thomas rubino wrote:Hi Nuno; Welcome to Permies!
That is a very nice water wheel you have, I'm jealous!
If I may ask, what is your goal ?
Power for a home ? Or is this a school project?
I'm no engineer , just a micro hydro guy, but your numbers look rpm dependent.
You should be able to gear the PMA to any reasonable rpm you want?
How were you thinking of driving the PMA ? With a direct flex drive coupler? Or with gears and a chain?
By your engineers numbers, it sounds like you have significant toque.
Give us some more information and we might be able to help you make your choice.
thomas rubino wrote:Well the fact your not wanting to make huge amount of power makes this easier.
A PMA and a standard auto alternator are normally similar in size.
I would experiment with different size pulleys from the wheel to a practice alternator.
Get your rpms close and then choose what PMA fits your needs best.
Of course, an alternator (PMA or regular) will spin slower when produsing power.
Hopefully you can get the rpms up enough to use a higher rpm PMA and lower your upfront costs.
EDIT) Your plan of using belts for a drive system rather than chain could be problematical. When they get wet they may want to stretch on you and slip. Chain drive is foolproof.
Also is this power going to a battery bank ? Or are you hoping to run directly off of the alt ? I assumed we were talking D.C. power, are you thinking A.C.?
thomas rubino wrote:Well you are certainly correct that a chain drive would be noisy. An insulated cover would mitigate some of that noise. With your plasma cutter pulley production would be simplified.
Belt drive would be virtually silent, with the ambient noise from the stream.
Making A.C. directly is slightly harder as rpms must be within a certain limit. D.C. would simply produce less power as the rpm's dropped.
Unfortunately I do not know any sure way to calculate the spin resistance when under load. Would your load remain constant? Or fluctuate with lighting needs?
I'm afraid you will need to experiment with rpms in the 4000 range in the hope you can maintain 3500-3600 under load.
Here is an idea. Use a small gas engine (they run at 3600) hook this to your PMG and apply your anticipated load. The engine will of course compensate to keep rpms at 3600, But you should get an idea by the amount of compensating you hear the engine do, how much draw (resistance) your PMG is creating.
I would build a dummy shaft that is the same diameter as your PMG shaft , fit it and the main shaft with pulley's . I realize that coming up with pulley's of the appropriate size is no doubt a problem as well.
Spin it up and see what you get.
I know this is not the answer you were wanting. I just do not have the engineering skills to calculate what you need.
Please do give us an update (with photo's) as you progress.