# Thermostat issues



## liam peel (Sep 26, 2011)

I posted about this a while back but felt like I should make a new post about it.

I have two thermostats on my snake rack, one just doesn't seem to heat up and the other gets too hit.
Two heat sources 1 for each thermostat.
Both are set to 32 degrees, thermostat 1 just never seems to be putting any lower out except on the rare occasion and I do mean rare, heat tends to be around 22 degrees except for the other day when it reached about 40 degrees.
Thernostat 2, set to 32 degrees 99% of the time its saying its putting out heat, quick temp check 5 minutes ago 44 degrees, it shuts off at 22 degrees but even when I turn it to 23 degrees its putting out power again.

I've tried resting the probe in the tank, on the wire, next to the wire all of the things that have been suggested changing heat sources too I just do not know what the issue is and I am really concerned about the heat variance can somebody please offer any advice.

Thanks.


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## ian14 (Jan 2, 2008)

What thermostats are they and what are the heat sources


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## liam peel (Sep 26, 2011)

Both habitat classics, 1 dimming 1 temperature thermostat. Heat wire for the heating source.
I never had these issues untill roughly a year ago when I got a new wire and new thermostat, I still have the old ones as I ran Into the problems with the new ones (new thermostat gets too hot old one not hot enough not sure on the wires).


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## ian14 (Jan 2, 2008)

The dimming stat is designed specifically for heat lamps, and has a minimum load requirement of 40W.
Your second one, is that a simple on/off stat like a mat stat?
If so, they are not the most accurate.


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## liam peel (Sep 26, 2011)

I've used the dimming one for years now and never had any issues u till last year, I thought it was on its way out so I purchased the new one as to which one it is im not 100% sure at the type but ill double check it when I can.

Which thermostat would you recommend? A pulse one perhaps?


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## LiasisUK (Sep 30, 2019)

Always make sure you are setting the temperature based on a thermometer and not based on the dial on the stat. The dial numbers on the stat is just a guide, it shouldn't be used to set temperatures, you have to set it then test with a thermometer and adjust accordingly. 

For the hatchling racks I have I mount the probe on the heat mat itself, as in on the shelf outside the tubs, but it then has to be set 5c higher than the desired temperature so that the tubs get warm enough. Heat is lost travelling through the plastic, substrate etc. 

For some of my larger enclosures the stat probes don't reach the hot spot, so have to sit a foot or so away, so they're often set to like 28c, but the hot spot gets to the desired 40ish. Just takes some trial and error, every setup is different.


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## liam peel (Sep 26, 2011)

So if I set my thermostat to 22 degrees it will reach 22 degrees and then shut off, if I set it to 23 degrees it will surpass it and not shut off.
Like I said they are set to 32 degrees but inside the enclosure reaching 44 sometimes it should have shut off 12 degrees earlier but it doesn't.


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## Malc (Oct 27, 2009)

The sensors used in most of the basic stats are thermistors, ie resistors who's value changes in a range depending on the temperature. They are not that precise, which is why you should always use a decent thermometer, ideally digital to "calibrate" the thermostat. With simple on/off types the overshoot can be as much as 10c when controlling a CHE or similar. Here are some graphs taken when a standard on/off stat was used to heat a 100w tube heater - set point was 32c










This is why pulse stats are better when using CHE or tube heaters as the over shoot is less and they can maintain a more static temperature. In this case the graph shows the same heater controlled by my one pulse proportional stat using a digital sensor with a set point at 33c


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## LiasisUK (Sep 30, 2019)

I mean..... 22c is probably just the air temperature hence why it doesn't come on. 

Sounds like your stat is broken, best way to test it is to attach to a light emitting heat source and see how the light behaves when the probe is subjected to different temps. If the light doesn't go off when the probe is placed somewhere hot then it is faulty. Much easier to test stats with heat lamps.


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## liam peel (Sep 26, 2011)

So I've just got home and thought I'd give them a quick check and its complete role reversal.
Thermostat one the one that never heats up is now heating up and sitting nicely at 30 degrees but I can lower the thermostat down to 20 degrees before it shuts power off.
Thermostat two that gets too hit, currently set to 34 degrees tubs only reaching 22 degrees and not putting any power out at all


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## Malc (Oct 27, 2009)

liam peel said:


> So I've just got home and thought I'd give them a quick check and its complete role reversal.
> Thermostat one the one that never heats up is now heating up and sitting nicely at 30 degrees but I can lower the thermostat down to 20 degrees before it shuts power off.
> Thermostat two that gets too hit, currently set to 34 degrees tubs only reaching 22 degrees and not putting any power out at all


Liam - please read my post above....given the technology you will see these swings... With any of the basic "analogue" thermostats you have to make small slight adjustments over several days to fine tune them, but they will never be as precise as any digital thermostat that uses a proper one wire digital sensor, and only dimmer or pulse proportional digital stats offer better precision, but then they cost twice or three times as much.

Also you mention Tubs... presumably you are using heat mats or cables ? - These don't heat the air, so any temperature readings using a traditional thermometer will be reading the ambient air temperature of the room they are kept in. 



liam peel said:


> Two heat sources 1 for each thermostat.


Are thermostats 1 and 2 of the same type (pulse prop / dimmer / on off ???) and are both the heating elements the same (same wattage heat mats or are they different ?). You will get differences if the two heat sources are different, or you are using different stats. Personally I would suggest using the same size and brand heat mats / strips on each shelf and basic mini stats with each controlling two but no more than three mats, especially if the rack is tall as you will get a thermal gradient from the top to bottom. Even with a standard mat stat you should be able to get and maintain the temperature with the probe taped to the edge of one of the panels of the heat strip / mat. You will sometimes see a difference between mats from different manufactures even though they are the same wattage

I developed my own fully digital pulse proportional controller that had provisions for an individual sensor and stat for each shelf so the hot spot of my hatchlings stay stable at 30c. The alternative would be to use 8 mat stats...


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