Incubator temp rises on battery back-up?

I made an incubator from an upright freezer. 8 foot of 11" flexwatt (400 watts) does the heating. 2 120mm PC fans provide circulation. The thermostat is a Herpstat orginal. I run the herpstat/heat and the fans on a 450W/750VA APC battery back-up.

Tonight I unplugged the backup to see how long the battery would provide back-up power. It lasted 15 minutes, but while doing so the temperature inside of the incubator went from set temp of 87.5 to 97 degrees F in that 15 minutes.

Who can tell me why it would do such a thing?

I have sent an inquiry to Spyder Robotics. If they give me any useful information I will share it here for those who wish to attempt the same setup.

I remember reading somewhere that proportional thermostats, like Herpstat, shouldn't be run through a surge protector. I would imagine that a battery backup unit has a surge protection feature (for when the power comes back on).
Of course, if the unit is inside (where the compressor lived), I would also wonder if it is generating heat which raises the inside temp.

This battery back-up does indeed have a surge protection feature. I'm not sure of the joule rating at the moment. And this particular model also has automatic voltage regulation to keep voltages stabilized when the lines drop below or rise above a set range, however I'm not sure that the AVR feature even works when the back-up is not plugged into a computer via the USB interface. That's something I'll have to include in my inquiry to Spyder Robotics. Appreciate that thought.

The back-up unit is outside of the freezer and should have no effect on the temperatures inside. It does generate some heat, but not enough to count I don't think.

Please keep us updated. I have that same battery back-up but I use wine cooler style fridges (smaller). I am going to unplug mine now and run the battery and check it. I am using a Ranco on the incubator though.

I just noticed a mistake with my setup. Is your fan connected into the battery back up also? Are you reading from a second thermometer?

17ish minutes and still at 89

Hello Focal.

My fans are also running on the battery. I'm not sure those 2 120mm fans will be enough circulation when I start filling up the incubator so I may add more or get a small box style fan and run it on low. It's empty right now so no worries.

I'm reading the temperature from the Herpstat. What does the general consensus find to be an accurate thermometer for measuring the incubator? I should get a second. I'm wishing this would work out with the herpstat... but I guess it has something to do with the way the herpstat accepts the voltage from the backup? My options seem to be either try another thermostat or drop the back-up. Also, if the heat were not running constantly while the back-up were unplugged I'm sure it would last much longer than 15 minutes. You should get a good looong time out of yours since you're only heating small coolers. It's better to be safe than sorry eh?

I hope Spyder Robotics will chime into my inquiry tomorrow sometime with some insight.

Well,

Dion, the owner of Spyder Robotics got back with me and he has written up a perfect explanation. Apparently proportional thermostats will not operate on cheap battery backup units.

http://www.spyderrobotics.com/home/support_ups.html

Oh wow.