Application of PTC Thermistor in Motor Overheat Protection Circuit
In view of the unstable factors in the power supply circuit, the circuit designed to prevent such unstable factors from affecting the circuit is called a protection circuit. In all kinds of electronic products, protection circuits abound. For example: overcurrent protection, overvoltage protection, overheat protection, no-load protection, short circuit protection, etc. In this paper, the common motor overheat protection circuit is sorted out.
Motor overheat protection circuit
Automatic lathes, electric oven, a ball mill continuous operation of mechanical and electrical equipment used in the production, and other device unattended. Because accidents caused by motor overheating or temperature controller failure occur from time to time, corresponding security measures need to be taken. The PTC thermistor overheat protection circuit can easily and effectively prevent the above accidents.
The following figure is a control circuit composed of a PTC thermistor and a Schmitt circuit, taking the motor overheat protection as an example. In the figure, RT1, RT2, and RT3 are three step-type PTC thermistors with the same characteristics, which are buried in the windings of the stator of the motor. Under normal conditions, PTC thermistors are at normal temperature and their total resistance is less than 1KΩ. At this time, V1 is turned off, V2 is turned on, and the relay K is electrically connected to the normally open contact, and the motor is operated by the commercial power supply.
When the motor is partially overheated due to a fault, as long as one PTC thermistor is heated beyond the preset temperature, its resistance value will exceed 10KΩ. Then V1 is turned on, V2 is turned off, VD2 displays a red alarm, K is de-energized, and the motor stops running to achieve the purpose of protection.
The choice of PTC thermistor depends on the insulation rating of the motor. The Curie temperature of the PTC thermistor is usually selected in a range of about 40 ° C lower than the limit temperature corresponding to the motor insulation level. For example, for a B1 insulated motor, the limit temperature is 130 ° C, and a PTC thermistor with a Curie temperature of 90 ° C should be selected.
Motor overheat protection circuit
Automatic lathes, electric oven, a ball mill continuous operation of mechanical and electrical equipment used in the production, and other device unattended. Because accidents caused by motor overheating or temperature controller failure occur from time to time, corresponding security measures need to be taken. The PTC thermistor overheat protection circuit can easily and effectively prevent the above accidents.
The following figure is a control circuit composed of a PTC thermistor and a Schmitt circuit, taking the motor overheat protection as an example. In the figure, RT1, RT2, and RT3 are three step-type PTC thermistors with the same characteristics, which are buried in the windings of the stator of the motor. Under normal conditions, PTC thermistors are at normal temperature and their total resistance is less than 1KΩ. At this time, V1 is turned off, V2 is turned on, and the relay K is electrically connected to the normally open contact, and the motor is operated by the commercial power supply.
When the motor is partially overheated due to a fault, as long as one PTC thermistor is heated beyond the preset temperature, its resistance value will exceed 10KΩ. Then V1 is turned on, V2 is turned off, VD2 displays a red alarm, K is de-energized, and the motor stops running to achieve the purpose of protection.
The choice of PTC thermistor depends on the insulation rating of the motor. The Curie temperature of the PTC thermistor is usually selected in a range of about 40 ° C lower than the limit temperature corresponding to the motor insulation level. For example, for a B1 insulated motor, the limit temperature is 130 ° C, and a PTC thermistor with a Curie temperature of 90 ° C should be selected.
