PTC, PT100 Temperature Sensor for Drive Motor

—-Working principle of drive motor temperature sensor—-

In order to avoid component damage due to excessive temperature, many motors use NTC/PTC temperature sensors to monitor the temperature of the motor stator winding.
The drive motors and temperature sensors of different models also have different specifications. There are positive temperature coefficient and negative temperature coefficient (NTC) drive motor temperature sensors. The resistance of the negative temperature coefficient sensor will decrease as the temperature increases and increase as the temperature decreases. Representative models are Geely EV300/EV450 and BYD e5. The resistance of a positive temperature coefficient sensor increases as the temperature increases and decreases as the temperature decreases. The representative model is BAIC EU260.

The drive motor temperature sensor is usually placed inside the stator winding, and the number is 2-3, namely U-phase temperature sensor, V-phase temperature sensor, and W-phase temperature sensor. For example, the BMW i3 rear-wheel drive electric vehicle is equipped with 2 temperature sensors, the Geely EV300/450 is equipped with 2 temperature sensors, and the BAIC EU260 is equipped with 3 motor temperature sensors. As shown in Figure 1, the BYD e5 drive motor temperature sensor does not directly measure the rotor temperature, but determines it based on the measurement value of the temperature sensor in the stator. Its signals are read and analyzed in analog form by the motor controller.

PTC temperature sensor for motor coil

Figure 1, BYD E5 drive motor temperature sensor

If the temperature of the motor rises to a critical value, hybrid and pure electric vehicle control systems will limit the motor’s maximum output and set a diagnostic trouble code (DTC). And at the same time, a warning light is displayed on the car dashboard.

—-Detection of drive motor winding temperature sensor—-

1. Use a multimeter to check the resistance value

During the actual maintenance process, it should be noted that the drive motor temperature sensors of different models have different types and resistance values. Table 1 gives the standard resistance values of drive motor temperature sensors for common vehicle models. Taking BYD Qin or e5 as an example, when measuring the temperature sensor resistance at a temperature of 10-40°C, use the two terminals of the ohm scale of the multimeter to connect terminals 3 and 6 of the external temperature sensor plug-in of the drive motor respectively. Check whether the resistance value displayed by the multimeter is within the range of 50.04-212.5kΩ.

Motor PT100 temperature probe wiring harness

Table 1. Resistance values of drive motor winding temperature sensors for common vehicle models

(1) Measurement of Geely EV300/450 motor winding temperature sensor

Geely EV300/450 has two motor winding temperature sensors, both of which use 10kΩ NTC negative temperature coefficient sensors. The temperature sensor model is SEMITEC 103NT-4, that is, at 25°C, the normal resistance value is 10kΩ. The resistance decreases as the temperature increases and increases as the temperature decreases. See Table 2 for resistance values at different temperatures.

Table 2, parameters of Geely motor temperature sensor SEMITEC 103NT-4 model

Taking Geely EV450 as an example, operate the start switch to turn the power mode to OFF, unplug the low-voltage plug BV11 on the motor controller, adjust the digital multimeter to the 20k resistance level, and check the circuit diagram. Next, measure the resistance values of the motor winding temperature sensor R1 and temperature sensor R2 respectively.

① Motor temperature sensor R1: As shown in Figure 2, use a digital multimeter to measure the resistance between pins 6 and 7 of the motor controller harness connector. When the ambient temperature is 29.5°C, the resistance of the motor temperature sensor R1 is 8.41kΩ, and the resistance value is within the standard range.

Figure 2, Measuring motor winding temperature sensor R1

② Motor temperature sensor R2: As shown in Figure 3, use a digital multimeter to measure the resistance between pins 5 and 13 of the motor controller harness connector. The actual measured resistance value is 8.53kΩ. Confirm that the resistance of the motor temperature sensors R1 and R2 is within the standard range.

Engine water temperature sensor

Figure 3, measuring motor winding temperature sensor R2

(2) Measurement of BAIC EU260 motor winding temperature sensor

BAIC EU260 electric vehicle is equipped with three PT1000 platinum resistance temperature sensors with positive temperature coefficient, namely U-phase temperature sensor, V-phase temperature sensor and W-phase temperature sensor. That is, at 0°C, the resistance value of the temperature sensor is 1000Ω. Every time the temperature rises by 1°C, the resistance value increases by 3.85Ω. For example, at about 20°C, the resistance value of the temperature sensor is 1077Ω.

① Measure the W-phase temperature sensor resistance: As shown in Figure 4, unplug the PEU 35-pin plug-in of the power electronic unit, and use the ohm setting of a multimeter to measure the resistance between pins 30 and 31 of the 35-pin plug-in. The actual measured resistance is 1075Ω. If there is no resistance or the resistance is infinite, check whether the wiring harness and terminals have withdrawn pins.

pt100 platinum thermal resistor motor surface mount probe

Figure 4, Measuring W-phase temperature sensor resistance

② Check the resistance of the V-phase temperature sensor: As shown in Figure 5(a), unplug the PEU 35-pin plug-in of the power electronic unit, and use the ohm block of a multimeter to measure the resistance between pins 32 and 33 of the 35-pin plug-in. Reference range: 0℃ resistance 1000Ω, the resistance increases by 3.85Ω for every 1℃ temperature rise. If there is no resistance or the resistance is infinite, check whether the wiring harness and terminals have withdrawn pins.

③ Check the resistance of the U-phase temperature sensor: As shown in Figure 5(b), unplug the PEU 35-pin plug-in of the power electronic unit, and use the ohm range of the multimeter to measure the resistance between pins 34 and 35 of the 35-pin plug-in. If there is no resistance or the resistance is infinite, check whether the wiring harness and terminals have withdrawn pins. When the ambient temperature is 19.5°C, the resistance value of the measured temperature sensor is 1075Ω.

Figure 5, measuring V-phase and U-phase temperature sensor resistance

2. Read the data stream using a diagnostic instrument
Use the diagnostic instrument, select the corresponding car model, and enter the motor controller (MCU). Different car models and diagnostic instruments have different names for motor controllers, such as Geely EV45. The diagnostic instrument should enter the integrated power controller (IPU) and read the data flow of the drive motor stator temperature, as shown in Figure 6. The stator temperature refers to the temperature of the stator winding of the drive motor, and the water-cooling plate temperature refers to the temperature of the cooling water-cooling plate inside the motor controller.

Figure 6, Temperature data flow

—-Drive motor stator winding—-

Insulation resistance to temperature sensor

Since most drive motor windings have temperature sensors embedded inside them, the insulation resistance between the stator winding and the temperature sensor should be measured separately during detection. The cold insulation resistance of the drive motor winding to the temperature sensor should be greater than 20MΩ.

When the neutral points of the windings are connected together and cannot be easily separated, measure the insulation resistance of all connected windings to the temperature sensor. That is, measure the insulation resistance between the U-phase terminal, V-phase terminal, W-phase terminal and temperature sensor A, temperature sensor B or C respectively.

Note that after the measurement, a discharge device needs to be used to discharge the three-phase windings of the drive motor.