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Thread: Facing a strange issue with Corsair CX550

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    Quote Originally Posted by jonnyGURU View Post
    Don't get in-rush and hold up confused. There should be no (or very little) inrush if the bulk caps are charged. As long as the transfer time from mains to battery is less than one AC cycle (50Hz), the PSU will not notice.

    I don't think in-rush is your problem. Never did. It's either harmonics from the UPS or too long of a switch over from mains to battery (longer than the hold up time available from the bulk caps).

    Quality UPS's have a transfer time of 6 tp 8ms, which is not noticeable to even the cheapest PSUs. Even cheaper line-interactive UPSs are less than 12ms. If the transfer time is 16ms or more, the PSU might bawk.

    Even a cheap Cyberpower or Tripp-Lite standby UPS has a transfer time of 4ms.
    I found this:
    http://www.apc.com/us/en/faqs/FA158939/
    Although computer power supplies draw only a fraction of their full capacity during it’s steady state(normal operation), PFC power supplies have the potential to draw their full capability during initial inrush. ""Inrush"" or ""Inrush Current"" refers to the maximum instantaneous input current drawn by an electrical device when first turned on.

    Resolution:

    A computer’s power supply may also be subjected to a period of inrush, while the UPS is changing state (switching from utility power to battery power and back). Back-UPS and Smart-UPS SCs may experience up to an 8ms transfer time during this period. This is just long enough to remove power from the PFC power supply, resulting in a momentary inrush of the PFC. Once the UPS changes states from ""Online"" (passing utility power) to ""Onbattery"" (passing power from the UPS's internal battery), the momentary inrush from the attached equipment subjects the UPS to the On battery power supply’s maximum power draw, resulting in a potential Overload condition or dropped load.

    An Energy Star 4.0 compliant power supply has to be more than 80% efficient. For example, if a attached power supply is delivering 600W output power, its ‘input’ power can be as high as 750W. .

    This ‘input’ power should be the basis for sizing the UPS, so as not to Overload the UPS. This can be calculated by taking the PFC power supply’s rated output power and multiplying it by 1.25 as follows;

    600W x 1.25 = multiplying
    Isn't it effectively saying that for an activePFC psu the UPS power should be more than 1.25 times the max rated power of psu?

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    Quote Originally Posted by jonnyGURU View Post
    I don't think in-rush is your problem. Never did.

    You are probably right, but let's do a small calculation

    * The energy in a capacitor is 0.5 C V^2; lets take two 470uF at 200V each; that's about 20J

    * Now lets take 300W for 1/120 th of a second (8 ms); that's about 2.5J

    So, the capacitors can easily hold out

    HOWEVER, with a square wave they are being recharged in a very short time, a lot less than a quarter cycle which is 4 ms; so lets say 2.5J in a half ms which is 5 kW


    So I am still not totally convinced it is not an inrush problem (on an ailing battery)

    Quote Originally Posted by whitestar_999 View Post
    I found this:
    http://www.apc.com/us/en/faqs/FA158939/

    Isn't it effectively saying that for an activePFC psu the UPS power should be more than 1.25 times the max rated power of psu?
    Which would support the larger UPS choice

    Quote Originally Posted by whitestar_999 View Post
    ...unless you can give some solid reason that 1100VA model batteries will last twice as long as 600VA model.
    and yes the batteries would last longer as they are not being so heavily taxed.
    Last edited by ashiekh; 05-18-2018 at 04:55 PM.

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    Quote Originally Posted by Per Hansson View Post
    The issue stems from the use of APFC as I mentioned.
    This is most interesting, so does that mean the issue lies with active PFC? and not an over-voltage on the part of the UPS. At one point you were blaming the UPS.

    Quote Originally Posted by Per Hansson View Post
    And some UPS units increase it well above 400v which is the issue at hand.
    This is all about learning and I am not criticizing you for exploring ideas.
    Last edited by ashiekh; 05-18-2018 at 04:56 PM.

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    With that quote I meant the discussion that Silversone showed.
    It was also confirmed by that thread on Badcaps that I linked.
    "The one who says it cannot be done should never interrupt the one who is doing it."

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    Quote Originally Posted by Per Hansson View Post
    With that quote I meant the discussion that Silversone showed.
    It was also confirmed by that thread on Badcaps that I linked.
    The 'scope plots seem to show the max voltage is not so high, the DMM readings otherwise; you explained that in terms of active PFC which I find fascinating (if correct). Then again, I haven't heard of a slew of failed primary capacitors, so maybe the primary capacitors in new units are of high enough voltage rating that we can continue with cheap UPS units.
    Last edited by ashiekh; 05-18-2018 at 05:11 PM.

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    Quote Originally Posted by ashiekh View Post
    You are probably right, but let's do a small calculation

    * The energy in a capacitor is 0.5 C V^2; lets take two 470uF at 200V each; that's about 20J

    * Now lets take 300W for 1/120 th of a second (8 ms); that's about 2.5J

    So, the capacitors can easily hold out

    HOWEVER, with a square wave they are being recharged in a very short time, a lot less than a quarter cycle which is 4 ms; so lets say 2.5J in a half ms which is 5 kW


    So I am still not totally convinced it is not an inrush problem (on an ailing battery)



    Which would support the larger UPS choice



    and yes the batteries would last longer as they are not being so heavily taxed.
    I only need 1-2 seconds of successful switchover from UPS to mains/inverter backup so even then is it heavily taxing to batteries(assuming full load for those 1-2 seconds on UPS batteries).

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    Do you also have the computer monitor connected to the UPS?

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    Quote Originally Posted by ashiekh View Post
    Do you also have the computer monitor connected to the UPS?
    No! Only desktop & nothing else.

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    Quote Originally Posted by whitestar_999 View Post
    I found this:
    http://www.apc.com/us/en/faqs/FA158939/

    Quote Originally Posted by APC
    Although computer power supplies draw only a fraction of their full capacity during it’s steady state(normal operation), PFC power supplies have the potential to draw their full capability during initial inrush. ""Inrush"" or ""Inrush Current"" refers to the maximum instantaneous input current drawn by an electrical device when first turned on.
    When first turned on. You're not turning the PC on while it's on battery. You're maintaining it's on state. So inrush does not play a part.

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    Quote Originally Posted by jonnyGURU View Post
    When first turned on. You're not turning the PC on while it's on battery. You're maintaining it's on state. So inrush does not play a part.
    Of course it does.
    The grid has gone away so the bulk capacitor is discharging.
    It will discharge until hopefully the UPS has switched over before it's depleted.
    And it will then charge instantly as the thermistor is hot (only works from cold boot)
    "The one who says it cannot be done should never interrupt the one who is doing it."

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