I'm a Mechanical Engineering senior, and as you all probably recall, that means it's senior project time. My question pertains not to my own project, but to the project of a good friend of mine who doesn't have Usenet access.
the basics of the question are these that follow, with a more detailed project explanation later if anyone is interested or if that helps define the problem better.
He's got a 12 Volt DC motor which is driving a shaft. He needs to have speed control on this motor. The motor has a rating of "amps at load = 800 milliAmps; amps at stall amperage = 3300 milliAmps".
He thought, as did I, that a big potentiometer would work. However, he's not finding them anywhere rated more than 2 Watts.
Is the wattage the packaging on the pot referring to not the wattage of the motor it's controlling? If so, what IS the wattage referring to on the pot?
Using Ohm's Law, V= IR, and P = I^2 R, it sure seems that 2 Watts divided by 3.3 Amps squared gives a really small resistance.
Electrical theory isn't my forte, obviously, but I told my buddy that I'd ask the vast knowledge base that exists out here, and see what came back.
Details of the project (insofar as much as I know them, this may not be100% accurate) follow if anyone's interested. * * *
- He and his team are building a 'table-top' size wave generator to be used in high schools, middle schools, and demonstrations. We have an amazing wave research center at our school, and they're sponsoring this development and build project. It's a long, skinny tank with a piston, basically, on one end to generate the waves. AFAIK, they did a whole bunch of research into different methods of wave generation and this seemed to be a good workable and buildable model. They can also create wind waves by pulling air across the surface of the water with some sort of vacuum, but that's not the part they're having issues with controlling. The piston is driven by a motor. The motor speed needs to be able to be varied. We know that there are plenty of power tools that run on DC that have the ability to vary their speed... What do they use? For a 12-V DC motor, what is appropriate?
Any and all advice/insight/comments appreciated! We all have only a few weeks left to really pull these projects together, so anything that's gonna help his team get it going right now will be really, really useful.
TIA, k wallace OSU