Found the below on a different forum
re: He too explains why "pure sine" is good for iMacs. And, sizing does matter as well
Hope this helps as well
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JoeJoe2009
Re: UPS/ Backup power information question
Jul 23, 2010 12:10 PM (in response to Stadler3D)
Hi Stadler3D,
The question you ask is very common, lots of people run into the same problem. Lucky for you that you're doing your research before buying and then having to return the UPS.
To address the issue of simulated vs. sinewave, you are better off going with a true sine wave unit. Some of the older Macs had non active PFC power supplies which worked well with the modified/square wave UPSs. However the newer Mac's have active PFC power supplies and need to have a UPS that outputs a sine wave. Otherwise when your standby UPS goes to batteries your Mac will restart, make humming noise and potentially damage the PSU.
The sine wave UPSs are usually much better models which offer better power filtering, surge protection and AVR Boost/Drop which is well worth it to protect your investment.
One common mistake people make is they buy the Back-UPS RS 1500. While it's a nice entry level UPS and can protect most PC's and lower end computers very well it doesn't function well with Mac power supplies because of the modified sine wave output. In the same series are the: Back-UPS SC, Back-UPS CS and other lower end APC series of UPSs.
The IMac 27" consumes 365W of power, you'd probably want to back up your cable/dsl modem (40W), router(40W), and maybe a voip phone or a light(50W). Your total load would be 495W. With that in mind, you have several options.
The entry level option would be to go with a unit like the APC Smart-UPS 1000VA LCD. This unit has a maximum capacity of 670W, surge protection, power filtering, AVR/Boost and drop, and outputs a sine wave. This UPS would provide you with 10 minutes of run time at 495W. if you're looking for a cost effective high vlaue alternative, an option would be going for a refurbished Smart-UPS 1000. Same run time, less money.
If you need more than 10 minutes of run time or if you have more than 495W, you could always go with a bigger unit, the APC Smart-UPS 1500VA LCD. This unit has a maximum of 980W, power filtering, surge protection, AVR boost/drop and outputs a sine wave. It's the bigger brother of the SMT1000. The SMT1500 would provide you a run time of 23 minutes at 495W. At higher load, the run time would go down obviously. A cost effective alternative would be a refurbished APC Smart-UPS 1500. It would provide you all of the features for a lower price point.
At the end of the day, you don't want to be sacrificing your hardware or data to power failures so you might as well get the unit that will do the job and do it well. There's no point of buying a unit that won't do the job. you'll risk your hardware, get frustrated and end up returning it. Do it right the first time around.
Mac G5, Mac OS X (10.4.8)
