College Project

Decon

Joined Nov 16, 2011
2
I have to convert the falling kinetic energy of water into electricity for my Mechanical engineering class. We are making a water wheel which will be attached to an electric motor. Me and my team have an AC 120v 60Hz rotary fan motor right now. Will this work? Also there are 4 wires comming out of the thing. RED BLACK WHITE and YELLOW. I dont know what the white and yellow are for. Also there is a capacitor hooked up to it. a BM CBB61. Will the capacitor effect the production of electricity as well? Thanks

R!f@@

Joined Apr 2, 2009
9,740
Welcome...

I doubt that you will get enuf AC out of that.

Why not use a universal motor instead.

And falling water does not produce enuf energy to rotate anything unless there is a gear mechanism to increase torque but this will reduce RPM.

To put enough strength in falling water u have to pour large amounts of water from high ground, which is not effective or even practical.

Water should be sent with high pressure to do anything.

So for ur method you should use small DC motors just to show that it is possible.

wayneh

Joined Sep 9, 2010
16,537
Me and my team have an AC 120v 60Hz rotary fan motor right now. Will this work?
Not likely. You'd be better off with almost any DC motor you can find, and you can test them by just giving it a spin with the leads hooked to a multimeter. Detecting a permanent magnet inside the motor is a positive sign also. A "bottle" generator for bicycling - one of those things you spin by friction against the tire - would be a good choice, since it's purpose-built for generating electricity at low rpm. But there are many other places you could find a DC motor. How much power do you think you'll be handling?

Decon

Joined Nov 16, 2011
2
Thanks for the quick feedback. The test fixture is 5 gallons of water being released from a height of 5 feet. We were debating on whether to get a small dc motor from radio shack etc. Im not sure how much power were dealing with. We are also having trouble deciding the size of the water wheel for the small motor. How small of a motor should i get?

R!f@@

Joined Apr 2, 2009
9,740
u can't tell without checking it for ur self.
These things are trial and error run.

Joined Dec 26, 2010
2,148
An estimate of the stored energy in the tank (think: mass, head of water, acceleration due to gravity) would be a starting point.
Then you might think of how quickly the water would be run out to estimate the maximum available power. Your water wheel and transmission* will lose some of that of course, probably quite a lot of it.

*Your optimum wheel speed may not be a good match for a small motor or dynamo, depending whether it is a fast turbine or say an overshot mill wheel, so gearing etc. may be in order.

Finally note that small electric machines are not generally that efficient: some of the cheap little motors come out around 35% as motors, and that is at optimum speed and torque. Run as generators in less optimum conditions, you may not get much.

Edit: By the way, I agree with the last poster that some trial and error will be needed in the end, but it will be good practice to do these estimations. Showing evidence of doing this might earn you some marks, depending on the level of this project (school or college?) and how the project is to be assessed.

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EarlAnderson

Joined Nov 13, 2011
166
if you are building a water wheel and you want to get 120 volts and 60Hz, it all depends on how big the motor is, how big the water wheel is, and how much water is flowing on the wheel. although it is possible to get 120 Volts AC out of the thing, it would probably be well over 60Hz because it takes a lot more force to generate that kind of voltage, so you would have to have a frequency regulator to keep the frequency around 60Hz. as far as the yellow and white wires go, i have no idea whatsoever, and the capacitor is probably a buffer capacitor to smooth out the voltage spikes when ever you would turn the motor on, i would just get rid of it if i were you as it will serve virtually no purpose.

Joined Dec 26, 2010
2,148
Unless your instructors actually require 120V output, it would seem far safer to use a lower voltage, say less than 24V, especially since you will be working with a set-up which may leak or splash water.

wayneh

Joined Sep 9, 2010
16,537
An estimate of the stored energy in the tank (think: mass, head of water, acceleration due to gravity) would be a starting point.
+1
Then think about how long it will take for the reservoir to drain, probably in the minutes range (ie. not seconds or hours). The total energy available divided by the time gives you the instantaneous power you can design around. It isn't much, so I think you'll want a "small" motor designed for low rpm. You don't want a 14,000 rpm Dremel motor, more like a VCR capstan motor. You'll still almost certainly want your water wheel to spin much slower than your motor, so you'll want a pulley reduction (like the front and rear gears on a bicycle) and maybe a gearbox. Trouble with a gearbox is the torque required to get it going.

Feign

Joined Mar 30, 2009
50
I'd suggest a Brushless outrunner type motor with hefty magnets. They push 200watts on the little rewound cdrom motors.

And cause i just can't resist. I'd use a variable gear system, lever and fly wheel, and drop the whole bucket at once. The most massive flywheel wins, no?

Bernard

Joined Aug 7, 2008
5,720
First compute the potential energy available in watt seconds. And not knowing anny better, I would build the water wheel first & measure output with Proney Brake. For low head, low flow rate I would choose a Michell { Banki ] turbine. Could be made from ABS pipe & sheet, or steel if welding is available. Look for a copy of: Producing Your Own Power, RODALE PRESS, CR 1974. Just gut feelings, 3 in dia, 3 in long, to give approx 1400 RPM.

Bernard

Joined Aug 7, 2008
5,720
A couple of drawings to give the idea of Michell turbine. Notice that on Fig 30- the nozzle is on wrong side.

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