Power supply makes loud buzzing noise when running off UPS battery

[CalvinHobbes]

Had to use a new UPS for the first time last night when the power went out during a storm. As soon as I was on battery power I heard a loud buzzing sound that I traced back to the power supply in my PC. I turned off the power switch on the PSU and the buzzing continued. I pulled the power plug from the back of the PSU and the buzzing was gone.

Anyone ever have any issues running a PSU off of a UPS.

 

[Modelworks]

Some ups, especially cheaper ones, have a modified sine wave output. Some power supplies don't like that.

 

[SparkyJJO]

Most UPSes don't have a true sine wave output, it is actually a triangle or square wave, or a "stepped" sine wave. This creates the noise you are hearing. It isn't hurting anything, just creates noise.

If you got a UPS with a true sine wave output the noise wouldn't be there, but those are quite expensive.

 

[CalvinHobbes]

Thanks for the explanation.