Another, ATX PSU modification thread.

[Fflint]

I have a 1000W ATX computer power supply. It is a nice device (Cooler Master M2 silent Pro) capable of sourcing over 80 amps of 12V current.

I have so far modified it to provide potentiometer adjustable voltage between 12.1V and 15.7V. It is being used as a large lead acid battery charger. I had to disable the overcurrent and overvoltage protection circuits so there is none. Therefore I'm not using it unattended. Just when I want to do a quick top up.

The PSU uses a Cm6802 PWM controller. So my voltage control is accomplished by inserting a 20k potentiometer into the voltage feedback path.

This works well for what I'm using it for, but I have another potential use for it mind. It is to periodically charge batteries from a generator while said batteries are connected to an inverter that is under load. I think the best way to do this would be for the ATX PSU to be a voltage limited constant current source. If the inverter is under a load that exceeds the PSUs set current it should lower the voltage down to as low as 10.5V (so the batteries can pick up the slack or the inverter low voltage cut off will shut it down). Unfortunately the PWM control circuit uses a built in reference voltage so I can't really lower the voltage below 12.1V with my current setup.

So I'm considering an external circuit for current control. For example a single IRFP3206 mosfet attached to a large radiator (possibly with a fan too). Biased with an LM317 voltage regulator controlled with a potentiometer. The current would be set for up to 50A at most. Maximum voltage drop expected on the transistor 4V. 200W is within the spec of the transistor.

Of course a buck converter would have lower losses, but I'm trying to keep it simple.

So what do you think? Is there an easier way to control the current of the psu, perhaps?

BTW, I'm following the usual high voltage safety recommendations. I have an isolation transformer a variac and a current limiting light bulb (I know not everyone is a fan of those, but they do work nicely). Also my AC is a dedicated circuit with a 6A breaker and an RCD.

For those interested here is a picture of the modified PSU before I made extra holes in the chassis.