电机启动型热敏电阻器
马达启动用正温度系数热敏电阻器，只要用于电冰箱、空调马达启动、空调变频机启动、马达过热保护等。
工作原理：马达启动器是利用ptc陶瓷的电流－时间特性，当电压施加于ptcr时，开始有大电流i流过，经过一定时间ts后，随着ptcr温度的升高，电阻值迅速增大，导致电流也急剧下降，这段时间ts可以从0.1s到几秒，其值取决于ptcr的热容量、电阻值、热耗散条件、负载电阻及工作电压，当外电压撤销时，ptcr将冷却至常温电阻值。利用这个原理，在家用电冰箱和空调机等电器马达启动上得到了广泛的使用。应该说明，当使用ptcr的延迟性能时，如果要重复同一延迟时间，应间隔一定时间tr（即所谓的恢复时间），使ptcr恢复到原始状态温度，所以应避免立即重复动作，否则ptcr不能持续的大电流，使压缩机无法正常启动工作，会导致压缩机烧毁。
电机在启动时，要克服本身的惯性，同时还要克服负载的反作用力（如冰箱压缩机启动时必须克服制冷剂的反作用力），因此电机启动时需要较大的电流和转矩。当转动正常后，为了节约能源，需要的转矩又要大幅度下降。给电机加一组辅助线圈，只在启动时工作，正常后它就断开。将ptc热敏电阻串联在启动辅助线圈， 启动后ptc热敏电阻进入高阻态切断辅助线圈，正好可以达到这种效果.
产品优势：采用带有ptcr的启动电路具有经济、可靠、电路简单等特点，优于过去的重锤式启动电路，它具有无触点、低噪声、高可靠、长寿命等特点。
ptc thermistors for motor-starting
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
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