Technical Information Site of Power Supply Design

2022.01.12 motor

Power Generation Principle

Brushed DC Motor

In succession to the previous article on the principle of motor rotation, here the principle of power generation is explained.

Principles of Power Generation in a Brushed DC Motor

The basic principle of power generation was explained here, drawing on related laws and equations. In this article, actual principles of power generation are explained using a schematic diagram of a brushed DC motor.

In a state in which a power supply is not connected to the brushes, we suppose that the coils (rotor) are rotating counterclockwise. As a practical example, there is a state in which the rotor is rotating due to inertia after the power supply of a rotating motor has been shut off.

In state , coil A is located midway between magnets N and S. The magnetic field due to the magnets is directed from N to S, and because coil A approaches magnet N through counterclockwise movement, the change in magnetic flux toward the rotation axis is positive (+) and is maximum (pink arrow). As a result, an emf occurs in coil A causing current (purple arrows) to flow from the rotation axis toward the outside.

Because coil B recedes from magnet N while coil C approaches magnet S, the change in magnetic flux is negative (-) (pink arrows), and because the positions are close to magnets, the change in magnetic flux is smaller than the maximum values. As a result, emfs occur in coils B and C causing current (purple arrows) to flow from outside toward the rotation axis.

When the emfs in coils A, B, and C are combined at this time, a positive (+) voltage occurs in the left-side brush relative to the right-side brush.

When state occurs, coil B is located midway between magnets N and S, and approaches S, so that the change in magnetic flux is negative (-) and is maximum. As a result, an emf occurs in coil B causing current to flow from the outside toward the rotation axis.

Coil A approaches magnet N, and coil C recedes from magnet S, so that the changes in magnetic flux are positive (+), and because the positions are close to magnets, the values are smaller than the maximum values. As a result, emfs occur in coils B and C causing currents to flow from the rotation axis toward the outside.

When the emfs in coils A, B, and C are combined at this time, a positive voltage occurs in the left-side brush relative to the right-side brush.

In this way, when the coils (rotor) are rotating counterclockwise, a positive (+) voltage is always generated in the left-side brush relative to the right-side brush. When the coils are rotating in the clockwise direction, the reverse operations cause a positive (+) voltage to be generated in the right-side brush. The generated voltage is rectified by the commutator to produce a DC voltage, and the higher the rotation rate, the higher is the voltage generated. Of course, a generator (dynamo) is based on this principle.

Key Points:

・Electric power is generated by the rotation of coils in a magnetic field, so that a DC voltage is produced across the brushes.

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