Whit is the reason for a Man capacitor on a motor? 2. Must a motor with a van ca
ID: 1717107 • Letter: W
Question
Whit is the reason for a Man capacitor on a motor? 2. Must a motor with a van capacitor have a start relay? 3. What is the purpose of a centrifugal switch in the end of an open motor? 4. Why can't you have a centrifugal switch tn a her-metic compressor motor? 5. Name two methods used in hermetic compressor motor to take the start winding out of the circuit when the motor is up to speed. 6. How is a start capacitor constructed? 7. How is a run capacitor constructed? 8. How arc capacitors rated? 9. Can a 230-V capacitor be used for a 440-V application?Explanation / Answer
1ans) motor start capacitor are used during the motor startup phase and are disconnected from the circuit once the motor reaches the speed.
2ans)A relay is not essential but larger motors have a relay which operates above a certain speed, to cut out the start capacitor, which improves the power factor and reduces power losses.
The compressor motor employs both a start and run winding. The run winding is energized during the complete cycle of operation, whereas the start winding is energized only during the starting period. The current-operated type of relay has a coil connected in series with the run winding of the compressor. Some current-operated relays plug directly onto the compressor while others do not. Most relays are mounted in a case located on the compressor. When the thermostat closes, the compressor attempts to start, drawing heavy current through the run winding and the relay coil. This strong current flow through the relay coil creates a magnetic field strong enough to cause the start contacts to lift and close, energizing the start winding. When the compressor reaches approximately 3/4 running speed, the current flow through the relay coil decreases (due to the countering electrical magnetic field in the motor) and as the magnet weakens, the start contacts fall open. This type of relay must be used with an overload protector and must be mounted in an upright position, so that the contacts can fall freely to the "open" position.
3ans)To stop a three-phase motor dead ('plugging'), rather than allowing it to slow to a stop, the motor controller interchanges two of the three lines -which applies a reverse torque to the machine. But before the motor then gets a chance to reverse direction, the centrifugal switch trips the starter and removes the supply.
4ans)The centrifugal switch that you refer to and can see in an open frame motor, is used to open the start winding of small HP single phase motors. Once the motor gets up to a certain RPM, the switch opens and the motor continues to operate on its run winding. When the motor stops, the switch goes back to its normally closed position in the start winding and awaits the next start operation.
5ans)There is a heated bimetallic strip that provides a time delay small overload protection. When its contact makes, it energizes a coil to trip the breaker. Some breakers are mechanical, though.
6ans)If the air conditioner has both,The start capacitor will only be in the circuit for a very short time, so overheating doesn't become an issue.
7ans)If the air conditioner has both, the run capacitor is likely the largest one. The run capacitor must be sized for continual use.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.