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testing capacitors

k.i.s.s.? exactly


  • Timco
    Timco Member Posts: 3,025

    I have a furnasty with a blower that will only run if you have spun it a bit prior to telling it to run. I am thinking capacitor but do not recall how to test the cap before calling it a motor. I get 120V at the lead (red) but no blower action...

    Thanks, Tim
    Just a guy running some pipes.

  • the only real way to verify a capacitor's value is with a meter that tests capacitance
    but if you don't have a meter or can't borrow one, an easy and inexpensive way is to simply replace the capacitor and see what happens. if that doesn't do it, it's the blower motor, and you haven't wasted the money on a new capacitor, because you'd want to replace the old capacitor with a new one anyway if you change the motor
  • 1. Take your meter and put

    it on the ohms scale.

    2.Disconnect the capacitor and discharge it.

    3. Place the leads across the connectors on the capacitor, it should register high then low in other words it charges then discharges.

    4. With an Analog meter it is easy because the needle should go up then down. If it does not do that replace it.

    Quick temporary fix, get a light bulb screw in fixture wire it across the wires that were previously connected to the capacitor, screw in a 100 watt bulb, flip the power switch and the motor will run until you get a new capacitor.
  • bob_46
    bob_46 Member Posts: 813

    you could hook the capacitor up to 110V and measure the current draw and the applied voltage. If it's a start capacitor don't leave it hooked up more than 10 sec.. Then multiply the current draw times 2650 and devide by the (measured) voltage the answer is in MFD ( micro ferrads) and should be within 10% of the MFD rating printed on the capacitor. Saves buying and lugging around another meter. Plus do what Tim said, that tells if it's shorted. bob
  • bill_71
    bill_71 Member Posts: 46

    whoa!! k.i.s.s.
    its only a capacitor
  • realolman
    realolman Member Posts: 513
    I would not do this

    without some convincing evidence that it is safe.
    What if it was shorted?

    The ohmeter thing is safe and probably a pretty good indicator of the capacitor's condition.

    The ohmeter has a small battery which charges up the capacitor. As the capacitor's voltage reaches the same voltage as the ohmeter's, the ohmeter will read less and less current flowing (milliamps), until the capacitor's voltage equals the ohmeter's and the current flow will stop.

    A digital meter will work, but an analog meter is much nicer, as the needle rises and falls... taking longer on larger capacitors.
  • realolman
    realolman Member Posts: 513
    Or in a nastier

    vein... keep it simple, stupid!
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