[GreenKeys] 33 motors part numbers

[Jones, Douglas W]

On Oct 25, 2016, at 3:52 PM, Dave Horsfall wrote:

> On Tue, 25 Oct 2016, teletypeparts at comcast.net wrote:
> 
>> Not sure but dont think so.  Good question tho.
> 
> Perhaps it's my limited understanding, but isn't a starting capacitor always
> required to provide the phase shift, and then gets switched out with e.g.
> a centrifugal switch?

No.  There are several other ways to start induction motors:

1) Capacitor run motors -- capacitor always in circuit, both windings identical and you change the motor direction by moving the (big) capacitor to the other winding.
2) Starting resistor -- resistor in series with one winding to provide phase shift.  The starting relay switches off that winding once the motor is up to speed.
3) Starting winding -- the phase shift comes from the self-resistance of the starting winding, which is cut out by the starting relay.
4) Starting capacitor -- in series with one winding to provide phase shift and cut out by the starting relay when up to speed.

The starting relay can be centrifugal or it can use the starting current surge.

I've seen a 50 watt starting resistor melt when the starting relay contacts were welded (by arcing) in the on state.  Drops of melted ceramic glaze don't do good things to what's under them.  That was in an early 1970's vintage disk drive.

		Doug Jones
		jones at cs.uiowa.edu