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Motor Protection Using Positive Temperature Coefficient (PTC) Thermistors

Connect the PTC thermistor input from the motor to analog input terminal on the drive.

The temperature resistance characteristics of three PTC thermistors in the motor stator winding protect the motor from overheat.

A PTC thermistor must have the characteristics shown in Figure 1 for each motor phase.

Figure 1. PTC Thermistor Temperature and Resistance

If the PTC input signal input to the drive is more than the overload alarm level, the drive detects oH3 [Motor Overheat (PTC Input)]. The drive continues the operation set in L1-03 [Motor Thermistor oH Alarm Select]. By default, the keypad shows oH3 and the drive continues operation.

The overheat fault level triggers an oH4 [Motor Overheat Fault (PTC Input)] fault, and outputs a fault signal. The drive outputs a fault signal and uses the stop method set in L1-04 [Motor Thermistor oH Fault Select] to stop the motor.

Note:

PTC is an acronym for Positive Temperature Coefficient.

The following shows the configuration procedure when you use terminal A2.

  1. Connect the PTC thermistor input from the motor to analog input terminal A2 on the drive.

    Figure 2. Connect Motor to PTC Thermistor Input

  2. Set drive DIP switch S1 to V (voltage).

    Figure 3. Settings for DIP Switches

  3. Set these MFAI terminals:

    • H3-09 = 0 [Terminal A2 Signal Level Select = 0-10V (LowLim=0)].

    • H3-10 = E [Terminal A2 Function Selection = Motor Temperature (PTC input)].

  4. Set these L1 parameters:

    • L1-03 [Motor Thermistor oH Alarm Select]

    • L1-04 [Motor Thermistor oH Fault Select]

    • L1-05 [Motor Thermistor Filter Time]