Treadmill Blows Fuse on PCB When Motor Starts

Discussion in 'General Electronics Chat' started by CamaLamaDD, Aug 23, 2015.

  1. CamaLamaDD

    Thread Starter New Member

    Aug 23, 2015
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    0
    Hi everyone,

    I recently purchased a second hand treadmill from a local. I've ran into problems with the drive motor blowing the 15A fuse on the PCB when it starts up.

    If I disconnect the motor leads from the board, the unit will be OK. I can start the treadmill, display screen works fine, the elevation motor runs smooth, no problems.

    Once I connect those motor leads to the board, the fuse cooks.

    I have re-soldered the positive blade connection to the board because it was quite loose, but that has not made a difference.

    I turned the treadmill on with the motor leads disconnected and put a volt meter on the positive terminal... I get 190 volts to ground and around 350 volts from + to - on the board connections. The treadmill motor is rated at 90 volts and 15 amps.

    I'm trying to ascertain my problem... bad motor or bad PCB? How can I diagnose exactly the cause of this fuse cooking?

    Thanks!

    [​IMG]

    [​IMG]
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Try the motor on an automotive 12v battery, see if it runs OK, smooth in both directions.
    Max.
     
  3. CamaLamaDD

    Thread Starter New Member

    Aug 23, 2015
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    0
    Hi Max,

    Seems like a logical test, I'll give it a shot tonight and report back to you. Thanks so much for trying to help.

    Because my motor is stamped at 90 Volts, I presume that during normal operation, this is what it is drawing, correct? Is the 12V battery simply to test basic operation? Just something I'm curious about.
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
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    If the motor is shorted or other, it should show up using the automotive battery, smooth rotation in each direction.
    If it normally rotates at 2000rpm at 90v, it should turn smooth at ~ 255rpm on 12vdc.
    The motor in use vary rarely hits 90vdc, it varies dependent on track rate.
    You can also use a 120v lamp in place of the motor to double check the controller.
    Max.
     
  5. CamaLamaDD

    Thread Starter New Member

    Aug 23, 2015
    3
    0
    Hi Max.

    Motor ran fine in both directions on the auto battery.

    Phooey.

    Next?
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Did you try the 100w lamp load in place of the motor?
    See if it dims or is on full.
    Also try the motor without the belt.
    Max.
     
  7. Aleph(0)

    Member

    Mar 14, 2015
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    321
    Meter may not be accurate for pwm power. 450v electrolytic could help readings but nasty if polarity reverse!
     
  8. Cam Roberts

    New Member

    Aug 24, 2015
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    I'm missing something. Any old 100w table lamp in place of the motor? Is the board not putting out higher voltage?
     
  9. Hypatia's Protege

    Distinguished Member

    Mar 1, 2015
    2,778
    1,211
    SMPS/PWM supplies can be 'quirky' when unloaded -- Also, as per post #7, most VOMs don't 'do well' with 'chopped' signals (especially if the instrument is non 'true RMS' indicating)...

    FWIW I suggest you take @MaxHeadRoom 's advice! --- Is the worst case scenario realized - a 100W incandescent lamp won't 'set you back' much...:)

    EDIT: --- It occurs to me that in the (unlikely) event that the motor control is of 'current mode' PWM topology - an inductive test load may be required...

    Good luck!

    Best regards
    HP
     
    Last edited: Aug 25, 2015
  10. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    759
    May be a shorted MOSFET or IGBT.
     
  11. MaxHeadRoom

    Expert

    Jul 18, 2013
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    +1 on the possibility of shorted semi.
    This is why I advised the lamp test.
    The motor has a large flywheel and is connected to the track with a belt, so these controllers are not capable of full voltage at switch on, the rpm is brought up slowly.
    If the semi is shorted, full voltage is applied to a stationary motor.
    The power supply on these are 120v rectified and smoothed (170v), as can be seen, the power cap is rated at 200vdc.
    Max.
     
  12. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Power cap may be 450VDC only if mains is 220VAC
     
  13. GopherT

    AAC Fanatic!

    Nov 23, 2012
    5,981
    3,712
    Your fuse appears to be one of those fast-blowing ceramic types used in multimeters. Track down the manual (or check the circuit board) for proper fuse. Some past owner may have installed the wrong type. Generally, you want a slow-blo fuse in things with motors and heaters.
     
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