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Random on-line to on-battery with minimal load?

Discussion in Back-UPS & Surge Protectors started by rick , 9/8/2018 5:30 PM
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  • VE7ASR
    Novice Novice
    rick 9/8/2018 5:30 PM

    My Back-UPS XS-900 has performed flawlessly for several years. Recently it began to behave strangely.

    First, this behavior happens ONLY on light load (likely under 25 watts). Under my "full" load Power Chute software suggests that I'm drawing nearly 100 watts. Under these conditions all is well. 

    When I turn off my computer the load goes to a minimum AND after some period of time the UPS will begin randomly switching from On-battery to On-Line. It does this 8 or 10 times and then settles back for some random period and starts again. It does this over and over.

    When this first began I noticed that the batteries were long in the tooth so I replaced them. That had no impact on the problem.

    A review of the Power Chute software indicates an input voltage of 103 volts. Measured voltage at the AC plug used by the UPS is 118 volts?

    Thoughts appreciated. Thanks!


  • brewmonkey
    New Member New Member
    AJ 10/5/2018 4:23 AM (in response to rick)

    Today my Back-UPS Pro 1000 just started experiencing nearly the same thing, although mine sits at a fairly consistent 66-75w all the time. Mine powers a FreeNAS server, so Power Chute is not available to see what the event log might show. Nobody replied to this issue here (as seems to be the case for many posts I see on here), but have you gotten any resolution to it elsewhere perhaps? It's more than a bit disturbing.

  • VE7ASR
    Novice Novice
    rick 10/5/2018 5:10 AM (in response to AJ)

    Thanks for the reply AJ. I have not resolved the problem "yet". I still think that the APC UPS  line voltage sensing circuit is the problem. It senses a voltage well below the actual line voltage and then if it makes an excursion of a few volts lower it sounds an alarm.

    I took the unit out of service and I "plan" to look into the box BUT without a schematic it's a long shot.


  • VE7ASR
    Novice Novice
    rick 11/7/2018 3:25 AM (in response to AJ)

    Hi again AJ.

    Well I have some info on MY problem. My APC Back-UPS Pro 900XS was on-line when the input voltage fell too low. That is too low according to the PowerChute software (the measured line voltage was 117 VAC.). Apparently this is a known problem. According to:


    The last item in this discussion explains "I talked with one of our engineers and discovered the issue is caused by the Back-UPS firmware. The issue has been addressed in later firmware releases. Unfortunately Back-UPS do not have upgradeable firmware."

    WHY APC hasn't answered our questions through this forum or through the PowerChute software is unclear.


  • wpasquil
    =S= Representative
    Bill 11/7/2018 6:25 PM (in response to rick)


    Sorry you are not happy with the unit. As listed in the post you linked the issue has been corrected within the firmware. You should contact local support if you feel the unit is not working as expected. If the unit is under warranty they will assist with a replacement. 

  • VE7ASR
    Novice Novice
    rick 11/8/2018 5:47 PM (in response to Bill)

    Thanks for the reply Bill. Unfortunately with the erroneous voltage reading the alarm periodically gets triggered and the UPS goes onto battery. I've seen input voltage readings (according to ACPUPSD) as high as 108 VAC and as low as 94 VAC. This happens even with a steady line voltage of 117 VAC. In addition, the MEASURED output voltage is now quite high (in excess of 130 VAC).

    This UPS has served me well but I'm afraid that trusting it much longer might be risky. So I think it's time to retire the unit.

    Again, thank you for the prompt reply.


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