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Thread: Facing a strange issue with Corsair CX550

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    Quote Originally Posted by Per Hansson View Post
    Any such UPS can damage the bulk filtering capacitors in a PSU.
    That is because to achieve ca 230v RMS they have to output a very high square wave voltage.
    In some UPS designs this can equal a voltage higher than what the bulk filtering capacitor is rated for.
    Doesn't the peak voltage of the modified sine wave equal the peak voltage of an actual sine wave? How can it be higher?

    Also doesn't the PSU have to boost the input voltage to 380V peak anyway?

    Actually IIRC that was the main issue with pure square wave inverters, that the peak voltage was too low for many applications, that is fixed by modified sine wave inverters.

    Or do you mean that the inverter could be oscillating?

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    Quote Originally Posted by Samueru Sama View Post
    Doesn't the peak voltage of the modified sine wave equal the peak voltage of an actual sine wave? How can it be higher?

    Also doesn't the PSU have to boost the input voltage to 380V peak anyway?

    Yes, the peak is made to match (the width is such that the RMS matches)

    No boosting needed, the bridge rides the peak (250 Sqrt[2] = 354V)

    Still it is hard on the circuit as the capacitors are charged in a shorter time (half the time, doubles the current which doubles resistive heating)
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    Quote Originally Posted by ashiekh View Post
    On start up a power supply can take 10 times or more current/power than usual (as the primary capacitors fill/refill), so this might be what is tripping the UPS; some power supplies have a softer start than others. What might be happening is that during the time it takes the UPS to switch in the battery the power supply has drained its primary capacitors to some extent and they need refilling. You may only be taking 200W of a 360W capacity, but this initial demand could trigger overload. The problem is that an NTC (Negative Temperature Coefficient) resistor is often used to limit the inrush (high resistance when cold, low resistance when hot), but will still be hot when the UPS switches over, so there is no inrush limiting in your case.

    For the sake of argument let us suppose the above mechanism is in play, and that a weakening battery is why you didn't see it before; this suggests that a higher power UPS is likely to be more tolerant of such a surge.

    My very first reply suggested that the battery may be overloaded



    Not meaning to be rude, but it would have been helpful if you had checked what battery it has. It is very hard for someone to say if another UPS of similar rating will work or not (even your present UPS worked initially).

    If a UPS is overloading its battery, I'd say the UPS design was at fault and not the power supply, even if the battery will hold out initially. I have been known to modify a UPS to take larger batteries so that those batteries would not be over taxed, and concerning using another battery for trials, they just need to be connected



    no hardware modification needed for a test; that is why I suggested a car battery, but...



    If I had to guess, a new battery for your present UPS might solve the problem, but it would not be a good solution. I even asked



    as it affects battery life, but no answer. This is why I eventually replied




    It may amuse you to learn that I once lived on the Navajo Nation, where electricity is not so reliable, and to keep my heated blankets running I needed sine wave UPS units, and even then only some such units would work; but batteries are expensive and since moving I no longer use UPS units.
    I appreciate your replies & found some of them to be quite good. However I assure you that if I don't follow any of your suggestion then it is not due to my unwillingness but due to practical & economical reasons in the place I live. I can not "open" my UPS because I never did it before & I don't even have anything other than a Philips screw driver not to mention I am not in a situation to experiment with a working UPS(with my other psu).I am not sure how you could possibly connect an external battery to a normal UPS without opening it first & then do some wiring modification to connect it to internal sealed batteries pack. I have assembled my PC & I could have taken the chance had it not involve big batteries & acid(the worst a wrongly assembled PC could do is failure to start,the worst a wrongly done acid battery job can do is fire & explosion!).The place I live in is not my own so even if after all this I still dare to try I doubt I will get the permission from owners of the place anyway. The temps in the room where UPS is placed is around ~30-33C in summer & ~20C in winter.

    Quote Originally Posted by jonnyGURU View Post
    Nice price for a Li-ion UPS. Considering the CyberPower w/ lead acid batteries isn't much cheaper, I'd go with the APC.
    So in light of above statement by @ashiekh about some activePFC psu drawing much higher inrush during switchover(which now I think is the case with my CX550) would you still recommend a 600VA UPS.

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    Quote Originally Posted by Samueru Sama View Post
    Doesn't the peak voltage of the modified sine wave equal the peak voltage of an actual sine wave? How can it be higher?

    Also doesn't the PSU have to boost the input voltage to 380V peak anyway?

    Actually IIRC that was the main issue with pure square wave inverters, that the peak voltage was too low for many applications, that is fixed by modified sine wave inverters.

    Or do you mean that the inverter could be oscillating?
    No, a true square wave UPS would be fine, the peak voltage would only need to be 325v to simulate a 230VAC TRMS sine wave.
    (230VAC has a peak voltage or resistive heating value if you will of √2 x 230v = 325v)

    But a modified square wave needs to spend some time at the zero crossing stage, so to compensate you increase the peak.
    And some UPS units increase it well above 400v which is the issue at hand.

    Silversone made a report that was dicussed in this thread:
    http://www.jonnyguru.com/forums/show...9&postcount=34
    That PDF is gone but I have found it here: http://digilander.libero.it/hibone/U...est_Report.pdf
    "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 whitestar_999 View Post
    ... I never did it before & I don't even have anything other than a Philips screw driver ...

    So in light of above statement by @ashiekh about some activePFC psu drawing much higher inrush during switchover(which now I think is the case with my CX550) would you still recommend a 600VA UPS.

    Ah, good to know, then best you don't; electricity is dangerous.

    The inrush is generic and not just for an active PFC supply

    I think the opinions differ on the use of a 360W UPS; I would be against it given your experience.

    Given your situation, why not just live with the 400W supply? this would be the zero cost solution.

    Quote Originally Posted by Per Hansson View Post
    Looking more closely at the 475V compared to the 329V, they both reach about the same height so I remain skeptical.
    Last edited by ashiekh; 05-18-2018 at 07:32 AM.

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    Quote Originally Posted by ashiekh View Post
    Looking more closely at the 475V compared to the 329V, they both reach about the same height so I remain skeptical.
    What?
    They measure the bulk capacitor voltage with a DMM, it wont lie.
    "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
    No, a true square wave UPS would be fine, the peak voltage would only need to be 325v to simulate a 230VAC TRMS sine wave.
    (230VAC has a peak voltage or resistive heating value if you will of √2 x 230v = 325v)
    It's my understanding that a square wave UPS will also emit a high EMI/RFI that's detrimental to the PSU.

    But that's just what I heard.

    And if it's true, could be the problem OP is facing.

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    Quote Originally Posted by ashiekh View Post
    Ah, good to know, then best you don't; electricity is dangerous.

    The inrush is generic and not just for an active PFC supply

    I think the opinions differ on the use of a 360W UPS; I would be against it given your experience.

    Given your situation, why not just live with the 400W supply? this would be the zero cost solution.



    Looking more closely at the 475V compared to the 329V, they both reach about the same height so I remain skeptical.
    400W psu is almost 4 years old & heavily used so thought of replacing it hence bought new CX550.

    Quote Originally Posted by jonnyGURU View Post
    It's my understanding that a square wave UPS will also emit a high EMI/RFI that's detrimental to the PSU.

    But that's just what I heard.

    And if it's true, could be the problem OP is facing.
    So getting a 600VA APC UPS will still not solve this issue?

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    Quote Originally Posted by whitestar_999 View Post
    So getting a 600VA APC UPS will still not solve this issue?
    Nobody can know that.
    But ideally APFC PSU's should be used with true sine wave UPS systems.
    That's because the APFC circuit is really only designed for true sine waves.
    The old Passive PFC or no PFC PSU's can all be used with any sort of waveform.
    They can even be fed 325VDC directly and work just as happily (if not better)
    But those days are long gone by now...

    The idea laid forth that it's too big of a surge created when the bulk caps fill up after a brownout is certainly feasible.
    But there is one issue: you stated the Corsair PSU used to work with this UPS.
    I think it's more likely that you have less holdup time in the Corsair PSU due to damage to it's bulk capacitor over time.
    Or that you have longer switchover time in the UPS.
    Neither thing is very easy to check without expensive equipment.

    I'm with ashiekh here, you have a PSU that works fine, why not use it?
    If it's out of warranty maybe open it up and check the capacitors.
    And while you are in there blow the dust out.
    "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 whitestar_999 View Post
    400W psu is almost 4 years old & heavily used so thought of replacing it hence bought new CX550.


    So getting a 600VA APC UPS will still not solve this issue?
    No. I said square wave. Not simulated square wave.

    Square wave is the super cheap UPSs (probably like the one you have). The APC is a simulated sine wave UPS. Should be fine.

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