# BookRiff

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## How do I know what capacitor to get for my 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 are motor capacitors rated?

The battery that keeps your HVAC motor running is called the capacitor. Capacitors are measured through two different ratings. The first is voltage, and the second is microfarads. That means the higher the microfarad rating, the more electrical current it can store.

Is it OK to use a higher UF capacitor?

Yes, you can replace a capacitor with one of a slightly higher uF, but try to stay as close as possible to the original number and don’t go lower. Replacing a capacitor is sometimes referred to as “recapping a circuit board,” and it’s important to match the new capacitor up to the old one.

Can I use a higher voltage start capacitor?

Much the same way, a motor will not run properly with a weak capacitor. This is not to imply bigger is better, because a capacitor that is too large can cause energy consumption to rise. Voltage rating must always be the same or greater than original capacitor whether it is a start or run capacitor.

### What is the voltage of a run capacitor?

1) Run capacitors are rated in a range of 3–70 microfarad (uF). Run capacitors are also rated by voltage classification. The voltage classifications are 370V and 440V. 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.

### What is the capacitor rating for a motor?

A typical start capacitor rating ranges from 25 µF up to 1,400 µF and 110 Vac to 330 Vac. Once the motor reaches a specific speed, the start capacitor is disconnected from the winding circuit by a switch (or relay).

What should the tolerance be for a run capacitor?

For most standard motors, a run capacitor will have a “tolerance” specified describing how close to the rated capacitance value that the actual value may be. This will be usually +/- 5% to 10%.

What should the capacitance of a HVAC motor be?

A typical tolerance on the capacitance of a motor run capacitor for HVAC applications is +/-6%. With this being said, that means that a 40 µF capacitor can rate from 37.6 to 42.4 µF and still be considered a passing capacitor. When engineers design motors, they take into consideration this type of tolerance range.