Editing Resistor (section)

===Carbon pile===
A carbon pile resistor is made of a stack of carbon disks compressed between two metal contact plates. Adjusting the clamping pressure changes the resistance between the plates. These resistors are used when an adjustable load is required, such as in testing automotive batteries or radio transmitters. A carbon pile resistor can also be used as a speed control for small motors in household appliances (sewing machines, hand-held mixers) with ratings up to a few hundred watts.<ref>Morris, C. G. (ed.) (1992). ''Academic Press Dictionary of Science and Technology''. Gulf Professional Publishing. p. 360. {{ISBN|0122004000}}.</ref> A carbon pile resistor can be incorporated in automatic [[voltage regulator]]s for generators, where the carbon pile controls the [[field current]] to maintain relatively constant voltage.<ref>''Principles of automotive vehicles''. United States Department of the Army (1985). p. 13</ref> This principle is also applied in the [[carbon microphone]].