On Mon, 06 Nov 2006 07:46:14 -0800, T-n-T wrote:


I am with you, fortunately this cable is not going in the water, the
link I provided on my post though, they do submerge it. If I needed it
to go under water I would just buck up and buy one. This just sits
atop or just under the soil. And my inhabitants, frogs and hermit crabs
probably wont chew it, but I am going with a lower voltage like 12V.

Maybe you can answer another related question, sometimes I ask a
question that is clear to me, but gibberish to others... i looked for
roof heaters here(Washington State) and the hardware store told me they
didn't sell them here.

Ok a 12 volt 1.2 amp wall transformer for example. What is the formula
to determine the amount of resistance I need to not burn up the
transformer? Because I did hook a transformer up to some resistive wire
and toasted a few transformers.

---

E 12V
R = --- = ------ = 10 ohms
I 1.2A

Then, the resistance will dissipate:


P = IE = 1.2A * 12V = 14.4 Watts


Looking at:

http://www.omega.com/toc_asp/framese...EN_SPECS_R EF

#20 Type K has a resistance of 0.596 ohms per double foot, so to
make a 14.4 watt heater using a 12V supply you'd need:

10R
l = ----------- ~ 17 feet
0.596R

or, about an 8-1/2 foot length of Type K thermocouple or
thermocouple extension wire.

Depending on the size of your terrarium and assuming that ~ 15 watts
isn't going to cook your critters, you may want to get larger
diameter wire so the length of your heater will be longer. That way
you could run it in a serpentine fashion under the sand and
minimize/avoid hot spots.

To make the heater you'd strip and tin each of the conductors on one
end of the cable and then twist them together and solder them to
each other. It works, I just tried it. Then connect the conductors
on the other end of the cable to your power supply and, VOILA!
heater.
---

BTW, thank all of you for your help.

---
You're welcome.


--
JF