# What size capacitor do I need for a 1 hp motor?

Contents

## How do you size a capacitor for a motor?

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.

## How do I know what size capacitor I need?

Multiply the full load amps by 2,650. Divide this number by the supply voltage. The full load amps and the supply voltage can be found in the owner’s manual. The resulting number is the MicroFarad of the capacitor you need.

## How do I choose a capacitor for an AC motor?

Select a capacitor with a voltage rating at or above the original capacitor. If you’re using a 370 volt capacitor, a 370 or 440 volt one will work. The 440 volt unit will actually last longer. A capacitor will have a marked voltage indicating the accpetable peak voltage, not operational voltage.

## How do you size a capacitor for a power supply?

C*ΔV = q = I*t, where ΔV is the voltage sag (ripple), C is the capacitance in Farads, q is the charge lost in Coulombs, I is Amps, t is time in seconds. So, if you will tolerate a ripple of 5V, C = I*t/ΔV = 10 * 10e-3 / 5 = 2e-3 F or 20,000 uF. 2V ripple would require 50,000 uF.

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## 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.

## Can you use a higher UF capacitor on a motor?

An electric motor start capacitors can be replaced with a micro-farad or UF equal to or up to 20% higher UF than the original capacitor serving the motor.