Coil whine, is it normal?

[Anonymous user]

Hi guys,

I always had UPS's from APC, but in the last months I realized something that is strange to me.

When my PC is using the UPS battery (for example, when a blackout occurs) and I'm talking with someone on Skype, etc, people complains that they can hear a strange "buzz" from my microphone (the mic is connected to the mic jack on the back of the PC).

From what I understand, this is caused by the APC UPS, because when there is a blackout the UPS starts making a sound similar to coil whine, and my PSU starts making it too (XFX PRO Series 650W).

So, my question is: Is this normal? Could it damage my PSU or other components?

UPS: Back-UPS ES 700

Thanks!

[voidstar_apc]

It's probably normal. The BackUPS uses a psuedosine wave which has a range of audible frequencies. It should not damage your pc.

[Anonymous user]

But why my PSU starts making the "coil whine" noise when using the UPS Battery? It doesn't make it when the UPS isn't using the battery.

[voidstar_apc]

The UPS only produces the psuedosine waveform when on battery. The rest of the time it feeds wall power directly to its output (your PSU).

[Anonymous user · Accepted solution]

On 9/18/2016 9:02 PM, Diogo said:

But why my PSU starts making the "coil whine" noise when using the UPS Battery? It doesn't make it when the UPS isn't using the battery.

When the UPS is running on battery, its output waveform is different from what your electrical utility delivers. Here's what your electrical utility should be providing when the power is on and everything's working normally:

When your Back-UPS is on battery, this is what the output waveform will look like:

Your power supply will not be harmed by this waveform, but it may produce more noise and buzzing than it would when running on AC line power. By the way, and for your own safety: do not attempt to inspect the AC power waveform unless you know EXACTLY what you're doing!