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Group 1: Chelsea Laswell Kiva Dobson Chris Godsil

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  1. Single-Phase Capacitor MotorsGT107November 19, 2012 Group 1: Chelsea Laswell Kiva Dobson Chris Godsil

  2. A capacitor is used to create capacitance by storing voltage and releasing it during voltage shortages. They do this by storing energy. • A capacitor is made of two conductive plates separated by a dielectric material. The conductive plates are connected to the circuit. • Current cannot pass through the dielectric material. Thus, one of the conductive plates builds up a negative charge and the other a positive charge. • Potential energy forms from a high concentration of electrons on the negative plate and a low concentration of electrons on the positive plate. Inside a capacitor

  3. Capacitors cont. • When a capacitor reaches its working voltage it no longer gains charge. • A capacitor’s working voltage is determined by the distance between the conductive plates, the area of overlap of the conductive plates, and the resistance of the dielectric material. • Capacitors can store large amounts of energy which produces high voltage circuits. • When a drop in voltage occurs in the circuit the capacitor discharges energy to the circuit to increase the voltage. Thus, a capacitor works to resist change in voltage in a circuit.

  4. Capacitor Start Motors • A modified version of a split-phase motor. A capacitor is connected in series with the start windings and the centrifugal switch to produce a phase displacement for starting.

  5. How It Works • Start windings and run windings are housed in a circular pattern within the stator at 90 degrees from each other. The starter coils and the running coils are the same size. Stator Starting Coils Running Coils

  6. How It Works (cont.)(refer to diagram on page 6) 1. A capacitor is placed in series with the start windings. This creates a much large phase displacement than a typical induction motor. The motor will also have a much higher starting torque because capacitor strengthens the magnetic field in the start windings. 2. Since the capacitor holds an electric charge, it has the ability to cause current to lead voltage in a typical sine wave.

  7. How It Works (cont.) 3. Once the motor gets going, the capacitor is then switched out of the circuit when the motor approaches about 75% of its full speed, so not to overheat the motor. 4. A normally-closed centrifugal switch is located between the capacitor and the start windings. When the motor reaches 75% of its speed, the switch is opened and then the motor is powered by the source power.

  8. 1. 3 4. Source voltage 2

  9. What Are The Advantages? • The capacitor start motor has a higher starting torque than an induction motor. • The Capacitor start motor draws less current without using any real power. • The capacitor in the capacitor start motor comes in a range of power ratings, from ¼ HP to 10HP. • Is a single-phase motor and therefore doesn’t require any special wiring, like a polyphase motor. This allows for easy home applications.

  10. What Are The Disadvantages? • They do not have a smooth constant speed, which creates a lot of vibration in the motor. • The Capacitor uses some of the electric power to recharge itself, therefor making it less efficient than a capacitor start- capacitor run motor.

  11. Capacitor Run Motors • Similar to the start motor this motor has a capacitor in series with the auxiliary winding. The capacitor is not sized to handle starting operation but rather continuous run time operation. • The capacitor run motor, also called correction capacitor, is a type of single phase motor designed to have little starting torque and high stabilization at running speed.

  12. How They Work • This motor type is well balanced due to the capacitors capability to shift voltage across to windings at 90-180 degrees. This voltage shift creates a “true” two phase motor when at full load. • When an electric motor is in operation the load may change. As the load changes, it can cause a deviation of the electrical distribution in the motor. This may cause an overall imbalance in the load of the motor, which can overheat the windings. This unbalance also causes the motor to command more power from the power supply. Since the function of a capacitor is to carry a charge, the capacitor that is attached to the run windings acts as a balance system and will ‘inject’ the motor with electrical power supply when needed. This allows the motor to ‘catch up’ and adjust to the changing load.

  13. Advantages • The capacitor increases the efficiency of the motor by delivering the stored charge, so not to call upon more power from the power supply during these load changes. • Capacitor motors are the most affordable and reliable because of their durability and cost. • Single-phase power

  14. Capacitor Start, Capacitor Run A capacitor start, capacitor run motor has capacitors in series with the start winding and in series with the run winding.

  15. How they work A capacitor in series with the start winding helps to start the motor with high torque. A capacitor in series with the run winding helps to run the motor under large loads with high torque. Once the motor reaches a running speed the centrifugal switch disconnects the start winding and only the run winding capacitor is being used.

  16. Advantages Capacitor start, capacitor run motors are used when high starting and running torque are needed for large varying loads. These motors use single-phase power, so they can be used in many home appliances.

  17. Uses of Capacitor Motors • Washers, dryers, air-conditioning and refrigeration units, air compressors, elevators, fans, furnace blowers, augers. (Top) Capacitor (black box) motor. (Right)Heat pump air-conditioning and heating unit. The motor is inside the compressor (shown).

  18. Sources: Bayne, G.K. “How capacitors work on a motor”. www.ehow.com. Barett, J.T. “The advantages of capacitor start & capacitor run motors”. www.ehow.com. • http://www.pumped101.com/singlephasemotors.pdf • www.google.com • http://www.marsm-a.com/images/Capacitor_Basics-98610.pdf Gerrish, Howard H., William E. Dugger, Jr., and Richard M. Roberts. 2009. “Electricity and Electronics 10th Edition”. The Goodheart-Willcox Company, Inc. 2008. “Lab 11: Capcitor start motor and capacitor run motor”. Lamar University. www.google.com.

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