What size capacitor do I need for a 5 hp motor?
Michael Henderson
Published Feb 12, 2026
What size capacitor do I need for a 5 hp motor?
| Small Motor Capacitor “Ballpark” Sizes Based on Motor Horsepower | ||
|---|---|---|
| Motor Horsepower 2 | Start Capacitor µF / Voltage | Run Capacitor |
| 2 Hp or 1.5 KW, 200-250VAC | 500-580 µF | 10-15 µF 370VAC |
| 3 Hp or 2.25 KW, 200-250VAC | 500-580 µF | 20-25 µF 370VAC |
| 5 Hp or 3.75 KW, 200-250VAC | 750 µF | 30 µF – 40 µF 370VAC |
How do you size a motor start capacitor?
Multiply 0.5 times the square of the voltage. Call this result “x.”. Continuing the example, you have 0.5 times 11.5 volts times 11.5 volts, or 66.1 square volts for “x”. Divide the start-up energy requirement, in joules, of the motor by “x” to arrive at the capacitor size needed in farads.
Does a motor need a capacitor to start?
Run capacitors Some single-phase AC electric motors require a “run capacitor” to energize the second-phase winding (auxiliary coil) to create a rotating magnetic field while the motor is running. If a wrong capacitance value is installed, it will cause an uneven magnetic field around the rotor.
What is the reason for a start capacitor on a motor?
A start capacitor is used to give a motor an extra electrical push to start it turning. A start capacitor is only used in the motor circuit for a second or two when it first starts to turn. Once the motor is up to speed, the start capacitor disconnects and is not used again until the next time the motor starts.
Can I use a bigger start capacitor?
Larger than needed microfarad values will not cause much of any problems (especially for a start capacitor). A larger than needed run capacitor will not have any real affect. Depending on the cap and motor it could improve efficiency or decease efficiency very slightly.
How do you tell a start capacitor from a run capacitor?
The start capacitor creates a current to voltage lag in the separate start windings of the motor. The current builds up slowly, and the armature has an opportunity to begin rotating with the field of current. A run capacitor uses the charge in the dielectric to boost the current which provides power to the motor.
What type of motor uses a start and run capacitor?
phase AC induction motors
Motor start and run capacitors are used in single-phase AC induction motors. Such motors are used whenever a single-phase power supply is more practical than a three-phase power supply, such as in domestic appliances.
Can I replace a start capacitor with a run capacitor?
Start capacitors give a large capacitance value necessary for motor starting for a very short period of time (usually seconds long). A start capacitor can never be used as a run capacitor, because it cannot not handle current continuously.
Which capacitor is start and which is run?
Capacitors with ratings above 70 microfarad (uF) are starting capacitors. Run capacitors are designed for continuous duty, and are energized the entire time the motor is running. Single phase electric motors need a capacitor to energize a second phase winding.
