Thermostat/uth fluctuations & lag time

[anadyne]

I have an uth on the underside of the viv glass. The thermostat probe and temperature probe are both on the inside of the viv sitting on the glass directly over the uth. I have about 1.5" of aspen covering.

The thermostat is the on/off kind. When the set point is, say, 83.5 F, it turns the uth on until it registers ~84 and then powers the uth off. However, the pad of the uth is still hot so with the lag time, the temperatures continue to increase to 87.5 before lowering again. The cycle takes about 15 minutes or so.

Is this okay for the temps to fluctuate so much, constantly?

Before this, in the winter, I was also using a heat lamp to get the ambient temps up in the viv, for when J was cruising around above the aspen. Since it's warmer now I've taken the lamp down & I now realize that the lamp was stabilizing the temperatures. So this is the first time I've seen this much fluctuation - and the first time my snake has experienced it, too...

 

[alan]

I don't get it, with power off the heater should start cooling immediately. Are you thinking it just takes time for the heat transfer? Still, it should start getting lower when no more heat is being produced.
Are you sure your thermostat is turning it off completely? Try letting the temp start to rise and then unplug it, see what happens?

 

[Nanci]

Alan, that's what happens with an on/off thermostat. If I was in that situation, I'd probably set the thermostat a couple degrees cooler, say 83, so it peaks at 85. The fluctuation won't hurt. But if you want a thermostat you will love, save up and get either a regular or Night Drop Herpstat. I don't use the ND feature, but that thermostat has a couple extra features that I like, such as a high/low alarm. They are _so_ worth it...

 

[Floof]

That's an interesting observation. I'll have to sit down one of these days and see if it does that on my tanks--the vast majority of them are on cheap zoo-med on/off thermostats, because I can't afford any more herpstats.

But, yes, Herpstats are SO worth it! I have a Herpstat II (got the Herpstat II for my first snake--thinking ahead, since I knew I would get a second...), and use the night drop feature just because it's there... Lol. It's never off by more than a degree--if that! And, yes, the high/low alarm is amazing. It's "saved" the temps in Mallie's viv more than once... As a little 'un, she had a habit of knocking her thermostat probe off the heat mat!

 

[anadyne]

Thanks for the rec - I've got a list going of better equipment for when J moves to his larger cage and I'll definitely check out the Herpestat. I've been bobbing up and down watching the temps move for 3 days now and I'm completely willing to save up for a nice one for some peace of mind.

 

[alan]

Thanks Nanci! Color me unobservant.
I just tested this several times. Mine continued to rise an additional 0.7° after the thermostat turned it off then it started to drop. Nothing like the 3.5° anadyne gets but I'm still surprised. When I adjust it of course I just set the high by the thermometer, I never check when the thermostat is turning on and off because it doesn't matter. I'm also surprised I wasn't nerdy enough to rig an "on" indicator light when I set it up.

 

[Nanci]

Alan, are you using a temp gun to check? That's another amazing discovery: how much the temps vary across the mat.

 

[alan]

Nope. When I first set it up I checked for the hottest place on the mats and put the thermometer probe there.
Last summer I left her in my spare after cleaning her viv and checked it again, the high spot was the same. I don't care if it's not even, I just don't want anything too high.

 

[anadyne]

I don't know why mine fluctuates so much. I too looked for the hottest spot on the mat and put the probes there. I tested it tonight by unplugging the mat and sure enough, the probe temp still rose 1.5 degrees as the heat still in the mat transferred to the probe on the other side of the glass. I have it set for 83 now with less aspen cover and it cools off faster, so only gets to 85 or so. I'm okay with this for now.

 

[bitsy]

I've used these simple on/off type stats for years and haven't had a problem (until they completely stop working, which is going to happen to any electrical equipment eventually). I think Corns aren't really sensitive to that level of fluctuation, for that short length of time.

 

[Nanci]

I don't know why mine fluctuates so much.

They just do that. Proportional thermostats are more accurate because as the temperature nears the set point the amount of power to the mat is decreased.

 

[Buttons]

Shouldn't the thermostat probe be between the UTH and the glass? Not inside the viv??

Would this make a difference in the temps? I'd think so because the thermostat probe is registering the temp after the heat goes through the glass.

 

[Nanci]

The place the temp matters, that you have to measure and control, is the place the snake can touch it. In the viv directly over the center of the UTH.

 

[bkelm18]

Would this make a difference in the temps? I'd think so because the thermostat probe is registering the temp after the heat goes through the glass.

This is what you want. You want to know the temperature where the snake can get to, not where it can't. The temp on the outside of the viv doesn't really matter at all, it's the temp on the glass on the inside that matters since your snake can touch it.

 

[Buttons]

The place the temp matters, that you have to measure and control, is the place the snake can touch it. In the viv directly over the center of the UTH.

This is what you want. You want to know the temperature where the snake can get to, not where it can't. The temp on the outside of the viv doesn't really matter at all, it's the temp on the glass on the inside that matters since your snake can touch it.

I understand what you're both saying but from what I've been told, you measure the temps inside the viv with a thermoMETER. The thermoSTAT probe should be between the UTH and the glass. That's the way I've read it on numerous sites and I know thats the way a lot of very large breeders do it.

 

[anadyne]

Actually, that makes sense in that it would do away with the lag time issue - when the mat itself reached 85 (or whatever), the thing would shut off. I guess effectively the mat would never be allowed to get hotter than the set point, so the tank bottom wouldn't ever rise to 88 as it was. It makes sense, as right now the mat gets to 88 to heat the glass to 85, then shuts off as the glass temp continues to rise.

 

[bkelm18]

I understand what you're both saying but from what I've been told, you measure the temps inside the viv with a thermoMETER. The thermoSTAT probe should be between the UTH and the glass. That's the way I've read it on numerous sites and I know thats the way a lot of very large breeders do it.

Well if you can figure out what the heat loss is across the glass then I guess you could do it like that. Just seems like an extra, unnecessary step.

 

[Buttons]

Actually, that makes sense in that it would do away with the lag time issue - when the mat itself reached 85 (or whatever), the thing would shut off. I guess effectively the mat would never be allowed to get hotter than the set point, so the tank bottom wouldn't ever rise to 88 as it was. It makes sense, as right now the mat gets to 88 to heat the glass to 85, then shuts off as the glass temp continues to rise.

This is the way I was told to do it, numerous other breeders/keepers do it this way with success. Just seems the best way to me. If you put the thermoSTAT probe in the tank and the snake either urinates on it or dumps its water bowl on it this will cause the the thermostat to act erratically causing drastic temperature changes. By having it on the outside of the tank between the UTH and the viv you'll be able to keep the temps much more stable.