Re: Motor start/run Circuits References

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "J. B. Weazle McCreath by way of Terry Fritz <twftesla-at-uswest-dot-net>" <weazle-at-hurontel.on.ca>

At 07:36 AM 28/12/00 -0700, you wrote:
>Original poster: "tesla by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<tesla-at-paradise-dot-net.nz>
>
>Team
>
>Lots of net searching and textbook reviews draws a blank on how motor run
>and start caps are connected  and used. Can readers suggest a net ref
>showing how extra windings are used wirth these caps. (The prospective
>purchase for a SRSG motor has many windings and of course no data)
>
>Rgds to all
>Ted L
>NZ
>

Hi Ted,

I can't refer you to a web site, but perhaps a quick explanation of
the hookup will do, as it's not overly complicated at all.

To keep it simple, let's assume that the motor is 120 volt only and
is 3600 r.p.m.  That means there will be four poles in total, two
for the run winding and two for the start winding.  The two winding
sets are offset from each other by 90 degrees.

The run winding is connected directly across the 120 volt line wires.
One end of the start winding is connected to one of the line wires,
with the other end connected to a capacitor and a centrifugal switch
in series and finally to the other line wire.

When power is applied, the closed centrifugal switch and capacitor
apply power to the start winding which is out of phase with that
which is applied to the run winding.  This causes a rotating field
which results in the armature (rotor) turning.  As the armature
increases in speed, the start switch is opened by weights on the
armature (rotor) shaft, disconnecting the start winding.

There is a variations to the above example.  Some motors will have two
capacitors, a start one of several hundred microfarad and a run one of
much smaller capacity.  You can tell them apart by their construction,
the start electrolytic being in a black plastic housing while the oil
filled run cap is in a metal can.

The oil filled run cap is connected across, or in parallel with, the
series connected start switch and electrlytic start cap.  It remains
in the start circuit all the time, feeding phase-shifted power to the
start windings even after the start switch has opened.  This improves
the efficiency of the motor, and helps with the starting torque too.

I hope that helps you out.  If you have any questions just e-mail me
directly and I'll try to answer them for you.




73, Weazle, VE3EAR/VE3WZL

Listening: 147.030+ and 442.075+
E-mail:    weazle-at-hurontel.on.ca
           or ve3ear-at-rac.ca
Web site:  www.hurontel.on.ca/~weazle