Low torque from single phase cap run motor
Low torque from single phase cap run motor
(OP)
A friend asked me to look at his commercial floor buffer. It would run with if tilted up with no load, but didn't have enough torque to start when normal on the floor. In the stall condition it draws about 40A, start cap about 18A, and the run cap about 2A. The run cap current seem a little low, but it is only a 20uF and my experince is that these caps either work or open. Opened up the motor and no signs of burning (color and odor) and all the winding have continuity and measure about 1.2 ohms. My field is more electronics and usually there are more obvious signs of a problem. What am I missing here? Thanks for any help.





RE: Low torque from single phase cap run motor
BK
RE: Low torque from single phase cap run motor
RE: Low torque from single phase cap run motor
operahouse: The 2A thru the 20 uF sounds about right, but what is the value of the starting cap? ( 18 A seems too high.)
BK
RE: Low torque from single phase cap run motor
RE: Low torque from single phase cap run motor
RE: Low torque from single phase cap run motor
RE: Low torque from single phase cap run motor
RE: Low torque from single phase cap run motor
The other common cause, is a problem with the rotor bars, but this would generally be accompanied by a low start current.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Low torque from single phase cap run motor
RE: Low torque from single phase cap run motor
For a given winding the capacitance must match optimum phase angle.
Test with two voltmeters while the rotor is locked. Maximum torque will be developed when V2 is close to 1.1xV1.
If you are far of such a condition replace the starting capacitor (Cs). If the capacitor is good and your voltage is lower, increase the capacitance.
If the voltage is larger reduce the capacitance. See diagram below.
RE: Low torque from single phase cap run motor
RE: Low torque from single phase cap run motor
RE: Low torque from single phase cap run motor
Can you provide a winding, capacitors, switch diagram?
RE: Low torque from single phase cap run motor