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Re: Re: OT: help with motor run capacitor sizing
Original poster: <a1accounting@xxxxxxxxxxxxx>
I stand corrected. There is a relatively simple formula assuming you
need a phase shift of 90deg between the currents of the
windings. C=(R^2)/L where C is the capacitance to be put in series
in Farads, R is the series resistance of the coil in ohms and L is
the series inductance of the coil in Henries.
I did double check it, very quickly, because no 2*pie*f is odd, it looked ok.
I don't know if it produces practical values of C.
Note the current will be different in the winding with C compared to
the winding without the C (assuming identical windings) so you may
have to change the power supply voltage to compensate. Assuming the
impedance of L > R then the voltage must be reduce to avoid over heating.
> From: "Tesla list" <tesla@xxxxxxxxxx>
> Date: 2006/06/20 Tue PM 01:46:45 EDT
> To: tesla@xxxxxxxxxx
> Subject: Re: OT: help with motor run capacitor sizing
> Original poster: <a1accounting@xxxxxxxxxxxxx>
> Hi David,
> I don't think anyone replied to you so.
> There is probably no one formula is it would be dependent on the L R
> ratio of your winding.
> You could try putting a diode in series with each winding. The idea
> being that each winding is powered by alternative half cycles. You
> may have to do this at a lower supply voltage because the L of the
> windings will not limit the current.
> > From: "Tesla list" <tesla@xxxxxxxxxx>
> > Date: 2006/06/18 Sun AM 12:41:02 EDT
> > To: tesla@xxxxxxxxxx
> > Subject: OT: help with motor run capacitor sizing
> > Original poster: David Speck <dave@xxxxxxxxxxxxxxxx>
> > Terry,
> > May I ask the EE types on the list for a little help with a not
> quite TC item.
> > I have a number of two coil motors, some of them steppers, that I
> > would like to use as simple AC motors by wiring them as capacitor
> > run motors. One winding would run directly across the power supply,
> > and the other winding would run in series with an AC cap to provide
> > a phase shift.
> > Is there a formula that would suggest the optimum run capacitor value
> > based on the inductance of the windings, or the current draw through
> > one winding at their rated voltage?
> > Thanks in advance.
> > Dave