Using Two ATX PSU's to provide 24V


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I'm currently working on a project at work whereby someone has built a box with two ATX PSU in them to produce 24V. When I arrived to it it was no longer producing a 24V output in any measurable way. So my mission was to both understand how it produced 24V and to fix it so that it did.

The setup of the box is as follows:

Two sets of posts (red/black) on the front, one providing 12v from the first board and the second providing 24V as a combination of both boards.
The first board functions fine, it has a 12V output as expected. This is where it gets very hazy for me. The second PSU has its DC GND connected to the 12V output of the first PSU. The 12V output of the second PSU is then connected to the red post to provide 24V. The GND of the black posts are linked together and also connected to the AC GND of the second PSU which then links to the GND's of the first PSU.

An AC connection to the second board is made by piggy backing off the first PSU's AC connection.

As per some instructions on the net I then connect the PS ON pin to earth as it's an active low, this will 'switch' the PSU on. I also put a 12V 5W Bulb (was told to do this as a replacement for using a 5Ohm 20W resistor) on the 5V line to act as a 'load' to emulate a connection (any 5V line?).

That's pretty much it.

Both PSU's are of a different make and I believe different Wattage ratings (only slightly).

Can this be done? If so what have I missed? If not how come? I'd like to understand the science behind this. I simplified the idea to be like connecting two batteries in series for the doubling in voltage however the grounding in this case is what gets me undone.

Any help would be awesome.

i wouldn't recommend having two different wattage power supply's from different manufacturers in series and i wouldn't recommend putting two atx power supplies in series at all. i would just spend $30 on a 24v from ebay.