Quote:
Originally Posted by vsmGuy
Attached is a clip of the sound that comes from the 22uF, 150V bipolar yellow capacitor(s) in both the models when charging the batteries.
At 45s into the recording, I turn off the line power - notice how the noise goes away completely when it's running off batteries in the 1000VA (the one which was running when I recorded the noise)
I am sure you will agree this is very different from the gentle hum of a transformer?
If this is a characteristic sound of APC UPS when the batteries are dying, I would like to know if there's a battery I can buy, from say Walmart or Home Depot etc just to see if a new battery makes the noise go away.
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Ah, you mean this. I heard that too with two BackUPS (those are the power cords with battery

) and yes, both had pretty much dead batteries. Swaped for good (well, with 2/5 of nominal capacity, but working normally) just for testing and it was OK again.
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