Can Enterprise

A braking resistor, or dynamic braking resistor (DBR), is a component used with an electric motor to dissipate the excess electrical energy produced during deceleration. When a motor's speed is reduced, it acts like a generator, feeding energy back into the drive (often a variable frequency drive, or VFD) and causing the DC bus voltage to rise. The braking resistor converts this surplus energy into heat, protecting the drive from damage due to overvoltage.
How a Braking Resistor Works

1. Motor as a Generator:During deceleration, a motor, especially one with a heavy load, acts like a generator, producing electrical energy. 

2. Energy Backflow:This electrical energy flows back into the power circuit, specifically to the variable frequency drive's (VFD) internal DC bus. 

3. Voltage Rise:The influx of energy causes the voltage on the DC bus to rise. If this voltage exceeds the safe limit for the drive, it can cause an overvoltage fault and damage the drive or motor. 

4. Dissipation:A braking resistor unit, which includes the resistor and a switching transistor, is connected to this DC bus. When the voltage limit is reached, the transistor activates, providing a path for the excess energy to flow through the resistor. 

5. Heat Conversion:The braking resistor then converts this electrical energy into heat, safely dissipating it into the environment. 

6. Controlled Stop:This process prevents overvoltage, allows for faster braking, and extends the life of the motor and drive. 

Key Design Considerations

Ohmic Value:A lower ohmic value allows for faster stopping but generates more heat. A minimum value is needed to prevent overcurrent, while a maximum value might limit its power dissipation capabilities. 

Power Rating (Watts):This determines the amount of heat the resistor can safely absorb without overheating. 

Duty Cycle:The frequency and duration of braking cycles, along with the peak power that needs to be dissipated, determine the required power rating. 

Heat Dissipation:For high-power applications, the braking resistor unit often includes external heat shields, cooling fins, or fans to increase its heat absorption capacity. 

ApplicationsBraking resistors are crucial in systems with heavy loads or frequent stops, such as: Cranes and hoists, Elevators and lifts, Heavy machinery and presses, Railway vehicles, and Hybrid and electric road vehicles.