How to choose a capacitor for a washing machine motor?
It’s great when it is possible to connect the motor to the desired type of voltage. But sometimes a situation arises that a three-phase motor has to be “powered” from a single-phase network. For example, if craftsmen take the engine from a washing machine and use it to create a lathe or other “homemade product”. In such cases, you will have to use a capacitor for the motor from the washing machine. But there are a lot of them, so it’s a good idea to figure out how to choose the right device.
If you need to start a three-phase motor
Selecting a capacitor for a washing machine motor is not easy. The most important thing is to correctly determine the capacity of the device. But how to calculate it? To more accurately calculate the indicator, a complex formula is used, but a more simplified version can be used.
How to quickly figure out which device is suitable in your case? To calculate the capacitor capacitance using a simplified method, you need to find out the power of the engine and for every 100 watts “throw” about 7-8 µF. However, it is important not to forget during calculations to take into account the voltage indicator affecting the stator winding. This value should not exceed the nominal level.
When the electric motor can be started only on the basis of maximum load, a starting capacitor must be included in the circuit. This device is characterized by a short period of operation - it operates for about 3 seconds until the rotor speed reaches its peak.
When choosing a starting capacitor, it is necessary to consider that:
its capacity should be 2-3 times higher than that of the working capacitor;
its rated voltage must exceed the network minimum by 1.5 times.
The main function of the starting capacitor is to bring the electric motor rotor to the optimal speed.
Having understood the nuances, you can select both the mains and starting capacitors for a three-phase electric motor. To avoid mistakes, it is important to follow all recommendations.
Selecting a capacitor for a single-phase motor
In the vast majority of cases, capacitors for asynchronous motors are used to connect to a “standard” voltage (220 V), taking into account the inclusion of the device in a single-phase network. However, the process of using them is much more complicated. Let's figure out why.
Three-phase motors operate on the basis of a constructive connection, while single-phase motors have to achieve a biased torque. This is ensured by an additional layer of rotor winding for starting. The phase is shifted by a capacitor.
Why is it difficult to choose a capacitor?
Although there are no significant differences, different capacitors for asynchronous motors require different methods for calculating the permissible voltage. Typically, approximately 100 watts per 1 µF of device capacitance is required. These motors have several possible operating modes:
a starting capacitor is installed, an auxiliary winding layer is organized (specifically for the starting stage). In this situation, the calculation of the device’s capacitance will be 70 μF per kilowatt of electric motor power;
a working device is installed, the capacitor capacitance of which is in the range of 25-35 μF.In this case, an additional winding and constant connection of the capacitor will be needed throughout the entire life of the motor;
A mains capacitor is used while simultaneously connecting a starting device.
In any case, it is important to monitor the heating level of the electric motor during its operation. If you notice overheating of engine components, you should take immediate action. If there is a working capacitor, you will need to reduce its capacity. Experts recommend using devices that operate on a power basis of 450 watts or more, as they are considered universal.
Even before installation, it is recommended to check the functionality of the capacitor with a special device - a multimeter.
A starting capacitor is a small element of an electrical circuit necessary for the engine to “pick up” the required speed as quickly as possible. The working device serves to maintain optimal load on the motor.
You can construct a fully functional circuit yourself. Between the electric motor and the PNVS button you need to install a working capacitor, and, if necessary, also a starting capacitor. Typically, the winding terminals are located in the terminal part of the engine, so the connection can be upgraded in any way.
It should be remembered that the operating voltage of the starting capacitor should be 330-400 Volts. This is explained by a “spike” of power when the engine starts or stops running.
So what is the difference between a single-phase asynchronous motor? This type of motor is more common in household appliances and requires an auxiliary starting winding and a phase shift capacitor to activate it. It can be connected based on many available circuits. There are three types of capacitors on sale:
polar;
non-polar;
electrolytic.
Polar ones are prohibited from being used to connect electric motors to an alternating current network. The dielectric inside the device will quickly collapse and a short circuit will occur.
Therefore, in this case it is necessary to use non-polar capacitors. Their plates will interact equally with both the current source and the dielectric.
It’s great when it is possible to connect the motor to the desired type of voltage. But sometimes a situation arises that a three-phase motor has to be “powered” from a single-phase network. For example, if craftsmen take the engine from a washing machine and use it to create a lathe or other “homemade product”. In such cases, you will have to use a capacitor for the motor from the washing machine. But there are a lot of them, so it’s a good idea to figure out how to choose the right device.
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