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Re: Dupla or Dennerle substrate heater cables?

> Date: Wed, 22 Aug 2001 19:35:39 +0200
> From: "Davy Cleys" <davy.cleys at skynet_be>
> As I live in Europe, I can buy either the Dupla heating cable or the
> substrate heater of Dennerle.
> Does anyone know which of the two heaters has the best performances?
> But I wonder: does the 75 Watt Dennerle substrate heater have enough
> to create those micro currents or should go with the 100 Watts anyway?

There is no clear information on this. The Dupla information I've seen
mentions some formulae for deciding how much wattage to use based on water
temp, tank type (glass/acrylic, open/closed top) and ambient temp. However,
after you carefully pick a cable, you find that it is more critical to match
the footprint of the tank (as you mentioned) since the anchors they sell
seem to dictate an "optimum" spacing. I was bitterly surprised when my
carefully calculated 250w cables were way too big for the glass, open top,
cool room 90g discus tank I set up in 1991.

I have never seen any information on watts/gallon for optimum results. As
mentioned before, I would go with a higher wattage if I had a choice.

> How
> much Watt does one need to provide the proper amount of heat to the
> substrate to generate the micro currents?

Would anyone want to engage in discussions to try to design an experiment
that could determine this?

I had thoughts along this line:

Take a relatively small tank (10-20g) and install cables with a known
spacing. Then install plexiglass barriers parallel to the cables, spaced
between them, running the full length of the tank, going from the water
surface and into the gravel a specified distance. The barriers would create
isolated water zones. Thr idea is to see if stuff in the water moves from
one zone to another.

Step 1. Start with distilled water or equivalent in the tank. Add a
concentration of easily measured ions to alternating zones. Calcium would be
good since it is cheap and easy to measure. Let the setup sit for a few
days. Some calcium should migrate from the high concentration zones to low
concentation zones by diffusion. Make a few measurements to get a baseline.
I would suspect the movement to be very slow, if even measurable.

Step 2. Connect the cables to a variable current source (a variac would be
good). Reset the water as best as possible to a baseline value. With heat
applied, again measure diffusion rates. Repeat with different current(heat)
levels. If my theory holds, at some heat level you will see a dramatic

Extra credit: Use a series of thermocouples (thermisters?) placed around the
coils to determine how the heat distribution changes over time. I would
expect big differences when the heating is just turned on. I would expect
very small differences (but higher overall temp) after a period of time.

Extra credit: Does transfer rate vary with a certain heat density if the
cables cycle at some optimum rate versus being constantly on?

I have a spare 29g tank and a variac. I don't have spare cables but could
build some from plain old wire. All I need is the incentive and time. I
could be famous!

George Booth in Ft. Collins, CO (booth at frii dot com)
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