Power supply card tested

Finished testing the power supply card and mounting the power supplies on a piece of plywood.  As mentioned before, it is four PC power supplies connected in series.  The last three power supplies have their grounds floating so that it the end power will be 48V.  The power supplies must be electrically separated since the chassis of the first supply is gnd, 2nd supply is 12V, 3rd supply is 24V, and the last supply chassis is 36V.  I plan on adding a plastic cage over the power supplies to make them a little safer.  The other option would be to take apart the power supplies and try to separate the chassis from the grounds.

If you look at the pictures there are a lot of extra power supply connectors that can be removed.  The main 24 pin connector and the extra motherboard 12V connector are used.

What’s the cost of this monster…

4 PC power supplies (just checked Amazon, and they are $10 each).  Board that ties the power supplies together ($27 and that got me 10 of the boards.  Who knows what I’ll do with the extras.)  Connectors to populate the boards (bought 75 connectors for $24 off ebay).  My total cost was about $100, with plenty of leftovers to make another 5 or 10 of these.

Here are the pictures:  First one shows the four power supplies with 48V on the DMM.  Second picture shows the card dwarfed by all the extra connectors.  Last picture shows the isolating power connector.

superpwr48v pswcard isolatedgnd


4 responses to “Power supply card tested

  1. does not look very safe. are these all single rail psu? Cant they handle such a draw on the single cable? my understand is you should really tie in all the other 5v/12v etc lines so not all the amps are coming off just one 12v connection. what gauge wire is the main atx connector?

    • You definitely wouldn’t want to tie the 5V and 12V lines together because you would over-voltage your caps inside the power supply. How it works is that the first power supply provides 12V. The second power supply uses that 12V as its ground, so it ends up generating 24V. The third power supply uses the second power supply output (24V) as its ground. That ends up that the last power supply is providing 48V. Each power supply is only providing 12V (difference or gain) at the rated current (20A in this case).

      If you would tie together all the 5V/12V lines, you would not get any voltage gain, but you would get a higher current power supply. (You would also have to worry about load balancing of the power supplies. Some FETs handle this well, meaning they increase in resistance as temp increases, so it shuffles the current to other less utilized FETs.)

      The power supplies have 2 12V connections on the main ATX connector, plus 2 12V connections on the supplemental mother board power connector. Each of those wires is 16 AWG and so that is 22A x 4 or 88A maximum current for chassis wiring which the chart is very conservative. The power supply boards then use flooded plains to attach the pins between the connectors. With the width of the plain that I used, it should be less than 10C rise in temp at maximum (20A) current.

      I’m planning on fusing the lines on the bottom of the playfield for safety.

  2. I dont mean tie the 5v to the 12v, I mean tie all the 5’s out to a 5v bus bar, and all the 12’s etc. so you can tap off the 12/5 for other things microcontrollery and lampy and such.

    • You can tie all the 5Vs in a single supply together. The second supply, the 5V is actually at 17V because its ground potential is at 12V (not ground).

      I have a connector that brings out a lot of the other voltages. I chose to bring out 3.3V (to run Raspberry Pi, and LED lighting cards), 5V to run the solenoid driver cards and any other general lighting that I want to run, 12V to run any flasher bulbs or things I need a little more kick (maybe a motor), 24V to run motors the bigger feature motors, and 48V to run the solenoids. There are a lot of over voltages that are available, but I chose those to be the most likely and put those out to a single connector.

      To get what voltages are available, its just (x*12V) + any PC power supply. (x can be from 0 – 3). If you happen to want 27.3V, you could simply tap off the 3rd power supplies 3.3V rail. 41V would be the 4th power supplies 5V rail.

      The only thing to watch for is each power supply is only rated for 20A on the 12V line. So if you need a lot of 36V power and 48V power, you are limited to 20A total since both of the are using the 12V of the first power supply.

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