New Smart UPS Lcd 1000 buzzing noise every 20 seconds.. is it normal?!?

[alessio1726_apc]

HI,
last week I have purchased a new 1000va SMT Lcd; before I used a backups 1000 APC and there wasn't strange noises.
I have attached a audio file, or it is possible to hear here:
http://www.mediafire.com/?69hlh0d3sltaqxt

When the batteries are at 100%, this noise start and it's go ahead every 20 seconds (you can hear it at the start of this audio file and 2 times after around 20 and 40 seconds).
It is possible to hear it also when the smart UPS is off, but with the current attached.
This isn't the normal sound of the batteries, I have recorded it at 30 centimetres; If I accosted my ear, I can hear the normal batteries works.
Another strange thing, sometimes there are loud noises when the smart UPS works, type sputtering, but it is one time every one or 2 hours.
The same thing when it is off, WITHOUT current.. even after 2 or 3 hours which is turned off; but I repeat, it is only a noise and stop.. but loud enough to wake me up..
My backups didn't produce these sounds.


Is it a normal sound? (every 20 seconds)
And the other sounds?

[BillP]

Good day! Can you provide the exact model number of the UPS? What I'd suggest is to de-energize/brain dead the unit, by doing so, you are expelling electrical charges that may be stuck in the capacitors of the unit, it's like a hard reset. 1. Turn the UPS off 2. Unplug the UPS from the wall outlet 3. Disconnect the battery and leave it disconnected for 10-12 seconds.Reconnect the battery, plug it back into the wall outlet, turn it back on and check if you can still hear the noise.

[alessio1726_apc]

Hi,
the model is APC Smart-UPS 1000VA LCD 230V
STM1000l

[Ironbuket_apc]

Hi, I have exactly this noise and behaviour on my SMT1000i which I only bought a few weeks ago. Did you ever find out if it was a fault or something normal?

I found that if I shutdown the UPS via the display and turn it off at the mains. Then mains back on and UPS back on, the sound will not be present anymore until the UPS is put under load. The sound occurring every 20sec then continues even when the load is later removed.

The online audio example you provided is the second example Ive found exactly matching what Im experiencing so that makes at least 3 of us. Im starting to think it may just be normal, but Im trying to check a bit more before I resort to moving the UPS to somewhere I wound hear it less.

[BillP]

Hi,

Sorry for the inconvenience. The noise in the audio is not normal behavior. The unit will hum when the battery is charging and when under load but that would be a constant hum not intermittent. 

Please feel free to contact local support if you think the unit is not performing properly and they will assist with trouble shooting and if needed provide a replacement. 

[Ironbuket_apc]

Thanks for the offer of support, unfortunately my unit is refurbished so my warranty is with a third party and not APC. The more I investigate this sound the more it begins to look like it may be normal behaviour of the UPS. Normal in the sense that the unit isn't faulty, not normal in the sense that every user would hear this sound. I found another case of someone experiencing this sound where they exchanged their new APC unit twice (so had 3 new units) and all made this sound. A comment made by someone over on Amazon reviews suggested the sound might be due to problems with the mains voltage (ie sounds associated with the UPS correcting). I have to get my mains supply checked but one of the questions asked of that person during their conversation was are you near a substation and in my case I am very near a substation. I also found another case where a unit was sent back and testing found nothing wrong - not a very scientific conclusion but you wouldnt expect anything to be found wrong if the issue was caused by the mains supply?

I could cold connect my UPS to the mains (display off) and leave it that way all day without a peep. I can turn the UPS on and apart from the noise from the start up test it will still sit there not making any sound at all. It is only after something connected gets turned on and it receives a load that the repeating sound begins. I noticed last night that even after I shut down the UPS (but still getting mains power) the repeating sound continues.

NB: I realise I may not get help for this on the forum, but Im putting up what info I do know as a resource for others that might experience this issue and go searching the net. There are very few reports that can definitely be matched to this specific sound and none of the cases I found (so far) ever had a satisfactory conclusion. It was only by searching for '20 seconds' that I found this one and there are plenty of complaints about hum, coil whine and transformer buzz etc to make picking out cases related to this sound particularly difficult.

UPDATE: I discovered something interesting this morning. Starting with the UPS off + wall power off. Turn on the wall power and leave it that way for a few mins. Turn on the UPS display and again leave it a few mins. When load was applied after that the 20sec repeating sound did not occur whilst the UPS was in operation under a load of around 25% After a couple of hours there was a noise like a solinoid and the repeating sound began. This occurred just after I had put some more load on it (30-40% i believe). I plan to investigate further later today

Update#2: I found a report on the net of a different sound but on the same 20sec cycle (a period that many seem to report). This person took their unit apart and measured the voltages and saw that the sound coincided with a 0.5v increase to the battery. Possibly a battery check cycle? Maybe this cycle doesnt begin until the unit goes under a certain load level? Anyone from APC willing to comment?

NB: If this gets too complicated I will start a new thread 🙂

[redecs_apc]

Same issue, same sound as the OP every 20 sec on a SMT1500i.

I've noticed that if I unplug the ever thing and let the battery  discharge, it doesn't produces the noise until the battery is back to 100%. Load on the UPS is ~10-15% in my case.

Unfortunately I didn't notice this until I moved the unit under my desk (with all the working from home changes) and the unit it's out of warranty. 

[Ironbuket_apc]

Couple of years since I last posted on this thread, just received an email about your reply and thought I would update my view on this. I still have the unit and it still does the same thing.

What I know now is that the intermittent buzz is almost 100% sure something to do with the circuit that checks if the battery needs charging. If you are in the mode of this sound occurring and then run off the battery for a while the buzz immediately stop. If you then return it to the mains, the unit will charge the battery without this sound returning. After the battery has been topped up again, still no sound. Then after a short period (20mins or whatever) it will start doing it again. Almost certain it is checking the battery level and seeing if it needs topping up. This unit doesn’t have constant charge of the battery like older units did, so must have something checking the battery level to see if it should switch on charge or not. Anyway, that’s my 2c. It’s likely similar to coil whine on GPUs, you might get a quiet one or you might get a noisy one – just random. Reject it when it is new, else you are stuck with it.

[Anonymous user · Accepted solution]

Hello!
I have exactly the same issue with my APC SMT1000i manufactured in January 2020 in the Philippines and purchased just a day ago (Russia).
I've noticed that the issue appears only when the UPS operates in the Green Mode. It is consistent with what I've read above as the UPS doesn't produce any similar noise during the first 1-2 hours after powering (then it switches to the Green Mode).
Bad news:

1) Green Mode cannot be disabled with PowerChute Business Edition or from the front LED panel of the UPS. You need to have a network card and access the UPS over the network to disable Green Mode. Local service centers refuse to perform such an operation if the only reason is this noise (also, perhaps the setting is not completely persistent?).
2) Even if the Green Mode is disabled, it will not help much in my case as I also hear a loud transformer sound about twice an hour for 3 seconds (a similar sound is produced when a hairdryer is turned on in a bathroom in half power; I have single-phase electricity in my apartments so UPS' transformer catches such serious interference). No such noise in the Green Mode as it bypasses the transformer part, but a buzzing noise every 20 seconds (and overall some extra buzz heard in this mode).
I will try to return the unit and get something more fitting for household usage.

Regards!

[mpk]

I've been investigating this issue on my SMT1500RMI2U for some time and found it to be related to C900 capacitor on daughter board.

MLCC caps may cause noise when an AC voltage is applied 

I don't recommend nor encourage anything, but mounting it in metal terminals like in some Murata series did the trick for me;)

[NickL]

I had a similar issue with the hum buzz every few second on my Backups pro 1000 and it was very annoying. I was able to resolve the issue by:

1. Unplugging the battery from the wall and letting it power my devices until it was completely dead.
2. When the battery dies plug the battery back in and let it fully charge. 
3. Once the charge was 100% the sound was gone.

Evidently, the charge controller might have been unaware of the topping charge that it needed to provide but the cycling of the battery gave it that info (maybe).

[Ironbuket_apc]

How long after you did this procedure did you post this message? Asking because, in my experience the sound will disappear for a period of time after running off the battery. The period before you will hear it again will be longer if it is completely discharged as the delay before the buzzing occurs only starts when the battery is back to full charge again. The same delay on the buzz returning will occur by just shutting the unit down and turning it back on again.

[NickL]

I posted within an hour of plugging it back in after the full discharge. Now that the battery has returned to full charge I do hear it cycling to top charge but the volume level of the buzz/humm is much less audible. I’m going to do another full discharge and see if that helps to improve it even more.