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  1. #1
    Join Date
    Jun 2005
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    14

    Post

    my fellow tech said it makes a difference to compressor operation, which voltage run cap you use. i say that voltage stated on the run cap is it`s dielectric limits, and the microfarads in new, should be same as old, at usual 208v to 240v conditions.

  2. #2
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,506
    Originally posted by somized
    my fellow tech said it makes a difference to compressor operation, which voltage run cap you use.
    Well I have to agree with that statement. I would rather use the correct mfd than volts in an emergency.
    __________________________________________________ ____________________________
    “Reality is merely an illusion, albeit a very persistent one.” –Albert Einstein

    “Experience is a hard teacher because she gives the test first, the lesson afterwards.”-Vernon Law

  3. #3
    Join Date
    Jul 2004
    Location
    West TN
    Posts
    983
    Use Same MFD
    Use Equal to or higher than Voltage rating.
    (i.e. its ok to replace a 370v with a 440v)

  4. #4
    Join Date
    Apr 2005
    Location
    NE PA
    Posts
    698
    You are right. The voltage is just a maximum operating voltage and has nothing to do with the function as a capacitor. Operating within its voltage limits, any capacitor with the same MFD value will perform the same.

    paul

  5. #5
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579


    The voltage rating on a capacitor is the voltage limit of the capacitor. Exceeding the capacitor's rated voltage may cause the dielectric to break down and the capacitor to short out.

    That said, you need to realize that a motor is an inductive device. When you the supply voltage is applied to the motor run winding, the voltage across the start windings will be increased to a higher voltage value. A motor acts like a transformer with the run winding acting as the primary and the start winding acting as the secondary.

    This is why the capacitor has a much higher voltage rating than the supply voltage.


  6. #6
    Join Date
    Nov 2001
    Posts
    1,874
    What problems would result in using a 35 mfd, when a unit had a 30 mfd ?

    Just wondering, They always say stay within a certain percentage
    If you try to fail, and succeed.
    Which have you done ?



  7. #7
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,510
    sopositly you can go up or down 5% but i always put in the same size mfd but only use 440v caps
    less to carrier on the truck
    5mfd and 7.5 mfd 370v and 440 v on truck

  8. #8
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,506
    Originally posted by tinknocker service tech
    sopositly you can go up or down 5%
    I always thought 20% but heck what do I know.
    __________________________________________________ ____________________________
    “Reality is merely an illusion, albeit a very persistent one.” –Albert Einstein

    “Experience is a hard teacher because she gives the test first, the lesson afterwards.”-Vernon Law

  9. #9
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,510
    mr bill it may be 20% i was tought so long ago 5% and have always gone by that

  10. #10
    Join Date
    Jun 2001
    Posts
    3,909
    I thought it was 10% over and 5% under.

  11. #11
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    15,506
    Originally posted by tinknocker service tech
    mr bill it may be 20% i was tought so long ago 5% and have always gone by that
    No, your probably right for some reason that just came to mind.
    __________________________________________________ ____________________________
    “Reality is merely an illusion, albeit a very persistent one.” –Albert Einstein

    “Experience is a hard teacher because she gives the test first, the lesson afterwards.”-Vernon Law

  12. #12
    Join Date
    Mar 2004
    Location
    Grottoes VA
    Posts
    5,856
    Had a blown up cap today at 5pm. It was a 40/3 370V cap and I didn't have one on the truck. So I took 2 10uf, and 4 5uf, and linked them with a 3uf so I could get them a/c until I could get the right cap. It was ugly and I had to strap it under the electrical box but it works.
    Karst means cave. So, I search for caves.

  13. #13
    Join Date
    Nov 2001
    Posts
    1,874
    I'll bet that looked like a time bomb strap to the undercarrage.

    No one has said what will happen if the higher mfd is used and not changed.
    If you try to fail, and succeed.
    Which have you done ?



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