2024-07-18
![Latest company news about [Useful Information] Q&A about Motor-related Knowledge](/images/load_icon.gif){kind=icon}
1.What is a motor?
A motor is a component that converts electrical energy from a battery into mechanical energy to drive the wheels of an electric vehicle to rotate.
2.What is a winding?
The armature winding is the core part of a DC motor, consisting of coils wound with copper enamelled wire. When the armature winding rotates in the motor's magnetic field, it generates electromotive force.
3.What is a magnetic field?
A magnetic field is the force field that occurs around a permanent magnet or an electric current, encompassing the space where magnetic forces can reach or act.
4. What is magnetic field intensity?
The magnetic field intensity at a distance of 1/2 meter from an infinitely long wire carrying 1 ampere of current is 1A/m (ampere per meter, in the International System of Units, SI). In the CGS (centimeter-gram-second) unit system, to commemorate Oersted's contributions to electromagnetism, the magnetic field intensity at a distance of 0.2 centimeters from an infinitely long wire carrying 1 ampere of current is defined as 10e (Oersted), where 10e = 1/4π×10^-3 A/m. Magnetic field intensity is usually denoted by H.
5. What is Ampere's Rule?
Holding a straight wire in your right hand, with your thumb pointing in the direction of the current, the direction in which the fingers curl indicates the direction of the magnetic field lines surrounding the wire.
6. What is magnetic flux?
Also known as magnetic flux quantity, it is defined as the product of the magnetic induction intensity B and the area S of a plane perpendicular to the magnetic field direction in a uniform magnetic field.
7. What is a stator?
The stationary part of a brushed or brushless motor during operation. In a hub-type brushed or brushless gearless motor, the motor shaft is called the stator, making it an internal stator motor.
8. What is a rotor?
The rotating part of a brushed or brushless motor during operation. In a hub-type brushed or brushless gearless motor, the outer casing is called the rotor, making it an external rotor motor.
9. What are carbon brushes?
Located against the commutator surface in a brushed motor, carbon brushes transmit electrical energy to the coils as the motor rotates. Due to their primary carbon composition, they are prone to wear and require regular maintenance, replacement, and cleaning of carbon deposits.
10. What is a brush holder?
A mechanical channel within a brushed motor that holds and retains the carbon brushes in position.
11. What is a commutator?
In a brushed motor, the commutator consists of insulated metal strips that alternately contact the positive and negative terminals of the brushes as the motor rotor rotates, reversing the direction of current flow in the motor coils to achieve commutation.
12. What is phase sequence?
The arrangement order of the coils in a brushless motor.
13. What are magnetic steels?
Commonly used to refer to high-intensity magnetic materials; electric vehicle motors typically employ neodymium-iron-boron (NdFeB) rare-earth magnetic steels.
14. What is electromotive force (EMF)?
Generated by the motor's rotor cutting through magnetic field lines, EMF opposes the applied voltage, hence its name counter-electromotive force (CEMF).
15. What is a brushed motor?
In a brushed motor, the coils and commutator rotate while the magnets and carbon brushes remain stationary. The alternating direction of coil current is achieved through the rotating commutator and brushes. Brushed motors in the electric vehicle industry are divided into high-speed and low-speed types. The primary difference between brushed and brushless motors is the presence of carbon brushes in brushed motors.
16. What is a low-speed brushed motor and its characteristics?
In the electric vehicle industry, a low-speed brushed motor refers to a hub-type low-speed, high-torque, gearless DC motor where the relative speed between the stator and rotor corresponds to the wheel speed. The stator has 5-7 pairs of magnets, and the rotor armature has 39-57 slots. Since the armature windings are fixed within the wheel casing, heat dissipation is facilitated by the rotating casing and its 36 spokes, which enhance thermal conductivity.
17. Characteristics of brushed and geared motors?
Brushed motors have the main hidden danger of "brush wear" due to the presence of brushes. It should be noted that brushed motors are further divided into geared and non-geared types. Currently, many manufacturers opt for brushed and geared motors, which are high-speed motors. The "geared" part refers to the use of a gear reduction mechanism to adjust the motor speed downwards (as stipulated by national standards, the speed of electric bikes must not exceed 20 km/h, so the motor speed should be around 170 rpm).
As a high-speed motor with gear reduction, it features robust acceleration, giving riders a powerful sensation during startup and strong hill-climbing capabilities. However, the electric hub is enclosed, and only lubricant is added before leaving the factory. It is difficult for users to perform routine maintenance, and the gears themselves undergo mechanical wear. After about a year, insufficient lubrication can exacerbate gear wear, leading to increased noise, higher current consumption during use, and impacting the lifespan of both the motor and battery.
18. What is a brushless motor?
A brushless motor achieves alternating changes in the current direction within its coils through the controller supplying DC electricity with varying current directions. There are no brushes or commutators between the rotor and stator of a brushless motor.
19. How does a motor achieve commutation?
Both brushless and brushed motors require alternating changes in the direction of current flowing through their coils during rotation to ensure continuous rotation. Brushed motors rely on a commutator and brushes to accomplish this, whereas brushless motors rely on the controller.
20. What is phase failure?
In the three-phase circuit of a brushless motor or brushless controller, one phase fails to function properly. Phase failure can be classified as main phase failure and Hall sensor failure. This manifests as the motor experiencing vibrations and being unable to work, or rotating weakly with excessive noise. Operating a controller under phase failure conditions can easily lead to burnout.
21. What are the common types of motors?
Common types of motors include brushed geared hub motors, brushed ungeared hub motors, brushless geared hub motors, brushless ungeared hub motors, and side-mounted motors.
22.How can we distinguish between high-speed and low-speed motors based on their types?
A) Brushed geared hub motors and brushless geared hub motors belong to high-speed motors.
B) Brushed ungeared hub motors and brushless ungeared hub motors belong to low-speed motors.
23. How is motor power defined?
Motor power refers to the ratio of mechanical energy output by the motor to the electrical energy provided by the power source.
24. Why is it important to choose the motor power? What is the significance of selecting the rated power of a motor?
Choosing the rated power of a motor is a crucial and complex task. If the rated power is too high for the load, the motor will often operate under light load conditions, not fully utilizing its capacity, leading to inefficiency and increased operating costs. Conversely, if the rated power is too low, the motor will be overloaded, causing increased internal dissipation, reduced efficiency, and shortened motor life. Even slight overloads can significantly reduce motor lifespan, while more severe overloads can damage insulation or even burn out the motor. Therefore, it is essential to select the rated power of the motor strictly based on the operating conditions of the electric vehicle.
25. Why do brushless DC motors typically require three Hall sensors?
In simple terms, for a brushless DC motor to rotate, there must always be a certain angle between the magnetic field of the stator coils and the permanent magnets of the rotor. As the rotor rotates, the direction of its magnetic field changes, and to maintain the angle between the two fields, the direction of the stator coils' magnetic field must change at certain points. The three Hall sensors are responsible for informing the controller when to change the direction of the current, ensuring this process occurs smoothly.
26. What is the approximate range of power consumption for Hall sensors in brushless motors?
The approximate range of power consumption for Hall sensors in brushless motors is between 6mA and 20mA.
27. At what temperature can a motor operate normally?
What is the maximum temperature a motor can withstand? If the temperature of the motor cover exceeds the ambient temperature by more than 25 degrees, it indicates that the motor's temperature rise has exceeded the normal range. Generally, the temperature rise of a motor should be below 20 degrees. The motor coils are wound with enameled wire, and the enamel coating can peel off at temperatures above 150 degrees, causing coil short circuits. When the coil temperature reaches 150 degrees, the motor casing may exhibit a temperature of around 100 degrees. Therefore, if we consider the casing temperature, the maximum temperature a motor can withstand is approximately 100 degrees.
28. The temperature of the motor should be below 20 degrees Celsius, meaning the temperature of the motor end cover should exceed the ambient temperature by less than 20 degrees Celsius. What are the reasons for motor overheating exceeding 20 degrees Celsius?
The direct cause of motor overheating is high current. This can be due to coil shorts or opens, demagnetization of the magnetic steel, or low motor efficiency. Normal situations include the motor operating at high currents for extended periods.
29. What causes a motor to heat up? What is the process involved?
When a motor operates under load, there is power loss within the motor, which ultimately converts to heat, raising the motor's temperature above the ambient temperature. The difference between the motor temperature and the ambient temperature is called the temperature rise. Once the temperature rise occurs, the motor dissipates heat to the surroundings; the higher the temperature, the faster the heat dissipation. When the heat generated by the motor per unit time equals the heat dissipated, the motor temperature remains stable, achieving a balance between heat generation and dissipation.
30. What is the general allowable temperature rise for a motor? Which part of the motor is most affected by the temperature rise? How is it defined?
When a motor is operating under load, to maximize its effectiveness, the higher the output power (if mechanical strength is not considered), the better. However, higher output power leads to greater loss of power and higher temperatures. We know that the weakest point in terms of temperature resistance within a motor is the insulating material, such as enameled wire. Insulating materials have a temperature limit. Within this limit, their physical, chemical, mechanical, and electrical properties remain stable, and their service life is generally around 20 years.
Exceeding this limit drastically shortens the lifespan of insulating materials and may even lead to burnout. This temperature limit is known as the allowable temperature of the insulating material, which is also the allowable temperature for the motor. The lifespan of the insulating material is generally equivalent to the lifespan of the motor.
Ambient temperatures vary with time and location, and a standard ambient temperature of 40°C is specified for motor design in China. Therefore, the allowable temperature of the insulating material or the motor minus 40°C is the allowable temperature rise. Different insulating materials have different allowable temperatures. Based on their allowable temperatures, the five commonly used insulating materials for motors are classified as A, E, B, F, and H.
Taking an ambient temperature of 40°C as the basis, the following table shows the five insulating materials, their allowable temperatures, and allowable temperature rises, corresponding to their respective grades, insulating materials, allowable temperatures, and allowable temperature rises:
31. How do you measure the phase angle of a brushless motor?
By connecting the power supply to the controller, which then supplies power to the Hall elements, the phase angle of the brushless motor can be detected. The method is as follows: Use the +20V DC voltage range on a multimeter, connect the red lead to the +5V line, and use the black lead to measure the high and low voltages of the three leads. Compare the readings with the commutation tables for 60-degree and 120-degree motors.
32. Why can't any DC brushless controller be connected to any DC brushless motor and expect it to operate normally? Why is there a concept of reversed phase sequence for DC brushless motors?
Generally speaking, the actual operation of a DC brushless motor involves the following process: motor rotation –– change in the direction of the rotor's magnetic field – when the angle between the stator's magnetic field and the rotor's magnetic field reaches 60 electrical degrees –– the Hall signal changes – the direction of the phase current changes –– the stator's magnetic field advances by 60 electrical degrees ––the angle between the stator's and rotor's magnetic fields becomes 120 electrical degrees –– the motor continues to rotate.
This clarifies that there are six correct Hall states. When a specific Hall state informs the controller, the controller outputs a specific phase state. Therefore, reversing the phase sequence is a task to ensure that the stator's electrical angle progresses in a single direction by 60 electrical degrees.
33. What happens if a 60-degree brushless controller is used on a 120-degree brushless motor, and vice versa?
Both situations will lead to phase loss and prevent normal rotation. However, the controllers used by JieNeng are intelligent brushless controllers that can automatically identify 60-degree or 120-degree motors, allowing compatibility and ease of maintenance and replacement.
34. How can the correct phase sequence be determined for a DC brushless controller and DC brushless motor?
First, ensure that the Hall line's power and ground wires are properly connected to the corresponding lines on the controller. There are 36 possible combinations for connecting the three motor Hall lines to the three motor lines on the controller. The simplest, albeit–wn, but caution and a certain order are required. Avoid large rotations during testing as they may damage the controller. If the motor rotates poorly, that configuration is incorrect. If the motor rotates in reverse, knowing the controller's phase sequence, swap Hall lines a and c and motor lines A and B to achieve forward rotation. Finally, verify the correct connection by ensuring normal operation at high currents.
35. How can a 120-degree brushless controller control a 60-degree motor?
Add a direction circuit between the Hall signal line (b-phase) of the brushless motor and the sampling signal line of the controller.
36. What are the visual differences between a brushed high-speed motor and a brushed low-speed motor?
A. A high-speed motor has an overrunning clutch, making it easy to rotate in one direction but difficult in the other. A low-speed motor rotates easily in both directions.
B. A high-speed motor's vehicle produces louder noise during rotation, while a low-speed motor's rotation is relatively quieter. Experienced individuals can easily identify them by sound.
37. What is the rated operating condition of a motor?
The rated operating condition of a motor refers to a state where all physical parameters are at their rated values. Operating under these conditions ensures reliable motor performance with optimal overall performance.
38. How is the rated torque of a motor calculated?
The rated torque output on the motor's shaft is denoted as T2n. It is calculated by dividing the rated mechanical power output (Pn) by the rated rotational speed (Nn), i.e., T2n = Pn/Nn. Where Pn is in Watts (W), Nn is in revolutions per minute (r/min), and T2n is in Newton-meters (N.M). If Pn is given in kilowatts (KW), the coefficient 9.55 should be changed to 9550.
Therefore, under equal rated power conditions, a motor with a lower rotational speed will have a higher torque.
39. How is the starting current of a motor defined?
The starting current of a motor is generally required not to exceed 2-5 times its rated current. This is a crucial reason for implementing current limiting protection in controllers.
40. Why are the rotational speeds of motors sold on the market increasingly higher, and what are the implications?
Suppliers increase speeds to reduce costs. For low-speed motors, higher speeds mean fewer coil turns, less silicon steel sheets, and fewer magnetic steel pieces. Consumers often perceive higher speeds as better.
However, operating at the rated speed maintains constant power but results in significantly lower efficiency in the low-speed range, leading to poor starting torque.
Lower efficiency requires higher currents for starting and during riding, placing greater demands on controller current limiting and negatively affecting battery performance.
41. How to repair a motor that is abnormally hot?
The general repair methods are to replace the motor or perform maintenance and protection.
42. What are the possible causes of a motor's no-load current exceeding the limit data in the reference table, and how to repair it?
Possible causes include excessive internal mechanical friction, partial short circuit in the coils, demagnetization of the magnetic steel, and carbon deposits on the commutator of DC motors. The repair methods typically involve replacing the motor, replacing the carbon brushes, or cleaning the carbon deposits.
43. What are the maximum no-load current limits for various types of motors without faults, corresponding to the motor type, 24V rated voltage, and 36V rated voltage?
44. How to measure the no-load current of a motor?
Set the multimeter to the 20A range and connect the red and black probes in series with the power input terminals of the controller. Turn on the power and, with the motor not rotating, record the maximum current A1 displayed on the multimeter. Rotate the throttle to make the motor rotate at high speed without load for more than 10 seconds. Wait for the motor speed to stabilize, then observe and record the maximum current value A2 displayed on the multimeter. The motor's no-load current is calculated as A2 - A1.
45. How to identify the quality of a motor, and which parameters are crucial?
The key parameters to consider are the no-load current and riding current, which should be compared with normal values. Additionally, the motor's efficiency, torque, noise, vibration, and heat generation are important factors. The best method is to use a dynamometer to test the efficiency curve.
46. What are the differences between 180W and 250W motors, and what are the requirements for the controller?
The riding current of a 250W motor is larger, requiring higher power margin and reliability from the controller.
47. Why does the riding current of an electric bike differ under standard conditions based on the motor's rating?
It is well known that under standard conditions, with a rated load of 160W, the riding current on a 250W DC motor is around 4-5A, while it is slightly higher on a 350W DC motor.
Example: If the battery voltage is 48V, and both motors, 250W and 350W, have a rated efficiency point of 80%, then the rated working current of the 250W motor is approximately 6.5A, while the rated working current of the 350W motor is approximately 9A.
Motors generally have lower efficiency points when the working current deviates further from the rated working current. At a load of 4-5A, the 250W motor has an efficiency of 70%, while the 350W motor has an efficiency of 60%. Therefore, at a load of 5A:
To achieve an output power of 168W (approximately the rated load) with the 350W motor, the power supply must increase, thus raising the efficiency point.
48. Why does an electric bike with a 350W motor have a shorter driving range than one with a 250W motor under the same conditions?
Under the same conditions, the riding current of an electric bike with a 350W motor is larger, resulting in a shorter driving range when using the same battery.
The selection of motor rated power generally follows three steps: First, calculate the load power (P). Second, preselect the motor's rated power and other specifications based on the load power. Third, verify the preselected motor.
Verification typically begins with thermal rise, followed by overload capacity, and if necessary, starting capability. If all verifications pass, the preselected motor is finalized. If not, repeat from the second step until successful. It is crucial to note that, under the condition of satisfying the load requirements, a smaller rated power motor is more economical.
After completing the second step, adjust the rated power based on varying ambient temperatures. The rated power is based on a standard ambient temperature of 40°C. If the ambient temperature is consistently lower or higher, adjust the motor's rated power to fully utilize its capacity. For example, in areas with consistently lower temperatures, increase the motor's rated power beyond the standard Pn, and conversely, in hotter environments, reduce the rated power.
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