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Anyone have any idea how I could fix the ~60ms transfer time of my UPS?

Discussion in 'Power Electronics' started by torveo, Sep 28, 2021.

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  1. torveo


    Sep 28, 2021
    I've got a cyberpower CP850PFCLCD UPS with an abysmal ~60ms transfer time. My PC can sometimes survive it if its idle, but even thats a 50/50 shot. Not exactly the protection I expect from this 180 dollar unit.

    This is actually the second unit thats done this. I RMA'd on the first one, but my replacement does the same thing so im guessing they sent me back the same one or its a design flaw of the product. Ether way they won't RMA anymore and its out of warranty which sucks. I've got some 1000v rated gloves, soldering iron, and some experience with high voltages from past projects and I think im ready to take a crack at repairing this thing. The only problem is, I have no idea what to do, or if its even possible to fix this type of issue. Could it be a relay that's not switching fast enough? Is there somewhere that I can put a large capacitor in parallel with the load, preferably on the 12v DC side...?

    On battery, the unit sustains 300w loads and holds 120v @ 60 hz fine, its just the high transfer time that's making it unusable. When I connected some lamps with incandescent bulbs, they flicker when switching to battery. They don't flicker at all when switching back to mains. I measured the transfer time by using my phone camera at 60 FPS and then counting how many frames the bulbs spent not lit up. It comes to 64ms for 4 frames. Yikes.
  2. Bluejets


    Oct 5, 2014
    Therein lies the problem.
    I'm sure if you shop around you will find an appropriate item to suit your needs, all-be-it requiring deep pockets.
  3. crutschow


    May 7, 2021
    The delay is likely due to the transfer time of the relay used to switch from the mains to the backup inverter.

    To avoid the transfer time you could use a UPS that operates off the inverter continuously, and just uses the mains to power the inverter and keep the back-up battery charged.

    Perhaps you could modify the UPS you have to do that.
    You would have to add a larger battery charger from the mains to both power the inverter and keep the battery charged.
    For 300W you would need a 12V charger of at least 30A.

    To avoid overcurrent to the battery when charging it after a power failure, you may need to add a small resistor in series from the charger to the battery.
    The charger can be isolated from the battery with Schottky diodes in series with the resistor and from the battery to the inverter.
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    A new PC power supply that tolerates the 60 ms outage is another venue. Difficult to find if you want the PC power supply to more or less match the power requirements of the PC (e.g. 300 W PC, 400 W power supply), but relatively easy if you use an overrated power supply (e.g. a 600 W power supply for a pc that requires only 300 W). The difference in power can in this case be used to prolong the time the power supply buffers the PC before the ups kicks in.
    Kabelsalat likes this.
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