Braking Resistor
A resistor used to dissipate kinetic energy returned from a motor during deceleration in variable-frequency drives, servo systems, elevators, cranes and electric vehicles when regeneration to the grid is not possible.
Definition
When a motor decelerates an inertial load, the kinetic energy ½ J ω² flows back through the inverter and charges the DC bus capacitors. If unchecked, the DC bus voltage rises until the drive trips on over-voltage. The braking resistor absorbs this returned energy: a chopper IGBT (the “brake chopper”) switches the resistor across the bus whenever the voltage exceeds a threshold (typically 780 V on a 400 V AC drive), holding the bus at a safe level.
Sizing is governed by three numbers: peak power = ½ V_bus² / R, average power over the duty cycle, and single-event energy = ½ J × (ω₁² − ω₂²). The peak power must not exceed the resistor's pulse rating; the average must stay within the continuous power rating; the per-event energy must fit the thermal mass before the next deceleration. A 22 kW VFD typically uses a 4 – 8 Ω, 5 – 10 kW (peak), 1 – 2 kW (continuous) aluminum-housed brake resistor.
Applications include hoists, gantry cranes, centrifuges, machine-tool spindles, regenerative braking in EVs and trains. Because the resistor sees chopped DC at 1 – 16 kHz, non-inductive winding is preferred for low EMI. Thermal switches and over-temperature monitoring are standard safety features.
Related terms
Aluminum-Housed Resistor
A power resistor in which a wirewound element is potted with silicone gel inside an extruded aluminum housing, designed to be bolted to a heatsink for high-density continuous power dissipation from 5 W to 1500 W.
Wirewound Construction
A resistor construction in which precision-drawn resistive alloy wire (nickel-chromium, constantan, Manganin) is wound on a ceramic or fibreglass core and finished with a protective coating or housing.
Pulse Power
The instantaneous power a resistor can absorb during a short pulse of defined duration and duty cycle, often much greater than its continuous rating because the heat is buffered by the element's thermal mass.
Non-Inductive Winding
A family of wirewound techniques (bifilar, Ayrton-Perry, reverse-layer) that reduce a resistor's self-inductance to negligible levels, enabling wirewound construction in high-frequency, pulse and switching applications.
Related products
Aluminum Housed Resistors
Aluminum-housed resistors with superior heat dissipation — ideal for inverters, servo drives and other high-power applications
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High-Power Resistors
Industrial-grade braking and discharge solutions covering 50W ~ 100kW
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Resistor Boxes
Integrated resistor cabinet solutions for industrial braking and energy dissipation
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