PTC Thermistors for Motor-Starting
Product Description
Applications
Motor-starting PTC Thermistors are mainly used in fridge and air-conditioner motor-starting, air-conditioner transducer-starting, motor over-heating protection.
Working Theories
Motor-starter is a machine that makes use of the PTC pottery current-time feature. When PTCR is put on by pressure, the heavy current begins to pass through, and after certain time, with the increasing of the PTC temperature, resistance value goes up sharply and cause current to fall down suddenly. During this time, ts can change from 0.1s to several seconds. The specific time depends on PTCR’s heating capacity, resistance value, heating dissipation condition, overloaded resistance and operating voltage. When the outer electricity pressure retreats, PTC will become cool and alter to normal resistance. Making use of this theory, PTC is applied extensively in household refrigerator and air-conditioner motor-starter and so on. One point should be noticed that when using the delay-time feature of PTC, we should make the PTC recover to its original temperature every certain time tr(That is what we called recovering time). So sudden repeated movements should be avoided, otherwise PTC cannot provide constant heavy current, and the compressor cannot start or work normally, which will cause the compressor burnt.
When the electricity motor is being started, it has to overcome its inertia and the counterforce of loading (eg: Its counterforce must be overcome when refrigerator compressor starts), so starting the electricity motor needs relatively heavy current and torque. When it runs normally, and the torque needed has to be brought down to save energy. Give motor electricity a circle assistant loop, and it works only when the motor starts and it will break up after the current goes regularly. This effect can be reached by connecting the PTC Thermistor in series in starting assistant loop and cutting off the assistant loop when PTCR enters the state of high resistance.
Advantages
The starting circuit with PTC owns the feature of being economic, reliable, simple which is better than the heavy hammer starting circuit Additionally, It has the characteristics of being contactless, lower noise, high reliability, long service and so on.
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