I have a ZM1250-Platinum model ATX Power Supply. It's the first I've considered making into a bench power supply that has two +12v outputs instead of just one: +12v1 @ 45A and +12v2 @ 65A. Even though they share a common ground, is there any configuration possible that could get these two supplies in serial and up to 24v? If not, what can I add to my knowledge as a take away lesson? Would it be possible if I really took the whole thing apart and somehow separated the common ground from one of the +12v supplies?

  • \$\begingroup\$ Only if they had isolated secondary coils. \$\endgroup\$ Commented Mar 13, 2018 at 2:54
  • \$\begingroup\$ Not without disassembling and converting the internals. \$\endgroup\$ Commented Mar 13, 2018 at 2:55
  • \$\begingroup\$ Tony Stewart. EE since '75 - would another name for "isolated secondary coil" be an "isolation transformer"? \$\endgroup\$
    – Lunchbox
    Commented Mar 13, 2018 at 2:59
  • \$\begingroup\$ almost, I doubt but they they could have isolated coils which would be on on the same core to reduce winding losses. \$\endgroup\$ Commented Mar 13, 2018 at 3:06
  • 2
    \$\begingroup\$ You have a steep learning curve in understanding the nuances of SMPS PSU design... mutual stray coupling, reactive loads and transformer leakage at high f, safety currents, DC stability and SCP:Short circuit protection OPP:Overpower (overload) protection OCP:Overcurrent protection OVP:Overvoltage protection UVP:Undervoltage protection. T'is Better to modify a 250W supply from a DIY Bench supply site with variable output and learn from that first, before you dive in over your head. \$\endgroup\$ Commented Mar 13, 2018 at 18:34

2 Answers 2


The only way way you could achieve a 24V output with PC or SERVER power supplies is to get one that specifically outputs 24V.

You cannot even try to use two separate but identical PC power supplies that output 12V because the negative terminal of the 12V is always connected to the common earth ground terminal at the input AC connection on the power supply. This means that you cannot stack the two 12V outputs.

So purchase the properly designed 24V power supply for you use.


It would be major surgery to isolate one 12 V supply, and you may find that impossible if the overcurrent detection shuts down both supplies.

If you are doing something professional then I'd suggest getting an ATX supply that includes a 24 V supply. They are available ....here's the Nipron NSP2-250-F2S. This has a separate 24 V supply.

If what you are doing is building a CNC (many require 5/12/24-36 V) you might do what I do ....add on a 12 V to 24-36 V boost convertor to an ATX power supply. I've had good success with the BST900W which is readily available on Ebay.
*NOTE** One little surprise is that the supply outputs 12 V as soon as the input 12 V ramps up, it then ramps to whatever voltage you set for power on.
I have not used mine above 250 W and would be very careful if you need higher power, as it does get hot.


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