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PTC Thermistors Motor Starter

PTCR Motor starter Description

PTCR Motor start packages can be economical solid state torque assist for heat pumps, room air, commercial and residential air conditioning and refrigeration systems. PTC thermistors can be used to protect the auxiliary starter winding of induction motors or single phase motors. Compared to the alternative start capacitor and relay, PTCR Motor start devices save several wires, occupy less panel space, mount more easily, and cost less.

PTC Thermistor Motor Starter Pellet Application:

Single-phase motor start assist in refrigerator systems, air-conditioning systems, heat-pumps, small compressors.
Inrush current generation.

PTC Thermistor Motor Starter Features:

Complete range of size resistance combination for 120V, 240V compressor motors.
Rugged silver electrodes well suited for long life pressure contact mounting.
Various pellet sizes for optimum inrush current and switching time.
Typical resistance @25C 4.7 ohm, 6.8 ohm,15 ohm, 22 ohm, 33 ohm.

PTCR Motor starter Operating Principles
Single phase induction motors (e.g in compressors for refrigerators and air conditioners) can effectively be started when an auxiliary coil is used in the starting phase. The auxiliary coil is cut off from the circuit after the starting phase. For this purpose, PTC thermistor is employed.
When high voltage is applied to the PTC thermistor, the high current causes PTC thermistor to heat up and eventually the resistance to increase. A high current flows initially (starting phase ) and then decreases in relation to the increase in resistance. After the starting phase, a low residual current flows the auxiliary coil.

PTC Thermistor motor starter Simple starter circuit for single phase AC motors

Simple starter circuit of PTC thermistor motor starter used in single phase AC motors.
The PTC thermistor is used for delaying the switch-off of the starter auxiliary winding (after the motor has accelerated) to protect the winding from damage.

PTC Thermistor motor starter current vs switch time
PTC thermistor motor starter charcteristics resistance temperature current PTC thermistor motor starter pellet construction

AMWEI PTC motor starter pellets (disk) data sheet

Nominal Resistance

Max. Voltage
Max. Current

Starting Time

Power Consumption

Recovery Time

Coil Resistance

Switching Temperature



4.7 ohm 180V 12A 0.5-2.5S 3.5W 100S 10 ohm




6.8 ohm 200V 10A 0.2-1.5S 3.5W 100S 25 ohm
15 ohm 350V 8A 0.2-1.5S 3.0W 100S 30 ohm
22 ohm 350V 7A 0.2-1.5S 3.0W 85S 30 ohm
33 ohm 350V 6A 0.2-1.5S 3.0W 85S 55 ohm
47 ohm 400V 5A 0.2-1.5S 3.0W 75S 55 ohm
4.7 ohm 180V 12A 0.2-1.3S 3.3W 85S 10 ohm




6.8 ohm 180V 10A 0.2-1.2S 3.3W 90S 10 ohm
15 ohm 350V 8A 0.2-1.2S 2.8W 100S 30 ohm
22 ohm 350V 7A 0.2-1.0S 2.8W 85S 30 ohm
33 ohm 350V 6A 0.2-1.0S 2.8W 85S 30 ohm
47 ohm 350V 5A 0.2-1.0S 2.8W 80S 30 ohm
PTC Thermistor Motor Starter Reliability Data
Test conditions
Switching test at room temperature IEC 60738-1 Imax Vmax Number of cycles: 10000 <25%
Rapid change of temperature in air IEC600628-2-14, Test Na T=TLCT, T=TUCT Number of cycles: 5 T:30min <20%
Endurance at max. operating temperature and max. operating voltage IEC 60738-1 Ambient temperature: +60C Maximum Operating Voltage Current limited to Imax. Time: 24 hours <25%
Storage in damp heat IEC 600628-2-3 Temperature of air: 40C Relative humidity of air: 93% Duration: 56 days <20%
PTC Thermistor Motor Starter Application Examples

PTC thermistor motor starter for RSI CSIR CRS PSC motors
Starting Circuit with PTC Thermistor Motor Starter

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