How to use relays to achieve forward and reverse rotation of DC motors?

1. Internal Principle of Relay

The interior of a relay consists of two parts: a coil and contacts.

When the coil is de-energized, the common is connected to the normally closed contact (Normal Close); when the coil is energized, the common is connected to the normally open contact (Normal Open).

2. Forward and reverse circuit composed of two relays

Two relays composed of forward and reverse circuit

3. How to use relays to realize forward and reverse rotation of DC motors

When a positive voltage is applied to both ends of a DC motor, the motor rotates forward, and vice versa. In industrial applications, the power supply is generally 12V, 24V or 48V.

When both sets of coils are de-energized, the common contact is connected to the normally closed contact, the circuit is disconnected, and the motor stops rotating.

When the first set of coils is energized and the second set of coils is de-energized, the common contacts of the first set of relays are connected to the normally open contacts, and the normally closed contacts of the second set of relays are connected to the common contacts.

At this time, the current loop is: the power supply VCC flows from the normally open contacts of the first group of relays through the common contacts to the A terminal of the motor, then from the B terminal of the motor through the common contacts of the second group of relays to the normally closed contacts, and finally reaches the power supply GND terminal, forming a loop. The motor voltage is A+B-, and the motor rotates forward.

When the second set of coils are energized and the first set of coils are de-energized, the normally closed contacts of the first set of relays are connected to the common contacts, and the normally open contacts of the second set of relays are connected to the common contacts.

At this time, the current loop is: the power supply VCC flows from the normally open contacts of the second group of relays through the common contacts to the B terminal of the motor, then from the A terminal of the motor through the common contacts of the first group of relays to the normally closed contacts, and finally reaches the power supply GND terminal, forming a loop. The motor voltage is B+A-, and the motor reverses.

When both sets of coils are energized, both sets of common contacts are connected to the normally open contacts, the circuit is blocked, and the motor stops.