Most of us must be familiar with the normal resistors like the Chip type, MFR type, etc. There are some of these applications where we have to handle high power. In such cases you use power resistors. There are many applications in which we use a molded power resistors in high power applications. We have to remember that most of these resistors are metal clad and mainly aluminium housing. Aluminium is most preferred as it is economical and also environmental friendly. Some companies even make custom resistors, shape and value desired as per the end user application.
There are some applications where the braking of the device generates electrical energy which can be absorbed at that instant or it flows back into the supply system. We call it regenerative braking or rheostat braking. Braking resistors are one kind which find application in motors. the main purpose of the braking resistors is to slow down the motor and drain out excess voltage. This helps the motor to be within safe tolerances. Under normal operating conditions of motor, it converts electrical to mechanical energy, but when motor is powered off, the magnetic field generates back emf which must be controlled for smooth power off of motor and keep it within safe tolerances. The braking resistor is used for the purpose. As we know, DC motors have permanent magnets which creates this electrical energy. In a AC motor, the generated magnetic field creates this effect.
Selection of braking resistor is a design challenge. The heat generated by the resistor on power dissipation is high and requires heat sink arrangement. this adds up to the cost. If the requirement is to stop the motor quickly, the resistor value must be less and dissipates more heat as it allows large current to flow through.
General ratings:
- Resistance (in ohms)
- Power dissipation (kW)
- Wire wound resistors
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