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Ups keeps tripping the CB

Discussion in 'Power Electronics' started by Thanduxolo, Apr 27, 2020.

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  1. Thanduxolo


    Apr 27, 2020
    1KVA online ups keeps on short circuiting and it has blown the mov..what could be the cause?


    May 20, 2017
    Could you expand on your description, it quite brief and doesn't tell us much.
  3. Thanduxolo


    Apr 27, 2020
    When I plug in the ups inverter on 230vac it trips on the circuit breaker from the power supply... I've opened it up and the mov and the ac fuse are blown
  4. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Remove the MOV, replace the fuse. Does it work now or still blow the fuse?
    If it works, replace the MOV by a new one (for testing it is o.k. to use the ups without MOV, but not for continuous operation).
    If the fuse still blows, you'll have to inspect the circuit board for other possible causes of a short circuit.
    Thanduxolo likes this.
  5. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    I am gonna guess it's an AOG (Act Of God) that proved your UPS really isn't.

    Was there any lightning activity near the power line coming into this UPS? Nearby cloud-to-ground strikes can induce severe spikes on the power line, enough to cause the MOV to short-circuit and blow the fuse. That is why @Harald Kapp has suggested that you first remove the now defunct MOV (which may be permanently shorted), replace the fuse, then see if UPS functionality has been restored. If the UPS then works, you can replace the MOV (which died, along with the fuse, to save your UPS) and your problem is solved!

    Do not operate the UPS, except for the functionality test, until the MOV is replaced.

    If the steps @Harald Kapp offered you do not restore operation, extensive troubleshooting is required. Are you up for it?
    Thanduxolo likes this.
  6. Thanduxolo


    Apr 27, 2020
    Thanks Harald..its working fine and I will replace the MOV
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