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capacitor-start motor? #56068
09/14/05 07:30 PM
09/14/05 07:30 PM
ape  Offline OP
Junior Member
Joined: Jun 2005
Posts: 2
T'ville, NL, Canada
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.

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Re: capacitor-start motor? #56069
09/14/05 09:13 PM
09/14/05 09:13 PM
golf junkie  Offline
Joined: Apr 2001
Posts: 507
York, NE
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.

Re: capacitor-start motor? #56070
09/14/05 09:38 PM
09/14/05 09:38 PM
mxslick  Offline
Joined: Oct 2004
Posts: 803
Atomic City, ID USA

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. [Linked Image]

Stupid should be painful.
Re: capacitor-start motor? #56071
09/15/05 06:37 PM
09/15/05 06:37 PM
ape  Offline OP
Junior Member
Joined: Jun 2005
Posts: 2
T'ville, NL, Canada
Thanks. Have the replacement on order.


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