Induction motor series resistor

[throbscottle]

Something I've noticed with 2 reclaimed induction motors now, is a low value resistance in series with one of the windings (I think it is the starting winding) - I'm not sure without a diagram in front of me but I think it gets switched out of circuit quite quickly. I think it's to increase starting torque, but can anyone confirm/refute this, shed any light on it?

Cheers

 

[throbscottle]

Ok, I've been doing a bit more research on the hoofernet. I now think it is for injection braking of the motors, which are permanent split capacitor types. This would agree with my previous finding that one winding makes the motor go one way, the other makes it reverse.

I've been looking some more at the control circuit for one of the motors (the other one just has a switch). It looks as though for normal running, the 2 windings are fed through diodes, one to either side of the capacitor, both with anode to a winding, cathodes commoned and fed by a triac (I didn't look further upstream than the triac's opto-isolator). I would have thought the motor couldn't work like this. Can anyone suggest what's going on?

 

[rumpfy]

Looks to me like U1 is an AC drive for the motor windings but U2 is a half wave DC drive which would probably stop the motor. Bu if U1 is for normal running, then I have NO IDEA why they use a 4.7 ohm resistor in the circuit.
The forward / reverse arrangement can ONLY be done by swapping the leads to either the main or the secondary winding.
Generally a 2 phase motor is nice because it does not need a starter switch, and also by proper proportioning of the secondary circuit, the nett motor phase looks like the motor is running at unity power factor.
Cant say much more than that.

 

[throbscottle]

Thanks for the input. From what little I've been able to find out the arrangement with the resistor is to limit the current when the winding is used for braking - so this arrangement is completely weird. I guess the only thing to do is wire it up and try it. Measuring the winding resistances might yield some info if they are different.