Heat cable for terrarium

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/

On Sat, 04 Nov 2006 09:24:52 -0800, T-n-T <lildog_at_donobi.net> 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.

Thinking more about it now I do want to err on the side of not killing
my terrarium inhabitants. So a wall wort transformer is the way to go.
the purpose of using wire and a resistor is so the wire can be sealed
in silicone tubing for fish tanks and siliconed on the ends., it just
seems easier to seal up. what theory do I need to apply to heat up say
4 feet of wire not just the resistor?

Thinking more about it now I do want to err on the side of not killing
my terrarium inhabitants. So a wall wort transformer is the way to go.
the purpose of using wire and a resistor is so the wire can be sealed
in silicone tubing for fish tanks and siliconed on the ends., it just
seems easier to seal up. what theory do I need to apply to heat up say
4 feet of wire not just the resistor?

On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T <lildog_at_donobi.net> wrote:

Thinking more about it now I do want to err on the side of not killing
my terrarium inhabitants. So a wall wort transformer is the way to go.
the purpose of using wire and a resistor is so the wire can be sealed
in silicone tubing for fish tanks and siliconed on the ends., it just
seems easier to seal up. what theory do I need to apply to heat up say
4 feet of wire not just the resistor?


Four feet of wire with a resistance... <g> OK, try this for size:

Go to a hardware store and get an eight foot gutter/roof eave heater.
Get the fixed length kind (the really cheap ones), that has just
simple resistance wire that forms a total loop length of about 16 feet
(don't get the kind that can be cut to length, it works on a different
principal!)

Now, we have 16 feet at 120 volts, so if we use only 12 volts (a good
safe voltage) we need a tenth of the length, or about 1.6 feet. If 1.6
feet is not sufficiently long, use two 1.6 foot lengths wired in
parallel.

Personally, I have no confidence you had make such a setup water
tight. I'd make sure the connections are outside the water if at all
possible. Also make sure that any silicone you use is rated for high
temperatures, and allow the silicone to cure for at least a week to
prevent out-gassing (the stuff gives off some nasty gases while
curing!)

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.

BTW, thank all of you for your help.

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.

BTW, thank all of you for your help.

In article <8o2sk21bm20qpsom6h6blp5400ukm0ni8f_at_4ax.com>, PeterD
peter2_at_hipson.net> wrote:

On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T <lildog_at_donobi.net> wrote:

Thinking more about it now I do want to err on the side of not killing
my terrarium inhabitants. So a wall wort transformer is the way to go.
the purpose of using wire and a resistor is so the wire can be sealed
in silicone tubing for fish tanks and siliconed on the ends., it just
seems easier to seal up. what theory do I need to apply to heat up say
4 feet of wire not just the resistor?


Four feet of wire with a resistance... <g> OK, try this for size:

Go to a hardware store and get an eight foot gutter/roof eave heater.
Get the fixed length kind (the really cheap ones), that has just
simple resistance wire that forms a total loop length of about 16 feet
(don't get the kind that can be cut to length, it works on a different
principal!)

Now, we have 16 feet at 120 volts, so if we use only 12 volts (a good
safe voltage) we need a tenth of the length, or about 1.6 feet. If 1.6
feet is not sufficiently long, use two 1.6 foot lengths wired in
parallel.

Personally, I have no confidence you had make such a setup water
tight. I'd make sure the connections are outside the water if at all
possible. Also make sure that any silicone you use is rated for high
temperatures, and allow the silicone to cure for at least a week to
prevent out-gassing (the stuff gives off some nasty gases while
curing!)


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.

BTW, thank all of you for your help.

On Mon, 06 Nov 2006 07:46:14 -0800, T-n-T <lildog_at_donobi.net> 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/frameset.html?book=Temperature&file=TC_GEN_SPECS_REF

#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.

On Mon, 06 Nov 2006 07:46:14 -0800, T-n-T <lildog_at_donobi.net> wrote:

In article <8o2sk21bm20qpsom6h6blp5400ukm0ni8f_at_4ax.com>, PeterD
peter2_at_hipson.net> wrote:

On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T <lildog_at_donobi.net> wrote:

Thinking more about it now I do want to err on the side of not killing
my terrarium inhabitants. So a wall wort transformer is the way to go.
the purpose of using wire and a resistor is so the wire can be sealed
in silicone tubing for fish tanks and siliconed on the ends., it just
seems easier to seal up. what theory do I need to apply to heat up say
4 feet of wire not just the resistor?

In article <etsuk2htteos9j56v0nk2e4el9oqbvvnns_at_4ax.com>, PeterD
peter2_at_hipson.net> wrote:

On Mon, 06 Nov 2006 07:46:14 -0800, T-n-T <lildog_at_donobi.net> wrote:

In article <8o2sk21bm20qpsom6h6blp5400ukm0ni8f_at_4ax.com>, PeterD
peter2_at_hipson.net> wrote:

On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T <lildog_at_donobi.net> wrote:

Thinking more about it now I do want to err on the side of not killing
my terrarium inhabitants. So a wall wort transformer is the way to go.
the purpose of using wire and a resistor is so the wire can be sealed
in silicone tubing for fish tanks and siliconed on the ends., it just
seems easier to seal up. what theory do I need to apply to heat up say
4 feet of wire not just the resistor?



Okay so I now know how to come up with the length of wire and
transformer. If I wanted to use a long wire and coil it, do the coils
absolutely have to not touch? What if they do? I believe a smaller wire
that is longer and coiled will give me a more pliable cable.

lildog

In article <etsuk2htteos9j56v0nk2e4el9oqbvvnns_at_4ax.com>, PeterD
On Mon, 06 Nov 2006 07:46:14 -0800, T-n-T <lildog_at_donobi.net> wrote:
In article <8o2sk21bm20qpsom6h6blp5400ukm0ni8f_at_4ax.com>, PeterD
On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T <lildog_at_donobi.net> wrote:

Thinking more about it now I do want to err on the side of not killing
my terrarium inhabitants. So a wall wort transformer is the way to go.
the purpose of using wire and a resistor is so the wire can be sealed
in silicone tubing for fish tanks and siliconed on the ends., it just
seems easier to seal up. what theory do I need to apply to heat up say
4 feet of wire not just the resistor?

Okay so I now know how to come up with the length of wire and
transformer. If I wanted to use a long wire and coil it, do the coils
absolutely have to not touch? What if they do? I believe a smaller wire
that is longer and coiled will give me a more pliable cable.

In article <071120060650151510%lildog_at_donobi.net>, T-n-T
lildog_at_donobi.net> wrote:

In article <etsuk2htteos9j56v0nk2e4el9oqbvvnns_at_4ax.com>, PeterD
peter2_at_hipson.net> wrote:

On Mon, 06 Nov 2006 07:46:14 -0800, T-n-T <lildog_at_donobi.net> wrote:

In article <8o2sk21bm20qpsom6h6blp5400ukm0ni8f_at_4ax.com>, PeterD
peter2_at_hipson.net> wrote:

On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T <lildog_at_donobi.net> wrote:

Thinking more about it now I do want to err on the side of not killing
my terrarium inhabitants. So a wall wort transformer is the way to go.
the purpose of using wire and a resistor is so the wire can be sealed
in silicone tubing for fish tanks and siliconed on the ends., it just
seems easier to seal up. what theory do I need to apply to heat up say
4 feet of wire not just the resistor?



Okay so I now know how to come up with the length of wire and
transformer. If I wanted to use a long wire and coil it, do the coils
absolutely have to not touch? What if they do? I believe a smaller wire
that is longer and coiled will give me a more pliable cable.

lildog


Ok, i don't know if this falls within the realm of electronics but you
guys may be able to point me in the right direction. Is there a formula
to determine the amount of heat coming off of on eof these cables?