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  1. #1

    Running IBM servers at both 110v and 220v at the same time for a few seconds?

    n our data center we are going to be moving all of our dual power supplied IBM servers (auto sensing 110/220) from an outdated 110 system of dumb power strips to an updated in rack 0u 220 monitored PDUs.

    In order to do this we will either need to power down each server one by one to move both power supplies from the 110 plugs to the 220 plugs or move each psu at a time which means having half in 110 and half in 220 for a few seconds while we move the wires. Has anyone ever done this? I have read on a couple data center blogs that it's not a problem, found a support thread on HP about their servers saying it's not a problem, but still want to ask if anyone else has done it. Being able to use different voltages will reduce the time needed for the conversion from a year to instead several months as down time for every single system will not be required.

    Again, these servers have dual, some quad, independent hot swappable power supplies that auto sense the incoming voltage and adapt accordingly.

  2. #2
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    i can only speak for HP (G5/G6):
    Not a problem, they eat anything from 100-260V if it has enough A/W.
    Since IBM is still a bit more expensive and "higher" than HP i guess they will do this just fine.

    If you have a spare server - why not try it with it?

  3. #3
    I am going to try it next week on a spare server on both an empty 110 and 220 strip. It sounds like it should work, IBMs documentation say it's not recommended but I can't find anything that says DO NOT do it. I wouldn't want to run on different voltages for a long time, this is just for the short migration, wires will be at the ready so it will only be a few seconds mixed.

  4. #4
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    You most likely want to have it running at both for 1-5min so that the capacitors in the 110V can load fully up.

  5. #5
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    The capacitors in a modern computer switched power supply will be fully charged in much less than a half of a second.

    In a server with redundant power supplies each power supply is fully independent of the other on the supply side. Obviously the output sides are tied together to the power busses in the computer.

    You can be absolutely certain that having one power supply tied to a 110V source while the other power supply is tied to a 220V source will not cause a problem as long as the neutral leads are both tied, ultimately, to the same building ground return.

    What will happen is that the switching behavior in the supplies will be different, with the power supply tied to 220V drawing less current, obviously, and most likely switching on and off at different points in the hopefully sine wave power input cycle.

    It also would not matter if one was getting 50Hz AC power while the other was getting 60Hz AC power although that situation would not be likely to arise.
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  6. #6
    There will not be any problems with this.

  7. #7
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    You want to run them both for a little while and then remove the power cord from the older one. Do you really even need to remove the entire PSU? if not just leave it there and remove the power. In either case do not try to swap them out fast like that. I personally would give it 1 day while it runs on both

  8. #8
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    Quote Originally Posted by multexsys View Post
    You want to run them both for a little while and then remove the power cord from the older one. Do you really even need to remove the entire PSU? if not just leave it there and remove the power. In either case do not try to swap them out fast like that. I personally would give it 1 day while it runs on both
    What is the benefit of waiting that long? I don't see much sense in waiting more than a minute or so. We've done this sort of thing several times before. As long as your electrical wiring is good and you're using quality power supplies you should have no issue.
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