krairach said:
I use an ATX PSU to power a 226W Peltier.
To reduce heat output of a peltier by reducing Voltage, can I just use a +3.3V as a GND and +12V as positive to get +8.7V?
The voltage regulation of the 3.3V rail is designed for current to flow
out of the 3.3V rail to ground. It is not designed for current to flow
into the 3.3V rail from a more positive rail. Doing this will cause the supply to either shut down or die.
You can get away with something like this (the 7V mod for fans) if there is a load between the 3.3V rail and ground that is greater (lower resistance) than the load between 12V and 3.3V. In other words, you could make this work if you connected a 50 Watt 0.22 Ohm resistor between 3.3V and ground. The 0.22 Ohm resistor would be dissipating 50 Watts though, and would need fairly serious cooling of its own.
With a setup like that:
About 13 Amps would flow out of the the +12V rail through the TEC.
About 15 Amps would flow through the 50 Watt resistor. (3.3V / 0.22 Ohms = 15 Amps)
The 2 Amp difference current would flow out of the 3.3V rail.
It can be done, but it's kind of ugly.
Unfortunately I don't know any solutions that are much better that don't cost a lot of money.
