Run Capacitor keeps burning up

Discussion in 'General Electronics Chat' started by dlbuilds, Feb 21, 2014.

  1. dlbuilds

    Thread Starter New Member

    Feb 21, 2014
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    Hi, new here but hope this site is helpful to me.

    So I have a Powermatic PF-41 power feeder. It has both a start and run capacitor. The run capacitor keeps burning up in about 4 minutes.

    I spoke to the factory and they said it was because I was running it from a old 100' extension cord. So I got a new capacitor just like the original one and plugged it into the wall straight from the motor. Now it looked good and I ran some wood through it on my shaper and it seemed good. I then walked away from it to help another gut in my shop and left it running just to make sure it was good. I started smoking in about 10 minutes. This is the third one now and I do not know why this very much like new but 5 plus year old feeder is burning these things up.

    I got it from craigslist's list and the guy said it was like new only used it for 2 small jobs and decided to sell it as it has just set on a shelf now for a few years. It got here and I was surprised that it looks brand new still.

    Any thoughts here for some help?

    Thanks
    Dave
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Probably not AC Run type, if it is start rated only then it will burn up, the other possibilities are winding fault or wrong cap value.
    Max.
     
  3. PackratKing

    Well-Known Member

    Jul 13, 2008
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    A run cap, will be an oval-shaped metal can, whereas your start cap will be a cylindrical bakelite...
    I'm guessing a 1/2 HP motor, which would call for about a 20 - 30 Mfd run cap, 5 - 700 Mfd start...
    Pictures of the motor rating plate / capacitor setup would be helpful...
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I had this issue. There is one thread of mine with pictures.

    The problem was just not enough Voltage rating of the cap.
     
  5. #12

    Expert

    Nov 30, 2010
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    I do a demonstration for a class where I teach the whole hour without telling them I have a capacitor plugged in. Then I show that I am unplugging a 10 uf, 370V run capacitor from a 240 volt power line, and it is not at all hot. A healthy run capacitor, properly rated, will not heat!
     
  6. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    That's what I was always told too. But my 5HP air compressor has both the start and run caps in a round bakelite type case. Even when the run cap burned out around 10 years ago, the replacement Graingers sold me was a round bakelite one. Go figure.
     
  7. dlbuilds

    Thread Starter New Member

    Feb 21, 2014
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    Great help here thanks. R!f@@ I am looking for your post now. I want to include the photos but I see only a link to a web site photo. Is there a easy way to just attach the three photos I have of this? When I try and insert the image its asking me for a web link. There on my hard drive.
     
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
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    And if you measure the current it is minimal.

    But then you have to explain how placing it in series with the run/start winding produces sufficient out of phase current for the winding.;)
    Max.
     
  9. dlbuilds

    Thread Starter New Member

    Feb 21, 2014
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    Thanks Max but I have no idea what you are talking about. I can barely fire a house this motor stuff has me spinning. I just need it to stop burning up. Last test went about 10 minutes and then started getting hot so I killed the machine and unplugged it so I would not burn another one up. It is a run capacitor and it is a 25mf 250volts should I have a higher mf it seems as if it just has to much power going to it.
     
  10. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Can you start and run your motor without the capacitor and will the motor get hot after a few minutes or not?

    On that type of electric motor the run capacitor should be an optional component so it shouldn't have any problems running without it other than the motors running amp load might go up an amp or two.
     
  11. #12

    Expert

    Nov 30, 2010
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    And the current is exactly what you would expect from Xc = 1/(2 Pi F C)
    That is a very important point because oil filled run capacitors do not measure correctly with a low voltage capacitance meter. You MUST put them in the condition they are built for to get a proper reading.

    and then I finish the lesson.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    As #12 pointed out, on direct AC supply the current through the cap is minimal.
    The winding current occurs because when Xc=Xl the current will be at maximum, any other point due to a change in a value of C will reduce the current, IOW there is an optimum value for the Capacitor.
    A value as low 25μf should not cause heating and would be typical for ~ a 1HP motor?
    Are you sure it an AC rated motor run cap?
    Max.
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I think 250VAC is not enough unless it is 120VAC motor
     
  14. dlbuilds

    Thread Starter New Member

    Feb 21, 2014
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    I tried that it did not work.... it popped load and even saw a small flash of flame.
     
  15. dlbuilds

    Thread Starter New Member

    Feb 21, 2014
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    it is 120 volt motor
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Tried what?
    Methinks something else is afoot.:rolleyes:
    Max.
     
  17. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Try a 375VAC cap
     
  18. tcmtech

    Well-Known Member

    Nov 4, 2013
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    Any chance of getting a voltage reading on the lines without the cap connected?

    BTW that thing is JET industries product so I have suspicions that most of it is over priced under built junk to begin with.

    If you end up with a bad motor a new better quality one of similar design is around $200 if you know how to do your shopping right. ;)

    The one you have I see retails for around $466.:(
     
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