Caps are rated to a certin charge UF

If there is a bad cell in the cap the unit will not start , they are easy to spot. bubble top

There is a plus minus range of 4-5% between rating and actual charge

In short a 45uF cap , may have a charge of 40.5 ( barely exceptable )

If the charge has droped to lets say 30-40 the unit will still start

but it will draw more amps at start and run
Testing proper charge on capacitors should be part of annual maint for proper system operation and to catch a future break down

The unit of capacitance is a farad. A 1-farad capacitor can store one coulomb (coo-lomb) of charge at 1 volt. A coulomb is 6.25e18 (6.25 * 10^18, or 6.25 billion billion) electrons. One amp represents a rate of electron flow of 1 coulomb of electrons per second, so a 1-farad capacitor can hold 1 amp-second of electrons at 1 volt.

A 1-farad capacitor would typically be pretty big. It might be as big as a can of tuna or a 1-liter soda bottle, depending on the voltage it can handle. So you typically see capacitors measured in microfarads (millionths of a farad).

If it takes something the size of a can of tuna to hold a farad, then 10,080 farads is going to take up a LOT more space than a single AA battery! Obviously, it is impractical to use capacitors to store any significant amount of power unless you do it at a high voltage.


Capacitors are rated in farads or as I stated at least 3 times above microfarads abv. Uf
capacitors store a charge this charge is used to even out large draws ( like LRA at start up )
Most smaller, single phase motors usually have a permanent magnet armature that is pushed / pulled around by the rotating inductive field produced by the stator (outside) windings. The inductive field rotates simply as a result of the positive / negative alternations of the 60HZ AC current flowing through the windings. The problem is that when the voltage is applied, the 60HZ is applied immediately, the rotation of the field through the windings begins immediately, and the armature has no chance to react (or catch up, as it were) to the field.

The start cap provides that electrical "push" to get the motor rotation started. It does this by creating a current to voltage lag in the seperate start windings of the motor. Since this current builds up slower, the armature has time to react to the rotating field as it builds up, and to begin rotating with the field. Once the motor is very close to it's rated speed, a centrifugal switch disconnects the start cap and start windings from the circuit. Watching a single phase motor starting you can see that this all happens very quickly.

Without a start cap (such as when one burns up) when the voltage is applied, the motor will just sit and hum. But if you were to grab the shaft and give it a spin, the motor would (usually) start and run normally

The run cap and aux. windings never drop out of the circuit in a cap-start, cap-run motor. The current to voltage lag is always present, which makes the motor act like a two phase motor. The advantage of a cap-start, cap-run motor over a cap-start, induction-run motor is that cap-run motors operate at a higher power factor than induction-run. Single cap-start / run motors use only one cap and are for lower torque applications. Two value cap-start / run motors use two caps, a higer value cap for starting, and lower value for running. The centrifugal switch switches from the high cap to the low cap, but the aux windings never leave the circuit. Two-cap motors are for higher torque applications. LIKE AC COMPRESSORS


Thanks though <!-- / message -->