Q: I am using your brushless DC motor BX series for a lifter application. In the manual, a regeneration unit is recommended for large inertia load or gravitational load type application due to the fact that back EMF generated from the motor may damage the driver circuit. I am trying to find out if there’s any way for me to calculate the regeneration power so I can also include some other components into my design to protect the circuit?

A: For our brushless DC, stepper motor and servo motor, it is important to connect the regeneration unit if it is a large inertia load or gravitation load. The main reason is that the rotor is made of permanent magnets and the states are copper coils. Therefore, when motor rotates, essentially it is a rotating magnetic field around conductor, thus it will generate current in the state coils, which is directly connected to the driver circuit. This induced current may damage driver internal electrical components.

Motor regeneration power can be estimated by using the formula below:

Regeneration power = 0.1047 x T x N,

Where T is the load torque, and N is the RPM of the motor (not the gearhead output speed). When you apply this formula, please note that the T and N in the formula are the load torque of the motor and actual motor speed, instead of the gearhead output torque and speed.

For example, if you have a 20:1 gear ratio for the application, and the load creates a torque of 1 N.m, and rotating at 100 RPM. Then the load torque will be 1 N.m divided by 20 divided by 90% (gearhead efficiency ) = 0.0555 N.m. The total RPM is 100 x 20 = 2000 RPM on the motor. Therefore the total regeneration power is 0.0555 x 2000 x 0.1047 = 11.62W.

## Regeneration Power Calculation

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