In this article we will discuss about different types of capacitors like motor start capacitors, motor run capacitors, and dual operation capacitors.
A motor capacitor is a special type of capacitor that works with AC induction motors. There are three types of motor capacitors: starting capacitors, operating capacitors, and dual operating capacitors. Each type has its own application in which it is used.
The starting capacitor installed in an AC motor provides a shock to the motor to start the motor. The motor run capacitors connected to the AC motor then sends out a series of regular shocks that keep the motor running. On the other hand, bi-operating capacitors are responsible for powering two separate motors. The most common application of motor condensers is in air conditioners. These capacitors work in conjunction with three different motors: compressor motors, blower motors, and fan motors.
Motor Run Capacitors
A rotating magnetic field is required to operate many single-phase AC motors. The motor run capacitors are responsible for powering the second phase winding (auxiliary winding) of the AC motor, as a result this creates a rotating magnetic field that keeps the motor running.
The starting capacitor is designed to be used continuously while the AC motor is running, as opposed to the starting capacitor which is only briefly in the circuit to start the motor. This is why low-loss polymer capacitors are used as operating capacitors as they have a longer life and lower current loss compared to electrolytic capacitors which are ideal for momentary use.
There are two different types of operating capacitors, wet mode and dry mode. Water-operated capacitors are filled with a liquid that prevents overheating of the condenser. The dry style comes with the same dielectric, but because it is not filled with liquid, this style weighs a lot less than the wet style. Most current capacitors come with a polypropylene or polyester insulating film.
The motor run capacitor has a constant capacitance and voltage, and a capacitance range from 1.5uF to 100uF.
The most common voltages are:
Motor Start Capacitors
The starting capacitor increases the starting torque of the AC motor, and causes the AC motor to turn on and off quickly. The starting capacitor remains in the circuit long enough for the motor to reach a certain speed (usually 75% of full power), and is removed from the circuit by a centrifugal switch. As a result, After the starting process, the AC motor will run more efficiently with motor run capacitors.
A start-up capacitor is an electrochemical device consisting of compactly rolled aluminum foil separated by layers of paper impregnated with a conductive electrolyte solution. Drilling the foil prior to forming and rolling it increases the effective surface area of the foil and the capacitance per unit volume of the final capacitor. The entire set is housed in a molded plastic case that is moisture and oil resistant. The start-up capacitors are rated to operate at ambient temperatures from -40°C to +65°C and frequencies from 50Hz to 60Hz (high frequency applications not recommended).
The starting capacitor has a constant capacitance and voltage. The amplitude range is typically 70°F and above.
The most common voltages are:
Note: Starting capacitors rated above 20uF are non-polar electrolytic capacitors with a non-solid electrolyte. That is, it applies only to temporary use.
Dual Drive Capacitor
A dual drive capacitor is a running capacitor that can power two electric motors instead of one. This capacitor combines two capacitors in one case, essentially saving space when in use. Bi-operating capacitors typically have at least three terminals or terminals labeled “C,” “FAN,” and “HERM.”
They are rated with two capacitance values, allowing capacitors to be used in two different applications simultaneously. An example is 20uF + 5uF at 370VAC. Dual operating capacitors are commonly found in air conditioners. Used to power both fan and compressor motors.