Summary
For a 220–230 V motor, you must use the capacitance in microfarads indicated on the motor's nameplate, the old capacitor, or the manufacturer's documentation. The 230 V mains voltage is not sufficient to determine the value. An incorrect capacitor can reduce torque, overheat windings, or prevent starting.
Permanent capacitor or start capacitor?
A permanent capacitor remains connected during operation. It is generally made with polypropylene film technology and is rated for continuous duty. A start capacitor provides a torque boost for a few seconds and must then be disconnected by a relay, a centrifugal switch, or electronics.
The two are not interchangeable. A start capacitor left energized can overheat and burst; an undersized permanent model may not provide the necessary starting torque.
How to read capacitor markings?
Note three pieces of information: the capacitance in µF, the allowable AC voltage in VAC, and the type of service. The replacement capacitance must remain within the tolerance allowed by the manufacturer. The allowable voltage can be equal to or greater than that of the original component, never lower.
Note: the 450 VAC marking on a permanent capacitor does not mean the motor operates at 450 V. It indicates the voltage the component can withstand in its circuit.
What to do if the original value is unreadable?
Look for the exact motor reference and its wiring diagram. Approximate formulas based solely on power only provide an order of magnitude: efficiency, power factor, number of poles, and winding design all alter the actual requirement.
A technician can check the current in the auxiliary winding and verify overheating. Do not choose a value at random just trying to obtain maximum torque.
What checks should be performed before installation?
- Cut and lock out the power supply.
- Discharge the old capacitor using an appropriate method.
- Check dimensions, mounting, terminals, and allowable temperature.
- Follow the manufacturer's diagram and replace protective covers.
A capacitance measurement out of tolerance, a swollen casing, or signs of leakage justify replacement. Any work on mains power must be entrusted to a qualified person.
Do not confuse electric motors with automotive engines
This question concerns a single-phase electric motor. For automotive equipment, please start with our catalog of parts and customization accessories and always check vehicle compatibility before ordering.