Dynamic Braking Resistors (DBRs) Information
Dynamic braking resistors (DBRs) produce braking torque and absorb the high amounts of energy generated by stopping electric motors. They are used in variable-speed drive systems such as elevators, cranes, and trains. Some DBRs are also used in related devices with high inertial loads. When a system load is decelerated, the kinetic energy is converted into electrical energy. Dynamic braking resistors absorb this energy and convert it to heat. Single resistors are standard, passive components with a single resistance value. Resistor arrays contain several dynamic braking resistors housed in a single package.
Selecting dynamic braking resistors (DBR) requires an analysis of specifications and features. Resistance range, tolerance, temperature coefficient (TCR), power rating, dielectric strength, and operating temperature are the most important performance specifications to consider. In terms of features, some dynamic braking resistors are air-cooled, water-cooled, or non-inductive. Others have a heatsink, a fireproof or electrically-isolated case, and a non-flame coating. Dynamic braking resistors that have a NEMA enclosure or that provide protection against electrostatic discharge (ESD) are also available.
There are four mounting or packaging styles for dynamic braking resistors (DBR):
- surface mount technology (SMT)
- through-hole technology (THT)
- bolt-on (chassis)
- panel mount
SMT adds dynamic braking resistors to a printed circuit board (PCB) by soldering component leads or terminals to the board’s top surface. By contrast, THT mounts components by inserting leads through holes in the board and then soldering the leads in place on the opposite side of the board. Chassis-mounted dynamic braking resistors bolt onto or within a structure’s supporting frame, typically in a metal-to-metal configuration for better heat dissipation. Panel-mounted dynamic braking resistors have a threaded bushing which surrounds the shaft.
Organizations, such as Underwriters Laboratories (UL), the International Electrotechnical Commission, and the Canadian Standards Organization (CSA), maintain standards for dynamic braking resistors. Products that are destined for sale in the European Union (EU) nations must meet the Restriction of Hazardous Substances (RoHS), End-of-Life Vehicles (ELV), and Waste Electrical and Electronics Equipment (WEEE) directives. RoHS compliant dynamic braking resistors contain only minimal levels of lead, cadmium, hexavalent chromium, polybrominated biphenyl, and polybrominated diphenyl ether. ELV compliant devices contain only minimal amounts of lead, cadmium, and mercury.
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