Reversing Rotation of Capacitor Start Induction Motor

[Dale7905]

While seaching for information on whether there are standards used by the electric motor industry for reversing the rotation of single phase fractional HP motors (eg: designated wire terminal numbers or color codes for the start and run windings wires.... which I think are in many (but not all) cases: terminal numbers from T1 to T4 for run windings and T5 to T8 for start windings; and red and black color wire for the start windings...not universal however, especially in older motors) I came across an interesting article at

http://www.homemetalshopclub.org/news/sep01/sep01.html.

The author explained how to reverse a single phase,1/2 HP, 3 wire, capacitor start induction motor by disconnecting the capacitor and inserting an inductor in the start winding circuit. This caused the current in the start winding to lag that in the run winding and thus caused the motor rotation to be the reverse of that when a capacitor was used. He noted that the starting torque was only about 1/3 that obtained when a capacitor was used so reaching the run speed was a bit longer, and that he obtained the value of the inductance needed to replace the capacitor by trial and error.

I thought this was an interesting way to reverse a 3 wire connected induction motor. I wondered if this technique is used very widely and if there was a way to calculate the needed inductance. I also wondered what precautions might be necessary to consider. I have a 3/4HP, capacitor start, single phase, Marathon motor with a 3 wire connection for the run and start windings I'd like to try this technique on. But I sure don't want to burn up the motor in the process. It would be nice if there were a way to calculate the needed inductance.

Thanks for any comments.

Dale7905

 

[waross]

This is not a good idea. It may work for some easy starting motors but the accepted way to reverse a single phase motor is to simply reverse the connections of the start winding.
yours

 

[ccjersey]

sounds more like a class demonstration of inductance and capacitance than a practical technique.