| Application |
Capacitor start motors are designed for high starting torque but require an extra 'push' provided by the capacitor in order to start. The function of the capacitor is to provide out-of-phase starting a current to the starting winding, forcing the motor to operate as a two-phase motor during the starting period. The starting capacitor is not intended for continuous duty and should not be used more frequently than 60 one-second, 30 two-second or 20 three-second starts per hour. These duty cycles are based on the necessity for proper heat dissipation to ensure maximum life. As the motor reaches full operating speed, the starting winding and capacitor are taken out of the circuit by either a centrifugal switch or a voltage or current sensitive relay. The average time for a motor to reach full operating speed is approximately one second. Rarely does it require more than three seconds to reach full operating speed. |
| MicroFarads |
100-125 uF |
| Failure Modes |
* Conditions which shorten life and increase failure rate are:
* Duty cycle greater than recommended
* High operating temperatures running speed
* Application of voltages in excess of ratings
* Physical damage to case or terminals
* Overloading, preventing motor from reaching running speed promptly
* Failure of starting switch to open promptly when motor reaches running speed
* Worn or frozen motor bearings causing excessive loads on the start cycles
* Low line voltage preventing motor from reaching running speed
* Incorrect capacitance rating (seldom encountered except where previous replacement was incorrect)
* Improper voltage rating (again seldom encountered except where previous replacement was incorrect). A higher voltage rating may be when motor reaches running speed used, but never a lower rating |
| Current Type |
AC |
| Information |
Replacement of a defective capacitor should be made by using an equivalent unit. When this is not available, the new unit should have the same capacitance rating and a voltage rating equal to or higher than the defective unit. The motor nameplate voltage bears little or no relationship to the required voltage rating of the capacitor, because the motor designer has several options at his disposal which can determine the rating required. Whenever replacement is attempted, an AC voltmeter should be used to monitor the voltage across the capacitor. |
