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The HP Proliant DL180 G6 has a power distribution board/backplane AC-063-2 A P/N 515766-001 with limits specified in the picture. +12 V has 62.5 A MAX

Backplane has connectors for 2 common slot PSUs. I use two 1200 W PSUs.

I need to increase amperage in my system. I believe this backplane uses some form of redundancy logic. I want to sacrifice this redundancy towards current sharing between 2 PSUs connected in parallel.

Theoretically 2 PSUs connected in parallel can privide twice their amperage; it would be great to add at least 50%. This article's advice is to use Schottky diodes to reduce losses.

How to modify this power backplane for current sharing of 2 PSUs? It would be great if the second PSU could be turned on/off automatically with the first PSU.

Unfortunately I have no schematic of this backplane. Maybe they are similar to others.

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Updated I tried to avoid too many pictures but after I read first answer I think it makes sense to show that this is only partially HP server: it has HP chassis and HP Power backplane and HP PSU. Motherboard is Supermicro and wires are solid and custom. The cables are several times thicker then necessary - 10 mm^2 per 10 A (except original wires from backplane to blue distribution board depicted on picture - this original wires are 16 awg - 12 cables) Likely these original cables need to be replaced to increase power. I believe that HP power backplane and its cables is the only bottleneck and dangerous component in this server. I use it for deep learning. I need to replace some videocards with more tensor cores and they require more power. enter image description here

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Backplane disassembled enter image description here

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  • \$\begingroup\$ That's a tough one- Not enough information to answer. One could imagine maybe soldering some bus bars to the PCBs and maybe re-cabling if necessary, but there are too many unknowns to say if there's even a chance that it would work. Lots of other issues that may get in the way. \$\endgroup\$
    – John D
    Aug 24, 2022 at 18:15
  • \$\begingroup\$ Such companies do not provide documentation. But they usually use similar approaches. And somebody may had experience with similar case. I understand that their are different ways to solve - different answers may contain different variants. Most of problems have more then one solution. I think this problem will be solved in couple of iterations. If it is feasible (I believe yes) I will take second the same backplane and will disassemble it. And will provide necessary information. \$\endgroup\$
    – Vlad
    Aug 24, 2022 at 18:27
  • \$\begingroup\$ Soldering and recabling is Ok. Would be great if solution will fit in the original server chassis. \$\endgroup\$
    – Vlad
    Aug 24, 2022 at 18:37
  • \$\begingroup\$ Off topic to the question: that backplane is what generates +5 V to the system as the redundant power supplies only gives +12 V. In the middle of a RAID rebuild, it failed in my server and most of the data was lost. If you crack it open, you will find the ORing MOSFETs. They will set your effective current limit. \$\endgroup\$
    – winny
    Aug 24, 2022 at 19:27
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    \$\begingroup\$ Paralleling PSUs can cause failures unless the PSUs are designed to be paralleled. In the best case, they just won't share current equally, which can lead to a situation where one PSU will provide all the current until it's overloaded, then the other one will after the first one shuts down, then the second will also shut down from overload, thus not actually giving you any more total power than a single PSU. In the worst case, they may interfere with each other's operation (especially if they have a remote sense feature), which could result in all manner of problems from EMI to destruction. \$\endgroup\$
    – Hearth
    Aug 27, 2022 at 15:42

2 Answers 2

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It's an excellent question, because it lets me discourage anyone from doing it - lest they cause damage and possible loss of life.

The rest of the server is not designed to have twice the current available from the power supplies.

What you're proposing is a nice way of getting a fire in the server rack. DO NOT ATTEMOPT.

I imagine that you want to add some heavy GPU load to the server - otherwise such a modification would be unnecessary. You'll need a server rated for such use.

In the current server, it's not only the power supply system that would need to be modified. Various intermediate connectors, possibly motherboard and mezzanine board traces, wire harnesses, protection circuitry. All of that was designed to work as a system. You can't just modify one part and expect success in such a scenario.

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  • \$\begingroup\$ Thank you! Other parts have been modified already and they are ready to consume more power :) I updated my question with some pictures. \$\endgroup\$
    – Vlad
    Aug 27, 2022 at 12:10
  • \$\begingroup\$ And you are right about protection circuitry - this is important thing. I'm not sure PSU protection will work as expected. I think it's necessary to test it somehow. For instance - this sever works about 1 year and ones I made mistake and created incorrect cable. This caused short circuit. GPU is damaged. But PSU didn't turned off - it was working - I disconnected AC power after couple of seconds. \$\endgroup\$
    – Vlad
    Aug 27, 2022 at 12:37
  • \$\begingroup\$ This blue box on picture is bus: 12 cables from HP power backplane are connected to this bus. So current is collected on this bus. Then group of cables connected to particular GPU or to CPU. This way I share current equally between original 12 cables from HP power backplane. \$\endgroup\$
    – Vlad
    Aug 27, 2022 at 12:50
  • \$\begingroup\$ And I think about security as first priority. A year ago 6 3060 consumed 6 * 120 W = 720 W (60 A) + not loaded 2X CPU 25 W each. 4x Delta coolers 4.8 A each powered with external PSU. But now I replaced 3060 with 3080. And systems consume more then 62.5 A. I don't like this therefore I decided to increase limit of current \$\endgroup\$
    – Vlad
    Aug 27, 2022 at 13:21
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Since the PSUs naturally output 12V and that is what you are trying to increase the usage of, you almost don't need to do much. The power backplane likely directly connects the PSU 12V output to the 12V wiring, maybe with MOSFETs to disable the output with the PSU still running.

You probably just need to connect your extra cables with as low of resistance as possible to the existing 12V bus bars in the backplane. Then you need to hope the backplane isn't adding extra over current protection that might kick in. They might just rely on the over current protection of the individual PSUs though.

HP PSUs use an internal voltage droop method of load sharing so that probably won't be an issue. However, HP usually does have a mechanism to let the server admin switch between having both PSUs running simultaneously with load sharing, or only have one enabled and the other in standby for higher efficiency. This is probably controlled via the 16pin RPS cable I'd guess.

This is all not a terrific idea though, since the card edge connector for the PSUs could melt if not rated properly, and the backplane traces and bus bars may not be rated for the extra current. I think you could get it to work though, not for double the current but maybe an extra 30%. Ideally you'd have a thermal camera to make sure nothing is overheating, which is your primary concern. Please be aware of the risks in going off the beaten path like this though.

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