Suggestions for debugging power quality issues?

[BillP]

This question was originally posted by Paul on APC forums on 4/4/2011

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I have two SMT1500's... one that has been running fine and a second in another room (the office) that suddenly started switching on and off of line power Friday. The logs indicate "Power Failed" and then "Power Restored" a short time later, and by the time I got home to investigate the attached computer had shut down due to low battery and the UPS was switching back and forth every second, indicating 60Hz or 0Hz as it did, with voltage right in the normal range (between 118 and 122V). The data logs show nothing unusual all day, other than battery voltage decreasing and temperature increasing as the UPS battery drained.

I moved the UPS to another room today and it's happily charging... so there seems to be a power quality issue in the office, but nothing evident from the data logs, and nothing I can see with my trusty old multimeter. Other than dragging an oscilloscope home... any other ideas? I suppose I could hook up a resistor divider to a sound card input for a poor-man's o'scope, but that's not my first choice.

Edit: After being offline for the weekend (I unplugged it to stop the constant switching on and off) I charged it back up in another room and tried it again in the office tonight... "Good" power quality setting and no complaints... I disabled the audio alarms and I'm just going to let it sit for a day logging to see if the problem recurs.

Message was edited by: pmiranda

[BillP]

This reply was originally posted by Angela on APC forums on 4/5/2011

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alrighty. thats a good start to adjust power quality/sensitivity settings.

[BillP]

This reply was originally posted by Paul on APC forums on 4/5/2011

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I think this particular UPS might just be having trouble. After a couple quiet hours last night it started switching on and off then threw a "AVR Relay Weld" fault and refuses to do anything new, so when I get a chance I'll call the 800 number and get an RMA.

[BillP · Accepted solution]

This reply was originally posted by Angela on APC forums on 4/5/2011

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yes, that is a good idea. relay weld is no good 😞

[cwholgm]

My issues are exactly as the OP describes but it is not a Relay weld. 

We have  UPS that switch  on and off battery intermittently.  This happens occasionally several times a minute but usually a couple times an hour.  IT happens  for a couple of days and then it goes away for a week or two.   

In our situation,   the switching on and off  happens across multiple UPS devices spread across the office on devices like a brand new Back-ups 1000 and 10 year old (new batteries!)  Back-UPS 1500 .  They do not click on and off all at the same time,  a click here and a click/beep there.   However it does not happen on ALL the UPSes... The one under my desk, a BackUps -750 of intermediate age is fine...   

First I thought it was bad batteries, nope.  Then, I thought it was the age of the UPSs  but new ones do the same thing.  I have tried adjusting sensitivity where that feature is available and that may help but not always.    We had an electrical contractor who does local industrial work come and shut down power for a day and do a "clean and torque" but that did not solve it either.  The electricians did find some loose neutral wires and it does seem like their visit might have improved the problem but has not solved it. 

I have watched the switching  happen with a multimeter connected to the line and there is no visible voltage drop or spike.  The power company lineman has come out and looked at the lines into the building and torqued those connections.  He saw nothing with a multimeter on the main service lines. 

For background, the building is light industrial with a delta high leg.  It used to be a laundromat and then a bakery.  We are light fabrication with  only 2  3 phase pieces of equipment  and the use of those does not seem to correlate with the issue.  We did install solar many years ago but shutting off the solar backfeed does not seem to affect the problem.  This problem started last fall and prior to that we had no problems for the previous 8-10 years we have been in the building.   No new major equipment was installed that would correspond to this problem starting. 

Any suggestions are tremendously appreciated.  It is driving us crazy! 

Many thanks!

Charles