Huge temp fluctuations. Solutions?

[albertagirl]

Hi, I'm having no luck at all searching for answers on this.
I am having ridiculous temp fluctuations and a really hard time getting them under control, and I don't know why or how to solve it.

My questions are:
Has anyone else dealt with this, and how did you solve it?
What range of temperature fluctuation on the hot side of the cage is ok, and at what point do I need to worry? To me, 10 to 12 degrees F seems like a lot. What do you think?
Does anyone think the thermostat itself could be the problem? Or does it indeed sound like a heat dissipation issue? Or does it sound like heat tapes going bad?

Pertinent details:
I'm using 2' of 12" heat tape under the 3x2 pvc cages (I think it's 1/2" pvc, but might be 3/8"?), and 1' of 12" tape under the 2x2's. I have a Vivarium Electronics Hobby Stat controlling 4 of the cages, and a Jump Start digital thermostat controlling the other 4.

The issue:
Both of my thermostats are controlled by a probe, which turns the heat tapes on and off to control temperature. The problem I'm having is that for some reason the cages on the Jump Start are continuing to increase in temperature for about another 4 degrees C (approx 7 F) even after the tape is turned off. I can't understand how this could be any different from one thermostat to the next since the heat tape is not only identical, but it's also OFF. The cages are also identical, as are the setups. Same approx depth of substrate, same thermometers, same cork bark hides over top.

Because of the temperature continuing to climb well after the heat has turned off, I have to set the thermostat really low so that it turns off well before the max target temp is reached, which would be fine except that this means that the temps then have to drop really low in order for the thermostat to turn back on again, resulting in a huge temp swing. So the thermostat is now set to 80F. Heat tapes turn on once temps drop below 78F, and then turns off at 82F and keeps climbing to about 89F before starting to drop again.

The only thing I can think of that might be the problem is that the heat is not dissapating properly? I've tried reducing the amount of substrate to allow for faster heat dissipation, with no real improvement. I could try increasing the amount of airspace below the cage (which would suck as it would mean tearing the whole stack down), but it has the same airspace as the others, so again, I'm not sure if that would help.

Thanks!

[Andy_G]

Do you have any spacing between the cages for the heat pads to breathe? This is important otherwise you'll have hot spots build up. Secondly, on/off thermostats such as the Jump Start will always maintain less constant numbers in comparison to a proportional thermostat, which is not really a big deal but that may be something to consider as well. Both of these are on/off so I find it a bit strange that your jump start is giving you problems and the VE is not.

[albertagirl]

Do you have any spacing between the cages for the heat pads to breathe? This is important otherwise you'll have hot spots build up. Secondly, on/off thermostats such as the Jump Start will always maintain less constant numbers in comparison to a proportional thermostat, which is not really a big deal but that may be something to consider as well. Both of these are on/off so I find it a bit strange that your jump start is giving you problems and the VE is not.

I am face-palming myself right now. In writing my response to you (which I have now edited) it occured to me that the cages with all the problems are the ones sitting directly on a 2 inch wooden surface as opposed to sitting atop another cage. OF COURSE the heat will build up!! Duh!

They are on little rubber feet, but with the weight of the whole stack, the feet on the bottom cages got a little squooshed and provide probably half of what the heat tape manufacturer recommends. I just couldn't figure out why only the bottom cages were having the worst issue though. I just now realized it's the table that's different between the two levels! Ugh!
They have always been about a degree above the others, which I always thought strange, but wasn't too concerned about, until tried to use them to run the thermostat.

I am going to have to tear the whole stack down and replace those rubber feet with plastic or wood. I am really not looking forward to this. :no:

Meanwhile, I'm sorry for having wasted anyone's time with this thread. I've literally tried to figure this out for two days now, but didn't realized the table was the key until I read your response Andy.

As a sidenote. Can you recommend a good proportional thermostat that will run me under a hundred dollars? Or over a hundred is fine if it can run two separate temperature zones.

[Andy_G]

Don't worry! All a part of learning! We've all been there. I hope that what you're going to do will fix your issue.

Unfortunately I don't personally know of any proportional thermostats under $100 or even slightly over $100 with more than one zone. The herpstat 2 is around $200 and would probably be the best choice but it doesn't really match your criteria in regards to price point.

[albertagirl]

Thanks. That's what I thought. I wish I had splurged from the beginning and bought one right from the start. Oh well, hopefully these new feet I just got will do the trick. Now the big job of pulling the cages down, sticking new feet on, and then setting them all back up again. At least I can inspect the heat tape and see how they're looking after 2 years of continuous use!

[Albert Clark]

Spyder Robotics is a real resource and they will be happy to discuss problems you may be having with a thermostat even if its not their herpstat products. The customer service department is very helpful to the herpetoculture community. They also run sales on their products intermittently. I bought a herpstat 2 redline for 139.00 not too long ago. Alberta, i think you are going to have to invest in a proportional tstat soon. I think Spyder Robotics wants emails first and then they will respond to you or call you if you give your phone # in your email.

[Albert Clark]

You can go directly to their website and generate the email there. They usually get back to you within a 24 hr. period.

[albertagirl]

You can go directly to their website and generate the email there. They usually get back to you within a 24 hr. period.

Thanks. I'm finding that things cost significantly more in Canada, but I will contact them. If I can get a good price it might save me some frustration in the future.