 gallon tank in one of my
closets. The real reason for not ever trying cables, however,  is that I
live in the South and during the summer, it is just TOO DAMN HOT. My tank
room stays several degrees warmer than the rest of the house, and the tanks
on the top rack can be in the mid to high 80's. I can't afford to have more
heat in those tanks. I have talked to some UGH beleivers who have installed
chillers, just to allow the use of UGH. To me that is an expense I can't
yet justify. Other people have suggested discontinuing it during the summer
which is a non-starter or running it for as little as 1-hr per day (this is
what some people told me about in Taiwan). From George's experience, I do
not doubt that UGH is useful and the right amount of heat is important. [I
would like to hear more if it helps with some plants more than others.]

Over the years I have actually been using another method to keep my
substrates warm. I have mentioned this before and it may already be in  the
FAQ, but it is easier to waste some more bandwidth that take the minute to
look for it <g>. First approach: I use 1/2 inch thermax insulation board
under the tank. I also use it on the back. THose are the 2 biggests
surfaces for heat loss, and this approach can save heating bucks in the
winter.  My tanks are on open metal frames, so this is easy to install
after the tank is in place... but it can also be done on any stand....
something people may do anyway to help cushion a large tank. The second and
probably more important approach: I have some plant tanks sitting directly
over the lighting  of another tank. The bulbs are generating heat which is
directly heating the substrate. I have never measured gradients, but it HAS
TO make the substrate warmer. So maybe I have some sort of UGH heating on
some of my tanks?? However, I don't have UGH or even insulation on other
tanks, and I am not dissapointed in those results either. As a footnote,
let me say that Takashi Amano does not use UGH.... at least he did not in
1995/6. He personally told me that his stainless steel undergravel plate
was designed only for aesthetic purposes - to assist with terracing AND to
conceal heaters. I took one home as a souvenier along with some neat
Japanese heating elements which use external thermostats. All are still in
their boxes. <g>. Other Amano-like aquatic plant fanciers in Japan also do
not use UGH. In fact one, does not use any heat and allows the temps in his
tanks to cycle up and down  (as in nature). Go figure <g>.

So the bottom line is that while UGH very well may make a difference (and
may give the techno-geeks a lot of pleasure and something to write about on
the APD) it would be the VERY LAST THING I would consider adding to a
setup... especially if it was my first large plant tank. To the newbies and
others without a lot of extra cash: you can have very nice success without


Dupla Cables

by "Christopher Coleman" <christopher.coleman/>
Date: Tue, 5 Jan 1999

George Booth wrote:

> I presented my HYPOTHESIS that heating cables produced
> convention currents which caused nutrient laden water to be pulled
> into the substrate where the nutrients were attracted to the negatively
> charged binding sites provided by laterite. Thus stabilized, the
> nutrients were available to plant roots for adsorption. This system
> is also HYPOTHESIZED to maintain a sufficiently (not overly) fertile
> substrate by constantly replacing the nutrients adsorbed by the plants,
> thus avoiding long-lasting and well documented problems caused by
> starting with an overly and usually poorly controlled "fertile" substrate.

Recently I received some Dennerle which make the "Boden-Fluter" heating
system (not available in US) available in various wattages (100 watt is
recommended for 300-1000L tanks).

What I found interesting is their reasoning, some of it also consistant with
1) By warming the substrate, increased matabolic rates of micro-organisms
    within the substrate encourage anaerobic condition through their
    (increased) consumption of oxygen
2)  In their overall substrate strategy (rich 'mineral' bottom later
followed by
    gravel), the heating coils are supposed to move the nutrients from the
    lower layer to the gravel. The theory is that this mimics tropical
    where the lower depth soils are richer in humus and the nutrients in the
    humus are delivered to the upper soil layers by gentle water movement.
    Thus the cable mechanism is to support convection based nutrient
    mixing between the different layers of their substrate.

I don't see any mention in their literature about what type of temperature
they are attemptng to produce.

Christopher Coleman

Cheap 24v transformers for DIY heating cables

Date: Sat, 13 Mar 1999

Hello all,

     This is off subject but I have just run across some info that DIY'ers
should find
helpful.  For those of you who are looking for the best price on 24 volt
for use with Dupla heating cables, I believe I have found the cheapest source.
Hosfelt Electronics:  1-800-524-6464.  Request a free catalog.  
     PN# 56-385 is a toroidal transformer rated at 24 VAC @ 6.2 Amps. Price:
Two of these could be purchased for $30 and wired in parallel for a 24 volt,
12.4 amp supply to power even the highest wattage Dupla heating cables.  The
Dupla 1000 (250 watt) heating cable draws about 10.4 amps so the above combo
would easily handle this load.  Smaller cables, such as 100 watts, could be
used with
a single 6.2 amp transformer without overheating it.  
     A temperature controller (the kind with the separate probe) could then be
purchased for about $35.00 to complete the project.  

I hope this helps someone,

"Transformers" at IKEA

by "Torsten Tiedtke" <ttiedtke/>
Date: Wed, 24 Feb 1999

Chris Wells mentioned that he found some "transformers" at IKEA 
which may be useful for undergravel heating setups...

Caution should be used when using power supplies intended for 
low-voltage halogen lighting as many of these supplies aren't actual 
transformers, but in fact are non-isolated switching power supplies. 
 Manufacturers are moving to switching power supplies to keep the 
size and weight down and to provide efficiencies as high as 98%.  
The danger is that many of these systems aren't isolated from your 
house mains and could pose an electrocution hazzard.

The best way to determine if the lighting supply is a transformer or 
a switching power supply is by it's size and weight.  Transformers 
are heavy and large (several pounds for a 200W unit), and 
switching supplies are compact and quite light (usually much less 
than one pound and smaller than a PC mouse in size)...

Have fun!

(in sunny Lynden ON)

re:"Transformers" at IKEA

by cwells <cdwells/>
Date: Sun, 24 Jan 1999

ate: Wed, 24 Feb 1999 09:42:52 -0500
From: "Torsten Tiedtke" <>
Subject: "Transformers" at IKEA

Chris Wells mentioned that he found some "transformers" at IKEA
which may be useful for undergravel heating setups...

Caution should be used when using power supplies intended for
low-voltage halogen lighting as many of these supplies aren't actual
transformers, but in fact are non-isolated switching power supplies.

Yes I agree - Caution is the key word
When I posted my reference I thought perhaps I should give a lecture on
safety too but assumed that those who are into DIY tinkering with
electricity and subscribe to this list have heard all about transformers
and the like.   Perhaps that was a bad assumption.   The units at IKEA i
talked about are transformers but there suitability is not assured
without some deeper inspection.  The units I reviewed had the
transformer exposed from the back of the cover and it was clear to see
the base construction and since the covering tape was clear I could see
the separation of circuits so on the surface they do look nice.
European safety standards would not allow the secondary circuit to be
common as in an autotransform, with the primary and then exposed to the
user.  IKEA most likely also has self contained units like the ones
Torsten refered too so one must know the difference!

If I were to pursue this further I would electrically test to see if the
primary and secondary were isolated with a ohm meter and regardless of
construction I would always fuse the primary, use a ground wire in the
tank and a Ground Fault Interupter circuit as extra protection.  IF YOU
get some help or buy an assured safe system that does not need to be
wired.  If you want to learn more I would suggest checking out the topic

Chris Wells

Cables, RFUG's & flourite

by "Thomas Barr" <tcbiii/>
Date: Mon, 10 Jul 2000

James wrote:
>In all of the pondering that has gone on over the years on the subject of
>substrate heat, very little attention has been paid to the fact that unless
>ambient room temperature is relatively low, the heating coils/pads/whatever
>will rarely, if ever be "on".

George responded to this as a "Ayep" also but went on to say that to be
truly high tech you should have air conditioning in your house essentially
going all the way with the high-tech approach<g>. My question to George: Do
you have a Dupla air conditioner on your house<G>?

1) This is the biggest bone I have to pick with cables. In order to work
""consistently"" the ambient temp needs to be a cool stable rate(like George
and Karla's place). Otherwise you have varying flows from too much to too
little going through the substrate depending on ambient temp. This always
bugged me. Maybe I can come over and set up my tank at George's? Please?

2)Cost is another bone I have to pick with cables. I built my own and they
worked as well as the Dupla and Sandpoint models IMO for peanuts. They
didn't look as nice but they preformed IMO the same. Folks should be very
careful building these. If your not sure about it: don't try this.

3)Simplicity is yet another bone I have to pick with cables. The flourite
method is the simplest method there is. It will not wear out or break ever.
No adding two different things in layers. No old nutrient poor substrates.
No worries that the substrate might be to blame for poor growth. Nothing to
plug in (the wall sockets have enough things plugged into them already). No
wearing out. No over/under dosing something. A no brainer. 

4) Aquascaping..........ahhhh forgot about that one didn't you? Cables and
RFUG require the same depth to work as do most other layering substrates and
keeping things layered properly over time can prove very difficult. I can
keep my gravel level down to 1/2 inch in front and 6-7 inches in back. With
cables? Yes you could but you would have to pull the cables back from the
Front edge. Using most sands and gravels this will not last long. Flourite
of all the substrates out there moves around the least. It stays put. **The
usefulness of the same depth is quite debatable using cables I admit.** Some
of the areas are shallow and some are deep & these pose little issue for
currents......if you can keep them consistent. That's why I went back to the
RFUG's. At least things were all the same in the substrate and with flourite
also this is the case. A nice homogenous substrate is a nice thing<g> for
aquascaping and terracing-sloping that doesn't move. Amano has some plates
that sort of may help this out keeping the the substrate from shifting.

5) replanting/trimming/hacking/attacking/disturbing the substrate. Try doing
this with Dupla laterite (I think it should be called "Dupla dust") and
sand. Or a nice soil or peat tank if you have good growth were you need to
remove lots of plants sometime/weekly etc. It can be done but care is
certainly needed IMO. I don't worry with the flourite. The cables get pulled
up when replanting many times due to roots being entangled in them so the
level they are placed in shifts and moves around also. I can push them back
down some (if I see it..... and notice it) but they do move somewhat over
time and use. I'm much too aggressive to take this much care when I
prune/hack n attack my tanks to wish to deal with this.

Germans may use them. Many Dutch tanks don't. Amano and many others have had
super tanks without them. I have had better success without them. 

There are many methods for a substrate involving flow but I think overall it
makes little difference. All of them work and can do well. So why not use
the simplest method? I really liked the RFUG and the cables. I have used all
three methods for several years with many different species of plants. 

Of the three general types of substrates only one doesn't have many trade

1) Hi-flow(RFUG's)-not much nutrients in the substrate, good for high fish
loads, trouble adding jobes sticks etc to it. Another thing to set up in the

2) Low Flow(cables)-cost lots (see above for more) don't have even flows due
to temps variations.

3) No flow (osmosis) soil, flourite, peat, sand etc..........

Heating pads, other outside heat devices seemed to do well. Hard to say due
to the ambient temp affecting things again. Cables did do better than these
devices FWIW IMO.

Soil and or peat tanks do well for a more low tech approach as does
flourite. Beyond this, I find extremely hard to find a good reason why I
would use something other than the flourite on a high tech/low tech tank. If
your going to set up a new tank that is...........if something is all set up
now would I tear it down? I doubt it. I think you can add things to the
substrate and or the water column dosing to get your balance and levels back
up to snuff.
Tom Barr   


re: Heating cables & plant growth

by George Booth <booth/>
Date: Thu, 6 Jul 2000

HooHah! Another one!

>From: Dwight <>
>Date: Tue, 04 Jul 2000 05:26:28 -0400
>This one is directed to those who use substrate heating cables.  I've
>noticed a growth tendency of some planted tanks with 10-15 different
>species to suddenly slow down and STOP!  Usually after being in opperation
>for over a year.  Nurient supplimentation has a negligable effect, Bulbs
>still bright enough to grow glossostigma, water changes reinstituted.
>Always had Co2 and still does.  No algae.  But the tank will only return to
>a tiny fraction of its former productivity.  Assuming all of the above were
>done correctly; has anyone had this experience?

Bingo. We had an "Almost Optimum Aquarium" (everything but heating coils) set up 
for a few years and experienced the same symptoms after 18 months.  Besides 
slower growth we also began to have algae problems (higher temperature discus 
tank). Vacuuming gravel, replanting, etc would help for a short time but nothing 
brought it back to its original state. 

A year after we started the AOA, we did a fully Optimum Aquarium with high 
wattage heating cables (250 watt Dupla cables in a 90 gallon tank).  This tank 
was super productive and perfectly stable for over 4 years. 

>Has anyone had this experience while using electric heating cables (the
>REAL ones not the "hot water" ones)?  

Interestingly enough, we tore the AOA tank down after two years and installed 
"low wattage" cables. We used Dupla 100 watt cables in a 100 gallon tank (again, 
higher temp discus tank). That worked OK for awhile but then began to exhibit 
the same problems. 

>If you have heating cables, have you
>ever been able to maintain vigorous growth indefinately w/o a major
>substrate overhaul?

In 1995, we remodeled the house and had to tear down and resetup three large 
tanks.  At that time, we put 200 watt cables in the discus tank, 150 watt cables 
in another 100 gallon tank (lower temp for Rainbows) and moved the 250 watt 
cables to a new 120 galllon tank.  All three tanks have been running perfectly 
since then (just about 5 years now). 

Lesson: You need a certain heat density in the substrate to be effective and 
that will vary with ambient water temperature.  From our experience, 20-25 watts 
per square foot of substrate area seems about right (use the higher end for 
warmer tanks). 

For more details on our experience, check out the "Super Show Tank" articles 
archived in The Krib.  The part summarizing our experience with heating coils 
and longevity is at
... or something like that. 

George Booth in Ft. Collins, Colorado ( 

UGH Cables

by "Schenck, Lyndle" <lschenck/>
Date: Tue, 2 Jan 2001

>I'd be careful with the tape. Most of the insulating tapes I have used
don't hold up well -- especially when wet. Maybe the silicone "stretchy"
tape would be OK. I have thought about heat shrink but decided it was too
much work. My personal solution is to just be a bit careful. The Teflon
stuff holds up pretty well as long as it doesn't get smashed by things. A
lot of the plastic dips (like plastidip) are water permeable over time.
Probably the best coating would be a thick waterproofing paint but there is
no telling what it might leech into the water. -Bill 
I agree with Bill.  I used Teflon-coated wire-wrap wire for my cables.
After 2 1/2 years of use they were retired after a move but are still in
good shape.  Unfortunately, finding 30g Teflon-coated wire wrap was
difficult even in 1995.
I was concerned about the thin gauge and the long length of cable required
for a typical 70 gal.  I solved this by wrapping the 30g wire around a piece
of 10g insulated stranded copper wire (yes it takes a while!).  To hold
everything in place I coated the whole length with silicone sealant.  The
result is a cable that closely approximates the length and diameter of the
commercial cables.  This makes installation much easier. 
 If anyone wants details please contact me off-the list.  This topic gets
beaten to death about once a year.   
BTW .  I installed the AZOO cables on my latest 180 gal tank and I couldn't
be more pleased.  These cables are at lease as insulated as the heaters and
power heads we already use.  And the price is right!
Lyndle Schenck

Substrate cables

by Dave Gomberg <gomberg/>
Date: Tue, 02 Jan 2001

At 03:48 PM 1/2/01 -0500, Lyndle Schenck wrote:
>A good source for transformers are at home improvement stores like Home
>Depot.  They sell low voltage outdoor lighting transformers with built-in
>timers that are cheaper than you can build them yourself.

Be very very careful.   Most cheap transformers are connected to one side 
of the line on the secondary side to save money (often called 
autotransformers).  There is nothing wrong with this design if you wire it 
up correctly and use a GFI to be doubly safe.  If you screw up, they carry 
you out in a box when something goes wrong (or worse yet, one of your 
kids).  Be triply sure you know what you are doing and that you did it right.

- --
Dave Gomberg, San Francisco  
NEW Planted Aquaria Magazine:
- -----------------------------------------------------------------

heating cable sources

by Bill Wichers <billw/>
Date: Mon, 01 Jan 2001

 >Our resident APD wire expert (who also will chime in if he wants)
 >thinks Dupla probably special orders the stuff. A minimum run would
 >involve many hundreds of feet with the bottom line having 4 digits.

That would be me :-) Yes, I do think Dupla has their cable specially made. 
It is a heavy-walled silicone-insulated wire similar to UL Style #3239 
(high voltage silicone wire), but with a resistive element inside that 
looks like nichrome and some nylon/spectra (not sure which) fibers 
presumably to prevent stretching from breaking the conductor. I haven't 
been able to find it, and my distributor who was looking for it is going 
out of business (stock tip: sell Anicom while you can ;-) My rep is moving 
to a new company though so the search continues...

If there was interest I would consider a special run from one of the custom 
wire manufacturers, but the minimum order is about 50 *thousand* feet. 
That's a *lot* of tanks. One could probably outfit even Dupla for a while 
with that much.

For now I have been recommending Teflon-insulated (PTFE) wire since it will 
not absorb water and will not deteriorate if immersed over a long period of 
time. It also handles very high temperatures (200+ ÂșC) OK which is a 
definite plus in this application. It unfortunately has thin insulated in 
most cases, so you have to be careful with it. Specifying 1000v wire will 
get a bit thicker insulation, but not much. You can get it in small 
quantities from Mendelson Electronics in Dayton OH ( in 
26, 24, and 18 awg. Dan's source is but has a 
$100 minimum (am I right here Dan?).

Power supplies are easy to build with a transformer and some fuses. Lots of 
DIY info is available on the Krib if you are looking to construct your own 


Thick coated wire

by Bill Wichers <billw/>
Date: Mon, 01 Jan 2001

>I found the right sized wire as well but it did not have the thick
>insulation I wanted. So I simply added insulating tape around this till I
>got a nice firm thickness. This solved the problem and worked the best. I
>think they have a dip coating that will do this as well.

I'd be careful with the tape. Most of the insulating tapes I have used 
don't hold up well -- especially when wet. Maybe the silicone "stretchy" 
tape would be OK. I have thought about heat shrink but decided it was too 
much work. My personal solution is to just be a bit careful. The teflon 
stuff holds up pretty well as long as it doesn't get smashed by things.

A lot of the plastic dips (like plastidip) are water permeable over time. 
Probably the best coating would be a thick waterproofing paint but there is 
no telling what it might leech into the water.


RE: Duplamat 300w transformer replacement

by "Charles Kuehnl" <ckuehnl/>
Date: Mon, 7 May 2001

Jon Wilson wrote:
>Subject: Duplamat 300w transformer replacement

>I realize this is a long shot, but my Dupla 300w transformer died this
weekend. I have been scouring the net and my local electronics places
looking for a replacement. After reading all the FAQs on DIY cable heat, it
seemed that I should be able to make my own replacement, but I can't find a
24v 12.5A transformer anywhere.

>As a sanity check, I'm hoping someone more electronically inclined than I
can make sure I am looking for the right thing and/or point out a source
that I have overlooked.

>The Dupla transformer says:
Primary 115V 50-60Hz, 2.9A
Secondary 24V Max, 12.5A

>If I had to, I'd be willing to spend the $270 for another Duplamat 300
transformer, but I can't find anyone selling them in the US either. (You'd
think they'd last more than 3 years at that price:)

>Any clues would be appreciated.

>Jon Wilson

The new Dupla importer is Hawaiian Marine Imports.  They are also the Eheim
importer.  Phone them at 800-993-4346 or or  They are just got started with the Dupla stuff at
the first of the year and are still learning about it.  Some of the product
will be imported and some will not, particularly the foods (mad cow).  If
the demand is there I would imagine that all the product line will be
available eventually.

(No Title)


If you decide to make your own, I want say that I am not an expert in this
stuff but I studied the communications and controls end of EE.  I remember a
little about transformers (though I sure studied them) so consult with the
manufacturer before you buy.  They should help you make a good decision.  Be
careful - electricity can be hazardous.  I worked primarily with lower power
control circuits but I still got burned pretty good a few times, even after
working with it for years.  My pride usually suffered the worst injury but I
often had a little burn on a finger that reminded me every time I picked
something up for the next couple of weeks.  Just last week I watched my
electrician zap himself working on an outlet in the backyard.  And don't
forget what happened to George Booth a year ago the first of last month.  As
I recall (I have a couple of small children so my mind has gotten feeble :))
it only takes about 250mA (1/4 Amp) to electrocute you.  Anything above that
and you may be held to the circuit.

First, you will want a transformer with a 5 to 1 turns ratio to step down
the voltage.  The Dupla cables run on 24V and the power outlet is 120V
(120/24 = 5).  Second, make sure the transformer is capable of handling the
power.  You mentioned 300W.  You might also tell them the primary and
secondary specs from the Dupla transformer.  Third, I would imagine that you
would want to find a transformer where the primary and secondary windings
are completely isolated physically.  In the event of a short on either side
(primary or secondary) the insulating material could melt away allowing the
conductors in one of the windings to make contact.  If the primary (connects
to the wall outlet) and secondary (runs into the tank) coils are physically
touching I would almost guarantee that a short or some other melt down would
bypass the electromagnetic coupling of the primary and secondary windings
and you might end up with primary voltage in your tank.  This would be sort
of like cutting a cord off an appliance, sticking the cut end in your tank
and plugging the other end in and outlet.  Needless to say, don't try this
at home kiddies :)

If you make it yourself, you will need electrical connectors for the Dupla
cables (I think they are banana plugs) and you will have to wire the primary
to a power cord.  You might also want to consider potting it in a proper
waterproof housing and an indicator light to see when its on (depending upon
your control scheme).

IMHO, I would check with Hawaiian Marine first.  I do not know what they
intend to sell them for, but if you can handle the price (it may be cheap
for all I know) it would save a lot of time and it would be done correctly.
I sort of am the type who would prefer to let someone else do it, mostly
because I don't have the time to hunt down all the stuff to build it and
make it look nice.  I used to R&D and manufacture electrical stuff and I
have had enough messing with potting compounds and the cleanup to last a
lifetime or two.  That sort of adds to my off-the-shelf bias too.

Good luck!


heating cable sources

by Dan Resler <resler/>
Date: Mon, 1 Jan 2001

On Sun, Dec 31, 2000 at 04:51:20PM -0700, George Booth wrote:
> One other option is DIY. 

Yes indeed.

>Another APD-ite (who will chime in if he wants)

That would be me.

> recently located and purchased a bulk quantity of Dupla-like low voltage
> cable. He is working on the details as I write.

Ummm, well, not exactly George. After spending literally hours trying
to source "Dupla-like low voltage cable", I came up short. Now I can
find the right gauge, materials, even color - the problem is the
*thickness* and *cost*. You can get the thickness (Dupla cable has
very thick insulation) but it's pricey, or you can go surplus but they
have nothing like what Dupla sells. So in the end I bought surplus
spools of 26g & 30g telflon insulated wire (if you're interested in
this stuff, write me ... I've got *hundreds* of feet of it!)

Our resident APD wire expert (who also will chime in if he wants)
thinks Dupla probably special orders the stuff. A minimum run would
involve many hundreds of feet with the bottom line having 4 digits.

Maybe Dave G. would be interested in setting up a PMDC business? ;-)

(Poor-Man's-Dupla-Cables, for the acronym-ly impaired)

- -- 
Dan Resler                            email:
Dept. of Mathematical Sciences          
Virginia Commonwealth University           
Richmond, VA 23284-2014 USA

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