APC BX1300LCD Emits 60 Hz Buzz/Hum After Two Hours on A/C

[Anonymous user]

I recently purchased an APC Back-UPS BX1300LCD UPS at a retail outlet. It passed the quality assurance test on 10/10/2007, and appears to operate normally when on A/C power, for the first two hours or so. After two hours, it gradually begins emitting a pronounced 60 Hz buzz which grows louder over time. I've chatted with APC technical support on two occasions, and they've asked me to run the self-test, which I have done. The results of the self-test are normal, and there are no indications otherwise, as far as I can see. The buzzing I hear is the same produced during the brief self-test which occurs seconds after start-up on A/C power. The unit is rated at 780 W, and yet the actual load is only ~100 W or so.

Is the UPS oversized for the application? Is there a problem with the UPS or with my utility power? How can I tell? Should I return the UPS? This is the first unit I've tried at this location, and the only UPS I own.

Thanks.

[Anonymous user]

I'm sorry, could you post that link once more? I believe it pointed me to this thread.

Thanks.

[Anonymous user]

My BX1300LCD does the same thing. It is unbearable after a couple of hours in any sort of a home/office environment (would be fine in a server room with louder cooling system, I suppose). I have an ES750 that is absolutely quiet in comparison, when plugged into the same outlet (not at the same time as the BX1300LCD) and with the same load devices.

Has a resolution been identified?

Message was edited by: cynan

Message was edited by: cynan

[BillP]

The Back-UPS models are designed for home use, not for server rooms. Can you tell where it's coming from? Is it the fan in the UPS, your computer's power supply? Does it make the same noise when you unplug it from the wall?

[TheNotoriousKMP_apc]

If it's the same sound you hear when the UPS first turns on, it's the UPS inverter that you're hearing. Why it's operating I'm not sure. Are you using any software in this setup to monitor what MAY be going on?

[Anonymous user]

Thanks for your prompt reply.

I am not currently running PowerChute or any other monitoring software. Initially, I had installed PowerChute Personal Edition, but then removed it, because the software appeared to complaining about an error installing or starting an associate service. Once I uninstalled the software, Windows recognized the device as a USB-connected UPS battery. I am running Windows Vista Home Premium 64-bit.

Your explanation makes perfect sense, but how can I be sure it's the inverter? I would think the battery icon would be showing on the LCD display if it were running on battery. Could it be a ferroresonant transformer making the noise? Are any transformers involved during normal operation?

[TheNotoriousKMP_apc]

I understand about the software, as I do not believe that we have 64Bit available for Vista yet, so you would be confined to using any Native shutdown support. Does the hum go away at all? Is there any consistency in the time of day when it hums? Any electrical work being performed nearby?

[Anonymous user]

Regarding the hum, I have not heard it subside once it starts. Typically, I'll power on the UPS in the evening, maybe watch a DVD or install updates (I'm testing a newly-built computer, using it mostly for watching video). After it has warmed up a good hour or two, l notice the humming. I typically only run the computer at night or on weekends, and am not aware of any electrical work in the neighborhood. I have the computer located in my bedroom. Last night I installed Windows Vista Service Pack 1. I let the installer run, then drifted off to sleep. I awoke an hour or two later, and the humming was quite pronounced. The only way to quiet it is to power off the UPS and let it cool down for 1/2 to 1 hour. Upon powering it on, it will be quiet for the first hour or so. It's a qualitatively different sort of humming from that which occurs on power-up self test. When it goes into self-test, first the line power icon blinks, then the battery icon blinks. While the battery icon blinks, the UPS hums, and my computer PSU hums along with it. It only lasts a few seconds.

[BillP]

Hi, the reason for the ambient noise is probably covered in this thread here.

[Anonymous user · Accepted solution]

The buzzing noise is coming from the UPS unit (UPS power supply?). It is constant when plugged in. The noise grows until about 1 to 2 hours after the unit is turned on. The noise persists regardless of what loads are plugged in (also occurs when nothing is plugged in to the UPS), time of day, AC circuit it is plugged into, etc.

The noise is similar to that when the UPS is unplugged from the wall while turned on (ie, when the battery kicks in), but perhaps a bit louder. Measuring with a decibel meter positioned about one to two feet above the UPS, when the UPS is off, it reads about 30 to 33 db (ambient noise). When the UPS is on after a couple of hours, with the similar ambient noise, the reading is around 45 or 46 db. I would consider a 12 to 15 db increase to be pretty significant in a quieter working environment.

As my unit was under warranty, I was able to get an RMA for a refurbished unit. I will post here if the new unit has the same issue (but no reason to think it would)

Message was edited by: cynan