Difference Between Capacitor Types

Thread Starter


Joined May 17, 2007
I am trying to find a simple answer to what is the difference between a motor-run capacitor & a motor-start capacitor? I have no prior experience with capacitors but want to learn more on a very simple, I am not an engineer or scientist level.



Joined Apr 2, 2007
we get single phase power supply at our homes from 3 phases.
the 3 phases are nothing but supply voltages separated by 120 deg in phase(120 deg in angle)

for a motor (induction motor) to work start than one phase is required
after the start it can run on single phase. actually a start can be givin by rotating the shaft manually.

we get single phase at our home and we don want to keep starting fans
and other machines by hands every ow and then do we :)
now a inductor or capacitor introduces a phase difference of 90 degree
in voltage and current thus we can have a two phase system.
hence a winding in which supply is given directly and other thru a capacitor
is used for startin purpose.

since we req two phases only to start the motor we can disconnect the second phase windings after the motor has gathered speed. but the motor can also work (little better) with two phases hence we can keep the second winding connected also.

if the second winding is kept connected then its motor run capacitor.
if starting is done with help of capacitor its motor start capacitor.

this link may explain better.