The Proven Role of the Dynamic Braking Resistor (DBR) in Motion Systems Stability

 

The Proven Role of the Dynamic Braking Resistor (DBR) in Motion Systems Stability

Every industrial operation demanding precise control over moving parts faces a fundamental

engineering imperative: safe, predictable, and rapid deceleration. In any motion control system,

particularly those utilising variable frequency drives (VFDs), the process of slowing down an electric

motor generates substantial electrical energy. This phenomenon, known as regenerative energy,

must be managed with absolute diligence.

If this excess regenerative energy is not adequately dissipated, the DC bus voltage within the drive

unit will spike. This voltage surge can cause the drive to fault, leading to costly downtime, or worse,

result in permanent damage to the expensive industrial drive components.

The traditional, time-honoured solution to this critical challenge is the Dynamic Braking Resistor

(DBR). This component stands as the most reliable, practical, and effective defence against system

instability, ensuring the longevity and predictable performance of your equipment.

The Mechanism of Stability: How the DBR Protects Your Investment

The principle behind the Dynamic Braking Resistor (DBR) is elegant in its simplicity and profound in

its effectiveness. When a motor is decelerated, it acts as a generator, feeding electrical energy back

toward the VFD. Once the DC bus voltage reaches a preset threshold, the VFD activates an internal

or external transistor (the chopper), which immediately shunts the excess energy to the connected

Dynamic Braking Resistor.

The Dynamic Braking Resistor then executes its core mission: converting this damaging electrical

energy into thermal energy (heat), which is safely dissipated into the surrounding environment. This

immediate and controlled removal of excess energy protects the drive’s internal circuitry, allowing

the deceleration process to proceed as commanded, maintaining precise motion control.

Ignoring the vital role of the DBR is a short-sighted strategy. A quality Dynamic Braking Resistor

(DBR) is not merely an accessory; it is a prerequisite for system reliability and safety. For decades,

engineers have relied on this methodology because it consistently delivers stable, dependable

results, the true measure of success in any industrial setting. Cermet Resistronics maintains a strong

opinion that this traditional approach provides the highest degree of operational assurance.

Critical Specifications: Sizing the Dynamic Braking Resistor for Maximum Performance

Selecting the correct Dynamic Braking Resistor is paramount. A poorly specified DBR will

compromise the entire system’s ability to stop reliably. The selection process revolves around three

key parameters, which must be assessed against the application’s unique duty cycle (the frequency

and duration of braking):

1. Resistance (Ohms): This value is critical for limiting the peak current during the braking

sequence. The resistance value is determined by the VFD or servo system manufacturer’s

specifications. Using a value outside the specified range can either result in inadequate

braking or potentially damage the internal chopper circuit.

2. Power Rating (Watts): This is the measure of how much energy the Dynamic Braking

Resistor (DBR) can safely absorb and dissipate. This rating is defined by both the peak energy

pulse during deceleration and the average power dissipation required across the entire duty

cycle. This continuous rating is the measure of the unit’s sustained performance.

3. Construction and Enclosure: The physical form of the DBR, its resistance element material,

housing, and IP rating must be robust enough to withstand the operational environment,

whether in a clean room or a harsh industrial setting. A robust construction ensures

longevity and dependable performance.

For applications involving frequent, demanding stops, such as in high-speed conveyors, cranes, or

complex servo system applications, the correctly specified Dynamic Braking Resistor (DBR) is the

essential guarantor of consistent operation and safety. We are confident in the proven

methodologies that emphasize practical, durable components. A high-quality DBR enhances your

system’s overall performance.

Strategic Installation: Ensuring System Longevity 

Even the best-specified Dynamic Braking Resistor (DBR) requires proper installation to deliver on its

promise of safety and performance. The placement of the DBR unit must adhere to sound,

traditional engineering practices, prioritizing heat management.

 Airflow: The Dynamic Braking Resistor generates heat. It must be mounted in a location with

unimpeded airflow to prevent the heat from becoming trapped, which can lead to

premature failure of the DBR or affect nearby sensitive electronics.

 Wiring: The connections from the drive to the DBR must use appropriate, high-temperature-

rated wiring and be as short as practically possible to minimize electrical noise and voltage

drop.

 Proximity: While adequate spacing is needed for cooling, placing the DBR reasonably close

to the VFD or industrial drive minimizes cable lengths, which is always a sound, practical

approach.

Cermet Resistronics holds a traditional outlook that simplicity and robustness are the true measures

of engineering excellence. By incorporating a correctly sized and properly installed Dynamic Braking

Resistor, system operators are actively protecting their most valuable assets, their industrial drive

electronics, and their operational uptime. The reliability of your DBR directly impacts the stability of

your entire motion control system.

In the complex landscape of advanced motion control, the reliable Dynamic Braking Resistor (DBR)

remains the practical and enduring foundation for managing regenerative energy and securing

predictable, high-level performance. This cornerstone component is necessary for true operational

stability.