maplearn I turn on the camera and try to reach -20 degrees (the ambient temperature is about 5 degrees), when the cooler gets close to -20 and is running at 100%
That does not sound right; the camera is advertised to be able to achieve 35ºC delta. If it is not a power supply problem, I would contact my dealer for a replacement.
That being said, there are two things to check and consider:
1) what is the voltage of the power supply and its available current rating?
My best guess is that the "n %" number is coming from a pulse width modulator (PWM) duty cycle value, and not an actual power measurement. If you are not supplying the full 12V (and capable of delivering 3A), the "100%" could be a meaningless number -- i.e., it is 100% of what the power supply is capable of, and not 100% of what the cooler is capable of.
2) (not an excuse, but just an observation) pushing this camera from -15ºC to -20ºC will not gain you much at all (take a look at the curves in the ZWO documentation) for a typical Bortle. It is IMHO much better to get a constant but higher temperature (from the perspective of calibrating dark and bias frames). As such, again IMHO, it is better to get a regulated temperature at 70% than a poorly regulated temperature at 95%.
I myself use -10ºC as the target temperature for my ASI2600MC because I don't even find -15ºC to be worth it in my borderline Bortle 5 to 6 skies (the noise from this camera is already lower than noise from the sky background). The cooler was running around 25% last night, although I have seen it go as high as 65% on a warm summer night.
Anyway, if your power supply is not the culprit, you might consider a replacement anyway, since the camera is not working to published specs, even if you don't ever use it to 35ºC delta.
Chen
