WireWound Potentiometer Derating Curve

How to derate a WireWound Potentiometer.

A wire-wound resistor is a resistor that uses wire as the resistive element. The actual wire could be of several types, with nickel-chromium resistance wire being common. In a variable wire-wound resistor, the wiper slides across the length of the wire, at least the portion at the top of the wind [the wire is coiled around a tube]. As the wiper slides down the wire the resistance is made greater as the length of the wire introduced in the circuit becomes greater. The graph below is generalized, as different case styles may produce slightly different results, shifting the end-point above or below 350C.

Temperature dereating for an Adjustable WireWound resistor
Percent Rated Power x Maximum Operating Temperature

Note because the element in a wire-wound component is just wire, the maximum temperature the component will work to is much higher than other components. So wire-wound devices operate up to two or three times the temperature of other components. Shown in the graph as a maximum temperature of 350 degrees centigrade, while most other components drop off near 125C or maybe just before 200C.

This doesn't mean that other components won't operate to as high a temperature, just that the wirewound resistor will not be required to be derated as much. That is, a higher percentage of the total power dissipation of the device may be used to a higher temperature. Which would also imply that there may not be a need to move to the next higher power dissipation device to operate at a higher temperature, translating into a small device at higher temperature [when comparing a non-wire wound potentiometer]. Although in many cases a wire-wound adjustable resistor is already in a larger package than a similar non-wire wound resistor.

How to derate a WireWound Potentiometer using a derating curve.
Potentiometer Derating Guide Lines

Potentiometer Manufacturers, Resistor Manufacturers, Definition of Resistor Terms

Wire-wound Variable Resistor
Wire-wound Variable Resistor

The graphic shows one example of a wire-wound resistor. This particular style of adjustable resistor uses a movable tap that may be clamped in place and secured to a panel [for example]. The wiper is moved to the desired position and the screw is tightened on the tap, so the tap is now fixed in place. As long as the screw remains tight, the adjusted value of the potentiometer doesn't change. The potentiometer is connected to the circuit via wires attached to the three cut-outs, one on each tap point.

Derating guidelines for components; How to Derating Electronic Components

MIL-PRF-22 slash 17 Panel mount Adjustable Wire-Wound resistor

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Modified 6/13/15
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