orfest temperature set to -20
The camera had a dedicated power adapter, 12V, 2.5A
Hmmm, what was the ambient temperature and cooler power?
The specs for the camera calls for a supply that can do 12V at 3A. Presumably when the cooler is running at near 100%.
Try setting the cooler setpoint to -5 ºC to see if longer exposures now work better. Also, wait for the temperature to reach -5 ºC before taking exposures, so that the cooler starts to draw less power. Trying to get to -x ºC will use more power than trying to maintain -x ºC once you have reached the temperature.
If you can now take long exposures, that cooler supply is the problem, since it is also being used to power the camera's electronics, not just the Peltier cooler.
Check too to make sure the wire gauge is thick enough (and wire length is short) so that there is insignificant I*R drop from your power supply. The resitance of a 18 AWG copper wire is 6.4 milli ohms per foot. A wire pair then contributes 12.8 milliohms per foot, and with 3A flowing though, the voltage drop is about 40 millivolts per foot. A 10 foot 18 AWG cable would therefore drop 0.4V from the original 12V.
If you can't keep the power cable short, you need to use heavier wires (I use 14 AWG wires over a 20 foot run, with the final 4 feet being 18 AWG).
FWIW, the ASI6200 don't realy need to be cooled down to -20 ºC for the dark current noise to be already way below the read noise, unless you are using very long exposures. -15 ºC should be ample for 180 second type exposure durations.
Chen
