Why did the new capacitor fail?

Discussion in 'General Electronics Chat' started by pgrodz, May 2, 2012.

  1. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    Good Afternoon,

    My 20" planer started tripping the breaker and not working. The planer would start winding up for about 2-3 seconds before the breaker would trip. I opened the motor circuit housing and found the one capacitor leaking oil, and the second was swollen.

    I purchased two new capacitors as per the specifications of the previous capacitors. Both were installed and the planer worked for about 1 hour before the breaker tripped again... and much to my dismay, smoke started wafting from the circuit housing.

    Attached are pictures of the old and new capacitor. I've also removed the motor shield and can see no loose wire or any exposed areas that might cause a short.

    If anyone has suggestions of where to proceed I would greatly appreciate the advice. I'm well versed with simple wiring and basic set-ups, but this is getting a little out of my grasp.

    Thanks
    Paul
     
  2. #12

    Expert

    Nov 30, 2010
    16,343
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    The blue one is a polarized electrolytic capacitor, not an oil filled motor capacitor. You bought an electronics part instead of a motor control part.
     
  3. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    The blue capacitor is for DC voltages. You need one for 250VAC.
     
  4. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    Oh the small details. Thanks for the help.
     
  5. MBVet05

    New Member

    Jul 21, 2011
    27
    1
    Don't sweat the small stuff! It's those big swollen exploding things that you have to worry about!!
     
  6. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    1,305
    If it's a capacitor start motor the cap is only connected by a centrifugal switch for a second when starting.

    If the switch has failed (often stuck closed, due to lack of lube) the cap can cook.

    :D on the "small details" comment.
     
  7. #12

    Expert

    Nov 30, 2010
    16,343
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    If it's a capacitor start motor, the start cap is usually a "dry electrolye" type (cheaper) and signals its death with billows of white smoke. They WILL fail if stuck "on", but these pix show oil filled caps. (PS, A dry electrolyte cap feels surprisingly light for its size.)

    As part of my teaching duties, I connect an oil filled motor capacitor directly to the power line and show the students that a healthy motor capacitor will not heat, even when directly connected to the power line for hours. However, the start winding will overheat if the centrifugal switch is stuck in the "on" condition.

    Sorry to disagree with one I respect so much :(
    but I do this for my day job.
     
    Last edited: May 3, 2012
  8. DerStrom8

    Well-Known Member

    Feb 20, 2011
    2,428
    1,328
    Because it didn't study for the test?

    :D:D:D

    Sorry guys, couldn't resist--the phrasing was a setup :p
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
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    Don't be sorry I appreciate the correction. I used to do it as my day job too but it was 1982 when I worked in the motor rewinding shop, and you know how memories go. ;)

    Hey at least I remembered SOMETHING can get cooked when the start switch gets stuck on. :)
     
  10. Lundwall_Paul

    Member

    Oct 18, 2011
    220
    19
    I would love to learn motor rewinding. But back to the caps, Have you contacted the manufacture?
     
  11. pgrodz

    Thread Starter New Member

    May 2, 2012
    15
    0
    Good Afternoon Gent's,

    Thanks for all of the feedback about the capacitor. I ended up completely removing the motor from the bowels of my planer (no easy task) and opened the housing. After careful inspection I discovered that the centrifugal switch was arcing and locking itself in the 'on' position despite the switch in the dis-engage mode. I sanded and cleaned up the contacts and re-adjusted the positioning of the switch weights.

    It's now been almost 3 months and no further problems. Thanks again for the help to all.

    -Paul
     
  12. osx-addict

    Member

    Feb 9, 2012
    122
    9
    Don't forget to ensure your planer blades are well secured!! We don't need to have you losing fingers or having flying projectiles in your shop! :eek:
     
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