How Electromagnetic (Fail-Safe) Brakes Work

How do electromagnetic brakes work?

An electromagnetic brake is fitted behind an electric motor to hold or stop its shaft. A fail-safe brake has three main parts:

• The friction disc, attached to the motor's rotor shaft.
• The pressure plate and springs.
• The electromagnetic coil.

When an electrical current passes through the brake, the coil pulls the pressure plate away from the friction disc, and the rotor turns freely. When no current passes through the brake, the springs push the pressure plate onto the friction disc and lock the rotor shaft.

The fail-safe principle

It is called a fail-safe brake because the brake engages when the power goes off, holding the rotor and the load in place. If there were no brake and the power supply failed, the motor would run freely and drop its load.

• Power on. The coil is energised and holds the pressure plate clear of the friction disc. The shaft spins and the machine runs normally.
• Power off or lost. The coil releases, the springs push the pressure plate onto the friction disc, and the shaft is locked.

This is why a lift or hoist does not drop during a power cut. The moment power is lost, the brake sets and holds the load in place.

Where electromagnetic brakes are used

These brakes suit any drive that has to stop safely and hold a load in position, especially where a power failure must not let the load move. Common uses include lifts and hoists, cranes, and machinery that needs a reliable emergency stop and secure holding. Mounted behind the motor as part of the gear motor assembly, the brake adds safe stopping and holding with minimal space and power.

How a brake is matched to a drive

An electromagnetic brake is matched to the drive it works with. The main points are:

• The torque of the motor that it has to stop.
• The motor and shaft size it mounts to.
• The power supply voltage.

If you want a brake installed on your motor, please mention it in advance, at the enquiry stage. The rotor shaft has to be longer to accommodate the brake, so it is planned with the motor rather than added later. AVM can then choose the correct brake for your motor.

To see the electromagnetic brakes AVM supplies, visit the electromagnetic brake category.

Frequently asked questions

How does an electromagnetic brake work?

When current passes through the brake, the coil pulls the pressure plate away from the friction disc and the shaft turns freely. When the current stops, springs push the pressure plate onto the friction disc and lock the rotor shaft.

What does fail-safe mean on a brake?

The brake engages when the power goes off, holding the rotor and the load. Without a brake, a power failure would let the motor run freely and drop its load.

Why does a lift not drop during a power cut?

As soon as power is lost, the springs set the brake on the motor shaft and hold the load in place until power returns.

Where is an electromagnetic brake mounted?

Behind the motor, as part of the gear motor assembly, where it can hold or stop the shaft directly.

Can a brake be added to a motor later?

Tell the supplier at the enquiry stage. The rotor shaft has to be longer to take the brake, so the brake is specified together with the motor.

Does an electromagnetic brake stop a load instantly?

It sets quickly when the current is removed and holds the shaft, which makes it suitable for emergency stops and for keeping a load in place once stopped.