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 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?

In article , PeterD
wrote:

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.

On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T 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?

You'd need some 2.4 ohms per foot resistance wire, and a 12 volt 1.5
amp transformer.

Nichrome wire is normally used, but stainless steel or phosphor-bronze
will also work if you can find it in the right size range. You could
coil the wire around a piece of tubing or some other substrate to get
by with different ohms/foot wire - you need 9.6 ohms, or close, to get
15 watts with 12 volts input.

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On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T wrote:

Someone on sci;.electronics.misc is offering some free SS wire for you


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On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T 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!)

In article , PeterD
wrote:

On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T 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.

T-n-T wrote:

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.

Ohms is a word that means volts per ampere. You have 12
volts and want the current to be 1.2 amps (or less). So
that resistance must be 12 volts per 1.2 ampere

12/1.2 = 10 ohms or higher.

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

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

In article , PeterD
wrote:

On Sat, 04 Nov 2006 15:09:41 -0800, T-n-T 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.

Called OHM's law... g

Try http://www.the12volt.com/ohm/ohmslaw.asp as an example, or just
Google 'ohms law' (no quotes) and you'll get several sites.

Quickly:

1 volt, 1 ohm, 1 amp, 1 watt

so

12 volts, 12 ohms, 1 amp, 12 watts

(divide voltage in volts by resistance in ohms)

To compute the other way (say you want 15 watts at 12 volts):

(volts * volts) / watts

that's volts squared divided by watts, or

(12 * 12) / 15

which is

(144) / 15 = 9.6

which is 9.6 ohms!

How much current?

Well there are several ways to compute it, but the easiest is just
watts / volts, or

15 / 12 = 1.25 amps

I'd use a trasformer rated at about 2 amps myself.

All the above are simple DC computations. They work well if the load
is purely resistive, and the frequency is low enough (which AC line
frequency is).

BTW, 15 watts, if misused (concentrated in too small an area) will
absolutely present a fire hazard... My pencil soldering iron is about
12 watts, and it gets hot enough to melt solder... Use caution, and
spread the heat out over as large an area as possible.

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.
======================================
You might consider using heating tape which produces heat in the order
of 15 - 20 Watts per metre . It is used to keep water pipes frost free.
For a short length as probably required for your terrarium you need a
transformer with voltage outputs in the 5 -24 V range , with a number of
voltage taps. This heating tape is insulated and can be found at
industrial electrical components suppliers.
For safety reasons do not apply voltages above 24 V and make sure that
metal parts of the terrarium are always earthed whatever the heater
voltage.

Frank

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.

Have you investigated simply purchasing another?

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.

Perhaps a
http://groups.google.com/groups/sear...troller+heater

The actual heating part of the cable is about four feet long,
the rest is just to get to the outlet.

Does it look like it has a sensor?

BTW, i have seen some online for planted aquariums

Google has many facets:
http://froogle.google.com/froogle?sc...title:aquarium
http://froogle.google.com/froogle?sc...ntitle:Reptile

FYI

If the heat tape you describe is like all the rest of standard heat tapes,
the knob on the end is not a resistor. It is simply a plastic cap filled
with silicone to keep out moisture and to prevent grounding of the two
conductive wires. Most commercial heat tapes use about 3 watts per linear
foot. The material between the two conductive wires is a resistive material
which heats up as current passes between the hot and neutral. If a heat tape
is cut too long, the resistance becomes too great for the current to
overcome it and the heat tape won't heat. The better tape kits have either a
little glass fuse in the plug or it will have a reset button.

Good Luck

Dan
"T-n-T" wrote in message
...
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/