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VFD Keeps Dying

Discussion in 'General Electronics Discussion' started by Richard Muller, Nov 3, 2012.

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  1. Richard Muller

    Richard Muller

    30
    0
    Oct 27, 2012
    Well this is a fun one

    I have a power flex 40 that keeps dying. We change it out and the machine will run for months and then die. It is very frustrating because there is never a fault it just dies. Any ideas on how I can catch it. The machine has a mirco logic I believe 1200 series. The drive runs a 1/4hp motor that runs a 40:1 gear box. There is a very low amp draw something like 1.2amps. We have put an amp probe on and used the max function and the highest draw is 1.5A. The FLA setting on the VFD is 2A so it doesn't die because of high amps. Its a mystery. Any help or ideas would be great.
     
  2. Richard Muller

    Richard Muller

    30
    0
    Oct 27, 2012
    I lied its a Power Flex 4. Sorry
     
  3. Y2KEDDIE

    Y2KEDDIE

    259
    15
    Sep 23, 2012
    Put a voltage data logger on the incoming line. I had a EATON unit fail intermittently. It turned out the power company had several over voltages on the line. The final one (during a storm) took out one leg of the 3 phase rectifier, and the output thyristor block.
     
  4. shrtrnd

    shrtrnd

    3,781
    499
    Jan 15, 2010
    Like Y2KEDDIE said. I use a Dranetz Power Line Monitor, and watch the incoming
    power line for voltage spikes over time. Usually, the problem I find most often with
    Variable Frequency Drives is damage to whatever thyristors are used, SCR's or Triacs.
    The VFD takes a bunch of incoming power spikes, and eventually, it gets one too many.
    You'll have to look for whatever other motor or pump is on the same incoming power
    line, and isolate it from the VFD you're losing. This typically happens when another
    large motor kicks-in elsewhere on the same power feed, causing voltage spikes to your
    VFD.
    Good luck.
     
  5. Y2KEDDIE

    Y2KEDDIE

    259
    15
    Sep 23, 2012
    I'm not sure if it would do a lot of good, but as acheap insurance I was thinking of putting a service entrance type surge protector ahead of my VFD.

    I would think the inductors inside the VFD would catch a lot of transiants, but obviously they didn't protect my unit.

    I'm using my unit to change sigle phase power to 3 phase,to drive an aircompressor as a soft start application.

    Area resisdents on the same line experienced a lot of blown out light bubs at the time my unit failed.

    Eddie
     
  6. shrtrnd

    shrtrnd

    3,781
    499
    Jan 15, 2010
    The surge protector will only help in the short term if you're getting a large number
    of large spikes. Don't get me wrong, if you can't monitor your power feed and aren't
    sure of the exact problem, the surge protector might actually solve it. But not knowing
    for sure is the problem.
    Is your air compressor a continuously used item, or only a once in a while for a sepcific
    application issue? If it's not something that sees continuous use, maybe you can just
    invest in a better circuit breaker.
    I will say this, because I'm thinking it.
    Are you sure you've got good grounds between your VFD and air compressor?
    When you start messing with three-phase, you have to be careful of your neutrals, or
    you can cross-phase. (Wind-up with 240v on one-leg, instead of 120VAC).
    It's the first thing to think of here. The wiring/grounding between single-phase and
    three-phase systems is critical. Too many opportunities for feedback on the neutrals.
     
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