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.
Definition
Aluminum-housed resistors (often called “chassis” or “thick-film on alumina” types — though wirewound is more common in higher powers) place the resistive element inside an extruded aluminum profile with integrated mounting flanges. The internal space is filled with thermally conductive but electrically insulating silicone gel that wets the element and conducts heat to the metal shell. The aluminum body is then bolted to a heatsink, a cold-plate or directly to the equipment chassis.
This construction delivers the highest continuous power per unit volume of any resistor type. A 50 W cement resistor in free air becomes a 250 W aluminum-housed unit with proper heatsinking. Forms include rectangular trapezoidal (Vishay RH style), oval, and slim profiles for stacked installations. Power ratings run 5 W to 1500 W single-element, with cabinet assemblies pushing into multi-kW territory.
The full power rating is only achievable with the specified mounting: a 100 W RH-100 needs roughly 100 cm² of dissipator area at 70 °C ambient and is rated only ~25 W in free air. Aluminum-housed resistors are standard in VFD braking, EV charging pre-charge / discharge, regenerative loads in elevators and cranes, and high-power test equipment. Operating temperatures up to 250 °C on the housing are common.
Related terms
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.
Cement-Encased Resistor
A power resistor in which a wound resistive element sits inside a ceramic shell filled with flame-retardant, inorganic cement, providing thermal mass, mechanical protection and UL94 V-0 safety performance.
Power Rating
Power rating is the maximum continuous electrical power, in watts, that a resistor can safely dissipate as heat at a specified reference temperature, typically 25 °C or 70 °C ambient.
Thermal Resistance
The opposition a thermal path presents to heat flow, expressed in kelvins per watt (K/W); it directly determines how hot a resistor's body becomes for a given dissipation.
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.
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