Calculate your braking resistor

In a variable frequency drive (VFD) application the motor will feed back braking energy into the DC link when it is in braking operation. This may cause a DC link voltage rise up to a critical level. A braking resistor will compensate this energy and convert it to thermal energy.

To calculate the right size of the resistor you need the characteristic data of the load cycle: brake time or duty cycle and the total cycle time. Furthermore you need the brake power Pbr and the minimum resistance value Rmin which is defined by the VFD.

Due to production tolerance and temperature coefficient the recommended resistance value is significantly higher than the minimum resistance value. Here we use a safety factor of 20 % (R = 1,2 x R_^min), effectively preventing possible damage to components of the VFD due to high currents.