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Re: BIG Tank Heating Cables?



>Just before Christmas I was offered, at a ridiculous price ($240), a 1000 
>gallon tank, glass construction, measuring 3.5x1.0x0.65metres 11.5ft x 3.3ft 
>x 2ft, naturally I took up the offer as I had the space for it!

Ohboyohboyohboy! Trade ya tanks ;-)

>Some problems occurr with a tank this size and the biggest headache I've 
>found is heating the thing! Obviously using normal heaters is going to be 
>expensive in both original price and electricity consumed, how many Jšeger 
>eaters would I need to use (hypothetical question, no need to answer as it's 
>not going to happen. I then thought about using a gas heat exchanger but the 
>problem there is the cost of gas burners. As a result I've turned to 

Your best bet if you need supplemental heating beyond that provided by the
cables (I think cables are your best bet as the "base" heat source) is to
use one of the fireplug heaters that I think is made by aquanetics. Petwhse
has them. The connect in line with the sump's circulation pump, and you ARE
going to be using a sump with your 1000 gallon tank, right?

>substrate heating cables as the only viable, efficient option. I was >thinking 
>of three cables, each of 10metres (33feet) long. From my calculations, 
>Though, this would leave me using a 240volt supply (3amps, 3mm cables) 

NO! Very bad! 240v, at least in the US, is nastier than 120v for more than
just the voltage. The reason is that in the US, the neutral is the
"middle", with one 120v "above" it and one "below" (for the techies, I'm
simplifying here so bear with me). With 120v at least one leg is at ground
potential. With 240 volts BOTH ends are 120v away from ground with 240v
between them. Also, while a 120v GFCI will run around $20-50, a 240v GFCI
is going to be $200+.

>without any protection from step-downs or whatever, this leaves me a bit 
>worried, would it be safe and if not what would you suggest? Perhaps 10 
>cables of 3.5metres each? On the same subject I found this site 
>http://www.hotfoil.com/ and though it looked quite promising, I know that my 
>parents have used the same system for frost-protection on the pipes in their 
>house and it was very reasonably priced ($100), any comments?

The pipe cables are not going to hold up well in a submersed application.
You absolutly do NOT want to trust them that way, especially when running
with 120v on them. 

Your best bet on your very large tank is probably going to be DIY since I
don't think anyone makes a cable any where near large enough for your tank.
You're probably looking at upwards of 100 feet of cable, so you can use
beefier heavy-gauge cable and get the durability it provides. For a 100
foot system at 24 volts, you would need (I'm using Ivo's 200w per 120
gallons number as a rough guide) an approximatly 1500 watt heating cable.
Wow. That's 62.5 amps at 24 volts. 18 awg wire has 0.006386 ohms per foot,
so the 100 foot cable would be 0.6386 ohms. That gives about 38 amps or
around 912 watts. Maybe enough? Remember that larger tanks need less heat
per unit volume than smaller tanks so maybe you'd be OK. If you ran two
parallel systems, you could get about 1800 watts or so with both running,
and I think that is right around the upper limit of the Medusa temperature
controllers range. You'll need some big transformers to run it though --
maybe even custom wound (think around $200-$300 for a custom wound
transformer like this). 

I'd use 18 awg (because it is easy to find) teflon or silicone insulated
wire for the cable (my preference being silicone), and 8 awg teflon (or
silicone if you can find it) wire for the lead outs to bring the
connections out of the tank. 

If you choose to go this route I'd be happy to provide sources for the
parts, especially the transformer since there is a good place I've used in
the past.

>F.Y.I. I'll probably be using either Sodium or MH lighting (2x400watts or 
>more) and will use a peat/black volcanic sand substrate with cork decoration 
>and a 300 litre (80gal.) sump to maintain a constant water level but not 

Use MH if you want to look at your tank. Sodium's red-shifted spectrum
makes everything ugly, IMHO. MH is supposed to be better when used as the
sole source of light too, since it provides a more balanced spectrum.
You'll be looking at 1500 - 2400 watts (250 or 400 watt fixtures,
respectivly) to light this tank, so plan for the electric load. At 120v,
you'll want two 20 amp circuits for the lighting alone (code requires
oversizing when a circuit is to be run at 70% load or greater for long
periods of time), a third 20 amp circuit for heating, and a fourth circuit
for pumps and everything else. You'll probably want all of those on GFCIs
for safety, so you might want to start looking at just installing a small
subpanel for only your tank. That's what I was planning on doing when I was
looking at setting up a 800 gallon marine system a while back.

>much 
>in the way of filtration (let the plants do that!). I'll then be using 
>various strategically placed pumps to ensure there are no "dead" spots.
>comments on other possible heating systems or the ones I've already >mentioned 
>would be very valuable and also anything else you might think of.

I recommend looking at the Dolphin pumps (Champion Lighting carries them).
They are the most energy efficient pumps I've found for high flow rates.
Remember that the pump will run 24 hours a day all year long and will be a
BIG contributor to your electric bill!

Have fun, and you HAVE to post pictures when you get it set up so we can
all drool all over it ;-)

     -Bill

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Waveform Technology
UNIX Systems Administrator