How Does Start Capacitor Help Start Motor - Permanent Split Capacitor Motors or PSC Motors use run capacitors to help the motor be more efficient while running. The start capacitor gives the motor a boost on start up. The run capacitor helps the motor run more efficiently. Many types of HVAC equipment use PSC motors as blowers and pumps.

So in HVAC you will have motors in most applications, including residential and commercial, that use capacitors for the motor no matter the application or purpose. These motors are a step above the shaded pole type of motor which was the original type of motor used for many applications.  A shaded pole motor could have power applied to it and not move or turn backwards from its intended direction. With the advent of PSC motors those problems went away. PSC motors will always start in the direction for which it is engineered to start with a few exceptions. Even in those few exceptions the PSC motor will fight to turn in the intended direction.

How Does Start Capacitor Help Start Motor - The Basics

We introduce the start capacitor which will only be in the circuit for a split second. Then a relay will take it out of the circuit. The relay is the potential relay or less commonly a current relay. A potential relay works off of back EMF while a current relay works off of current. So after covering the basics how does a capacitor work to help the motor? The answer is that a capacitor whether it is a start capacitor or a run capacitor changes the phase angle when the motor is powered up. By changing the angle you give the motor a little more push. If you push straight down on the rotor you expending energy in the wrong way to get the most out of the rotor. However, if you push from an angle then you change the ease of which you apply the energy.