Brake Resistor (Brake / Dump Resistor)
It is the power resistor that prevents the line voltage from rising by turning the energy flowing back into the supply during braking into heat. It is usually switched in through a switch when the voltage exceeds a set threshold and switched out when it falls below the threshold. It is needed in systems working with power supplies that cannot absorb energy.
The resistance value is chosen so that the braking current stays below the limit the driver can carry; the power rating is found from the energy released per braking event and the repetition frequency. In stops repeated at short intervals the average power grows quickly, so looking only at the peak value is misleading.
You can tell whether it is needed as follows:
- If you measure a noticeable jump in the supply voltage during deceleration, energy is flowing back.
- If the power supply shuts down on protection during braking or the driver gives an overvoltage fault, that is a direct indication.
- In battery-supplied systems it is mostly not needed, because the battery accepts this energy.
Watch out for heat when mounting the resistor: because the energy is converted into heat the surface temperature is high, and cables and the enclosure must be kept away. A cheaper alternative is to reduce the returning power in the first place by lengthening the deceleration ramp.
The context in which this term is used: DC Motor Driver Selection Guide