Reptile & Amphibian Forums

I have a proportional thermostat. I had heard that proportional thermostats were suposed to keep the temps within 1 degree or better accuracy but I have found mine keeps the temps within 2 or 2.5 degress accuracy. Is this normal? The temps drop mabie 1 degrees below set temp and 2 to 2.5 degrees above. Usualy the temps are within a degree of setpoint or exactly on setpoint but these differences are the extreme cases max/min. Do I have a unacurate thermostat or are these variations to be expected? Would that temp difference be bad for reptile eggs? The variations in temp are not held for long usualy bounces back to correct temp quickly. Its a lot more accurate than the on/off type I used to have but was wondering if its an accurate unit the on/off type had agreater difference in temps. Mostly concerned if it will be bad for reptile eggs?

Are you measuring temps at the same spot that the thermostat probe is located?

Also, is the thermostat probe inside of a closed eggbox or otherwise in a seperate compartment from the heater element?

The thermostat probe records the temps. It has a max temp and min temp reading stored that you can display if you want wich you can reset any time. Its like during the day its set to 88.5 and 95% of the time I look at the thing its 0.0 - 1.0 degrees within what I set it for but once in a while if I check the max/min temp readings for daytime it might get as hot as 90.2 or at night its set to 82.0 degrees and 95% of the time its 0.0 - 1.0 degrees in range but if I reset the max/min temp recording to see the range at night it might have gotten as cold as 79.9 degrees. The amount it goes below 88.5 during the day or above 82.0 during the night would be about 1 degree from max/min readings.

Pretty much I think its just the extreme temps of the cage over night or during the day. The temperatures are not fluxuateing 4 degrees every 15 min. Its not like it reads 90 degrees and fifteen min or a half hour later its 86 degrees then back up to 90 fifteen min later. I was interested in breeding some of my lizards and was told I need to use an accurate prop thermostat not an on/off. I know if I had one of those mini fridge looking incubators the temps would stay stable more than in one of those hovabator types. Just wondering if the thermostat was normal for temp ranges and if it was safe for an incubator?

Sorry for the double posts, right now I have it controlling a reptile tank.

I have not done any fiddling with incubators yet. Hopefully though I will be able to experience the joy and frustrations involved just as you are, someday soon.

It sounds to me like either the enclosure needs to be better insulated to stailize the temps, the room needs to be stabilized temp wise or maybe your heating element needs to be beefed up to keep up with the changing room temps.

My guess is a little of all of these things.

Yeah just checking if the readings are showing a bad thermostat or if its normal. One tanks a screen top glass terrarium and another is a vision cage. I am sure an insulated refrigerator type incubator is easier to keep tolerances tight than a glass terrarium.

What is the difference between ambient temperature and the set temperature on the thermostat? I have heard that they work best when ambient temperatures are at least 10* cooler than the desired cage/incubator temperature.

I have also heard that proportional thermostats struggle with heaters that are too powerful for the cage or incubator they are heating. In other words, they will be more accurate when used in conjunction with a heater that will warm the cage/incubator just a bit more than you need at full blast.

And when all else fails, increase thermal mass helps with stablizing temperatures.
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Currently keeping:

6.10 Gonyosoma oxycephalum (Javan, mixed colors)

0.0.4 Rhynchophis boulengeri

1.1 Philodryas baroni

1.1 Lampropeltis triangulum multistriata

0.0.1 Rhamphiophis rubropunctatus

0.0.2 Morelia viridis (Aru & Merauke locale types)

1.0 Rhodesian Ridgeback

The ambient temp of the room ranges from 69 at night (its been really cold lately) to 74 if the heater is on for the house. On hot days its 73-78 degrees. The device runs from a low internal temp of about 70 degrees to high of 87. It has a fan that turns on to cool it down.

I think these fellas have told you right.

It sounds to me that your proportional thermostat is working as it's supposed to. Now comes the fun part of getting all the other factors where they need to be so they can work uniformly with the thermostat. And its really not hard to do but can take some time, finagling and trial & error.

I can't remember who all said what so, guys, please forgive me for not crediting you individually.

The better insulated the cage/incubator, the less temperature fluctuations. Probe placement & the full-power of the heating source plays vital roles, too.

Case in point:
Last year I converted an old refrigerator into an incubator for Burmese python eggs. I used a Helix DBS 1000 and installed two light fixtures in the bottom of the fridge.

I started out with two 75-watt light bulbs for my heat source. Placed a tub with a lid on it, filled with my incubating substrate mix, on the top shelf of the fridge and put the thermostat's probe inside the tub along with a decent mercury thermometer.

After a day or two of testing & checking the mercury thermometer I found out that the two 75-watt bulbs were too powerful for my particular setup. When temps dropped & thermostat turned on the lights for more heat, by the time the inside of the tub was heated to appropriate temps the inside of the fridge was hotter, eventually making the inside of the tub too hot.

I first tried placing the temp probe somewhere outside of the tub but couldn't achieve steady enough temps on the inside of the tub. To make an already long story short - I found out that two 25-watt bulbs and thermostat probe placed inside the tub easily kept temps within one degree, all day long - day in, day out. The machine was finally well-tuned and was humming right along. Out of 26 eggs I had a 100% hatch rate.

Took about two or three days to sort it all out. That's why it's strongly suggested to build your system & have it up & running smoothly before you need it.

It's the same with caging. The caging material, amount of ventilation, the amount of power of the heat source, probe location, etc, all play vital roles and need to be fine-tuned in order to achieve the maximum effectiveness of the "machine."

Most eggs have a broad enough range of incubating temps that minor temp fluctuations like you're experiencing now shouldn't be a problem. If you can only narrow your setup down to a 2 - 3 degree variance, then aim for the middle of the suggested temps. A lot of experienced breeders even believe that minor temperature and humidity fluctuations actually produce stronger, healthier hatchlings.

Sorry for this being so long, especially since everything has already been mentioned.

Best wishes!
HH
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Due to political correctness run amuck,
this ol' hillbilly is now referred to as an:
Appalachian American

www.natures-signature.com

Regarding eggs: colubrid eggs can experience quite wide temp differences and be fine. Done this too many times to say otherwise. If you keep them between 75 and 85, that is great. They can handle lower and higher than that too for limited time easily.

Back to my favorite subject..
Insulated cages always make for better temp control. That was a good point by LarryS. This is true with any temperature controller that uses feedback (a probe).

What controllers cannot do is be perfect in every circumstance when the physics just isn't there to make it possible, as others have mentioned. For example, if I have a 4 watt bulb in a 20 gal screen top glass tank, even the best controller in the world couldn't maintain 85 deg if the ambient room temp is cool and the probe is well away from the bulb.

Similarly, if I have a 150 watt bulb in a 5 1/2 gallon tank and the probe is right near the bulb, it would be very difficult to maintain a perfect 80 deg without swing. Heater in that case is sized way too large and the probe can't even respond that fast as the bulb heats up.

Which brings up a point: the probe can only react so fast to temperature changes, especially these rubber or vinyl coated probes often used by herp temp controllers. If my cage goes from 80 to 100 deg in 15 seconds, the probe may only show 85 or so at 15 seconds. It takes time. So probe placement must be where the eggs are, not by the heater. Again, just giving theory, not saying you are doing one thing or another. This scenario can account for why a desired temp is actually higher than the setpoint.

Even with proportional controllers, one needs to size the heater to a reasonable level for the intended results. The proportional controller is always trying to find the "sweet spot" where the power to the heater is just right to hold temperature. There is a range where that sweet spot functionality works. Outside that range, the proportional acts more like an ON/OFF. So if for example a heater was sized much too small or much too large, or the ambient air temp is far too warm or far too cool for the intended results, the proportional controller is really just an ON/OFF controller as far as results are concerned. Not saying this is true for you (I'm sure it isn't in a house), but if it was, then the proportional controller will not hold a tight temperature.

So to sum it up, good insulation, proper probe placement coupled with a heater that is not too large or too small for the intended results will result in very good control when using a proportional controller.

Or else your controller is malfunctioning.. lol
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Mark