Marcellus Jacobs: Wind-Power Generating Inventor
(Page 7 of 12)
November/December 1973
By the Mother Earth News editors
What you look for, of course, is the neutral zone...the one small area where your brushes will throw the least spark as they leave one coil and go to the next. This isn't too hard to find and when you've got a fixed speed on your engine and generator you can set everything just right to make use of it.
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A windplant isn't like that, though. It's set to kick its generator into operation at about 125 rpm and it reaches full output—3,000 watts or whatever—up around 225 rpm. Now that's OK...but every time the rpm varies—and it can change a thousand times a day—the neutral zone shifts. No matter how you adjust your commutator, then, your windplant's brushes are going to be set to throw a much bigger spark than you'd like as they move from coil to coil during the greater part of the plant's operation.
Everyone in the business faced this problem, of course, but none of the others ever licked it. We did. I developed a brush made up of a layer of graphite, then carbon, then graphite, then carbon. This gave us a brush with a high cross-section resistance. The DC current would practically quit flowing before the brush made its jump from one coil to the next and that was just what we wanted.
We tried to get National Carbon to make these, special brushes for us but they weren't even interested enough to send a man out to see us. Stackpole couldn't understand what we wanted either but they did build the brushes to our specifications and that licked the commutation problem. We've had plants run ten or fifteen years on their original set of brushes. That's unusual. Ask anyone who's operated other manufacturers' windplants.
PLOWBOY: Didn't you also make some noteworthy breakthroughs in the way you regulated the voltage of your units?
JACOBS: Yes. That's another tough situation you have to face with DC. To change the irregular power generated by the wind into a steady flow of current for use, you have to go through batteries. The only trouble is that you can't let your generator feed the same amount of electrical energy to the batteries all the time or you'll burn the storage cells out. As a charge is built in a battery-as the battery becomes more nearly "full"—you want to charge it at a slower and slower rate.
Well, Wincharger and all the others tried this and that but they never came up with the voltage regulators and cutoffs they needed to solve the problem. That's why you always had to get up at two o'clock in the morning or some other unhandy hour and shut those plants off to keep them from burning out their storage banks.
We had the only windplant that didn't have this trouble because ours was the only one which was completely voltage regulated. Our control—we called it the Master Mind—inserted a resistance into the generator fields to weaken their output as the batteries filled up.
Now that was a problem in itself because the Master Mind contained a set of points that had to open and close thousands of times a week. This meant thousands of arcs and flashes. Eventually the points would stick and make the generator begin to run like a motor as soon as the wind died down. That wasn't good, you know, because it would soon drain all the energy stored in the batteries.
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