A motor capacitor , such as initial capacitor or run capacitor (including double run capacitor ) is an electric current-changing capacitor to one or more winding single-phase AC induction motors to create a rotating magnetic field. There are two common types of motor capacitors, capacitor run and initial capacitor . The unit of capacitance is labeled in microfarad (Ã,ÂμF). Old capacitors can be labeled with the term obsolete "mfd", which means microfarad and "MFD" means millifarad.
Motor capacitors are used with air conditioning, hot tub/jacuzzi spa pumps, powered gates, large fans or forced-air heating furnaces for example. A "dual run capacitor" is used in some AC compressor units, to improve both the fan and the motor compressor.
Video Motor capacitor
Start capacitor
Start capacitor briefly increases the motor's initial torque and allows the motor to cycle and turn off quickly. A fixed start capacitor in the circuit is long enough to rapidly carry the motor to a predetermined speed, which is usually about 75% of full speed, and then removed from the circuit, often by a centrifugal switch released at that speed.. After that the motor works more efficiently by running the capacitor.
The capacitor has a rating above 70 Ã,ÂμF, with four main voltage classifications: 125 V, 165 V, 250 V, and 330 V. Examples of motor capacitors are: 35 Ã,ÂμF, at 370 V, running capacitor, or 88- 108 ÂμF in capacitor 250 V start.
Start capacitors above 20 ÃÎμF are always non-polarized electrolytic aluminum capacitors with non-solid electrolytes and therefore they are only applicable for short start time motors.
The motor will not work properly if the centrifugal switch is damaged. If the switch is always "open", the initial capacitor is not part of the circuit thus preventing the motor startup. If the switch is always "closed", the start capacitor is always activated, thus possibly damaging the capacitor. If the motor does not start, the capacitor is much more likely to be a problem than a switch.
Maps Motor capacitor
Run capacitor
Some single-phase AC electric motors require a "run capacitor" to energize the second-phase winding (auxiliary coil) to create a rotating magnetic field when the motor is running.
Run capacitors are designed for continuous tasks when the motor is turned on, which is why electrolytic capacitors are avoided, and low-loss polymer capacitors are used. Run the capacitor most of the polypropylene film capacitors and be energized all the time the motor is running. Run capacitors are rated in the range of 1.5 to 100 Ã,ÂμF, with a voltage classification of 370 V or 440 V.
If the wrong capacitance value is installed, it will cause an uneven magnetic field around the rotor. This causes the rotor to hesitate in uneven places, resulting in irregular rotations, especially under load. This doubt can cause the motor to become noisy, increase energy consumption, cause performance down and the motor becomes too hot.
Double run capacitor
A dual "run capacitor" supports two electric motors, such as in large AC or heat pump units, with both fan motor and compressor motor. This saves space by combining two physical capacitors into one case. Double capacitors have three terminals labeled "C", "FAN", and "HERM", which stands for C ommon, Fan , and HERM the compressor is closed ethically.
Double capacitors are available in various sizes, depending on capacitance (Ã,ÂμF), such as 40 plus 5 ÂμF, and also voltage. A 440 volt capacitor can be used in place of 370 volts, but not 370 in place of 440 volts. Capacitance must remain the same in 5% of its original value. The cylindrical double rotary capacitors are generally used for air conditioning, to assist in starting the compressor and condenser fan motor. An oval double run capacitor can be used instead of a round capacitor, but the mounting rope must be modified to better fit the oval shape.
Failure mode
An incorrect run capacitor often becomes swollen, with the sides or ends bending or protruding out farther than usual: it can be obvious to see that the capacitor has failed due to swelling or even rupture causing the electrolyte capacitor to leak out. Some capacitors are built with the design of "Interrupter Sensitive Pressure" which causes them to fail before internal pressure can cause serious injury. One design causes the top of the capacitor to expand and disconnect the internal cables.
"Weak Capacitors" - Over the years using capacitance from the decreasing capacitor. As a result the motor can fail to start or run in full force.
If the motor runs during a lightning strike on the electrical grid, the capacitor being run may be damaged or weakened by voltage spikes, requiring replacement.
IEC/EN 60252-1 2001 specifies the degree of protection for motor run capacitors
- P0 - no protection;
- P1 - failed open circuit or short circuit
- P2 - failed only on open circuit
Security issues
Motor capacitors, which are components of the hot water circulating pump, can become overheated if damaged. This poses a fire hazard, and the US Consumer Product Safety Commission (CPSC) has received over 100 reports of excessive heat incident from motor capacitors, with some fires started.
References
External links
- "CPSC, Company Announces Recall of Infinity and Lifestyle Spas", AS CPSC, Washington, DC, 2003-12-09.
- http://highperformancehvac.com/run-start-capacitors-hvac-motors-1/
- http://www.capacitorformotor.com/motor_capacitor.html
- http://www.wikihow.com/Check-a-Start-Capacitor
- http://electronics.stackexchange.com/questions/101408/what-is-the-purpose-of-the-motor-run-capacitor
Source of the article : Wikipedia
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