Low-pitched hum/buzz sound from Back-UPS

[Anonymous user]

Hello.

I just recently purchased a new APC Back-UPS NS 1250 and in the past week it has begun a steady hum/buzz sound that appears to be there 24/7.

The LCD indicates that 19 minutes worth of backup time available, so I doubt that I'm straining the unit.

My concern revolves around the fact that none of my other (and older) 10 or so Back-UPS (of various capacities) have anywhere near the sound level as this new unit.

Do I need to be concerned?

Thanks,

C.C.

[BillP]

Yet it doesn't occur to any of our other Back-UPS.

So long as it doesn't get louder, it should be acceptable.

[BillP · Accepted solution]

Yes, it has the LCD screen.

Load is approximately 220-230 watts.

It's a very definite electrical buzz, and less of the hum you might associate with a fan, but anything is possible, I guess.

Message was edited by: Cold Canuck

[Cap1_apc]

Hello,

You probably don't need to be concerned.

Perhaps the noise you are hearing is the fan? Is this the LCD model? Can you let us know what the load in watt is?

[Anonymous user]

We have a brand new Symmetra LX and it also has a hum. What you hear is coming from the transformers.

When current reverses 60 times a second the iron core of the transformer undergoes magnetetostriction twice during each cycle. In other words, 120 times per second induced fields cause the core to stretch slightly; a meter-sized transformer might stretch or shrink by only a micron but this would be enough to set up an audible 120-Hz hum.
From : http://www.aip.org/pnu/2004/split/690-1.html

[Anonymous user]

I worked as an industrial electrician and instrumentation technician at a paper/pulp mill. We generated our own power with 8 turbines. We generated 24.8K volts. Most of our large transformers had a noticable hum. The 12 Kva Symmetra LX is the largest APC ups I've worked with. We have 3000Kva APC matrix and may other APC 3000Kva ups and less. The Symmetra LX is the first APC that I noticed hum. I was onced told hum was due to an imperfect transformer. Just curious what APC says.

I am not concerned about our Symmetra humming. I am surprised a UPS as small as 1250va hums. Is it 120V? Are the other APC ups the same voltage and va? If you call APC please let me know what they say.

[BillP]

We have a number of different styles of Back-UPS with the same voltage rating, but varied va ratings (500-1250).

BUT, this is the only one that is an NS model, most of the others are those pale gray brick models, the only two other 1250va Back-UPs we have are the tall stand up type.

I'm not about to contact APC even if it gets worse, if anything, I'd just take it back to the seller and get a replacement.

Like I said, all of the other Back-UPS are quiet as mice.

I do appreciate your response, thank you.

[BillP]

The buzzing is your transformer wasting energy