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iMac 27 and APC UPS: Noise from iMac

I am running iMac 27 using APC Back-UPS RS 800. When iMac 27 runs Online there is no noise from Mac. But when it runs On Battery (power cut) there is irritating noise from iMac. APC says everything is okay from UPS side - it supplies right parameters. APC UPS is tuned to sensitive mode (other modes also has same problem). Anyone faced the problem?

iMac, Mac OS X (10.6.3)

Posted on Apr 11, 2010 12:38 AM

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3 replies

Apr 11, 2010 6:40 AM in response to Abhishek S

Welcome to Apple Discussions,

Are you connecting just the power connection to your APC drive or are you also connecting a USB connection to it? If you are using a USB connection then try disconnecting it. It's also possible the power in your area is noisy (check with your local power company) and if that is the case there isn't much to do about it unless you get a UPS that also supports noise suppression.

Regards,

Roger

Apr 12, 2010 8:38 AM in response to Abhishek S

This is a very common problem, unfortunately the RS RS 800 is not suitable for the iMac 27". The iMac 27" can not work with a UPS that doesn't output a sine wave, the power supply is sensitive to this.

When the UPS is in normal operating mode, it's like a power bar and passes utility power to your Mac. When the UPS goes on battery, it generates the power from the battery and outputs a simulated or a square wave. The Mac power supply reacts by making noise and restarting or doing some other strange things.


To solve your problem, you need to get yourself a Smart-UPS that outputs a sine wave. For the iMac 27" which consumes around 350W, you need to get yourself a minimum of a APC Smart-UPS 750VA LCD SMT750. This unit outputs a sine wave and will not make your iMac 27" have difficulties while on battery power. The 750 will provide you around 9 minutes of run time to safely shut down your Mac.


If you need a bit more run time or have additional items you'd like to back up, you need a unit like the APC Smart-UPS 1000VA LCD SMT1000. This unit outputs a sine wave and has all the features of a data center UPS, but also has 670W of power. With this unit and the iMac 27", you'd have a run time of 19 minutes.


Either solution would work, as long as you get yourself a back up that outputs a sine wave. The little APC RS units are great for small PC's, but don't work with the Mac's.

Message was edited by: JoeJoe2009

iMac 27 and APC UPS: Noise from iMac

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