Motor run capacitors

redhawk

I recently replaced a 1/4 HP,  230V blower motor.  Did not replace the capacitor, which is 5.0 mfd 370V.  A couple questions:

1)  The original blower & cap were over 30 years old.  The cap showed no physical sign of damage, but I see some info on the web indicating they may fail with age.  Is it a good idea to install a new cap with a new motor...?  (Note: the original motor had not failed, I will keep it as an emergency spare.   I see an oiler hole on each bearing.  What kind of oil should be used on the bearings...?

 2)  If I replace the cap, would I be increasing the reliability if I use a 5.0 mfd, 440V cap instead of a 370V cap like the original...?  I see a Dayton cap of either voltage in the same size.  Is Dayton a good brand.  What's the best...?

3)  What is the effect on the motor if the cap fails...?  Does it just sit there and pull start-up current...?  Is start-up current the same as LRA...?  (I have measured normal run current on this motor of 1.5 Amps.)  Any guesses as to what LRA would be...?

Thanks...!

freddrow2002

capacitors

are cheap usually buy a new one when replacing any fan motor



only way to truly tell what a capacitor is doing is to test with a capacitor tester



use only the capacitor speced on the motor. on the label of the motor it says what capacitor rating is required do not use a 440 on a motor rated for a 330 you could however use a 5.5mfd 6.0mfd or whatever instead of a 5.0mfd



some people use 3in1 oil some use 5w30 motor oil



dayton is an ok brand i dont really have a specific brand i like for capacitors



if a capacitor fails motor usually doesnt start. but it will pull amps trying to start may even over heat



LRA = locked rotor amps as in the amp reading one would expect to see if the bearings went and the rotor was stuck

Jamie Hall

I'll go with Fred...

caps are really cheap, and they fail with time.  Worse, they fail gradually -- and you may get into a situation where the motor sometimes starts and sometimes just sits there blowing fuses.



Replace it.

Ironman

Capacitor Voltage

The voltage rating of a capacitor indicates the voltage that the insulation in the capacitor can withstand; it does not mean that the capacitor is sending that voltage into the motor. Therefore, you can always put a capacitor of a higher rated voltage in to replace a lower voltage one. But the micro-farad rating must be the same, within 10%. In other words, you can replace a 370V cap. with a 440V, but you cannot replace a 40mfd. cap. with a 50mfd. That would be 25% over-sized.



The "Turbo 2000" multi-tap replacement is 440V and can be used to replace any 370V cap. that falls in its micro-farad range. A higher voltage rating indicates a more durable cap. Capacitors can also be paralleled to achieve a higher mfd. rating. The rating will be the sum of all the caps. in parallel.

redhawk

Motor run capacitors

Bob, what you said was exactly why I thought a 440V cap might be more reliable than a 370V cap in a 370V application.  If they weaken with age, seems the ones that start out a little tougher will last longer.  At 5 mfd, there's not much difference in price.

Thanks to all...!

alotlikeearl

A little more info.

Ironman said it well but would like to add; if you use capacitors in parallel the "mfd" rating becomes the sum of the two capacitors while the voltage rating will be the lesser of the two if they are different.

We always relace the capacitor anytime we replace a motor.  We would also test the capacitor before we changed the motor.  A lot of motors get changed when it is just a weak capacitor.

Have a great weekend all!