A few weeks ago, we had some discussion about thermostats, heat mats, and the reasons why a thermostat is needed with a heat mat. I mentioned that I'd like to bounce some ideas off of a controls systems engineer friend at work and get her feedback. She doesn't own reptiles, but she's reptile-friendly and has seen some of their setups in addition to being a good engineer.

Heat mat failure mode - She wasn't surprised at hearing that people have had heat mat failures where the temperature suddenly became very high. While she's never seen the way the heat mats are built, she said that they are bound to have a resistor or something that regulates power flow through the heating elements. If whatever regulates that flow suffers a short, then the full power that can come through the cord could come through the mat. In that case, the mat could become very hot. She agreed from an engineering perspective with what everyone has been telling me from their experiences. She was glad to hear that I'm getting thermostats.

I had previously called the reptile supply place that's located in my area to ask similar questions, but they never returned my calls. I still don't have as detailed an explanation as I'd like, but my curiosity is more satisfied than it was previously.

Thermostats, proportional vs. on/off - She wasn't prepared to say whether one or the other would give better life for the heat mats. She said that some kinds of devices don't respond well to a power supply different from design. If the heat mats are made that way, using a proportional thermostat (or a rheostat) would damage them over time because the power coming to the heat mat wouldn't be the voltage that normally comes through the cord. The on/off cycles of an on/off thermostat might also damage the heat mat, but she thinks that an on/off thermostat would be a less risky choice from the perspective of maximizing heat mat life. If herpers' experience has shown that proportional thermostats maintain heat mat life better over time, I can accept that fact, but I was curious what she would think based on engineering experience. Of course, our heaters in the plant are completely different from heat mats, so the comparison is rough.

Her other concern about the proportional thermostat is that if the heat mat fails badly enough, the thermostat may not be able to dial the power back far enough to keep the temperature from getting too high. The on/off thermostat will just cut the power completely when the temperature gets too high. Again, I'll defer to other folks' experience in keeping reptiles, but I thought her comment was interesting. Has anyone ever had a runaway heat mat that a proportional thermostat couldn't control?

She said that regardless of what I get, I need to check my mats regularly to be sure that a mat hasn't failed and put the thermostat in the position of trying to control something that is unsafe regardless of control.

By the way

I had ordered my thermostats two weeks ago before I had this conversation. I talked to Matt at MG Reptiles, and he persuaded me that the Johnson thermostat would be fine for my needs. He's been backed up a bit, but my thermostats are in transit. I'm looking forward to setting them up and getting better control of my temperatures. I bought some plexiglass at Home Depot, and I'm going to cover part of the top of my aquarium in hopes of maintaining better humidity and temperature control. I've also ordered some reflective stuff from MG Reptiles that is supposed to help with temperature and humidity. These engineering changes plus the addition of another climbing branch will be part of Katrina's next home makeover.

Bill
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It's not how many snakes you have. It's how happy and healthy you can keep them.