Apc Back Ups Pro 1000 Is Making a Funny Noise

New APC UPS is emitting a constant buzz, is this normal?

• Thread starter BentValve
• Start date Jun 10, 2004

• #1

I picked up a new APC 750VA UPS today (first one) and it beeped once and the green light is on constantly so according to the manual everything is ok, however it emmits a constant low level buzzing sound. Is this normal ?...Perhaps its just while it takes on the inital 16 hour charge?

Also I noticed when I first turned it on that somehow some pretty ugly noise came out of my stereo speakers...I hope this thing does not cause more problems than it solves.

• #2

UPS's hum, is that what you mean by "buzz"?

• #3

Yes I suppose one might classify it as a hum. Is this normal? Gosh I hope not because I am not using it for my PC but my stereo system...any extra noise is not good.

Aug 25, 2001

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• #5

It could be three things:

1) It could be defective. However this is probably the least likely possibility, given that it is new.

2) That UPS is a model in which the inverter is active, all the time.

This means that it is an "On-line" UPS, rather than "standby" UPS. A "standby" UPS only turns on the inverter and switches to battery power when the AC line power goes out of tolerance. Until then, you computer is running on AC line power. An "on-line" UPS, conditions and filters the power, so that your computer is always hooked up to the output of the inverter, and never directly to the AC line power. The battery is charged, while the AC line power is within tolerance, otherwise it drains while powering the inverter circuit.

3) The UPS behaves differently when it is doing the initial battery charge, causing the hum. Some "smart" or "microprocessor-controlled" UPSes, actually monitor the UPS during the initial charge cycle, to determine a "profile" of the battery, that is then used to determine the remaining power capacity when running off of the battery.

Personally, I suspect that the "hum" is due to reason 2, above, and that you are not likely to get rid of it.

My suggestion is to put the UPS somewhere out of the way, perhaps around a corner or behind furniture, so that the hum will be less noticable. The alternative, would be to get a "stand-by" UPS instead of an "on-line" model, which will only "hum" when the power actually goes out. (Usually they make a lot more noise too, mine makes a rather loud and annoying alarm "BEEP" every 10 seconds until power is restored or the battery charge runs out.)

If you check your UPS specs, and you in fact do have a "stand-by" model, not an "on-line" model, then I would have to say that the reason is either 1 or 3, with 3 being the most likely.

In either case, you can let it charge fully, and then see if the "hum" goes away or not. If not, then I hope that I've given you a fairly complete picture of your alternatives.

(Another possibility, is that you are putting too much load on the UPS, and that is causing it to emit more noise than it normally should, because the inverter is being loaded-down outside of it's normal operating specs. However this is fairly unlikely, because most have some sort of overload protection, and will shut themselves down if this is the case. This is a pretty unlikely possibility, and is probably in the same range of probability as reason 1, above.)

• #6

It's normal for a UPS to hum but usually it's not very noticable. As everyone else suggested I'd see if it goes away after the UPS is fully charged. However I must disagree with VirtualLarry, it is not an online UPS. APC does not even make online UPS's. I'm going to guess you got the Back-UPS 725ES (or is it BB?) which is a Stand By UPS. Though even if it's not, it is still not an online UPS.

Aug 25, 2001

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• #7

Originally posted by: MWink
It's normal for a UPS to hum but usually it's not very noticable. As everyone else suggested I'd see if it goes away after the UPS is fully charged. However I must disagree with VirtualLarry, it is not an online UPS. APC does not even make online UPS's. I'm going to guess you got the Back-UPS 725ES (or is it BB?) which is a Stand By UPS. Though even if it's not, it is still not an online UPS.

I did not know that APC does not make "on-line" UPSes, actually. (That does surprise me - I mean, APC is *known* for their UPS, I'm quite surprised that they only make one type.) But if it's not an "on-line" type, then it has to be a "stand-by" type. There isn't another type for it to be. (Some companies make "power conditioners" too, which use inverters like an "on-line" UPS does, except that they have no battery, and do not function as a UPS.)

So in that case, it's probably reason number 3 (or 4).

Aug 21, 2002

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• #8

APC makes online UPS's but they're very expensive... definately not something you'd pick up at Best Buy or CompUSA. I think APC refers to them as "line-conditioning" rather than "online."

*EDIT* APC's "Smart-UPS" are the "online/line conditioning" ones.

mechBgon

Super Moderator<br>Elite Member

• #9

None of the APC UPS's I've worked with produce audible noise, except when they are running off of battery power. At initial plug-in they run a self-test on battery power, so perhaps that's what BentValve is/was hearing.

• #10

Let me set the record straight. In regard to APC's consumer UPS's (not the Symmetra Power Array, etc.) they do not have ANY Online UPS's. The low end Back-UPS's are mostly Standby units. The higher end Back-UPS Pro's and Smart UPS's are Line Interactive.

Standby UPS's are either on AC or battery. Line Interactive UPS's have the ability to boost or trim the voltage without using battery power. Online UPS's (which APC doesn't make) always run on battery to provide constant consistent power (though I'm not 100% sure about Online UPS's). I hope this clears things up. There are 3 types.

Aug 25, 2001

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• #11

Originally posted by: MWink
Let me set the record straight. In regard to APC's consumer UPS's (not the Symmetra Power Array, etc.) they do not have ANY Online UPS's. The low end Back-UPS's are mostly Standby units. The higher end Back-UPS Pro's and Smart UPS's are Line Interactive.

Standby UPS's are either on AC or battery. Line Interactive UPS's have the ability to boost or trim the voltage without using battery power. Online UPS's (which APC doesn't make) always run on battery to provide constant consistent power (though I'm not 100% sure about Online UPS's). I hope this clears things up. There are 3 types.

After I posted that, I actually did some reading, found some good material at PCGuide.com on various UPS types, features, etc. They show 4 different types, although some are just minor variations of another. The "Line-Interactive" type, seems to be basically a hybrid of both a Standby and an On-Line UPS design, with the power outputs of both the battery/inverter circuit and the AC line power coupled into the output power-supply using a transformer. (So it seems that I was wrong about there only being two types.)

PCGuide UPS reference

I also spent quite some time on APC's site, trying to find where they described their UPS's as "on-line" models or not. I couldn't find any, although I did see the reference to the line-conditioning features of their Smart-UPS line.

This page on PCGuide may explain the reason for the humming noise. My personal experiences with stand-by UPSes, is that they should only hum when running off of battery power (the inverter is running). I'm not sure why one would be otherwise, except as possibly part of some automatic testing function, or it is defective somehow.

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Source: https://forums.anandtech.com/threads/new-apc-ups-is-emitting-a-constant-buzz-is-this-normal.1337188/

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