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Thread: PSU buzzing question

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    Default PSU buzzing question

    There seems to be a lot of different posts about PSUs and buzzing noises but no one seems to know why there's is buzzing. Well I found out why mine is and I'm curious if I should be concerned.
    Basically the story is when our downstairs dimmer is on both my ups and psu buzz. The level of noise changes on how dim the lights are. Completely on it's barely, halfway it's a little louder, and off completely no noise. We have two dimmer switches both create the same level of buzz. Not enough to be sitting up straight and hear it but if I get to the back of it I can hear it. So it's not loud but I'm still concerned if it's damaging or just an annoyance that I know is there just can't hear unless I'm close.
    My psu is an Evga 850 g2 if that matters and my ups is a CyberPower CP1350PFCLCD PFC Sinewave UPS 1350VA 810W PFC Compatible Mini-Tower. Thanks.

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    Quote Originally Posted by Cinx787 View Post
    There seems to be a lot of different posts about PSUs and buzzing noises but no one seems to know why there's is buzzing. Well I found out why mine is and I'm curious if I should be concerned.
    Well... Certainly a lot of people here know. Probably should have asked here first.

    We also tend to tell people that there's no reason for concern.

    The buzzing or whining that a power supply can do is caused by loose windings, improperly assembled windings and/or improperly fastened windings. These windings occur in either coils or transformer and, in some cases, polymer film capacitors.

    Electricity ALWAYS causes windings to vibrate, but typically they do so at a frequency much higher than human hearing. When the frequency drops below a certain level, they become audible. Since most modern power supplies change switching frequency with load, the noise can come and go.

    Now, all that said, the PFC coil could be buzzing in reaction to the waveform coming from the UPS. So I suggest trying the PSU with and without the UPS to see if the buzzing goes away. Of course, if the buzzing noise bothers you, you should just RMA the unit and, odds are, the next unit should not buzz the same way.

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    Default

    So I guess my next question is why does my dimmer switch downstairs cause my psu to buzz?

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    So it probably is your PFC choke that's buzzing. Light dimmers in houses work off of a PWM type of control and not just a reduction of voltage to reduce the bulbs' luminescence. Your UPS is line interactive, so as long as the PC isn't on battery power, it's not getting any kind of mains filtering as long as it's on main's power. Doesn't matter if it's "true sine" or not as that only applies to when the UPS is running off battery power.

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    So you're saying it's just going to be a cosmetic type of issue? Not damaging?

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    More like annoying, but not damaging, no.

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