Why is capacitor used in a motor

That is an initial torque is required for the motor to get started. The starting torque can be given to the motor by applying a mechanical rotation to the motor shaft. Once the motor has started it can continue its rotation unless its supply is OFF.

But the mechanical starting is not always convenient and easy, especially for large motors, ceiling fans fixed at heights, etc.

Thus we have to employ some electrical methods to self-start the motor. In a single phase motor, the field created by the stator winding is positive on one-half cycle and negative in the other half cycle. It will produce a magnetic field that pulsates in sinusoidal which results the net field becomes zero. That is the field polarity reverses after each half cycle, but the field does not rotate; thus the torque is zero. There must be a revolving magnetic field or rotating magnetic field to create a torque for rotating the rotor.

To generate a revolving magnetic field two or more phase line is required. So in an induction motor, a two-phase supply has created from a single phase supply with the help of additional starting windings or auxiliary winding along with a capacitor. In Ideal case, the additional auxiliary winding of a stator with a capacitor, create a phase difference of 90 degrees to the main winding.

The two fields which are almost 90 degrees to each other, creates a rotating magnetic field which starts the motor. The capacitor value should select to obtain a starting winding current which leads 80 degrees with respect to the main winding current. As mentioned before, a mechanically applied starting torque is enough to start the motor. And the motor can continue its rotation when the rotor has enough speed to keep rotating.

Similarly, once the motor has rotated a forward field can maintain a positive torque for rotation. So the auxiliary winding with the capacitor can now be removed from the circuit. When the motor attains a sufficient speed, i. This capacitor is also known as a "self-healing SH capacitor". Although most of the previous capacitors used paper elements, the plastic film capacitor has become mainstream in recent years due to its compact design.

The rated conduction time is the minimum design life of the capacitor when operated at the rated load, rated voltage, rated temperature and rated frequency. The standard life expectancy is 40, hours. A capacitor that breaks at the end of life may smoke or ignite.

We recommend that the capacitor be replaced after the rated conduction time to avoid potential issues. Oriental Motor products use capacitors with UL recognized safety features that have passed the UL requirement of a 10, A fault current test. Capacitors are rated in capacitance, working voltage, tolerance, leakage current, working temperature, equivalent series resistance For the purpose of motor matching, the 2 most important specifications are capacitance and working voltage.

The voltage rating is typically about double the value of the motor's rated input voltage in volts there's actually a formula to determine the capacitance for a motor, but we'll save that for later.

These specifications are listed on both the motor label and the capacitor label. The use of a capacitor with a different capacitance can increase motor vibration, heat generation, power consumption, torque variation, and unstable operation.

If the capacitance is too high, motor torque will increase, but overheating and excessive vibration may occur. If capacitance is too low, torque will drop. Using a capacitor exceeding the rated voltage may cause damage and the capacitor may smoke or ignite. Every single-phase AC motor from Oriental Motor includes a dedicated capacitor that is sized for the motor to operate at its highest efficiency and performance.

No capacitor sizing is necessary. To ensure that the motor is operating at its highest efficiency, always use the dedicated capacitor that is included with the motor. The dedicated capacitor creates a 90 electrical phase shift from the auxiliary capacitor phase to the main phase. Using the wrong capacitor can shift this away from the 90 degrees, and the resulting inefficiency can cause the motor to overheat with inconsistent torque or speed performance.

Notice "Rated Speed" and "Rated Torque". This operating point where these two intersect on the curve is where the highest efficiency occurs. Every motor is designed for a rated load. This is why oversizing isn't the best way to size AC motors.

A difference in the capacitance in the capacitor will affect both rated speed and rated torque as the operating point shifts away from its maximum efficiency.

If you use 2 of the same exact motors with vastly different capacitors, you will produce vastly different results. Once maximum efficiency is lost, heat generation increases for the motor. Excessive heat can degrade bearing grease and decrease long term life of the motor. There are some important reasons why capacitor is used in DC motor which are explained below.

When the motor is in running condition, there is very frequently connect and disconnect happens between the brush and commutator. So the motor armature winding also connects and disconnect to the power supply frequency. This connection and disconnection are happening too fast.

For this reason, the changes in motor current also happen too fast which creates magnetic interference and create disruption in nearby radio devices such as FM, AM receivers.

So to reduce this interference, a capacitor is connected across the motor terminals. Capacitor reduces the spikes in the motor current and reduces the magnetic interference. So the motor current also changes which will produce noise and interference. In this case, also capacitor is used to reduce the noise and interference. When frequently changes occur in the motor load then the motor draws a frequently changing current from the power supply.

Here the capacitor helps to keep constant the motor current and smooth the motor speed.