[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: (ET) motor run caps
A note aabout starting caps;
If the start cap is open on an AC motor, the motor won't start when you
turn it on. However, if it's a motor with a shaft (like a grinding wheel
or belt drive power tool) you can strt it by turning the power on, then
giving it a spin by hand (be careful).
Dave
Weymouth MA
On Fri, 28 Jul 2006 09:04:23 -0400 "Konstanty, Walter \(GE Indust,
ConsInd\)" <Walter Konstanty ge com> writes:
> >From the Standard Handbook of Electrical Engineers:
>
> - Starting capacitors
> A centrifugal switch is used to disconnect it from being in
> parallel with the motor winding. Typically, low voltage
> electrolytic capacitors are used. Oil ones are used for more severe
> starting conditions or higher voltage. The value of the capacitor
> is calculated to provide maximum starting torque while limiting
> thermal stress. Basically they limit the voltage to the winding
> during accleration to full speed.
> - Run Capacitors
> Used in some small motors where starting torque is quite low.
> With the capacitor in the circuit, the motor losses increase.
> Larger capacitor run motors have an auxiliary winding in series with
> the capacitor to improve operating characteristics. Fan motors are
> a common run capacitor motor.
>
> So Wombat, you're pretty much right. Start cap doesn't boost, it
> limits inruch current by restricting the voltage as the cap absorbs
> it. Capacitors don't like dv/dt (changes in voltage per time) while
> inductors don't like di/dt (changes in current per time)....that's
> why designers use one or both depending upon need.
>
> ...Walt
>
> -----Original Message-----
> From: elec-trak-bounces cosmos phy tufts edu
> [mailto:elec-trak-bounces cosmos phy tufts edu]On Behalf Of Neil
> Dennis
> Sent: Thursday, July 27, 2006 5:01 PM
> To: elec-trak cosmos phy tufts edu
> Subject: (ET) motor run caps
>
>
> Mike, if you go to an electrical supply house rather than an
> electronics
> house, they can tell you the difference. I think the difference is
> that
> the start cap just is to give a boost to the motor at startup while
> the
> run cap actualy "tunes" the circuit.
>
> wombat - somebody tell me if I'm wrong, pse
>
> _______________________________________________
> Elec-trak mailing list
> Elec-trak cosmos phy tufts edu
> https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
>
> _______________________________________________
> Elec-trak mailing list
> Elec-trak cosmos phy tufts edu
> https://cosmos.phy.tufts.edu/mailman/listinfo/elec-trak
>