Do all line-interactive UPSes "hum"?

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Do all line-interactive UPSes "hum"?

Post by Derpington » Sun Jan 10, 2016 4:12 pm

I have a fanless Tripp Lite UPS of the line-interactive type. It constantly emits a low hum, which is mostly masked by computer fans so it's not a big deal. But this thing is approaching 4 years of age and I figured instead of replacing the batteries I could buy a new and quieter UPS. Just another small step in the ongoing quest for silence.

Here's the thing though: I've read a post on this forum which said that all line-interactive or online UPSes produce noise because of how they work (the inverter is always on). Does this mean I have to look for offline (aka standby) UPS if I want it to be silent?

Line-interactive is superior in that it can do AVR and reacts to outages a bit faster than offline type UPS. But if noise is the price perhaps it's not worth it.

I think the popular APC Smart UPS are line-interactive type, so I'd appreciate any input from their owners.

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Re: Do all line-interactive UPSes "hum"?

Post by edh » Mon Jan 11, 2016 12:59 am

Every UPS I have ever seen hums. What I would first ask though is what the use case is? If it's for work and it's mission critical that you need power then put the UPS is another room and run a power cable through so that the hum is out of earshot.
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Re: Do all line-interactive UPSes "hum"?

Post by CA_Steve » Mon Jan 11, 2016 7:45 am

I've got a couple of the APC BE750G's. They are line-interactive and fanless. No noticable noise or hum until there's a power event or self-test. If I put my ear against the unit there is a slight whine that can't be heard from farther away.
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Re: Do all line-interactive UPSes "hum"?

Post by cmthomson » Fri Jan 22, 2016 2:10 pm

I have a couple of APC CS500's, and they are silent in normal operation. They hum during discharge, recharge and self-test.
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Re: Do all line-interactive UPSes "hum"?

Post by Abula » Fri Jan 22, 2016 10:03 pm

My Cyberpower 1x CP1500AVRLCD and 3x CP1500PFCLCD are silent on standard operation, all hum but when they are on battery use or when the UPS intervene into correcting something, but standard all day operation are silent.
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Re: Do all line-interactive UPSes "hum"?

Post by Behemot » Mon Jan 25, 2016 12:46 am

cmthomson wrote:I have a couple of APC CS500's, and they are silent in normal operation. They hum during discharge, recharge and self-test.
Back-UPS CS (BK500EI) is off-line unit.

Please always use part code as the BK500EI above, APCs website structure is PoS and searching for anything without knowing the codename is pain in the ass. It's always on a small white sticker on the unit.

Anyway, basically all the line-interactive units make some noise, but often it is almost inaudible. Battery operation is usually the worse the further the waveform is from sinewave. Generally, all transformer-based devices (incl. motors) don't like sharp edges and fast changes of the waveform, so anything which is not a sinewave. Check my database ... waveforms/

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