Power Supply Noise question

[faumble]

Quick question, my power supply is making a weird noise, not sure how to describe it, its not a click, more like a buzz. Happens for a few seconds after I turn ON my UPS (its an APC 1500) while it is on battery mode.
The UPS does this thing: every time I turn it on it runs for a few seconds on online/normal mode, then it tests the battery running on battery mode for a few seconds, this is when the Power Supply of the Mac pro makes a weird noise, after the UPS goes back to normal mode the noise stops. I guess it is normal but wanted to double check, and why does it makes this noise?
Thanks in advance

 

[nanofrog]

Yes, it's normal.

When you switch the UPS on, it initiates a self-test. During this test, it switches to the battery. Now you've got DC being converted to AC. The actual output isn't a pure AC sine wave. This causes the transformer in the PSU to hum or "buzz".

Simple solution:
Leave the UPS "ON", unless you will be away on vacation. If not, you won't have a full charge in the battery if the power does go out.

Almost forgot. Physical placement of the compute and UPS may help. Try relocating them from each other.

Hope this helps.
Nanofrog.

 

[faumble]

Thanks nanofrog, appreaciate it will try relocating it.
Was wondering, if relocating it doesnt work, is it bad to leave the UPS ON for a long time? (say 2 weeks)
and could this not pure AC sine wave in some way damage the PSU/transformer?
Thanks again

 

[nanofrog]

The UPS is meant to stay "ON".
This is so the battery maintains a full charge, and protection is available.

I wouldn't worry about PSU damage.
Though it's technically possible (design flaw), you won't be running it from the battery 24/7. Only during a power outage, and it only provides maybe an hour or so (depending on actual power draw).

 

[Loa]

Hello,

[Note: found the solution to the problem, see after description.]

Sorry to resuscitate an old thread, but my problem is very similar.

I just got a APC 1500 LCD today and it's been plugged all morning and afternoon, and it was perfectly silent.

But now I'm getting this very clear buzz from the UPS, and not from the Mac Pro. It's online and the battery is not working, but the buzz is definitely there.

Is that normal? And if so, why was it silent all day long?

------------------------------------

Solution: After shutting down my Mac to investigate, I unplugged it from the UPS. Wanting to plug something less "sensitive" than my Mac, I unplugged my halogen torchiere lamp. The buzz disappeared from the UPS. The halogen lamp was dimmed down at 50% power. After replugging the lamp and pushing it to 100% power, the buzz disappeared again.

Very interesting interference here!

Loa

 

[nanofrog]

Hello,

[Note: found the solution to the problem, see after description.]

Sorry to resuscitate an old thread, but my problem is very similar.

I just got a APC 1500 LCD today and it's been plugged all morning and afternoon, and it was perfectly silent.

But now I'm getting this very clear buzz from the UPS, and not from the Mac Pro. It's online and the battery is not working, but the buzz is definitely there.

Is that normal? And if so, why was it silent all day long?
------------------------------------

Solution: After shutting down my Mac to investigate, I unplugged it from the UPS. Wanting to plug something less "sensitive" than my Mac, I unplugged my halogen torchiere lamp. The buzz disappeared from the UPS. The halogen lamp was dimmed down at 50% power. After replugging the lamp and pushing it to 100% power, the buzz disappeared again.

Very interesting interference here!

Loa

Dimmers are known for noise (try one while running audio equipment ). Best to keep it off the circuit if possible.

 

[Loa]

Dimmers are known for noise (try one while running audio equipment ). Best to keep it off the circuit if possible.

Yep, I already "heard" that noise as "translated" by a sound system. (Got to be careful with the two definitions of "noise" here!)

I didn't think it would affect other electrical systems...

Can that be "bad" for, let's say, a computer on that circuit?

Loa

 

[nanofrog]

Yep, I already "heard" that noise as "translated" by a sound system. (Got to be careful with the two definitions of "noise" here!)

Actually, it's usually referred to as hum, and is just EMI. In the case of audio equipment, AC is the signal that drives the speakers, so it becomes really notable. In the case of the UPS, it's interfering with the coils in the transformer(s) in it's PSU section.

I didn't think it would affect other electrical systems...

It does, especially if it has a coil(s), like a transformer.

Can that be "bad" for, let's say, a computer on that circuit?

Loa

Yes, it's possible, but not absolute. So it's best to think in worst case IMO, and keep it off the same circuit. Easy, and cheap.