Anyone with any electrical/wiring knowledge?

OK, being a PROFESSIONAL ELECTRONIC TECHNICIAN with experience in everything from microvolts to kilovolts, and at frequencies from DC to Daylight, let me add my 2 cents worth here.

First off, it depends on the type of thermostat you're using. Many inexpnesive thermostats use a bimetal system which makes and breaks a low voltage contact depending on thermal expansion/contraction. For most household furnaces, these contacts control a 24 - 28 VAC low current line which tells the furnace when to kick on and off. They work strictly on surrounding air temperature, with no real "feedback" from the furnace. They're cheap, usually effective, with minimal parts to go wrong. Fancier thermostats use a digital thermometer system to control a small relay inside, which likewise controls the furnace control voltage. In most cases, you do NOT want to run any kind of higher potential voltage through these contacts. The initial current surge when they make contact can start to burn and pit the contacts, resulting in loss of conductivity, or worse, welded contacts that never turn off. Always look that the contact rating of such a device, and make sure it well exceeds the power requirements of what you're controlling. Were I controlling, say, a 60 Watt ceramic heater, I would want a control system capable of handling at least 100 watts, preferably 150. You really don't want to run close to the ragged edge on such stuff.

Can household thermostats be used to control heat tape? Certainly, with a little extra parts thrown in for proper control. To do so, what I would do is to use a small low voltage AC adapter, such as would be used to power a personal electronic device like a CD player. This low voltage would be what was routed through the thermostat contacts. The thermostat applies or removes this voltage from the control contacts of a solid state relay. SSR's can be bought which use low voltage direct current to control high voltage or high current, either AC or DC. Unlike a mechanical relay, which uses a control voltage to set up a magnetic field to pull mechanical contacts together, a SSR uses a low control voltage to turn on or off an electronic "gate" for the voltage; no moving parts, and very low current draw on the control side.

The advantage of such a system is that your high current potential voltage (110 VAC for your heat tape) does not have to actually enter the reptile enclosure if the heat tape itself is on the outside radiating in. You have a low current potential low voltage in where the animals are (posing less risk in case something gets damaged or damp). Watching my BP nose around things in his enclosure, this can be a very good thing.

How reliable are such things? Well over ten years ago, I got sick and tired of the heat controller on our water bed, and using an electronic thermometer module I bought at Radio Shack, made a thermostat for our water bed. It utilizes the 1.5 vdc output logic of the thermometer to toggle a 5 vdc logic chip, which in turn controls the solid state relay. I set the thermometer to the temperature I want the bed to stay at, and it holds within 1 degree of that temperature year round, even when we lived in the High Desert of California, where our winters dropped well below the 20's range. It's been working flawlessly since I made it. Too bad Radio Shack doesn't sell those thermometer modules anymore. I'd use a couple of those to make controllers for the Reptile enclosures, too.

Back to what's available, though. For a reptile enclosure, I would spend a bit more money and buy a digital thermostat. They tend to be a lot more accurate and reliable, and a lot easier to set where you want them, instead of having to spend time with "hit or miss" calibration of where exactly the temperature trips the old bimetal contact system. As I recall, you can get digital thermostats from places like Walmart for under $20.

Well Randy, I think you found the answer to the Topic of Your post.

Hoomi.....Can you explain that in Layman's terms? Or was that? :lol:

I read your post like 3 times and still got lost......I guess that's why I spent almost 20 years in a china factory spraying toilets.

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Originally Posted by Ironhead

Well Randy, I think you found the answer to the Topic of Your post.
Hoomi.....Can you explain that in Layman's terms? Or was that? :lol:
I read your post like 3 times and still got lost......I guess that's why I spent almost 20 years in a china factory spraying toilets.

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Well said, Ironhead! LOL! :D

Hoomi, I'm just a public servant, so most of that went way over my head! Thanks for what I'm sure was a very information packed post, but could you dumb it down a little for me? I understood this part:

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As I recall, you can get digital thermostats from places like Walmart for under $20.

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Am I correct in saying that you are telling me that I CAN use a Walmart thermostat for heat tape? And you recommend a digital? And to really show off my IQ (or lack thereof), how many wires will be exiting the thermostat, and if there are more than two, which should I wire to the heat tape? And it WOULD have to be mounted inside the enclosure, yes?

Thanks for the post, Hoomi, but all the SSR, magnetic field, 110VAC, potential voltage stuff went zooming right over my poor, stupid head! :oops:

After spending quite a while typing out what I'd hoped was a more basic, "layman's terms" explanation, the forums decided I wasn't logged in and sent me to the login page, and my browser isn't letting me go back to where I had all the text typed in. Argh!

Quick summary. It isn't about being smart or "stupid". It's simply about what we're familiar with. I've been doing this electronics stuff for nigh on 25 years now. Sometimes I see this stuff in my sleep. To really simplify it, I'll draw up a basic sketch and scan it in to post here tomorrow.

Let's just say for tonight that, when it comes to electricity, we want to keep the dangerous levels of it out of reach of our scaly friends, lest our Ball Pythons become Great Balls of Fire.