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Not getting the required output from vfd

Discussion in 'Troubleshooting and Repair' started by Sheel, Oct 30, 2018.

  1. Sheel

    Sheel

    2
    0
    Oct 30, 2018
    Hi,
    I have one of the KEB COMBIVERT F5 inverter on one of our machines. The output voltage from the drive when the motor is running should be 120VAC(phase to phase), but we are getting 220VAC(phase to phase). Also, in stand still condition there should be no output voltage to the motor but we are getting around 50VAC(phase to phase), causing the motor to hum and in some instances rotate in the reverse direction.
    Any idea what could be the possible cause of such behavior and how to solve would be a major help.
    Thank you.
     
  2. shrtrnd

    shrtrnd

    3,665
    453
    Jan 15, 2010
    I didn't look for a schematic on your unit, but from my memory of working VFD's 20 years ago, the symptom you describe was usually traceable to the SCR's. You may have other damage if you've continued to try to run the VFD when it's not working, but I'd start with failed SCR's.
    Good luck.
     
  3. Tha fios agaibh

    Tha fios agaibh

    1,892
    599
    Aug 11, 2014
    I would first verify that all the parameters are set specifically to your motor and its application. It's worth spending the time to know and understand these parameters.

    One parameter not set correctly can cause odd behavior. Also, if analog inputs are used, they can be sensitive to noise which can lead to motor drift and erratic behavior.

    If you know all is correct, then check the SCRs as shrtrnd suggested, although VFDs often throw a buss fault if a SCR is bad.
     
  4. Minder

    Minder

    2,826
    585
    Apr 24, 2015
    Evidentally it is not a typical VFD by the look of the description, a link to the manual would help.
    BTW VFD's typically do not use SCR's , IGBT's are the common switching devices or Mosfets, in some cases.
    M.
     
  5. shrtrnd

    shrtrnd

    3,665
    453
    Jan 15, 2010
    Well, it HAS been 20 years since I worked on them. Didn't know SCR's became out-of-fashion.
    Those old hockey pucks were pressed between two heat sinks, and you couldn't even read-em unless they were under pressure.
    How's about it Sheel? Any luck troubleshooting this thing yet?
     
  6. Minder

    Minder

    2,826
    585
    Apr 24, 2015
    The modern style VFD came in around 4 decades ago due to the introduction of new switching devices such as the IGBT, Mosfet etc. These created variable frequency and PWM of the wave form.
    The old 3 phase SCR drives did not control the frequency as they operated in a full wave bridge configuration across the 3 phase 50hz or 60hz..
    I remember a common cause of failure was during power outages when they would random fire as the voltage collapsed!
    M.
    .
     
  7. Sheel

    Sheel

    2
    0
    Oct 30, 2018
    Sorry for not replying... The problem seems to have been solved by tuning some of the parameters.
    Thanks for the responses, appreciate it.

    Cheers
     
  8. shrtrnd

    shrtrnd

    3,665
    453
    Jan 15, 2010
    Thanks for letting us know that you believe the problem is solved.
    When all else fails, read the manual.
     
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