#24 - Braking resistor in a VFD

There are several possible motor / variable frequency drives (VFD) configurations. One of the important parameters is in relation to the type of brake and we will comment on some points in this post. The motors can be mounted with or without a brake (usually installed near the fan at the rear of the motor and the drive shaft ) and with or without an external brake resistor to dissipate the motor energy during braking. 

When there is no external brake installed on the motor, the motor braking is managed only by the inverter electrically. If there is no external brake resistor, the energy generated by the motor during braking is not dissipated. Machines that operate in intense cycles of acceleration and deceleration of the engine, and cycle time of a few seconds, will stress the system and the parameters commented above are fundamental for the smooth functioning of the engine without failures and interruptions. 

Installing a brake resistor in an inverter is simple and depends on the model. It is necessary to check the model and resistance size indicated by the manufacturer for the inverter model and the value can vary from a few ohms to several hundred ohms. The wiring is simple, just connect the two wires of the resistance. It is necessary to follow the manufacturer's recommendations for installation within an electrical panel and respect distances and directions.

In addition to this electrical connection, it is important to check that the motor is correct in relation to the transmission tension, in the case of belts, and also that the lubrication of the bearings of the moving parts is correct.

In order to complete, it is also worth checking the acceleration and deceleration ramps of the inverter and check that it is in accordance with the requirements of the process.

Notes: Some breaking resistors come with a third wire for grounding as well as shield. Be careful when wiring these (earth and shield) to an inverter in the field when there is not a proper earthing and grounding in place, as they could introduce noise to the system and cause motor faults such as communication fault or other intermittent issues.