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Diodes failing after getting really hot. Attached to UPS system.

Discussion in 'General Electronics Discussion' started by Leonard Slattery, Sep 23, 2015.

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  1. Leonard Slattery

    Leonard Slattery

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    Sep 23, 2015
    Hi guys I am new to this forum, I am an engineer for an instrument company. I have a problem that has me stumped.

    We have an instrument in the field and that is failing. This instrument is attached to an APC UPS system. Various parts of the system have been failing in a weird way. We use 230V Cal controllers. The 230 V input side is malfunctioning. A diode is getting red hot and failing.(3 in a month and we haven't seen these fail before in 15 years.) There is also a 12 - 24 DC - DC converter that gets it's 12 v from an embedded P.C. A diode in this also failed in the exact same manner got red hot and failed.

    Both these seem to be using the same style of standard circuit for power regulation. I don't have the exact schematic.
    It looks like a standard diode that is failing not a zenor.

    These are too coincidental not be related. Could there be something with the to do with a bad sine wave that is killing the components.

    The information I got from the customer about the UPS is that it's running at a 230V with 2 volt fluctuation. They haven't checked the line with a scope.

    Thanks in advance.

    Lenny.
     
  2. shrtrnd

    shrtrnd

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    Jan 15, 2010
    If I understand your problem, your INSTRUMENT is failing, but it's fed by a UPS that you believe is causing the failure.
    If that's the case, somebody needs to take a look at the UPS output.
    There's not much sense in trying to repair your instrument, if the UPS is just going to fry it again later.
    Is that the correct situation?
     
    Leonard Slattery likes this.
  3. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Without any information on the UPS model or output type or load, it's kinda hard to say.

    1. If this is in one installation only, and everything that fails is connected to the ups, how hard is it to swap in a replacement ups for a while and see if the problem continues?

    2. When the failed assemblies were repaired/replaced, did they always fail again? How soon after reconnect? "3 in a month" - 3 out of how many?

    3. Can you hang a Dranetz or some other recording power quality monitor on the ups to capture a transient or surge event?

    ak
     
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  4. Leonard Slattery

    Leonard Slattery

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    Sep 23, 2015
    Thanks for the replies,

    shrtrnd that is exactly the situation.

    AnalogKid We haven't replaced any equipment yet. No point until we know why they are failing. 3 out of 4

    The equipment is on another continent so I have no access to it. I am pretty confident that it is the UPS blowing up the power regulation in the instrument. The customer is blaming our equipment and that it is faulty (which its not). I need some concrete ideas so I can point to the UPS and say "test this and that it is your problem."

    What I am really asking is has anyone ever heard of UPS's affecting power supplies in this way before..
     
  5. AnalogKid

    AnalogKid

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    Jun 10, 2015
    Yes, but not after years of normal operation. Some downstream systems do not like the squarewave AC from a low cost UPS, but that usually shows up in a few hours (or *much* sooner).

    And while we're focusing on the UPS, what kind is it? More importantly, did the failures occur when running on batteries or passing through AC power?

    ak
     
  6. shrtrnd

    shrtrnd

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    Jan 15, 2010
    My input is that you probably don't know what this other continent user is doing.
    A lot of other countries also have notorious problems with line-power regulation. (Yeah, I know they're using an unknown UPS, ... or they say that they are)
    Your failure is at the power-input to your instrument. If you don't have a representative near the customer, ask them to email you pictures of their set-up and connections to your instrument.
    Your instrument may have an electronic component age-related problem, but it sure doesn't sound like it.
    If the customer is serious about solving the problem and not assigning blame, the least they can do is monitor the output of their UPS and tell you what they've got (if they're actually using a quality one).
    Good luck.
     
  7. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    What country is the unit installed in? Not near Finland by any chance?
    Thanks
    Adam
     
  8. Leonard Slattery

    Leonard Slattery

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    Sep 23, 2015

    It's in Sweden... Do they have some issue up there with dirty electricity..



    Thanks for the input.
     
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