UPS... buzzing noise when on battery?

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blade52x

2[H]4U
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Sep 9, 2006
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This morning the power went out so my UPS switched on. Anyway, I heard a buzzing sound when it switched on. Initially I thought it was coming UPS. But upon closer inspection I it was coming from computer. And this was a loud buzzing noise. My guess is that it was the PSU making this noise. But the computer itself was running fine. The voltages were all normal - nothing seemed unstable... So I powered down the computer, and even when off, there was still this loud buzzing noise from what sounded like the PSU. It wasn't until I hit the switch on the back of the PSU that the buzzing noise stopped.

At the time only the monitor, computer, and external were actually on. Few other things connected were off.

It's an APC 1300VA UPS. It's got a step approximated sine wave. Is this damaging to the PSU over long periods of time?
 
This is pretty much normal for the stepped sine UPSes. While it can be damaging to some types of electronics, i.e. I wouldn't want this feeding my AV receiver, computer PSUs are quite resilient to minor fluctuations in voltage, frequency, etc. Personally I don't think there is any long term damage that would occur from running off it. Really you never (should) be running off it for extended periods of time anyway right? :)

My LCD monitor actually makes a pretty nasty buzz when it goes onto battery power too, but with no real ill effects. I guess if I were in an area where power was bad enough that I was being switched to UPS power a lot, I would probably want to invest in a true sine wave UPS just to be safe. Though that kind of place would have many more problems I guess.
 
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