Motors

[JdoubleU]

I am still trying to fully understand Motors. I thought that a single phase motor always needed a capacitor in order to start, and that was because it needed the phase shift. I was told today that there are some single phase motors that don't need a capacitor to start. How do they start then?

 

[Electric-Light]

I am still trying to fully understand Motors. I thought that a single phase motor always needed a capacitor in order to start, and that was because it needed the phase shift. I was told today that there are some single phase motors that don't need a capacitor to start. How do they start then?

it *always* need a phase shift to start. There are other means of starting it, such as using an auxiliary short loop in the core (shaded pole motor, that you see on table fans and such) and LR circuit. Using a starting winding with a significant resistance creates a phase shift that provides the push on the back like turning the spindle by hand.

Such starting method is often used in refrigerator compressors . The start winding is simply isolated after starting by a relay or a PTC (low resistance when powered up, but sustained voltage increases resistance and effectively cuts off starting winding)
LR circuit explained:
http://www.allaboutcircuits.com/vol_2/chpt_3/3.html