I have a Supermicro Redundant Power Supply with two units in it. I also have two UPS units, one for each of the Power Supplys. I was watching the LCD on the UPSs for the watt usage. The total watts equal about 400 Watts. This is where it gets strange. I observed the following, something that i have not seen on any of my 30 other Supermicro Redundant Power Supply setups.

It starts with...
    UPS1 200 Watts UPS2 200 Watts.
    Stays the same for 3 seconds and then changes with in a second to...
    UPS1 0 Watts UPS2 400 Watts.
    Stays the same for 3 seconds and then changes with in a second to...
    UPS1 200 Watts UPS2 200 Watts.
    Stays the same for 3 seconds and then changes with in a second to...
    UPS1 400 Watts UPS2 0 Watts.
    Stays the same for 3 seconds and then starts the cycle over again. 

The wattage is sloshing back and forth 200 Watts at a time from one UPS to the other. I know it has been doing this for at least 6 hours now and i am not sure how if it was doing this before or not.

Does anyone have any ideas of what may be going on. Maybe some things i could try?

  • UPDATE: This stopped on its own. Not sure why/how. It is split 50/50 right now. – xriri Jul 8 '17 at 18:40

What type of behavior do you expect?

Compare your BIOS settings to the other servers and modify the configuration to match the existing systems in your environment.

See: How do servers with redundant power supplies balance consumption?

  • 1
    All of the 30 other Supermicro Redundant Power Supply setups split the load evenly. I would expect this setup to have the load be UPS1 300 Watts and UPS2 300 Watts. – xriri Jan 19 '17 at 6:04
  • As for the BIOS settings there are none. The system has no idea on what is giving it power. – xriri Jan 19 '17 at 6:05

I would have to suggest that this is an issue with the back plane of the redundancy module. Power switching such as this is going to either be an issue with the UPSs (unlikely) or (more likely) the firmware that controls the individual usage per PSU. I'd contact SM and see about a replacement.


With the maturation of engineered obsolescence, even supposedly reliable equipment, such as enterprise-grade modular UPS systems, fails within a few years. Rather than a redundant PSU, try having two redundant servers, each with a regular PSU. Any component could fail, not just the power delivery.

As for the root cause of the phenomenon observed, I suspect the beat between the inverters with slightly different output frequencies.


The inverters shouldn't be running when he's on-line in most UPS systems. I suspect rather that it's a failure in the switching power supply manager(s) inside the system. Either the control logic system that manages the interactions between the two power supplies and the PC's power busses or one or both of the power supplies is failing intermittently.

Given the nature and rhythm of the failure, the control logic is the more likely culprit. I'd contact super micro and swap out the chassis.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.