Buzzing from Power Supply

[jmohr_apc]

I had my Mac Pro plugged into a 750VA/ES. I thought the problem I was having was because it didn't have enough power, so I just purchased a 1500VA/XS........

The problem I am having is, when the UPS goes to battery power, I can hear the power supply in the Mac Pro buzzing. (I know it's not the UPS I am hearing because I ran an extension cord to the other room on a totally different circuit even --- but it sounds similar to the UPS' buzzing sound... line noise??).

I chatted online with an APC rep, and they originally said it sounded like the Mac Pro wasn't getting enough power - so that's why I got the 1500VA. According to the LCD readout on the APC UPS, the Mac Pro isn't consuming much power at all - around 125 W I think it was.

Is the buzzing I am hearing from the power supply of the Mac Pro normal? Can anyone confirm that they have the same issue on their PC or Mac? I really don't want to have to take my new system in for repair - especially since it weighs over 50 pounds.

The noise is only heard when the computer is on battery power (regardless of if it is actually on or not).

Thanks for your assistance.

-Jim.

[Anonymous user]

No the trim and boost are normal. Thanks man

[Smart_apc]

Different cars use different fuel. Why do you think that different computers use the same fuel? I would double check what type of fuel to use before going...on an expencive car.

[BillP]

does the buzzing happen all of the time or only when the UPS is on battery? what is the load percentage on the UPS via the LCD front panel or the load bank LEDs?

[Anonymous user]

It happens all the time and the load is at 2 of 5 led bars.

[Anonymous user]

Hi!

Your Mac Pro probably has an Active PFC Power Supply.

I can't really tell why APFC PSUs make a buzzing noise whilst on battery power, but I'm almost certain this won't harm your Mac's PSU or any other PSU.

My PC has an APFC PSU and it's been 4 months on a APC UPS and it's still working fine after a few blackouts. I know some people who has an APFC PSU for more than two years running off a UPS and have no problems at all.

This buzzing noise is caused by the Quasi-Sinusoidal or Stepped Approximated Sinewave that the UPS outputs when operating off battery. The Smart-UPS series and more expansive ones outputs a true sinewave and won't make your PSU go buzzing. Some people say a true sinewave is healthier for the PSU, some say the Approximated Sinewave is better for the PSU and some others say this is not true, that this type of wave can harm the PSU. My opinion is in the middle of that. I say the approximated sinewave is good for a few minutes of use, just to give you time to save everything and correctly shut the PC down and not to running your computer indefinitely. I also recomend turning the UPS off after powering down the PC. Which opinion is more correct? I don't know. I'm sticking in the middle. 😉

Message was edited by: rau

Message was edited by: rau

[BillP]

Hi Jim,

Here is some information on what Rau mentioned in regards to a step approximated sine wave which the Back UPS models produce on battery:

Often people confuse the on-battery output of Back-UPS, a stepped approximation to a sine wave, with a square wave output UPS. Because the RMS and peak values of the square wave output UPS are identical, the on-battery output voltage is typically high, around 140 Vrms, at the beginning of an extended outage. This is so that the output voltage will be high enough, around 97 Vrms, near the time of low battery for the load to be supported.

Obviously, any load with a resistive element will be overstressed somewhat during the time the voltage is above 132 Vrms (the limit to which most equipment is designed). In the past, many UPSs had on-battery square wave outputs because it was a relatively inexpensive method of generating the power. Many computers had no trouble running with such an output, but the overstress issue remained for some load types, so now only cheap clones are found with such outputs. Unlike a square wave output UPS, the output from a stepped sine Back-UPS has peak and rms values equivalent to the sine wave.

The most common problem we see with Mac's (and a lot of server type computers) is that they still do not like the step approximated sine wave and prefer the pure sine wave as mentioned above - found in our Smart UPS line UPS and above models. (Another issue which your particular Mac doesnt seem to have is the transfer time from online to battery.)

Also, take a look at this article relating to Power Factor Corrected Power supplies and our step approximated UPSs: http://nam-en.apc.com/cgi-bin/nam_en.cfg/php/enduser/std_adp.php?p_faqid=8883

Essentially, I believe it is probably the step approximated sine wave causing this issue (since it only happens on battery) so the only thing that you can do to avoid it is maybe taking a look at the Smart UPS product line if the buzzing is bothersome: http://www.apc.com/products/family/index.cfm?id=165

[jmohr_apc]

I guess my question now is -- Is that what I am experiencing? I have a call in to the Apple Tech. department to get more information about my Mac Pro's power supply. I asked them if it was APFC, and at first they said no -- but I am waiting to see if they say something different (they didn't seem to know right off).

I don't to have to exchange the 1500XS Backup-UPS I just bought for something so much more expensive, only to find out that it wasn't the problem.

I'd really like to have someone tell me they've tried their Mac Pro with and without the Pure Sine battery backup and that the approximaged sine buzzed, while the pure sine didn't.... When I first spoke with an APC tech., they hadn't heard of any buzzing issue with the Mac Pro while on battery. It's only while it's on battery power though, which really leads me to believe it's due to the approximated sine -- but I would really like some sort of confirmation.

- Jim.

[Anonymous user]

I can assure you the buzzing noise is caused by the step aproximated sinewave, you won't hear this noise on a pure sinewave UPS, that I can also tell you for sure. I think the question that remains is, does this type of wave demages or reduces the power supply lifetime? That I can't answer. The more I read about this subject, the more confused I get and no one seems to have a final answer on this, not even APC do, I think.

Message was edited by: rau

[Smart_apc]

http://www.macmall.com/macmall/shop/detail.asp?Redir=1&description=Apple%2DMac+Pro+8%2DCore+Workstat...
I am not sure why it is not very easy to find spec about PSU in your Powerful computer. The link says: Power Details Line voltage: 100-120V AC or 200-240V AC (wide-range power supply input voltage) . So, it means that formally AC only required. Please ask Apple and double check that 100-120AC ( sinusoidal voltage), they have to provide required information to you because you have rights for it - how to use the computer and which power lines to use. Please note the voltage regulation is less then 10%. It means you need a premium fuel for computer. I hope this helps. Again, please ask Apple to confirm it.

[jmohr_apc]

"Smart", I am Trying to find out, but no one has any concrete answers. Some say that the approximated sine wave is ok, some say I have to go with pure. So, I called Apple Support to ask them about it (what type of power supply, etc), and they were supposed to call me back. They don't know; and I am still waiting for the returned phone call. No one seems to know. Though it will cost me twice as much as the APC I just bought, I am willing to get the Pure Sine, IF that will fix the problem. I plan on purchasing it online, because it tends to be cheaper - but the draw back is "returns" if it isn't the problem. I am in total agreement with your point... If my computer requires "premium fuel", I have to make sure it's taken care of. I don't want to do any harm to the system. ....... Thanks for your reply.

[Smart_apc]

Please let me know more details about your computer. If you have a link at a web site please tell me the link. Also, please have a look at you computer - you power supply should have a label with text about power parameters or something like this. Please tell me the information too. Then we'll search internet together to find more detail about PSU. I hope it helps.

[jmohr_apc]

This is a Mac Pro, 2.8 GHz Quad-Core Intel Xeon (that's 2 processors). The booklet contains no useful info regards to this... As for the power supply and sticker... I haven't opened the case yet. I am not sure if they just slapped a sticker on it or not (Apple probably made it less visible, as they tend to do with this sort of thing).

The Web site would be on Apple's Mac Pro page, http://www.apple.com/macpro/

If I have to, as a last resort, I will open the case and look - but I am still leery of doing so (probably because it's still new... I have been several PCs, but I am still holding off opening the Mac Pro for the first time 🐵 ...)

[Anonymous user]

As far as I know, all MAC PROs and I think old G5s as well, come with PSU with Active Power Factor Correction (APFC). And again, if I'm not mistaken, only APFC PSUs make the buzzing noise. I've never seen a "regular" PSU making noises while on battery power.

If money is not the problem, I would definitely buy a pure sine wave unit since that's the type of wave you get from your wall outlet so it is logical the pure sinewave unit is better for the PSU, since it was designed with pure sine wave in mind not an approximated type of wave.

You say the PSU has a 10% regulation. No! MAC PROs usually come with a full range PSU which means they can work from 100-240V on the fly. When they say 100-120 and 200-240 it means on a 120V grid the input voltage can range within 100-120V (without counting the SMPS tolarance) or a 220v grid, from 200-240V (without counting the tolarance as well). The cited numbers means the PSU can go from 100-240V to work anywhare in the world. Switched mode PSUs have a much wider tolarance, about 30% from it's nominal input voltage. To be completely within the specs, the PSU should be between 100-240V, but they can sure work from 90-260V without problem, you can ask any power supply maker that produces APFC units.

Message was edited by: rau

[jmohr_apc]

The funny thing is, when I asked the Apple Care rep. if the power supply was APFC, she said no. I think she was wrong. If they actually had said, YES, then I wouldn't have made this such an issue. Why in the world the Apple Web site (or elsewhere for that matter) can not just come out and say APFC PSU is beyond me! It would have saved a LOT of time.

[Anonymous user]

Well, the only thing I found about the new MAC PRO PSUs was this information on the User Guide PDF:

Power Supply
AC line input
 Voltage ranges: 100–240 V alternating current (AC)
 Current: Maximum of 12 A (low voltage range) or 6 A (high voltage range)
 Frequency: 50–60 Hz

Assuming the Xeon Macs have a high power PSU and that Apple products is sold all over the world, including Europe and in Europe theres this strict regulation that states all Switched Mode Power Supplies above 70watts (if i'm not mistaken) must have APFC, i don't think apple would put a different PSU in the units intended to be sold in Europe, the costs doesn't justify this choice I think. I don't know... I'm still searching for information on the MAC PRO's PSUs, if I find something I'll let you know.

Message was edited by: rau

[jmohr_apc]

Thanks to everyone for posting.
I went ahead and purchased the APC SUA1500 Smart-UPS to see if it would make a difference. I unplugged it from the wall, and it works great! No more buzzing from the Mac while it's on battery. That makes me feel SO much better. I guess it WAS an APFC power supply -- even though Apple never did call me back to confirm (not sure why - maybe the guy went on vacation, I don't know). Anyway. Thanks again. Hopefully these posts will assist someone else... And, if APC reads this - Note: The Mac Pro Early 2008 model works best on a Pure Sine UPS.

-Jim.

[Anonymous user]

That's a good purchase!

I myself am looking foward to buying a pure sinewave unit in the near future. The only thing that is keeping me from it is the money, because here in my country these models are very expensive.

I'm sticking with the psudo-sinewave since it's not conclusive this type of wave is harmful. I have never had any problem with it apart from the buzzing noise and I still haven't found someone saying: "The stepped approximated sinewave killed my PS". Well, I've actually found one person saying something like that, but it hasn't been proved that the UPS did it and all the evidences were against his PS not the UPS...

[Anonymous user]

we have the smart up 1000 va with PURE SINE WAVE it BUZZES ALL THE TIME LOUDLY, battery or not on the BUZZ and HUM is always there, poor design, cheap parts and assembly = BUZZES AND HUMMING ALL DAY AND NIGHT!

[Anonymous user]

we have 2 1000 va smart ups and they BUZZ and HUMM loudly as soon as they are plugged into the wall power in 5 different outlets whether the battery is on or not on the BUZZ and HUMM is on. Crapola poor design anyone who would okay a product with this BUZZ and HUM and call it okay is poor = F product.

[Anonymous user]

I just purchased a Smart 1500 UPS to power my 2006 Quad 2.66 Mac Pro and immediately noticed a very loud buzzing coming from my Mac Pro power supply that is not present on outlet power. I have just the tower, monitor, modem, router, and an external hard drive hooked up. The power in my house is not the best but it doesn't present a problem when all the same equipment is hooked directly. I went for this model due to the sine wave hype but am not impressed. Any tips?

[BillP]

hm ok. well this UPS has a topology so that while it is online, it is just passing power straight through to the equipment.

i know you mentioned you have several items connected to the UPS. can/have you tried unplugging them all and connecting and turning them on one by one to ensure it is actually the power supply buzzing? perhaps there is a ground loop some place which is buzzing because there should not be an issue at any point here, especially, while the UPS is online.

it'd be good to ensure that the buzzing starts as soon as load is connected or if it does it by itself all the time.

[Anonymous user]

It's the computer power supply doing the buzzing- doesn't matter if I am on battery or pass through. Doesn't occur when plugged into the wall. I unattached all other components and it continues.

[BillP]

and if you turn off the mac it stops? nothing else causes it to buzz? i just want to be 110% sure it is the mac and it is not the UPS by itself or another piece of equipment. if you have eliminated every other thing, the only other thing i can think of is a ground loop/another issue that i don't know about. did you try to plug the UPS into the same outlet that you directly connected the Mac to or is it a completely different outlet?

[Anonymous user]

The UPS is plugged into the same outlet the computer used to be plugged into. The sound is clearly coming from the upper rear of the computer case and couldn't be anything else as the UPS is about five feet away and it has been silent so far. The computer is plugged directly into the back of the UPS the other items are on a six-way bar. No fluorescent lights on the same circuit... I don't know...

[BillP]

hmm well i dont know to be honest with you. if it does not do it with anything else, i have to assume its an incompatibility for some reason. 😕

not sure if anyone else knows anything different. i have not personally seen this issue with a Smart UPS before.

[Anonymous user]

Full disclosure: Its an IBM 1500TLV and refurbished. Supposedly the same as the Smart UPS but with a couple extra features. Thanks for the help though. I may have to return this...

[BillP]

you're welcome. i agree, that should not be an issue but maybe there is something wrong with it. there is no boost or trim LEDs indicated on the front, is there? that would make a small buzzing noise but i guess not since you mentioned the buzzing is definitely coming from the PSU. just thought i'd throw it out there.

[BillP · Accepted solution]

wo-man 😄