Invertor Hot Line Coil Resistance Meter

Importance of motor coil resistance test

The resistance of motor coils affects the temperature rise and energy loss.
Therefore, resistance testing on motor coils is important to ensure safety and to design high-efficient electrical equipment.
DAC-HRI-3 is designed to conduct temperature rising test of coils in inverter (PWM) drive equipment, such as EV (Electric Vehicle) motors, DC brushless motors and compressor motors.
Knowing the actual temperature rising value in the coil windings during operation is very helpful for safety evaluation and minimizing energy loss in electrical equipment.


(Test voltage Max AC450V)


(Test voltage Max AC700V)

True resistance under motor operating condtions

Until recently, the coil winding resistance is confirmed while the motor is stopped. This method assumes a natural logarithmic change in resistance after stop of operation, but complex products do not always follow this principal. In particular, the coils of motors with fans cool rapidly, and there can be a large different between the off-line value and the actual value.
To verify and ensure the safety of the product, it is ideal to measure the coil temperature while it is in operation state. Accurate measurement is possible with DAC-HRI-3.

PC Software

Measurement Display (Graph)

Measurement Display (Table)
(3-phase data is available when DAC-HRI-3 is used with the option unit DAC-SCB-3.)

Test Materials

● EV Motor
● Brushless Motor
● Compressor Motor for Air-Conditioner

Option Items

- Auto 3-phase switching unit model DAC-SCB-3
- DC Cut Capacitor Box for 3 phase measurement (From 2A to 450A or more, please specify the test current)

Connection diagram for DAC-HRI-3, DAC-SCB-3 and the capacitor box DAC-C45AXC7A-C

(The diagram is when 45A is used)

By using the 3-phase switching unit DAC-SCB-3 and software, continuous measurement is possible while automatically switching each phase (U-V, V-W, W-U) at optional interval time through PC.

Why is DC Cut Capacitor necessary?

Fig. 1

DAC-HRI-3 measures the resistance (Rx) by passing a DC measurement current (DC I) through the measurement sample (Lx) and detecting the generated voltage drop.
DC Cut capacitor is required to prevent the measurement current (DC I) from diverging into the power supply of the sample.

Related standards

● JIS C4203 Single Phase induction motors
● JEC 2137 Induction motor
● JEC 60034-1 Rotating electrical machines - Part 1: Rating and performance


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