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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?

Lunchbox
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  • Only if they had isolated secondary coils. – Tony Stewart EE75 Mar 13 '18 at 02:54
  • Not without disassembling and converting the internals. – Laszlo Valko Mar 13 '18 at 02:55
  • Tony Stewart. EE since '75 - would another name for "isolated secondary coil" be an "isolation transformer"? – Lunchbox Mar 13 '18 at 02:59
  • almost, I doubt but they they could have isolated coils which would be on on the same core to reduce winding losses. – Tony Stewart EE75 Mar 13 '18 at 03:06
  • You would have to poke around with a DMM live https://content.hwigroup.net/images/products_xl/156725/3/zalman-zm1250-platinum-1250w.jpg I see twin transformers , so its a maybe – Tony Stewart EE75 Mar 13 '18 at 03:13
  • @Lunchbox, no, there always is an "isolation transformer" in a PSU. But to get stacked 12-V supply from 2 outputs, you need two isolated secondary coils, and perform serious surgery to PCB to separate filter capacitors and coils from common ground, which is likely impossible, all grounds are always connected on modern supply's PCB. – Ale..chenski Mar 13 '18 at 03:14
  • @Lunchbox. These power supplies monitor voltage and current of each output. On top of cutting the common return traces, you would have to adjust some resistors or trim pots so a 12 volt line is now regulated to be 24 volts, at 1/2 the original current. –  Mar 13 '18 at 03:18
  • Possible duplicate of Connecting two atx power supplies in series – winny Mar 13 '18 at 06:44
  • @winny - I'll read through your link and see what I can cull from it. The unique thing I've seen about this proposed question is that the one I'm looking at has two +12v "rails", a +12v1 @ 45A and +12v2 @ 65A.

    Sparky256 - I'll write down the note of 24v at 1/2 the amperage as a possibility.

     – Lunchbox Mar 13 '18 at 18:00
  • @TonyStewart.EEsince'75 - thanks for pulling that image up. I have take a few myself but I wasn't sure of how to upload them. – Lunchbox Mar 13 '18 at 18:06
  • @TonyStewart.EEsince'75 - I'm a little inexperienced in EE but I'm trying to learn as fast as I can. Do you have a good resource that I could use to help identify each different component on this PCB shown in the link you provided? – Lunchbox Mar 13 '18 at 18:19
  • @Lunchbox That complicates things further, but you main issue remains the same. – winny Mar 13 '18 at 18:22
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    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. – Tony Stewart EE75 Mar 13 '18 at 18:34
  • @TonyStewart.EEsince'75 - I certainly do, but a steep learning curve is just the kind of challenge I gravitate towards. Right now I'm just trying to become familiar with the Stack Exchange community, how it works, and where the best resources are that I can learn from. Hopefully someday I can offer the same service to the community that you all do. I'll probably end up getting a variable bench supply in the end but was hoping to learn with what I have on hand to start with. – Lunchbox Mar 13 '18 at 19:45

2 Answers2

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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.

Michael Karas
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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.

Jack Creasey
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