Back-UPS CS 500 misbehaving

[beneix_apc]

This was originally posted on APC forums on 2/3/2015

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I have a Back-UPS CS 500 that I have owned for about 6 years. It runs a modest load of perhaps 150W. On occasion, perhaps three times per year, it will seemingly mis-detect a power outage, but in a strange way. It starts switching between mains and battery power and back, quite quickly. The internal relay can be heard clicking and the "On Line" and "On Battery" lights take turns lighting up. After a bout of switching, it will start emitting the "power lost" beep and keep switching back and forth.

This can go on for anything from 5 to 30 minutes. Pressing the reset button on the back does nothing. Turning the unit off for 5 or 10 minutes does nothing. Disconnecting the mains does not stop the problem once mains is reconnected.

I replaced the battery about two years ago, thinking that it might be the culprit - but that did not seem to make any difference.

When it happened this morning, I decided to measure the mains using a true RMS meter. It showed nothing out of the ordinary - 248V, 50.1 Hz.

Do I simply have a faulty unit or is this a known issue with this model?

Thanks.

Newbie - couldn't get the "Insert video" function to work, but I have posted a video of the UPS here: http://youtu.be/_1RkFP92Uwo

[beneix_apc]

This was originally posted on APC forums on 2/23/2015

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Bump!

20 days, 86 views, not a single reply...no thoughts out there?

[BillP · Accepted solution]

This reply was originally posted by Angela on APC forums on 2/24/2015

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Sorry for the delay. I'll see if anyone has any ideas based on your video. What I first thought to try was changing the UPS sensitivity to incoming power if it is seeing some type of power problem it cannot react quick enough to. You can do this through the PowerChute software if you use it or via the front button on the UPS when it is turned off but plugged in. Instructions are here http://www.apcmedia.com/salestools/ASTE-6Z5KMM/ASTE-6Z5KMM_R1_EN.pdf on the bottom of page 1.

Beyond that, I'd suspect a problem with the UPS if it is not a problem with the incoming power. I realize this may also be a little unpredictable and you cannot replicate it easily but you could also try it at a different physical location if you're able to. Or at least another circuit at your current residence or facility when the problem happens.

I'll report back if anyone else gives me any other ideas or debunks my thought based on your video.