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Participant

Join Date: Nov 2009
Posts: 3

Motors and Capacitors

11/05/2009 10:25 AM

Actually there is a Geofarad(brand)PRS, defective,capacitor 60mfd, -0+8%,330 v DB HSFPU-360 v DB HSFQV, 60 Hz.

I have in stock a 43-53 mfd 250v AC 50-60 hz OR a 86mfd +20%-0%, 250v AC 50-60 Hz. Which one should I use?

Somes are telling me that the 43-53mfd could be insufficient to start the motor, and I have read that a higher mfd could be damagable for the motor????

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Power-User

Join Date: Jan 2008
Location: NY
Posts: 348
Good Answers: 18
#1

Re: Motors and Capacitors

11/05/2009 9:14 PM

Is the lower voltage rating on your "in stock" capacitors going to be safe for the application?

Participant

Join Date: Nov 2009
Posts: 3
#3
In reply to #1

Re: Motors and Capacitors

11/06/2009 9:32 AM

I supposed so because the operation voltage of the motor is 110 v ac and I have been told that the higher voltage rating on a capacitor is to protect the capacitor...?

Commentator
Belgium - Member - New Member

Join Date: May 2007
Location: Flanders (Belgium)
Posts: 97
Good Answers: 3
#2

Re: Motors and Capacitors

11/06/2009 5:34 AM

Does this motor have a centrifugal switch ( or a start current sensing switch "klixon") to disconnect the capacitor ?

If the broken capacitor is used as permanent connected capacitor, it can NOT be used, because the voltage over the capacitor will probably to high.

Why not connecting two or more capacitor in series or parallel to obtain the correct capacity and voltage ?

Participant

Join Date: Nov 2009
Posts: 3
#4
In reply to #2

Re: Motors and Capacitors

11/06/2009 9:37 AM

there is no centrifugal switch, the capacitor is permanently connected,

thanks for the parallel or series solutions, I understand that a 86mfd+ capacitor will push to high the voltage operation of the motor.

Commentator
Belgium - Member - New Member

Join Date: May 2007
Location: Flanders (Belgium)
Posts: 97
Good Answers: 3
#5

Re: Motors and Capacitors

11/07/2009 7:29 AM

Keep in mind the following things

1) The motor and auxilairy winding are working as a kind of transformer. This means that the ratio between the motor winding number and the auxilairy winding number determs the voltage that comes across the capacitor. You can not change this ratio unless you rewind the motor. This means that the capacitor has to have a minimum working voltage.

2) When you decrease the value of the capacitor 43 µF in stead of 60 µF The starting torque of the motor will be less. This can be a solution in case the motor is not used at full load. A motor not used at full load will turn smooter with a smaller capacitor, because the magnetic field inside the motor will be more circular (and less eliptical). Only at full load and with a correct sized capacitor you will have a circular magnetic field inside the motor. This means less vibration and less noise.

3) When you increase the value of the capacitor 86 µF in stead of 60 µF, the current through the auxilairy winding will be to big. This can result in a burning of the auxilairy winding. An acceptable current through the auxilairy winding will be 6 - 8 A/mm2 cupper surface of the auxilairy wire

4) When connecting capacitors in series, the working voltage will increase. If capacities are equal, the working voltage doubles.

5) When connecting capacitors in parallel, the inverse values (1/value) have to be counted together and this result has to be inverted.

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