470 OHM 10W Ohmite Wirewound Resistor

Wirewound ResistorsWirewound resistors are commonly made by winding a metal wire, usuallynichrome, around a ceramic, plastic, or fiberglass core. The ends of the wire are soldered or welded to two caps or rings, attached to the ends of the core. The assembly is protected with a layer of paint, molded plastic, or anenamelcoating baked at high temperature. These resistors are designed to withstand unusually high temperatures of up to 450°C.Wire leads in low power wirewound resistors are usually between 0.6 and 0.8mm in diameter and tinned for ease of soldering. For higher power wirewound resistors, either a ceramic outer case or an aluminum outer case on top of an insulating layer is used – if the outer case is ceramic, such resistors are sometimes described as "cement" resistors, though they do not actually contain any traditionalcement. The aluminum-cased types are designed to be attached to a heat sink to dissipate the heat; the rated power is dependent on being used with a suitable heat sink, e.g., a 50 W power rated resistor will overheat at a fraction of the power dissipation if not used with a heat sink. Large wirewound resistors may be rated for 1,000 watts or more.Because wirewound resistors arecoilsthey have more undesirable inductancethan other types of resistor, although winding the wire in sections with alternately reversed direction can minimize inductance. Other techniques employbifilar winding, or a flat thin former (to reduce cross-section area of the coil). For the most demanding circuits, resistors withAyrton-Perry windingare used.Applications of wirewound resistors are similar to those of composition resistors with the exception of the high frequency. The high frequency response of wirewound resistors is substantially worse than that of a composition resistor.