The difference between brushless motor and brushed motor

Why do power tools (such as hand drills, Angle grinders, etc.) generally use brushed motors, rather than brushless motors? If you want to understand, this is really not in a sentence or two.

Dc motor is divided into brush motor and brushless motor, the "brush" here refers to the carbon brush. So what does a carbon brush look like?

So why do DC motors need carbon brushes? What's the difference between a carbon brush and no carbon brush? Let's keep looking down!

Dc brush motor principle

As shown in the figure, this is a DC brush motor structure model diagram. Two fixed magnets of the opposite sex are placed in the middle of a coil, both ends of the coil are connected to two semicircular copper rings, the two ends of the copper ring are in contact with the fixed carbon brush, and then the carbon brush is connected to the DC power supply.

At this time, the carbon brush is just in the middle of the gap between the two copper rings, and the entire coil loop has no current. But under the action of inertia, the rotor still continues to rotate.

When the rotor is turned to the above position under the action of inertia, the coil current is shown in the figure. According to the left hand rule, the blue coil is subjected to a vertical upward electromagnetic force; The yellow coil is subjected to a vertical downward electromagnetic force. The motor rotor continues to rotate clockwise, after rotating 90 degrees, as shown: at this time, the carbon brush is just in the middle of the gap between the two copper rings, and the entire coil loop has no current. But under the action of inertia, the rotor still continues to rotate. Then repeat the same steps, and the cycle continues.

Dc brushless motor

As shown in the figure, this is a DC brushless motor structure model diagram. It is composed of two parts: the stator and the rotor, in which the rotor has a pair of magnetic poles; There are many groups of coils wound on the stator, and there are 6 groups of coils drawn in the picture.

When we pass a current to the stator coils 2 and 5, the coils 2 and 5 will generate a magnetic field, and the stator is equivalent to a bar magnet, where 2 is the S (south) pole and 5 is the N (north) pole. Because the same magnetic poles attract each other, the rotor N pole will rotate to coil 2 position, and the rotor S pole will rotate to coil 5 position.

Then we remove the current of the stator coils 2 and 5, and then pass the current to the stator coils 3 and 6. At this time, coils 3 and 6 will generate a magnetic field, and the stator is equivalent to a bar magnet, where 3 is the S (south) pole and 6 is the N (north) pole. Since the same magnetic poles attract each other, the rotor N pole will rotate to coil 3 position, and the rotor S pole will rotate to coil 6 position, FIG. 7.

Similarly, the stator coil 3, 6 current is removed, and then the stator coil 4, 1 through the current. At this time, coils 4 and 1 will generate a magnetic field, and the stator is equivalent to a bar magnet, where 4 is the S (south) pole and 1 is the N (north) pole. Since opposite magnetic poles attract each other, the rotor N pole will rotate to coil 4 position, and the rotor S pole will rotate to coil 1 position.
So far, the motor has rotated half a revolution.... The second half of the circle and the front principle is the same, here is not to repeat. We can simply think of brushless DC motors as, like fishing a carrot in front of a donkey, so that the donkey will always move towards the carrot.

So how do you get the exact current through the different coils at different times? This is where the current commutator circuit...... I won't go into details here.

Comparison of advantages and disadvantages

Dc brush motor: fast start, timely braking, smooth speed regulation, simple control, simple structure, cheap price. The point is cheap! The price is cheap! The price is cheap! Moreover, it has large starting current, large torque (rotational force) at low speed, and can carry a very heavy load.
However, due to the friction between the carbon brush and the commutator, the DC brush motor is easy to produce sparks, heat, noise, electromagnetic interference to the external environment, and low efficiency and short life. Because the carbon brush is a loss product, it is easy to fail, and it needs to be replaced for a period of time.

Dc brushless motor: Because the DC brushless motor eliminates the carbon brush, it has low noise, no maintenance, low failure rate, long service life, and the running time and voltage are relatively stable, and the interference of radio equipment is small. But it's expensive! It's expensive! It's expensive!

Power tools are very commonly used tools in life, brand types are very many, fierce competition, we are very sensitive to the price. And power tools it needs to take a very heavy load, must have a large starting torque, such as hand drill, percussion drill. Otherwise, when drilling, the motor is easily unable to operate because the drill bit is stuck.

Just imagine, brush DC motor low price, starting torque, can carry heavy load; Although the brushless motor has a low failure rate and a long life, it is expensive and the starting torque is far less than that of the brushed motor. If you had to choose, what would you choose? I think the answer is self-evident.