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Posted to alt.binaries.schematics.electronic,alt.binaries.schematics.electronics,alt.books.electronic,alt.electronics,be.science.electronics
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Heat cable for terrarium
On Mon, 06 Nov 2006 11:34:42 -0600, John Fields
wrote:
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.
---
Oops... That should read: ..."a 17 foot length"...
--
JF
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