A Failed Braking Resistor

Ah the BR Fault. Usually when one sees the BR error code it means that the drive is detecting a short in the Braking Resistor Circuit in your motor control. The solution to this fault in many variable frequency drive manuals we have seen reads “Replace the VFD.” Please do not. While yes this is what some may consider a catastrophic hardware failure, it is also one that is most of the time repairable. But what does a Braking Resistor Fault mean?

What is a Braking Resistor?

As we covered in my last blog a motor that can convert electrical energy into mechanical energy can also do the opposite. By the principles of inductance, a motor that does not have current but is still spinning will instead generate a current. A Braking Resistor is a power resistor that absorbs and dissipates as heat, this is extra energy thus slowing down or “braking” the motor. This is often referred to as “Dynamic Braking” and is very useful in safely controlling motor stops, increasing efficiency and lessening mechanical wear and tear.

What causes a Braking Resistor to fail?

There are many factors that can cause a braking resistor to fail and many of them may not be self-evident. What we run across most often in the field is cooling. You see, the main function of the resistor is to take the extra current and dissipate it off as heat. The amount of energy that can be dissipated in the circuit is relative to the resistor’s wattage rating. If the resistor is not properly cooled this will in time degrade the base material of the component, most often some sort of ceramic, and lead to a premature failure. Another common failure is related to the amount of load that the brake is trying to slow down. Excessive line loads will also cause damaging spikes of energy and destroy the resistor.

Are drives with failed Braking Resistors repairable?

The short answer is absolutely. By design, braking resistors are isolated from other circuits. The reason for this is that factory engineers know that they will be putting off a good amount of heat and heat equals bad news for other components. Usually the brake circuit is placed well away from other components for this reason and should they smoke catastrophically the drive is usually not damaged elsewhere.

Remember, if you get that ole BR fault… give us a call! Also be sure to visit us online at gesrepair.com or call us at 1-877-249-1701 to learn more about our services. We’re proud to offer Surplus, Complete Repair and Maintenance on all types of Industrial Electronics, Servo Motors, AC and DC Motors, Hydraulics and Pneumatics. Please subscribe to our YouTube page and Like Us on Facebook! Thank you!

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