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When electric motor-driven machinery is stopped it generates energy, which can be fed back into the drive system through the motor acting as a generator. This excess energy needs either to be regenerated into the power supply or dissipated as heat. An external braking resistor provides a compact, cost effective method of controlling braking and dissipating the excess energy produced.
We offer a standard range of braking resistors for this application on short lead times. We can also supply non-standard units, especially adapted to your specific application or requirement.
Application Considerations
The external braking resistor is switched On/Off by the drive braking module.
Energy generated by braking is absorbed into the resistor elements causing them to heat up and dissipate the braking energy to the surrounds by natural convection and radiation.
Resistor Design
Cressall braking resistors are based on two types of resistor elements:
HP Coils, spiral wire-wound on ceramic formers
ZC Coils, edgewound coiled strip on ceramic former
Both elements offer high overload capacity and rapid cooling. The resistance material is a nickel-chrome (Ni-Cr) or iron-chrome-aluminium (Fe-Cr-Al) alloy. These alloys have low changes in resistance over the temperature range, max 18%. Designs using R304 stainless steel can increase in resistance during the heating cycle by as much as 50%, which results in lower current and less effective braking.
The enclosures are made of galvanized steel. HP and DBR Series enclosures are also available in stainless steel. Ingress protection is IP 20. HP and DBR Series can be equipped with an optional canopy to achieve IP 21.
Selection, sizing
See: Calculating the size of a brake resistor
Thermal capacity
Extensive research and testing of individual resistor element make it possible to predict the temperature rise in the resistor for any application. Contact us for assistance.
ES Series, 0.6 - 4.5 kW Continuous:
• Spiral wire wound resistor element on ceramic former
• Negligible noise
• Low inductance
• Temperature stable design, low increase of resistance value
• Optional thermal switch
• Terminal block mounted at one end of the enclosure, cover for terminal block, allow for ingress protection IP 20
Cressall Resistors Ltd, Evington Valley Road, Leicester, LE5 5LZ U.K. Tel: (+44) (0)116 273 3633