Why Motor Start Capacitors Are Essential For Your Motors?

Motor Start Capacitors are single-phase induction capacitors that use motors in the auxiliary winding circuit to produce a large phase difference between the currents in the main and auxiliary windings. The name of the starting capacitor itself indicates that the motor uses the capacitor for starting purposes.

Motor starting capacitors are used to increase the starting torque of single-phase electric motors by increasing the current through the starting windings during starting. They usually only stay in the circuit for a few seconds before being turned off  by centrifugal force or an electronic switch inside the motor. If a single-phase motor will not start, the starting capacitor (if present) is most likely bad. This is a common failure mode for single-phase motors.

A Single-Phase Motor

Motor Start Capacitors is always present in single phase motor. Working capacitors have a lower rated capacitance than start-up capacitors and are always present in the circuit and are therefore designed for continuous operation. Motor Start Capacitors are not designed for continuous operation, so, it is important not to replace the starting capacitor with a running capacitor. Caldwell Electric can diagnose electric motor problems and provide solutions for repair or replacement.

Selection of Starting Motor Capacitor

This is usually printed on the capacitor as a number or upper number followed by the letters (MFD or uF). Replacement capacitors should match the original capacitance as soon as possible.

Voltage Rating: 

The voltage rating of the replacement capacitors should be at least the same as the original Motor Start Capacitors. If the replacement capacitor has a higher voltage rating than the original, it's actually better. However, in general, higher the voltage, larger the total capacitor. So size should also be considered.

Size: 

The physical size of the replacement capacitor should be suitable for the motor capacitor. In general, increasing the capacitance or voltage increases the size of the capacitor.

Content:

• Characteristics
• Application

A Motor Start Capacitors has two windings on the cage rotor and the stator. They are known as main and auxiliary rolls or starting rolls. The two coils are placed 90 degrees apart. The CS capacitor is connected in series with the starting coil. An SC centrifugal switch is also connected to the circuit. IM is the current in the primary winding that lags the auxiliary current IA by 90°. Therefore, the single-phase supply current is split between the two phases. The two coils are electrically 90° out of phase, the same size as the MMF, but 90° out of phase over time. The motor operates as a balanced two-phase motor. As the motor approaches rated speed, the auxiliary coil and starting capacitor are automatically disconnected by a centrifugal switch located on the motor shaft.

Characteristics

Motor Start Capacitors produce much higher torque, approximately 3 to 4.5 times full load torque. Two conditions are necessary to obtain high torque. they are:

• The starting capacitor value must be very large.
• The starting resistance of the valve winding should be low.

Due to the high voltage rating of the capacitor requirements, electrolytic capacitors of approximately 250°F are used. 

High torque

The cost of this motor is higher compared to a split-phase motor due to the additional cost of the capacitor. A Motor Start Capacitors can be reversed by first bringing the motor back to rest and then reversing the connection of one of the windings.

Uses of Motor Starting Capacitor

Various uses of motors are:

• These motors are used for high inertia loads that require frequent starts.
• Used for pumps and compressors
• It is used in refrigerator compressors and air conditioners.
• It is also used in transmission devices and machinery.

That concludes our discussion of Motor start Capacitors.