pot n rheo

[Lalit]

Hi all !
What is the difference between a potentiometer and a rheostat ?
How r we to decide which to use where?
Regards,
Lalit

 

[laroche73]

rheostats and pots

Both are variable resistive elements. Rheostats are generally wound with nichrome wire and can be used with high power levels. Most pots use carbon as the resistive element, and handle much lower currents.

 

[daviddoria]

and as far as i know rheostats have only 2 leads, where pots have 3, letting you tap it like a transformer, and possibly even using it as a voltage divider.

 

[seeker]

Hi Lalit,
Speaking as an "old fart" , rheostats back in the old days were generally wire-wound and could handle rather large power loads. Potentiometer is a newer term and means the same thing but they are usually made with a carbon film instead of a coil of resistive wire. They both are variable resistors.

Rheostats can have 2 or 3 terminals as do potentiometers.

Bottom line.......same thing, different names
wrench and spanner, boots and galoshes, car and horseless carriage, wife and umm...

 

[Dean Huster]

Pots & rheostats

Rheostats ALWAYS have only two connections since they're current-adjusting devices and go in series with a load. As mentioned, they are/were usually wire-wound units with high power ratings and have mostly been replaced with solid-state controls, e.g., a triac lamp dimmer. Old theater lighting and motor speed controls used to use huge, heat-producing rheostats.

Potentiometers (the name kind of gives it away here) ALWAYS have three connections since they're voltage dividers. Pots were (and somewhat still are) commonly used as the volume control in a radio where signal was fed to one stationary terminal, ground to the other and the variable audio level was picked off the wiper and ground.

If you look through today's industrial electronics catalogs, you won't find much in the way of rheostats. Since the only thing missing from a rheostat is a terminal (the insides are all there), they usually make them as high-power potentiometers and let the end user ignore one terminal if he needs it as a rheostat. That way, they only need to make and stock one part number vs. two for each value and power rating.

Dean