Motor starting capacitor

 
Motor starting capacitor

Motor capacitors AC induction motors, also known as asynchronous motors, use a rotating magnetic field to produce torque. Three-phase motors are widely used because they are reliable and economical. The rotating magnetic field is easily achieved in three-phase asynchronous motors because the phase angle offset between the individual phases is 120 degrees. However, single-phase AC motors require external circuitry which creates the phase angle offset in order to produce a rotating magnetic field. This circuitry can be realized using advanced power electronics, or more simply using a motor capacitor. The video below shows an easy to understand explanation of the working principle of the AC induction motor. AC single-phase induction motors Single-coil AC induction motors AC induction motors usually use two or more coils to generate a rotating magnetic field, which produces torque on the rotor. When a single coil is used, it will generate a pulsating magnetic field, which is enough to sustain rotation, but not sufficient to start the motor from a standstill. Motors with a single coil have to be started by using an external force, and can rotate in either direction. The direction of the rotation depends on the external force. If the motor was started in a clockwise direction, it will continue to rotate and build up speed in the clockwise direction, until it reaches a maximum speed which is defined by the power source frequency. Similarly, it will continue rotating counter-clockwise if the initial rotation was counter-clockwise. These motors are not practical due to their inability to reliably start rotation on their own. Start capacitor AC induction motors One way to improve on the single coil design is by using an auxiliary coil in series with a motor starting capacitor. The auxiliary coil, also called starting coil, is used to create an initial rotating [… read more]

Polymer Capacitor

 

What are polymer capacitors? Polymer capacitors are capacitors which use conductive polymers as the electrolyte. They use solid polymer electrolytes instead of liquid or gel electrolytes that are found in ordinary electrolytic capacitors. By using solid electrolyte, the electrolyte drying is completely avoided. Electrolyte drying is one the factors that limit the lifetime of ordinary electrolytic capacitors. There are several types of polymer capacitors, including aluminium polymer capacitors, polymerized organic semiconductors and conductive polymer capacitors. In most cases, polymer capacitors can be used as direct replacements for electrolytic capacitors, as long as the maximum rated voltage is not exceeded. The maximum rated voltage of solid polymer capacitors is lower than the maximum voltage of classical electrolytic capacitors: usually up to 35 volts, although some polymer capacitors are made with maximum operating voltages of up to 100 volts DC. Polymer capacitors have a number of qualities superior to ordinary electrolyte capacitors: longer lifetime, higher maximum working temperature, better stability, lower equivalent series resistance (ESR) and a much safer failure mode. These qualities come at a price of lower maximum voltage rating and a narrower capacitance range, as well as a higher cost compared to wet electrolyte capacitors. This type of capacitor is not that new: production started in the 1980s and since then, they have been used in many applications including server motherboards and computer graphic accelerator cards. Polymer capacitor definition A polymer capacitor is a capacitor which uses solid polymers as the electrolyte. They have a number of superior qualities including a safer failure mode, lower losses and a longer lifetime than electrolytic capacitors. Characteristics Equivalent series resistance Compared to ordinary electrolytic capacitors, polymer capacitors have a lower equivalent series resistance. This allows polymer capacitors to withstand higher ripple currents during normal operation. A ripple current is the AC component [… read more]