Questions and answers about basic motor knowledge(Five)

06/07/2019

★How to repair the abnormal heat of the motor?
A: The method of maintenance and repair is generally to replace the motor or to perform maintenance.

★When the no-load current of the motor is greater than the limit data of the reference meter, it indicates that the motor has a fault. What are the reasons? How to repair
Answer: Click on the internal mechanical friction; the coil is partially short-circuited; the magnetic steel is demagnetized; the DC motor commutator is carbon. The maintenance method is generally to replace the motor, or replace the carbon brush to clean the carbon deposit.

★ What is the maximum limit no-load current of various motors?
Motor type rated voltage 24V rated voltage 36V
Side-mounted motor 2.2A 1.8A
High speed brush motor 1.7A 1.0A
Low speed brush motor 1.0A 0.6A
High Speed ​​Brushless Motor 1.7A 1.0A
Low speed brushless motor 1.0A 0.6A

★How is the motor idle current measured?
A: Place the multimeter in the 20A position and connect the red and black watch to the power input of the controller. When the power is turned on and the motor does not turn, record the maximum current A1 of the multimeter at this time. Turn the handle to make the motor rotate at high speed and no load for more than 10s. After waiting for the motor speed to stabilize, start observing and recording the maximum value of the multimeter A2. Motor no-load current = A2-A1.

★ Comparison of common electric motors for electric vehicles:
Motor form Transmission form Motor efficiency Hill climbing performance Maintenance cycle Volume Maintenance content Noise Cost
Brushless and toothless Brushless low-speed outer rotor motor, direct drive 〉 80% Normal No Large No Small Low
Brushless and toothed high speed brushless motor, planetary gear reduction 〉 83% good 3 years or so small lubrication gear medium high
Brushed toothed high speed brush motor, 2 stage gear reduction < 78% good 1 year or so large Replace carbon brush, lubricate gear high
Brushed toothless low speed brushed outer rotor motor, direct drive < 76% difference 2 years or so small replacement carbon brush, clean carbon deposit small low

★ How to identify the quality of the motor? What are the key parameters?
A: Mainly the magnitude of no-load current and riding current, compared with normal values, and the efficiency and torque of the motor, as well as the noise, vibration and heat generation of the motor, the best way is to test the efficiency curve with a dynamometer.

★ What is the difference between a 180W and a 250W motor? What are the requirements for the controller?
Answer: The 250W riding current is large, which requires high power margin and reliability of the controller.

★Why in a standard environment, the riding current of an electric car will vary depending on the rating of the motor?
A: It is well known that under standard conditions, the rated current is 160W, the riding current is about 4-5A on a 250W DC motor, and the riding current is slightly higher on a 350W DC motor. For example, if the battery voltage is 48V, two motors 250W and 350W, and their rated efficiency points are 80%, the rated operating current of the 250W motor is about 6.5A, and the rated working current of the 350W motor is about 9A. The efficiency point of the general motor is that the farther the operating current deviates from the rated working current, the smaller the value is. Under the load condition of 4-5A, the motor efficiency at 250W is 70%, and the motor efficiency of 350W is 60%. Under the load of 5A,
250W output power is 48V*5A*70%=168W
350W output power is 48V*5A*60%=144W
In order to achieve 168W (almost rated load) for the output power to meet the riding requirements, the 350W motor only increases the power supply, which increases the efficiency point.

★Why in the same environment, is the 350W motor shorter than the 250W motor electric vehicle?
A: Due to the same environment, the 350W motor's electric vehicle has a large riding current, so the mileage will be short in the case of the same battery.

★ How should the electric bicycle manufacturer choose the motor? According to what to choose the motor?
A: The most critical factor for motor selection for electric vehicles is the choice of motor power rating.
The motor power rating is generally divided into three steps:
The first step is to calculate the load power P
In the second step, according to the load power, pre-select the rated power of the motor and others.
The third step is to check the preselected motor. Generally, the temperature rise of the heat is checked first, then the overload capacity is checked, and the starting ability is checked if necessary. All passed, the pre-selected motor was selected; it was not re-run from the second step until it passed.
Do not meet the requirements of the load, the smaller the rated power of the motor, the more economical.
After the second step is completed, the temperature is corrected according to the ambient temperature. The rated power is carried out under the premise that the national standard ambient temperature is 40 degrees Celsius. If the ambient temperature is low or high all the year round, the capacity of the motor should be fully utilized in the future, and the rated power of the motor should be corrected. For example, the annual temperature is low, and the motor rated power should be higher than the standard Pn. On the contrary, if the annual temperature is high, the rated power should be reduced.
In general, in the case of determining the ambient temperature, the motor of the electric vehicle should be selected according to the riding state of the electric vehicle. The more the riding state of the electric vehicle can make the motor approach the rated working state, the better the riding of the electric vehicle. The line status is generally based on road conditions. For example, if the road surface in Tianjin is flat, a small-power motor is sufficient; if a motor with a larger power is used, energy is wasted, resulting in a short mileage. If there are many mountain roads in Chongqing, it is suitable to use a motor with a higher power.

★ 60 degree DC brushless motor is more powerful than 120 degree DC brushless motor, right? why?
A: From the market, when it comes to communicating with many customers, there is a common fallacy! The 60 degree motor is considered to be more powerful than 120 degrees. We think this is probably a propaganda for manufacturers of 60-degree brushless motors. From the principle of the brushless motor and the facts, it is proved that the 60 degree motor is also good, the 120 degree motor is worth mentioning! The so-called degree is only used to tell the brushless controller when to make which two phase lines are turned on. No one is more energetic than anyone else! The same is true for 240 degrees and 300 degrees. No one is more energetic than anyone else.