WHATS BIG CAN BE SMALL?

[Yianie123.]

I was wondering if anyone has tried to use a permanent magnet alternator with a gear box, to increase the RPM's, and then instead of using blades for a 4 ft diameter windmill, increase the blades to 6 - 8ft to overcome gearbox losses?  Isn't that how the big guys do it?

[joestue]

what you describe is mostly a wash.

there are a number of factors regarding the dispensation of public coffers, but from what i can gather, the largest, 5 to 7 megawatt wind turbines, the generator inside them is direct driven, no gear box, and is larger (measured in kilograms) than a 100MW hydro turbine. *


there are about a dozen other factors involved for wind turbines less than 20-50KW that dwarf the kilogram dollar per kilowatt peak power math regarding the generator.

*cost is about the same per kilogram, 1$/lb for steel, and 9$/lb for copper.

[Flux]

There seems little point in any speed increasing device for something as small as 4ft.

Long ago before decent magnets were available I used a gearbox on a 7ft machine. It worked, the losses were not excessive but noise was far from good and the gears didn't last long. I came to the conclusion that a roller chain was much simpler and better.

With present day magnets it may be worth speed increasing with ferrite magnets for machines 12ft or larger. Chris Olsen has made some nice ferrite machines with chain speed increase but at the 4ft level it would never be justified. The few watts available for a 4ft machine is well within the range of ferrite magnets with direct drive and for such a tiny machine the cost of neo is no big deal.

Yes the early big commercial units did use gearboxes especially with induction generators. The gearbox was a big source of trouble. Most big machines are now direct drive to a synchronous alternator coupled to the grid via a dc link and working at variable speed.

What works best at megawatt levels is not always the best approach for small stand alone wind machines.

Flux