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Capacitor replacement for pedestal fan

Discussion in 'Troubleshooting and Repair' started by bigone5500, Aug 1, 2014.

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  1. bigone5500

    bigone5500

    712
    120
    Apr 9, 2014
    Not exactly electronics...but does use electricity...

    I have a fan that has a 1/2hp motor and a 20mfd capacitor. The cap has gone bad and I am going to replace it. The cap has a rating of 20mfd +/-6% 370vac. I tested a 12mfd +/-5% 300vac cap and the motor started and ran fine. My concern is that the motor will possibly overheat and cause a fire. What is a safe range to stay with when substituting caps?

    The original is an aluminum can and the one I tested with is a small solid state with radial wires.
     
  2. davenn

    davenn Moderator

    13,710
    1,911
    Sep 5, 2009
    hi there

    The voltage rating is more so the important one

    One of the others more up on caps across mains powered motors may comment further
    Personally I would have preferred something between 15mfd and 25mfd and preference to the cap being a high side value ( 22 or 25mfd)

    cheers
    Dave
     
  3. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    I've seen some requirements as far as X and Y rated Capacitors if they are connected to mains.
    This is due in part to them specifically designed as to not cause a hazard if/when they fail.

    You should be save to use a Cap with a higher voltage rating just fine, but try to stick with the original (or close to) capacitance.
    There are more details from here: https://www.electronicspoint.com/threads/capacitor-replacement.269249/#post-1613797
     
  4. bigone5500

    bigone5500

    712
    120
    Apr 9, 2014
    Thanks for the input guys. I talked to a coworker about this and he said that the 30uf would be fine on a fan. However, my curiosity was eating me. I got a 24uf and put it on the fan. The 30uf makes the fan start very quickly. This is due to the higher current supplied to the starter winding. The 24uf cap makes the fan start smoothly and just from what I can hear, creates just about the same rpm.

    These are the ways we learn....
     
  5. elebish

    elebish

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    12
    Aug 16, 2013
    There are different types of electrolytic capacitors. Most are used for filtering (passing) small amounts of ac but blocking larger amounts of dc. The types used for motors are actually used to balance out the reactance of the inductive capacitance of the motor windings. The trick is to make the circuit look 'resistive" to the ac. These motor caps are designed to pass large ac currents and do not deal with dc. Regular caps are rated in dc and motor caps are rated in ac. Do NOT interchange! Ed.
     
    Last edited by a moderator: Oct 13, 2014
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