I've made a cooler box for a DSLR to keep it cool while doing long exposure astophotography. It uses 2x 12706 12V 5.8A peltiers which are water cooled. Peltier spec on amazon says VMAX 15V IMAX 6A QMAX 72W.
The box works really well and I'm able to cool 25 Degrees Celsius below ambient temperature in 15 minutes but I'm seeing something strange..... When I power the peltiers on, the Voltage drops to around 6-7V drawing around 4A. I am using an 800w ATX PSU with a 5-60V DC input 20A PWM speed controller to control the temperature. The label on the PSU states a total load of 125A/648W on the 12V rail.
I think I understand from some other reading on here that if the psu cannot deliver enough current it drops the voltage. I'm sure that's a very simplistic way of looking at it but if that is the case. Why am I getting a drop in voltage when the PSU clearly is capable of delivering enough current? Am I missing something obvious?
With nothing connected to the PSU it is giving me 12.2V. With only one peltier connected I get a drop to around 9V.
I have tried connecting one and both of the peltiers directly to the PSU without the PWM controller and get the same readings. Anyone any ideas please ?