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Start Run Motor Capacitor

Discussion in 'Sensors and Actuators' started by sstouk, Jul 11, 2017.

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  1. sstouk


    Jul 10, 2017
    Hello guys,

    I have an issue with a medical compressor not being able to restart the motor once the first pressure level is reached and motor stopped. After pressure level drops - engine used to re-start automatically but after a few years the power need to cycle on the compressor to make the motor work again (and then it repeats - motor never restarts automatically as it used to do before).

    Manufacture suggested replacing a motor capacitor and sent a replacement.

    The rating on currently installed capacitor is 22.5 uF and the replacement I got is rated 15 MFD (same voltage range)
    I am hesitant to install it because I feel the difference is too big (over the 5% tolerance).
    I sent my concern to manufacturer but I am being assured that the capacitor they sent me would be OK.
    I'd like a second opinion on how dangerous it may be to replace a Start/Run motor capacitor with a smaller value because replacing the whole motor on this equipment will be quite expensive if it burns.
    Thank you!
  2. Chemelec


    Jul 12, 2016
    Yes it Will be OK to use it.
    However since it is a LOWER Capacitance, You may Still lack the POWER on RE-Start.
  3. Bluejets


    Oct 5, 2014
    Many compressors use an unloader valve. Best check this first if it has this arrangement fitted. Since you have had the compressor for a time, perhaps you are aware of a pressure release noise as the motor shuts off. This is the unloader.
  4. Tha fios agaibh

    Tha fios agaibh

    Aug 11, 2014
    I agree with you that it's too small. There isn't and real danger of installing it, other than it'll probably just burn out prematurely.
    I try to be within 10% of start caps value.

    It is wise to monitor start and run current. Your problem may be the compressor and not your motor.
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