Dimensioning of the braking resistor

Notice

Braking resistor overload

If the braking resistor is insufficiently dimensioned, it can be destroyed by overload.

  • The braking resistor should be dimensioned such that it can withstand the expected heat development without damage.

A braking resistor of 10 Ω is recommended. This results in a pulse current of approx. 5.28 A to 5.76 A. The maximum expected continuous power is 125 W. However, the value typically lies significantly below that.

Power estimation

PN = IN² x R

PN = (5 A)² x 10 Ω

PN = 250 W

A maximum duty cycle of 50 % is possible. This results in a maximum continuous power of 125 W.

A motor efficiency of 80% is usual in practice.
The motor thus converts 80% of the nominal electrical power into kinetic energy when accelerating.
Conversely, when braking, the motor (as a generator) converts 80% of the kinetic energy into electrical power.
This results in a practical braking power of:

PChopper = PN/2 x 80/100 x 80/100

PChopper = 125W x 80/100 x 80/100

PChopper = 80 W