6 Replies Latest reply: Mar 3, 2010 9:34 PM by aliascraig
Armydave1 Level 1 Level 1 (105 points)
I have been reading of the incompatibility of UPS square wave outputs of UPS devices and the new energy star 4 or 5 computers. The new iMac is energy star-5 compliant. The power supply output of a UPS will not work with new computers.

Does anyone have any information on this issue?

iMac 2.93 new 10/09, Mac OS X (10.6.1)
  • 1. Re: iMac -- Compatible with UPS Square Wave Voltage
    Michael Lafferty Level 6 Level 6 (16,080 points)
    It's not the DOE Energy Star rating per se that is the issue, but the presence of a power-factor correction power supply in your computer. Rather that attempt to run any critical data, audio or video processing task on a machine coupled to a square wave or step-approximated square wave UPS unit—which many lower end, relatively inexpensive units are—you should look to a product family like the Smart UPS series.

    Less expensive product generally output sampled sine wave or step-approximated square wave forms, when running off of battery power, which degrade as the backup battery is discharged. While not running on backup power, your machine receives the standard sine wave power passed through it from your utility company.

    If your machine is mission critical and must run unattended during extended outages, then sine-wave power is the only way to to. It if is just a matter of minutes you require, or a time sufficient to perform an orderly shutdown, then sampled sine wave or step approximated square wave output will get the job done for substantially less money, in most cases.

    It's really an issue of your requirement for power: short term leading to a rapid, orderly shutdown, or longer term replacement during an extended outage.
  • 2. Re: iMac -- Compatible with UPS Square Wave Voltage
    Armydave1 Level 1 Level 1 (105 points)
    I am looking for a UPS to run the computer long enough to shut down through native power management on the iMac. Some smart labeled UPS devices have stepped square waves. These are cheaper than sine wave output UPS devices.

    I read a review at Amazon that said the newer computers would not work with the square wave type UPS outputs. This was due to a change in their power supplies. That is probably what you were talking about in the first sentence of your post. Thank you for the information.

    If I get a new smart UPS with a stepped square wave output will it work with my new iMac? Maybe apple can answer that question.
  • 3. Re: iMac -- Compatible with UPS Square Wave Voltage
    aliascraig Level 1 Level 1 (0 points)
    I’ve been trying to find the same answers for my 24”, intel,Core 2 Duo extrerme, 2.8GHXZ, iMac (mid 2007) that Apple Engineering says has Active Power Factor Correction power supply.
    All I want from an UPS is decent time to unmount my external H.D., save my working data, and shut down the iMac properly. After the better part of two weeks I believeI have found the answer for my situation. Disclimer: I am not a tech nor experienced in electrical matters but just a guy who hung in there trying to make sense out of many conflicting bits of information. This is not meant to tell you what you should or should not do. Just what I believe I’ve found and what I have done about it
    after talking to lots of tech people. Corrections/updates welcomed!

    1. Apparently, there are some recent models of computers that have an updated power supply commonly called Power Factor Correction power supply (PFC), more specifically called Active Power Factor Correction Power Supply. As I understand it they were previously found mostly in the higher end of computers and not commonly found in the type that the average guy would use. Now Apple Engineering has told me via Apple Care that my 2007 iMac has an Active Power Factor Correction power (akaPFC) supply and that all wide range voltage supplies are PFC. I take that to also mean late model iMacs and most likely Mac Pros have this type of power supply.
    Mine has it and it is a 2007 iMac, I’m not sure when they started using it in iMacs.

    2. So what ? Well, if you tell an UPS mfg. your computer has an Active Power Factor Correction power supply or even if you drop the word “Active” (and use PFC) they will commonly say you need an UPS battery that sends electricity via a Pure Sine Wave to the computer. They are very costly units, easily $500 and up.

    3. What is an Active Power Factor Correction power supply, aka Power Factor Correction supply (PFC)? Paraphrasing and editing a statement from a battery mfg support page: Although a computer power supply draws only a fraction of its full capacity during its steady state (normal) operation, Power Factor Correction (PFC) supplies have the potential to draw their full capacity ( which I assume is the stated watts on the computers data sheet), instantly when passing battery power to the computer’s Power Factor Correction power supply.

    So what? well, the UPS may experience up to 8ms transfer time during this period which is just long enough to remove power from the computer’s Power Factor Correction supply which subjects the UPS to the maximum power draw of computer’s Power Factor Correction supply (PFC). This could result in a potential UPS overload or dropped power load ( computer restart, shut down ) because the UPS does not have the ability to furnish the amount of demanded power (watts).

    4. I solved my problem of what kind and reasonable cost UPS would work with my Intel iMac after talking with APC , local Apple Authorized repair & CyperPower. First I determined the max watts draw of my iMac x 3 ( to allow sufficient excess watts when in an instant max watts demand from the Computer’s Active Power Factor Correction power supply ) and added the max watts draw of my external H.D. and FIOS Router to determine the total UPS watts that would be required to aid in the UPS selection process.
    I purchased a CyberPower UPS model CP1500AVRLCD 900W , which successfully sent Simulated Sine Wave power just fine to my computer’s Active Power Factor Correction power supply when testing it two times. No need for costly Pure Sine Wave UPS. Cyberpower says this unit will work with the iMac but not work with the Mac “Tower” / Mac Pro and I suspect it has to due to the huge difference between them in maximum watts that can be instantly drawn when the Active Power Factor Correction power supply instantly demands the full watts power from the UPS.

    APC UPS model BR 1200 (also a non pure Sine Wave UPS) is recommended by a local Apple Authorized Repair facility (vendor) to his customers as working with the current iMacs.

    I personally think the difference in working and not working is getting the right amount of excess watts in the UPS, can’t think of any other reason it works. I really don’t care as long as it works.
  • 4. Re: iMac -- Compatible with UPS Square Wave Voltage
    aliascraig Level 1 Level 1 (0 points)
    On 12/20/09 Apple Care advised me engineering said my iMac does not need Pure Sine Wave power.
    That's good, confirms what I have experienced and what some others have said. In my opinion this still does not removed the need for careful evaluation of the ratio of the UPS battery power to the amount of wattage draw for the items connected to the battery side of the UPS when you consider the way an Active Factor power supply can, in instant, demand its maximum watts from the UPS.
  • 5. Re: iMac -- Compatible with UPS Square Wave Voltage
    aliascraig Level 1 Level 1 (0 points)
    Correction. I didn't use all the correct nomenclature for the power supply, I should have said Active Power Factor Correction power supply. Sorry. Two finger typing in a hurry will do this every time!
  • 6. Re: iMac -- Compatible with UPS Square Wave Voltage
    aliascraig Level 1 Level 1 (0 points)
    Thought I'd check back to see if there were any recent comments and it occurred to me I did not say how I tested the UPS. Rather than just pulling the UPS plug from the wall outlet, leaving, in my opinion, ungrounded power output from the UPS, I tripped the circuit breaker supplying power to the wall outlet being used by the UPS with its grounded plug. This test method was recommended in a number of threads in APC forums and it made sense to me.