HISSING from Back-UPS Pro 1000

[Anonymous user]

Hi ALL,

I have bought many APC UPSs in the past and have always been satisfied with them.  The one for my PC was many years old and I just upgraded to a new Back-UPS Pro (BR100G) bought from Amazon and it seems to be working fine.  However I discovered that when the unit is switched off it makes a "hissing" sound!  Its not real loud but I definitely can hear it.  I use the unit's power switch as a master switch to turn my PC and monitor on or off and they are plugged into the battery backup outlets at the back.  Also, I power off my PC via the UPS when I'm not using it so the UPS is off for lengths of time.

Of all the APC UPSs I've had in the past I never heard this kind of hissing when the unit is off and although the unit is fully functional in all other aspects, this hissing is kind of creeping me out.  Has anyone heard this hissing when their UPS is off?  Is this normal?

Thanks,

Gerry

[BillP]

I have an SMX1500RM2U and it buzzes/hisses.  I think it is one of the internal switching power supplies making low level noise.  Do you hear it when it is turned on but not on battery?

[Anonymous user]

Hi BlueSky,

Thanks for the quick reply!

Actually, when I turn it on (and its not on battery) the hissing stops.  I'm familiar with what a switching power supply is and your comment makes perfect sense.

However, I still would like to hear from some others with mine or similar models of UPSs to see if they also hear a hiss or slight buzzing when its off.  If I can get a few more who say they have the hissing/buzzing when its off then I'll consider it normal and forget about it!

Thanks again,

Gerry

[Anonymous user · Accepted solution]

Many UPS produce a  "hissing like" sound; its a by-product of their power supply / inverter / conversion stage circuitry which operates at high frequency. The volume of the sound can indeed go up and down with load. What you do want to watch out for is if your batteries are at end of life and have been left too long inside a UPS ( well past the day the battery fault light came on) it is possible for the batteries to overheat , swell up, crack their battery cases open and release gas having a sulphur smell which could be accompanied by a hissing sound as the gas is released !