Marcellus Jacobs: Wind-Power Generating Inventor
(Page 6 of 12)
November/December 1973
By the Mother Earth News editors
See, the whole idea of high-speed propeller design is to throw the wind that hits the blades...the whole idea is to throw it out quickly. You don't want it to drag all the way along the back of the blades. That's a tremendous amount of friction—a tremendous force—and you want to eliminate it. Sometimes a very little change—a 64th of an inch—in the curve on the back of a propeller can affect its power output a seemingly immeasurable amount.
RELATED CONTENT
John Shuttleworth discusses his experiences living the self-reliant life that Mother Earth News is ...
A Plowboy Interview with Shuttleworth, who discusses everything from the business of the magazine i...
The Plowboy Interview with Amory Lovins, author of the 1976 essay, "Energy Strategy: The Road Not T...
The Plowboy Interview: Frank Herbert May/June 1981 SCIENCE FICTION'S "YELLOW JOURNALIST" IS A HOMES...
Well forty years ago, I designed a special machine that would let me determine just how efficient a blade design might be. I had a test stand made up that extended out two feet past the end of a propeller and at each foot along the arm we mounted a separate wind pressure gauge. We checked a lot of blades on that stand until we knew exactly how to design a propeller that was as efficient as we could make it.
PLOWBOY: And then you built a generator to match the prop?
JACOBS: Yes. We had to balance the generator's load to match the efficiency of the propeller. If your blades work best at a certain rpm in a 7-1/2 mph breeze, they should turn exactly twice as fast when the wind blows 15 mph, shouldn't they? They won't catch all of that 15 mph wind unless they do, will they?
OK. The trick is to design the generator so that its load increases just fast enough to allow the propeller to double its rpm as the force of the wind doubles. And that's what we did...right up to the top speed we wanted, which was 18—20 mph.
Now this wasn't easy, because a conventional generator doubles its output when its speed increases by only something like 25%. Obviously that wasn't a very good match for our propeller...so we tried several things until we finally came up with a special alloy for the field poles in the generator. We finally got a combination that made the load of the generator fit the output power curve of the propeller over the entire range of windspeeds up to 22, -3 or -4 miles an hour...where the blades were set to feather out.
It was a lot of trouble, but it was worth it. Wincharger, for instance, didn't take the time to balance the components of its plant in this manner and that unit was only one-third as efficient as ours at higher windspeeds.
PLOWBOY: Wow. You really took pains to design and build the best possible windplant, didn't you?
JACOBS: Oh yes. I've only told you a part of it. We came up with our own special brushes in the generator, you know.
It's not too hard to set up a big DC generator and run it with a stationary engine, see, because you've got a fixed speed of operation and you can adjust everything so it's working the best for that rate of output. Now I'm particularly thinking of the commutator arm and its brushes which slide from one wound coil to another inside the generator. Every time those brushes move from coil to coil, you know, they want to throw a spark. When you break DC you get an arc...and those flashes will burn little rust spots on the commutator and then it'll just grind the brushes off in a matter of months.
Page:
<< Previous 1 |
2 |
3 |
4 |
5 | 6 |
7 |
8 |
9 |
10 |
11 |
12 |
Next >>
