A rheostat is an electronic device that can adjust resistance in a circuit. A rheostat can be used as a potentiometer to divide resistance.
To select a rheostat, one should know the maximum resistance. Then, one should select the maximum voltage. Then, determine the rheostat's wattage:
P = V2 / R
The rheostat is constructed using ceramic material.
The 12.5 Watt rheostat is good for power ratings between 1 Watt and as high as 12.5 Watt. These extremely small rheostats 7/8" are high quality at a size smaller than a standard 2 Watt potentiometer. The shaft is 1/8" diameter.
The attached chart shows the Wattages, Unit Diameter, and the Ohmage Range.
|SHAFT DIA||WATTAGE||MODEL||DIAMETER||RESISTANCE RANGE|
|1/8||12.5||E||7/8||1 ohm - 5 Kohm|
|1/4||25||H||1 9/16||1 ohm - 5 Kohm|
|1/4||50||J||2 5/16||0.5 ohm - 10 Kohm|
|1/4||75||G||2 3/4||0.5 ohm - 10 Kohm|
|1/4||100||K||3 1/8||0.5 ohm - 10 Kohm|
|1/4||150||L||4||0.5 ohm - 10 Kohm|
|3/8||225||P||5||1 ohm - 2.5 Kohm|
|3/8||300||N||6||1 ohm - 2.5 Kohm|
|3/8||500||R||8||1 ohm - 2.5 Kohm|
|3/8||750||T||10||1 ohm - 2.5 Kohm|
|3/8||1000||U||12||1 ohm - 2.5 Kohm|
Rheostats from 12.5 Watt - 150 Watt can come with a shaft for a knob, or a 1/2 inch locking bushing with a screw driver adjust shaft.
Models of 225 Watt through 1000 Watt have a shaft of 3/8 inch diameter. These shafts are usually flatted to make a tight fit for a knob.
The typical rheostat is linear in taper.
At TEDSS.com you will also find rheostats that can be adjusted to an OFF position.