How to measure whether the electric vehicle motor is faulty?

Electric vehicles are widely used in our daily life now. The core component of an electric vehicle is the motor. Once the motor is damaged, the electric vehicle will lose power, which can be troublesome for us. This article mainly discusses the testing of electric vehicle motors. Even if you are an amateur repairer, you can still find some help from this article.

Tool Preparation

Before checking the electric bicycle motor, you should first prepare some commonly used and indispensable repair tools. Such as a flat shovel for disassembling the motor housing, a multimeter, a voltmeter, an open-circuit transformer, a tachometer, an adjustable power supply box, etc. In addition, you also need to prepare some testing equipment, such as a short-circuit tester, an armature tester, etc. When testing a DC motor, you also need to measure power, efficiency, etc. If you want to measure accurately, you need to use a standard adjustable power supply box.

Motor testing items

The testing of automotive DC motors mainly focuses on performance aspects, such as windings, commutators, bearings, as well as rotor and armature center deviation, air gap, etc. Some projects are quality inspection standards for large motors or manufacturers, which we may not be able to achieve. Therefore, we can determine based on our own capabilities and conditions.

Motor Measurement

Motor testing mainly includes motor testing, motor + controller testing, motor testing under vehicle conditions, determining the working performance of motors under different conditions, and other testing items. According to the national standard GB17761-1999 "General technical conditions for electric bicycles", the testing items for vehicle motors are divided into three conditions:

  • No-load performance of electric bicycle motor: measuring voltage, current, and speed;
  • Performance test of electric bike motor load: measuring voltage, current, speed, and torque;
  • Overload performance of electric bicycle motor: measuring voltage, current, and torque.

The motor tester, also known as the motor dynamometer, is divided into two types: magnetic powder type and hysteresis type. The characteristics of the two types are as follows:

  • Magnetic powder type: suitable for the detection of low-speed, high-torque motors. The disadvantage is that there is friction in the internal magnetic powder, and the starting torque is relatively high.
  • Hysteresis type: suitable for high-speed, low-torque, even up to 10000r/min and as low as millinewton meters (mN·m) motor testing. The disadvantages are large size, high price, easy to burn under high torque, must have sufficient cooling measures, and continuous testing is limited.

Measurement of motor speed

The speed of the test motor needs to be measured using a tachometer, which commonly comes in two types: contact and telemetry. Handheld tachometers are contact type and can be used to measure the output speed of column motors and detect the rotation center of the shaft; non-contact telemetry tachometers can be used to measure the speed of automotive wheel hub motors. There are two common types of tachometers.

  • Digital Tachometer: The principle of this type of tachometer is to convert the speed of an object into pulses, and then calculate the speed by measuring the pulse frequency. This type of tachometer includes magnetic-electric type, capacitive type, Hall element type, and photoelectric type. The commonly used one is the photoelectric tachometer, such as the dt2234a model, which has two ranges: 5~6000r/min and 1000~10000r/min. The disadvantage is that it requires retroreflective tape. Retroreflective tape is a consumable item that needs to be replaced.
  • Stroboscopic instrument: This type of tachometer is widely used, easy to operate, small in size, wide in range, high in accuracy, can measure up to 150,000 r/min with flash point measurement, accuracy is 1%, can measure object speed without contact.

Currently, a new type of motor testing instrument has appeared on the market, which adopts a more advanced, simpler, more accurate, faster, and lighter mode. It uses advanced technologies including torque deformation shaft patches, deformation disc patches, magnetic powder, hysteresis, etc. The patches mainly cause current changes by changing the resistance value of the patches during deformation, converting them into various useful data to achieve measurement results. This new type of motor dynamometer has gradually developed into miniaturization and integrated circuitization. It can use tiny changes in information to transmit the information to the measurement circuit, then to the computer, and analyze and synthesize multiple results through pre-programmed specialized software, and draw curve graphs and reports through a printer.

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