What is an electric motor ?
A: The motor is a component that converts electrical energy from the battery into mechanical energy to drive the wheels of an electric vehicle to rotate.
★What is a winding?
A: The armature winding is the core component of a DC motor; it consists of coils wound with copper enameled wire. When the armature winding rotates within the motor's magnetic field, it generates an electromotive force (EMF).
★What is a magnetic field?
A: The force field that occurs around a permanent magnet or an electric current, and the space or range of magnetic force that can be reached.
★What is magnetic field strength?
A: The magnetic field strength of an infinitely long conductor carrying a current of 1 ampere at a distance of 1/2 meter from the conductor is defined as 1 A/m (ampere per meter, SI). In the CGS unit system (cm-gram-second), to commemorate Oersted's contribution to electromagnetism, the magnetic field strength of an infinitely long conductor carrying a current of 1 ampere at a distance of 0.2 cm from the conductor is defined as 10e (Oersted), 10e = 1/4.103/m. Magnetic field strength is usually represented by H.
★What is Ampere's law?
A: Hold the wire with your right hand, aligning your outstretched thumb with the direction of the current. The direction your bent four fingers point is the direction in which the magnetic field lines are wound.
★What is magnetic flux?
A: Magnetic flux is also called magnetic flux quantity: Suppose there is a plane perpendicular to the direction of the magnetic field in a uniform magnetic field, the magnetic induction intensity of the magnetic field is B, and the area of the plane is S. We define the product of the magnetic induction intensity B and the area S as the magnetic flux through this plane.
★What is a stator?
A: The non-rotating part of a brushed or brushless motor. The motor shaft of a hub-type brushed or brushless gearless motor is called the stator; this type of motor can be called an internal stator motor.
★What is a rotor?
A: The rotating part of a brushed or brushless motor during operation. The outer casing of a hub-type brushed or brushless gearless motor is called the rotor; this type of motor can be called an external rotor motor.
★What is a carbon brush?
A: In a brushed motor, brushes press against the surface of the commutator. When the motor rotates, electrical energy is transmitted to the coils through the commutator. Because their main component is carbon, they are called carbon brushes, which are prone to wear. They should be maintained and replaced regularly, and carbon deposits should be cleaned.
★What is a brush grip?
A: A mechanical guide groove inside a brushed motor that holds and maintains the position of the carbon brushes.
★What is a commutator?
A: Inside a brushed motor, there are mutually insulated strip-shaped metal surfaces. As the motor rotor rotates, the strip-shaped metal surfaces alternately contact the positive and negative poles of the brushes, realizing the alternating positive and negative changes in the direction of the current in the motor coil, thus completing the commutation of the brushed motor coil.
★What is phase sequence?
A: The order of the coils in a brushless motor.
★What is a magnetic steel?
A: It is generally used to refer to magnetic materials with high magnetic field strength. Electric vehicle motors all use neodymium iron boron rare earth magnets.
★What is electromotive force (EMF)?
A: It is generated by the rotor of the motor cutting magnetic lines of force, and its direction is opposite to that of the external power supply, hence it is called back electromotive force.
★What is a brushed motor?
A: When the motor is working, the coil and commutator rotate, while the magnets and carbon brushes do not. The alternating change in the direction of the coil current is accomplished by the commutator and brushes, which rotate with the motor. In the electric vehicle industry, brushed motors are divided into high-speed brushed motors and low-speed brushed motors. There are many differences between brushed motors and brushless motors. As the names suggest, brushed motors have carbon brushes, while brushless motors do not.
★What is a low-speed brushed motor? What are its characteristics?
A: In the electric vehicle industry, a low-speed brushed motor refers to a hub-type, low-speed, high-torque gearless brushed DC motor. The relative speed between the stator and rotor is the same as the wheel's speed. The stator has 5-7 pairs of magnets, and the rotor armature has 39-57 slots. Because the armature windings are fixed inside the wheel housing, heat is easily dissipated through the rotating housing. The rotating housing is also woven with 36 spokes, further facilitating heat conduction.
★What are the characteristics of a brushed geared motor?
A: The main concern with brushed motors, due to the presence of brushes, is brush wear. Users should be aware that brushed motors are further divided into toothed and gearless types. Currently, many manufacturers use brushed toothed motors, which are high-speed motors. The term "toothed" refers to the use of a gear reduction mechanism to lower the motor speed (because national standards stipulate that electric vehicle speeds should not exceed 20 km/h, the motor speed should be around 170 rpm). Because it's a high-speed motor with gear reduction, it provides a strong starting power and better hill-climbing ability. However, the electric wheel hub is sealed, and lubricant is only added before leaving the factory. Users find it difficult to perform routine maintenance, and the gears themselves experience mechanical wear. After about a year, insufficient lubrication leads to accelerated gear wear, increased noise, and increased current during operation, affecting the lifespan of the motor and battery.
★What is a brushless motor?
The controller provides direct current in different directions to achieve alternating current directions in the motor's coils. Brushless motors do not have brushes or commutators between the rotor and stator.
★How does a motor achieve commutation?
A: When a brushless or brushed motor rotates, the direction of energization of the coils inside the motor needs to be alternated to achieve continuous rotation. Commutation of a brushed motor is accomplished by a commutator and brushes, while that of a brushless motor is accomplished by a controller.
★What is a phase loss?
A: In the three-phase circuit of a brushless motor or brushless controller, one phase may be malfunctioning. Phase loss can be categorized as main phase loss or Hall effect phase loss. Symptoms include motor vibration and inability to operate, or weak rotation and excessive noise. Controllers operating in a phase loss state are highly susceptible to burnout.
★What are the common types of electric motors?
A: Common types of motors include: brushed geared hub motors, brushed gearless hub motors, brushless geared hub motors, brushless gearless hub motors, and side-mounted motors.
★How can you distinguish between high-speed and low-speed motors based on their type?
A: Brushed geared hub motors and brushless geared hub motors are high-speed motors; B: Brushed gearless hub motors and brushless gearless hub motors are low-speed motors.
★How is the power of an electric motor defined?
A: The power of an electric motor refers to the ratio of the mechanical energy output by the motor to the electrical energy supplied by the power source.
★Why choose the motor's power? What is the significance of choosing the motor's power?
A: Selecting the rated power of a motor is a very important and complex issue. Under load, if the motor's rated power is too high, it will frequently operate under light load, failing to fully utilize its capacity—a case of "overpowered motor pulling a small cart." This also leads to low motor efficiency and poor performance, increasing operating costs. Conversely, if the rated power is too low, it's like "underpowered motor pulling a large cart." The motor current exceeds the rated current, increasing internal losses and reducing efficiency—a minor issue compared to significantly impacting the motor's lifespan. Even minor overloads can significantly shorten the motor's lifespan; severe overloads can damage the insulation material or even burn it out. Of course, an underpowered motor may not be able to drive the load at all, causing it to overheat and be damaged due to prolonged starting. Therefore, the motor's rated power should be strictly selected based on the electric vehicle's operating conditions.
★Why do typical brushless DC motors have three Hall effect sensors?
A: In short, for a brushless DC motor to rotate, there must always be a certain angle between the magnetic field of the stator coils and the magnetic field of the rotor's permanent magnets. The process of rotor rotation is the process of the rotor's magnetic field direction changing. To maintain this angle, the direction of the stator coil's magnetic field must change after a certain point. So how do we know when the stator magnetic field direction needs to be changed? That's where the three Hall effect sensors come in. You can think of these three Hall effect sensors as telling the controller when to change the current direction.
★What is the approximate power consumption range of a brushless motor Hall effect sensor?
A: The power consumption of a brushless motor Hall sensor is approximately 6mA-20mA.
★At what temperature can a typical electric motor operate normally? What is the maximum temperature a motor can withstand?
A: If the temperature of the motor cover exceeds the ambient temperature by more than 25 degrees Celsius, it indicates that the motor's temperature rise has exceeded the normal range. Generally, the motor temperature rise should be below 20 degrees Celsius. Motor coils are typically made of enameled wire, and when the temperature exceeds approximately 150 degrees Celsius, the enamel coating will peel off due to the excessive heat, causing a short circuit in the coil. When the coil temperature is above 150 degrees Celsius, the temperature exhibited by the motor casing is around 100 degrees Celsius. Therefore, based on the casing temperature, the maximum temperature the motor can withstand is 100 degrees Celsius.
★The motor temperature 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. However, what could be the reason for the motor overheating to over 20 degrees Celsius?
A: The direct cause of motor overheating is high current. This is usually caused by a short circuit or open circuit in the coil, demagnetization of the magnets, or low motor efficiency. Under normal circumstances, it is caused by the motor running at high current for an extended period of time.
★What causes a motor to heat up? What is this process?
A: When a motor is under load, there is power loss within the motor, which is ultimately converted into heat energy. This causes the motor temperature to rise, exceeding the ambient temperature. The difference between the motor temperature and the ambient temperature is called temperature rise. Once the temperature rises, the motor must dissipate 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 no longer increases and remains at a stable temperature, that is, it is in a state of equilibrium between heat generation and heat dissipation.
★What is the typical allowable temperature rise for a motor? Which part of the motor is most affected by the temperature rise? How is it defined?
A: When a motor is under load, to maximize its performance, the higher the load, i.e., the higher the output power (if mechanical strength is not considered), the better. However, higher output power means higher power loss and higher temperature. We know that the weakest point in a motor's temperature resistance is the insulation material, such as the enameled wire. Insulation materials have a temperature limit. Within this limit, the physical, chemical, mechanical, and electrical properties of the insulation material are very stable, and its service life is generally about 20 years. Exceeding this limit, the lifespan of the insulation material is drastically shortened, and it may even burn out. This temperature limit is called the allowable temperature of the insulation material. The allowable temperature of the insulation material is the allowable temperature of the motor; the lifespan of the insulation material is generally the lifespan of the motor.
Ambient temperature varies with time and location. When designing motors, 40 degrees Celsius is specified as the standard ambient temperature in my country. Therefore, the allowable temperature rise is the allowable temperature of the insulation material or motor minus 40 degrees Celsius. Different insulation materials have different allowable temperatures. Based on their allowable temperatures, the commonly used insulation materials for motors are A, E, B, F, and H. The following table shows these five insulation materials and their allowable temperatures and allowable temperature rises, calculated using an ambient temperature of 40 degrees Celsius:
How to measure the phase angle of a brushless motor?
A: By connecting the controller power supply, the Hall element can be powered by the controller, allowing the phase angle of the brushless motor to be detected. The method is as follows: Use the +20V DC voltage range of a multimeter, connect the red probe to the +5V line, and use the black probe to measure the high and low voltages of the three leads respectively. Refer to the commutation table for 60-degree and 120-degree motors for comparison.
★Why can't any random DC brushless controller and DC brushless motor be connected and start rotating normally? Why is there talk of phase inversion in DC brushless motors?
A: Generally speaking, the actual operation of a brushless DC motor follows this process: the motor rotates ---- the rotor magnetic field direction changes ---- when the angle between the stator magnetic field direction and the rotor magnetic field direction reaches 60 electrical degrees ---- the Hall signal changes ---- the phase current direction changes ---- the stator magnetic field advances forward by 60 electrical degrees ---- the angle between the stator magnetic field direction and the rotor magnetic field direction is 120 electrical degrees ---- the motor continues to rotate. Thus, we understand that the Hall signal has six correct states. When a specific Hall signal tells the controller, the controller outputs a specific phase current state. Therefore, the phase reversal sequence is designed to achieve this task: to ensure that the stator's electrical angle always advances in 60-degree steps in one direction.
★What would happen if a 60-degree brushless controller were used with a 120-degree brushless motor? And vice versa?
A: Both will result in a phase loss and prevent normal rotation; however, the controller used by Jieneng is an intelligent brushless controller that can automatically identify 60-degree or 120-degree motors, thus being compatible with both types of motors and making maintenance and replacement more convenient.
★How can the correct phase sequence be determined for a DC brushless controller and a DC brushless motor?
A: The first step is to ensure that the power and ground wires of the Hall effect sensors are properly connected to the corresponding wires on the controller. There are 36 ways to connect the three Hall effect sensors to the controller. The simplest, albeit cumbersome, method is to test each state one by one. Switching can be done without interrupting power, but it must be done carefully and in a specific order. Be careful not to turn the lever too much each time. If the motor does not rotate smoothly, this state is incorrect. Turning the lever too much can damage the controller. If reverse rotation occurs, if the phase sequence of the controller is known, simply swap Hall effect sensors A and C, and swap phase A and phase B of the trigger wires. This will reverse the rotation to the forward direction. Finally, verifying the correct connection is that it operates normally under high current.
★How to control a 60-degree motor with a 120-degree brushless controller?
A: Simply add a directional line between phase b of the brushless motor Hall signal line and the controller sampling signal line.
★What are the visual differences between brushed high-speed motors and brushed low-speed motors?
A: High-speed motors have an overrunning clutch, making it easy to turn in one direction but difficult to turn in the other; low-speed motors can turn the bucket in both directions with equal ease.
B. Vehicles with high-speed motors are noisier when running, while those with low-speed motors are quieter. Experienced people can easily distinguish them by ear.
★What is the rated operating condition of a motor?
A: When a motor is running, if all physical quantities are the same as its rated values, it is called the rated operating state. When the motor is operating under the rated operating state, it can run reliably and has the best overall performance.
★How is the rated torque of an electric motor calculated?
A: The rated torque output on the shaft can be represented by T2n. Its magnitude is the rated output mechanical power divided by the rated transfer speed, i.e., T2n=Pn, where the unit of Pn is W, the unit of Nn is r/min, and the unit of T2n is NM. If the unit of PNM is KN, the coefficient 9.55 should be changed to 9550.
Therefore, it can be concluded that if the rated power of the motors is the same, the lower the motor speed, the greater its torque.
★How is the starting current of an electric motor defined?
A: Generally, the starting current of a motor should not exceed 2 to 5 times its rated current. This is an important reason why current limiting protection is implemented on the controller.
★Why are the motor speeds on the market getting higher and higher? And what are the implications?
A: Suppliers can reduce costs by increasing the speed. For the same low-speed click, the higher the speed, the fewer the number of coil turns, which also saves on silicon steel sheets and the number of magnets. Buyers think that high speed is good.
When operating at rated speed, its power remains unchanged, but its efficiency is significantly lower in the low-speed range, meaning it lacks power when starting.
It is inefficient, requires a large current to start, and the current is also large when riding, which puts great demands on the current limiting of the controller and is also bad for the battery.
★How to repair a motor that is overheating abnormally?
A: The general repair methods are to replace the motor or perform maintenance.
★If the motor's no-load current exceeds the limit data in the reference table, it indicates a motor malfunction. What are the possible causes? How can it be repaired?
A: The causes are: excessive internal mechanical friction; partial short circuit in the coil; demagnetization of the magnet; and carbon buildup in the DC motor commutator. The general repair methods are to replace the motor, or replace the carbon brushes and clean the carbon buildup.
★What is the maximum fault-free no-load current for various types of motors?
Motor type with rated voltage of 24V and rated voltage of 36V
Side-mounted motor 2.2A 1.8A
High-speed brushed motor 1.7A 1.0A
Low-speed brushed motor 1.0A 0.6A
High-speed brushless motor 1.7A 1.0A
Low-speed brushless motor 1.0A 0.6A
★How to measure the no-load current of a motor?
A: Set the multimeter to the 20A range and connect the red and black probes in series to the power input terminal of the controller. Turn on the power, and with the motor not running, record the maximum current A1 measured by the multimeter. Rotate the throttle to make the motor run at high speed under no-load for more than 10 seconds. After the motor speed stabilizes, observe and record the maximum reading A2 measured by the multimeter. Motor no-load current = A2 - A1.
★Comparison of commonly used motors in electric vehicles:
How to identify whether a motor is good or bad? What are the key parameters to look at?
A: The main factors to consider are the magnitude of the no-load current and the riding current, their comparison with normal values, the efficiency and torque of the motor, and the noise, vibration, and heat generated by the motor. The best method is to use a dynamometer to test the efficiency curve.
★What are the differences between 180W and 250W motors? What are the requirements for the controller?
A: A 250W riding current is large, which places high demands on the power margin and reliability of the controller.
★Why does the riding current of an electric vehicle vary depending on the motor's rating under standard conditions?
A: As is well known, under standard conditions, with a rated load of 160W, the riding current of a 250W DC motor is around 4-5A, while the riding current of a 350W DC motor is slightly higher. For example, if the battery voltage is 48V, and both 250W and 350W motors have a rated efficiency of 80%, then the rated operating current of the 250W motor is around 6.5A, while the rated operating current of the 350W motor is around 9A. Generally, the efficiency of a motor decreases as the operating current deviates from the rated operating current. Under a 4-5A load, with a 250W motor efficiency of 70% and a 350W motor efficiency of 60%, under a 5A load, the output power of the 250W motor is 48V * 5A * 70% = 168W, and the output power of the 350W motor is 48V * 5A * 60% = 144W.
In order for a 350W motor to achieve an output power of 168W (approximately the rated load) to meet the riding requirements, the power supply must be increased to raise the efficiency point.
★Why does an electric vehicle with a 350W motor have a shorter driving range than one with a 250W motor under the same conditions?
A: Under the same conditions, the electric vehicle with a 350W motor has a higher riding current, so its range will be shorter if the battery is the same.
★How should electric bicycle manufacturers choose motors? What criteria should they use to select a motor?
A: For electric vehicles, the most critical factor in choosing a motor is selecting the motor's rated power.
Selecting the rated power of a motor generally involves three steps:
The first step is to calculate the load power P.
The second step is to pre-select the rated power of the motor and other parameters based on the load power.
The third step is to verify the pre-selected motor. Generally, the temperature rise is verified first, followed by the overload capacity, and the starting capacity is verified if necessary. If all of these are passed, the pre-selected motor is chosen; if it fails, the process is repeated from the second step until it passes.
It is important to avoid the misconception that a lower rated power motor is more economical while still meeting load requirements.
After completing the second step, temperature calibration should be performed based on the ambient temperature. The rated power is based on the national standard ambient temperature of 40 degrees Celsius. If the ambient temperature is consistently low or high, the rated power of the motor should be adjusted to fully utilize its capacity. For example, if the temperature is consistently low, the rated power of the motor should be higher than the standard specification Pn; conversely, if the temperature is consistently high, the rated power should be reduced.
In general, given a fixed ambient temperature, the choice of electric vehicle motor should be based on the riding conditions. The closer the riding conditions are to the motor's rated operating condition, the better. These riding conditions are generally determined by road conditions. For example, in Tianjin, where roads are generally flat, a small-power motor is sufficient; using a larger-power motor would waste energy and result in a shorter driving range. In Chongqing, where there are many mountainous roads, a larger-power motor is more suitable.
★Is a 60-degree DC brushless motor more powerful than a 120-degree DC brushless motor? Why?
A: In our market research and conversations with many customers, we've found a common misconception: that a 60-degree brushless motor is more powerful than a 120-degree one. We believe this is likely a marketing tactic used by manufacturers of 60-degree brushless motors. Based on the principles of brushless motors and practical experience, whether it's a 60-degree or 120-degree motor, the degree rating simply tells the brushless controller when to activate which two phase wires. There's absolutely no question of one being more powerful than the other! The same applies to 240-degree and 300-degree motors; neither is inherently more powerful.
