SUA 1500 - continuously buzz

[Anonymous user]

Hi,

I bought a SUA 1500 RM2U. it seems to wokr OK, just I can hear the quiet buzz like sound comming form UPS. The sound is like it use to be in the case of a big power transformer - just this sound is really quiet. I can hear it even when there is no load connected to the UPS or when connected to the different outlet.

Just for a curiosity I asked tech support about this, and I was told it is a transformer missalignment. I received the replacement for the UPS, but the new one acts the same.

I wasn't sure if it is a faulty UPS even in the first case, but now when support told me about the "transformer missalignment" - I don't know what should I think about it.

Does your UPS produce any sound when it is just connected to the power outlet? Note, that this sound is really quiet, actually I noticed it only when I was doing work in a rack cabinet and I was really close to the UPS.

Thank you for any idea.

[Anonymous user]

Thanks for confirmation. I was wondering if it is a common case or something exceptional, even more after technical suppoort response about the transformer.

[Erasmus_apc]

New SUA units have a fan that is always on. It can either be at a "low" speed setting or a "high" speed setting depending on the unit state. Below is an excerpt from a public Knowledge Base regarding this:

*Later SUA model units utilize a 2 Speed fan. On these units the fan will always be on in low speed mode, and will switch to high speed mode should one of the following events occur:

1. The UPS is on battery.
2. The UPS is charging the battery.
3. The UPS has a load greater than 75%.
4. The internal temperature of the UPS has reached greater than 104 degrees F (40 degrees C).*

So if the UPS has a slight buzz coming from it, it could certainly be the fan. Was this possibility checked already?

[Anonymous user]

When I connected UPS to the power outlet, yes, I heard the fun. After a while it stopped. It is possible the fun is running at a low speed now.

Just the type of sound I hear, is not produced by the fun. For example a cheap electric alarm clock produces that type of sound.

[Erasmus_apc · Accepted solution]

Well...there is an active tap-transformer in our Smart-UPS systems to allow our AVR Boost/Trim functionality. Basically that allows us to regulate voltage by adjusting XFMR taps based on what the unit sees as input voltage. If I kneel down this tower-version of an SUA1500 here at my desk I can also here a faint electric "rattle/buzz" from inside. It is very faint though and I can't hear it unless my ears are right next to the unit.

The same sound is also coming from an SUA1500, SUA3000, and very faintly from some of our rack-mounted Smart-UPS systems in our test lab here. It seems to vary between units but that faint electrical sound is definitely present.

I would try a self test on the unit and continue to monitor it as this is likely just the usual operational sound.