Brake Resistor Overheating in Roll Forming Machines – Causes, Drive Braking Faults, Inspection & Repair Guide
Brake Resistor Overheating
Roll Forming Machine Electrical & PLC Failure Guide
Brake resistor overheating is a power electronics problem in roll forming machines where the braking resistor used by a variable frequency drive (VFD) becomes excessively hot due to repeated or excessive energy dissipation.
Many roll forming machines use VFD-controlled motors to drive machine components such as:
main roll forming drive motors
flying shear carriages
servo feed systems
coil handling equipment
stacking systems
When these motors slow down rapidly, the motor may act as a generator and return electrical energy back into the drive system.
This phenomenon is known as regenerative braking.
If this energy is not dissipated safely, it can raise the voltage in the VFD’s DC bus to dangerous levels.
To prevent this, braking resistors are installed in the drive system.
The braking resistor converts excess electrical energy into heat and safely dissipates it.
However, if too much energy is generated during braking or if the resistor cannot dissipate heat effectively, the resistor temperature may rise above safe limits.
This condition is known as brake resistor overheating.
Brake resistor overheating commonly affects roll forming machines producing:
metal roofing panels
metal wall cladding panels
standing seam roofing systems
structural deck profiles
C and Z purlins
light gauge steel framing components
Typical production symptoms associated with brake resistor overheating include:
VFD overvoltage alarms
drive braking faults
frequent drive shutdowns
burning smell near resistor unit
resistor temperature alarms
machine stopping during rapid deceleration
If overheating continues, the braking resistor may fail or damage nearby electrical components.
Maintaining proper braking system configuration helps prevent overheating.
Causes of Wear or Failure
Brake resistor overheating usually occurs when the braking system is forced to dissipate excessive energy.
Several factors may contribute to this condition.
Excessive Motor Deceleration
Rapid stopping may generate large regenerative energy.
Undersized Brake Resistor
Resistors with insufficient power rating may overheat.
Poor Ventilation
Restricted airflow may trap heat around the resistor.
Continuous Braking Cycles
Frequent deceleration events increase heat buildup.
Faulty Brake Chopper Circuit
Malfunctioning drive circuitry may overload the resistor.
High Machine Inertia
Heavy rotating equipment may generate large braking energy.
Why It Happened and What Caused It
From an electrical engineering perspective, when a motor controlled by a VFD slows down rapidly, the mechanical energy stored in the rotating system is converted back into electrical energy.
This energy flows into the DC bus of the drive.
If the energy is not removed, the DC bus voltage may rise above safe operating limits.
To prevent this, the VFD activates a braking chopper circuit that directs the excess energy into the braking resistor.
The resistor converts the electrical energy into heat.
However, if braking events occur frequently or if the resistor is undersized, the heat generated may exceed the resistor’s cooling capacity.
As the resistor temperature rises, the drive may detect overheating and trigger protection alarms.
In severe cases, resistor insulation or internal components may fail.
Proper braking system design ensures safe dissipation of regenerative energy.
How to Inspect the Problem
Inspection Procedure
Diagnosing brake resistor overheating requires inspecting both the braking resistor and the drive system configuration.
Step 1 – Inspect Brake Resistor Temperature
Check whether the resistor is excessively hot during operation.
Step 2 – Inspect Resistor Ventilation
Ensure proper airflow around the resistor.
Step 3 – Check VFD Alarm History
Look for overvoltage or braking-related alarms.
Step 4 – Inspect Deceleration Settings
Verify drive deceleration parameters.
Step 5 – Inspect Brake Resistor Connections
Check wiring and mounting condition.
Step-by-Step Technician Guide – How to Fix
Correcting brake resistor overheating typically requires improving braking system configuration and cooling.
Method 1 – Increase Deceleration Time
Slower deceleration reduces regenerative energy.
Method 2 – Install Larger Brake Resistor
Higher power-rated resistors handle more energy.
Method 3 – Improve Cooling
Ensure adequate ventilation around the resistor.
Method 4 – Inspect Brake Chopper Circuit
Verify correct operation of the drive braking system.
Method 5 – Reduce Machine Inertia
Adjust machine operation to reduce braking load.
Preventative Maintenance Tips
Preventing brake resistor overheating requires proper drive configuration and cooling.
Monitor Brake Resistor Temperature
Temperature monitoring helps detect overheating early.
Maintain Adequate Ventilation
Airflow helps dissipate heat.
Inspect Drive Parameters
Correct deceleration settings reduce braking stress.
Inspect Electrical Connections
Loose connections may increase heating.
Monitor Drive Alarm History
Frequent braking alarms may indicate overheating risk.
FAQ Section
What causes brake resistor overheating in roll forming machines?
Rapid motor deceleration or undersized braking resistors may cause overheating.
Can brake resistor overheating stop machine production?
Yes. VFD protection systems may shut down the drive.
How can brake resistor overheating be detected?
Excessive heat, drive alarms, or burning smell may indicate the problem.
Can deceleration settings affect brake resistor temperature?
Yes. Faster deceleration increases braking energy.
Should brake resistors be cooled?
Yes. Adequate ventilation helps dissipate heat safely.
How can brake resistor overheating be prevented?
Proper resistor sizing, drive configuration, and cooling help prevent overheating.