Dynamic braking resistors, also abbreviated as DBRs or PBRs (for power braking resistors), are typically designed to remove excess energy from a system in the form of heat. DBRs are normally connected in series with a chopper transistor labeled “IGBT7” across the DC bus which allows the resistor to bleed off excess voltage. Typical applications involving excess regeneration include decelerating high inertia loads and overhauling loads causing regenerative power.

Heavy duty resistors are rated at 125% braking torque and a maximum of 50% overhauling duty cycle or 100% decel rate on a two-minute period (ie. one minute on, one minute off for 50% overhauling cycle). Standard duty resistors are rated at 40% braking torque and a maximum of 20% overhauling duty cycle or 40% decel rate.

Heavy duty resistors are recommended for regenerative applications while standard duty resistors are only recommended for applications with nuisance overvoltages. DBRs must only be used in conjunction with thermal protection properly rated for the resistor’s capacity and an input contactor to open the input three-phase power to the ASD in the event that a DBR over-temperature condition occurs.