I'm a second year electrical apprentice. Was out of the trade for a while then came back in working at a shipyard on ferry refit. Dirty work (between the welding and the blasting) but has a little bit of everything: DC, motor controls, emergency systems, fire alarms, etc.
Anyway, I was sent to check out a vent fan motor in the shop which wouldn't start. 120v, 4amp FL, 60hz, single phase, capacitor start. I checked the capacitor(7 microF, 375 max voltage, 60Hz)and it wouldn't read on my meter for any capacitance but it wasn't shorted. I put a 13microF, 375 max voltage, 60Hz capacitor on to check and the motor started up and ran fine.
Would this 6microF change hurt the motor? Its 150ohms less in series with that starter winding. Time cycle should be effectively unchanged. As near as I can figure, it should have marginally lowered the resistance at start-up of the motor.
Thanks for any help.

Hi Ape,

Don't know if the different cap would hurt the motor or not but I'd just get the proper replacement and be done with it.

ape:

Welcome to the ECN!

I don't think the extra capacitance will hurt the motor at all, especially if it is usually started once or twice a day for example.

Many electrolytic caps have a rating tolerance in the very high percentage range anyway (I think + 100%, -35% or more) so I really don't see a problem here.

If you have a clamp-on ammeter a quick check of the running current (if at or below nameplate you're good to go) will answer any concerns.

This has been my experience in the past with projector motors, you actual experience may vary.

Thanks. Have the replacement on order.