home made incubator temp fluctuation

okay today i made a home made incubator, this is what i used
48 qt cooler with a hole cut in the lid with a piece of glass duct taped on for a window
i ordered i bi-metal thermostat for incubator warehouse which is connected to 11"x12" piece of flex watt tape for a heat source.
i also wired up a computer fan to a 12v cell phone charger pointed at the thermostat. (found online that would make the thermostat more sensitive).
lastly i have a zoomed prob thermometer running to inside the egg box and a digital thermometer/hygrometer outside the egg box.

now my only concern is the temperature fluctuation. it drops as low as 86.5 and spikes as high as 90. i can raise or lower the thermostat but i know to much heat is really bad and I'm sure less then 86 isn't good either.

so my question is how can i get more steady temps?
or are mine okay now? iv heard many mixed opinions.

thanks

First, I'm not an expert on thermostats. Your inquiry intrigued me so I did a little research. The problem may be in the bi-metallic thermostat. It does not "control" temperature as precisely as a proportional thermostat like the Herpstat brand. The temperature fluctuations you are seeing are normal for a bi-metallic thermostat...from what I can tell. Of course those temperature fluctuations are not appropriate for the needs of ball python eggs. I use a Herpstat on a newly set-up cooler (check my DIY incubator post) and the temp doesn't fluctuate more than 0.5 degrees Fahrenheit as measured by two thermometers placed in the incubator. I'd recommend a proportional thermostat like a Herpstat for more precise temperature control.

Matt

Agreed, the bi metal system that is used on commercial incubators works very poorly. They typically cannot control accurately inside a 5º window. A proportional system is massively better.

Better thermostat for sure. Proportional would be the way to go.
The fan is there to circulate air and even temps out, I would not have it blowing on my thermostat probe.

I have a Herpstat controlling my incubator. You can get them direct from www.spyderrobotics.com. I got mine 3 days after ordering. Get the Herpstat 1. It is $139. You get Hi, low alarms. dimming and pulse control options. safety power relay. and more. Well WELL worth the price. If you have a rack then order the herpstat 2 and control both :)

do you think my current fluctuation is too much? i got the bi metal one
because of the affordability

In my incubator I get a fluctuation of less than 1/4 of a degree. Mine is made from a very well insulated wine fridge. The difference really is in the thermostat. My herpstat keeps it so tight because it controls the amount of power going to the heat tape (which it displays it on the thermostat). it feathers it slightly up and down to keep it spot on. If I open the door and the temp drops a degree or two it powers to 100% then slowly feathers it lower till it lands right on my setting. Make sure your window you cut is sealed tight and then get a good thermostat.

An incubator is the last place you really want to pinch pennies

ok so i did something dumb here i think so bare with me..

the thermometer iv been reading these temps off of has the probe running right into the snake box.

when i was putting it together i was thinking it would be better to know the temperature where the eggs
will be rather then the temp around the egg box . i put a digital thermometer ontop of the egg box and the swing was less then 2 degrees.

thoughts on that?

How accurate is the thermometer? Many inexpensive digitals have specs at +/- 2ºC (loosely 4ºF) some are better and have 2ºF in error it is possible for the swing to be out by 6 either way or 4 either way. Incubators need accuracy you could buy a thermometer that is around the 0.8ºF +/- accuracy or a thermostat that is that accurate (herpstat, helix, ecozone, herpkeeper all do) at the end of the day either way you will spend around 120$ or either stat or thermometer.