How a Brake Chopper (Braking Unit) Works
A brake chopper or braking unit is used in drive systems with a variable frequency drive (VFD) to safely dissipate excess energy.
When an electric motor decelerates or needs to hold a load, energy can be fed back into the drive.
This energy increases the voltage in the DC bus of the variable frequency drive (VFD).
The brake chopper continuously monitors the DC bus voltage.
When this voltage exceeds a predefined threshold, the brake chopper automatically switches a braking resistor into the circuit.
This converts the excess electrical energy into heat and prevents the VFD from tripping or shutting down.
Brake Chopper and Regenerative Operation
When an electric motor is mechanically decelerated or when a load moves downward, the motor can operate as a generator.
This is known as regenerative operation.
In this situation, the motor feeds electrical energy back into the drive.
Without a brake chopper, this energy would increase the DC bus voltage until the
VFD
generates a fault or shuts down to protect its electronics.
By using a brake chopper in combination with a braking resistor, this energy is safely dissipated.
The brake chopper activates the resistor when the DC bus voltage becomes too high and switches it off once the voltage returns to a safe level.
More technical background on VFDs and braking systems can be found in the
Fluxcon variable frequency drives wiki.
Applications of Brake Choppers
Brake choppers are used in applications where energy must be dissipated during motor deceleration or load braking.
Typical applications include:
- Hoisting systems and cranes
- Winches and lifting mechanisms
- Fast machine positioning
- Conveyors with high inertia
- Fans with large rotational mass
In these applications, the brake chopper ensures safe and controlled deceleration without overloading the VFD.
Selection of a Brake Chopper
When selecting a brake chopper or braking unit, several parameters are important.
First, the chopper must be compatible with the DC bus voltage of the VFD and the drive power.
In addition, the brake chopper must be correctly matched with a suitable braking resistor.
The resistance value must fall within the allowable ohmic range of the VFD and have sufficient thermal capacity to dissipate the generated energy.
For questions about selecting brake choppers or braking resistors, please visit our
frequently asked questions about VFDs.
Aluminium Braking Resistors IP67
- easy installation
- waterproof
- brand-independent
Braking Resistor Selection
When selecting a braking resistor, the correct resistance value is essential.
Each variable frequency drive specifies an allowable resistance range.
If the resistance is too low, the current can become too high and damage the drive.
If the resistance is too high, the drive may not be able to dissipate sufficient electrical power.
The thermal capacity is also critical.
Depending on your application, varying amounts of excess energy must be converted into heat, as well as the duration of energy dissipation.
For advice, please contact Fluxcon specialists.
Brake Chopper
Up to 15 kW, brake choppers are integrated in the compact VFD series.
These built-in brake choppers can handle up to 50% of the drive’s nominal current to the braking resistor.
An external brake chopper can handle up to 150% of the nominal current.
Above 15 kW, brake choppers are typically not integrated in the drive.
In these cases, an external brake chopper is required when regenerative energy is present.
The brake chopper monitors the DC bus voltage and activates the braking resistor when the voltage becomes too high.
Brake Choppers
- optional on drive
- up to 150% nominal current
- brand-independent
Fluxcon Product Range – Drive Technology Components
The Fluxcon product portfolio consists of electronic components for controlling electric motors.
The range includes variable frequency drives (VFDs), soft starters, braking resistors, brake choppers, line reactors and EMI filters.
Customers choose Fluxcon based on practical engineering and reliability.
We offer an excellent price-performance ratio and fast delivery.
Fluxcon engineering provides straightforward, effective solutions.
Simple solutions are often the best.
Fluxcon values transparency and works closely with customers to find the optimal solution for each process or application.
All products are brand-independent.
For example, braking resistors can also be used with VFDs from other manufacturers.
