Motor running capacitor...

Thread Starter

Externet

Joined Nov 29, 2005
2,182
Hi.
I have two equal 230VAC squirrel cage fan airhandlers for dwellings central airconditioning and heating. One has a motor with a 3μF run capacitor; the other uses a 7.5μF run capacitor. Both units have 3 speed selection, both are preset for 'high'
What in the motor characteristics/specifications determine the capacitor value fitted ?
 

MisterBill2

Joined Jan 23, 2018
17,814
Usually the capacitor value is determined by the motor power rating. That includes both the running torque and the starting torque, and the running speed. A motor with a lower starting torque will usually take longer to reach the rated speed, which mightbe desired in some air handling applications.
 

MaxHeadRoom

Joined Jul 18, 2013
28,513
Hi.
I have two equal 230VAC squirrel cage fan airhandlers for dwellings central airconditioning and heating. One has a motor with a 3μF run capacitor; the other uses a 7.5μF run capacitor. Both units have 3 speed selection, both are preset for 'high'
What in the motor characteristics/specifications determine the capacitor value fitted ?
As a general rule the 1ph capacitors are aimed at achieving a 90° phase shift of the start winding, WRT the run winding. if this is a multi speed version the centre is aimed at 90° and the other windings either side of it.
 
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