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Computer Grade Power and Double Conversion UPS

  1. Dec 4, 2009 #1
    What is computer grade power in Double Conversion Online UPS?

    Powercom website says "Computer Grade Power can be defined as AC power that has a stable ground reference with less than 0.5 volts of level change of the ground reference and less than 10 volts of noise on the AC waveform."

    What is this 10 volts referring to, in the above definition? How can this be seen on the power analyser?

    What would the THD(current) on the Online UPS OUTPUT be, for it to be called computer grade power?

    [THD-voltage] should be less than 5% on UPS output, I am aware of this.
  2. jcsd
  3. Dec 4, 2009 #2


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    Staff: Mentor

    Welcome to the PF. The main consideration would generally be switching noise from the inverter process. If you get too much hash and noise on your AC Mains waveform going into some devices (like some PCs, I guess), that can cause problems for the switching power supply in the device. It can also potentially compromise the radiated EMI performance of the device, and definitely could cause issues with any RF transceivers in the device.
  4. Dec 4, 2009 #3
    Hi Berkeman,

    Thanks for the response.

    I am not an electrical engineer.

    But I am in the process of selecting a 3 KVA online UPS for my office.

    I have asked the UPS manufacturers to demonstrate the UPS output power quality at my office premises.

    They all will get a power analyser to demonstrate their Online UPS.

    My question is.....

    What readings to look for? What VALUES to look for, on the Power Analyser.

    THD (v)? THD (current)? For line, neutral both?

    How to determine whether the Online UPS is supplying correct power that will not hurt the delicate devices at my office?
  5. Dec 4, 2009 #4


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    Science Advisor
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    THD is Total Harmonic Distortion and is measured in percent (%). Here is a wiki page: http://en.wikipedia.org/wiki/Total_harmonic_distortion" [Broken]
    Last edited by a moderator: May 4, 2017
  6. Dec 4, 2009 #5


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    Staff: Mentor

    I'm no expert in power quality, especially as it pertains to the AC Mains input into computers, servers and such. But as a power supply designer, I definitely care what kind of noise is coming in the power input, since it can mess with the stability of my SMPS control loop. So one thing I would look at is the amplitude and bandwidth of the noise at the UPS AC Mains output port.

    BTW, since you have multiple UPS vendors coming at different times, you should be able to ask them these questions, and compare their answers. Ask them what the important things are to check, and what kinds of PC problems you might run into if you used a unit that did not do well on that check.
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