Australia's Science Forum

Hi All,
Does anyone know anything about rheostats?? I need to buy a couple of new ones but have no idea what it all means:
500w 75ohm 2.5A, Rheostat Slide Carbon Brush - 16 Ohm 6 Amp, 11ohm, 5amp, 50 ohm, 2.3amp.
Help!!

Two schools I work in use the 11 ohm 5A (5.6 Amp) type with the carbon brushes .
Carbon brushes ( the bit that contacts the resistor ) are better than the ones without ....That's why the ones with carbon brushes are dearer. ....and why they will out last the ones with metal brushes .

The 16 ohm 6A would also be a practical unit to have .but if all the other units you have are 11 ohm then probably best to stick with that.
The IEC units we have have got the resistance and maximum current on the slider knob .

Thanks for replying. I thought it might be a long shot.
Hmm.. Ok I have no idea what the ones we have are. They seem like a mish mash of different kinds. I will have to check before ordering.

Just had a good look at ours and we have 3 different types here too .They all have the resistance (ohms) and current (amps) on the adjuster knob .
Ours range from 10.5 - 11.5 ohms with currents from 5 - 5.6 amps .

It would seem its not too critical so long as its in this range .
( The 50 -75 ) ones are probably for some obscure application not common in the classroom.

Out of interest I measured the resistance of one of our 11 Ohm rheostats with a Multimeter .....it measured 12.5 ohms .This may be a handy way for you to check what you have if you can't find a value on them .

Another thing is that most schools seem to use the IEC power packs which can supply about 4-5 amps before cutting out .
Rheostats rated at 5 amps or above will be fairly bullet proof however the ones rated at 2.5 amps may turn their toes up if not used correctly.