On Sat, 04 Nov 2006 09:24:52 -0800, T-n-T wrote:

I was wondering if anyone could help me with a design of a heat cable
for my new terrarium. I have on fairly expensive cable and would like
to duplicate it. It has a 110v plug at one end and is about 8 feet
long. The end has a small knob which I assume is a resistor of some
sort. The actual heating part of the cable is about four feet long, the
rest is just to get to the outlet. Oh yeah it is 15 watts. I think for
someone who knows how this works should be a no brainer. I recently saw
an article somewhere that suggested using a toaster or aquarium heater
element, halved , coiled around a small wire and threaded into a
silicone tube. Any advice would be excellent, thank you.

BTW, i have seen some online for planted aquariums that use a long
length of wire, which is exactly what I need but seems to be really
long.
http://www.thekrib.com/Plants/Tech/

Do recognize that putting line voltage into an environment that is wet
(your's may be very dry, I don' t know) is risky...

A simple heater might be easily made from a wall wart that gives 12 to
14 volts AC at about 1.2 (or more) amps. Use a 15 watt resistor (maybe
Radio Shack) that is about 10 to 14 ohms in resistance. An AC wall
wart will work well in this application. That will limit voltages in
the terranium to a safe value (don't want your livestock chewing on
the cables, right?) An improvement woudl be to clamp the resistor to
an aluminum plate (say 4 x 4 inches or 100 mm square) that is perhaps
an 1/8" thick. That will help spread the heat out and limit hot
spotting some.