~//~
“I ride a bike. In the Winter, I ride inside on rollers or on the ‘hamsterbike.’ I eat food, and then I make a lot of power. But I just let that power go to waste. I wonder if I could run some lights, or charge batteries with the bike?”
~//~
I would venture to guess that just about every cyclist has had thoughts like that. Some years ago, I got the idea that I could use the bike to develop a reasonable amount of electrical power. Power meters were not readily available then, so I was estimating my power output, based on things that I read and my rough understanding of the work necessary to move a bicycle.
I had a generator lighting system on my bike. This was a 12-volt system, driven by a “bottle” generator. That’s the kind of generator that works by having a little wheel rubbing against the tire of the bike. It had problems. It tended to wear out tires. It didn’t emit a lot of light. When I was climbing a hill (common in that area) the light dropped to almost nothing. When I wasn’t moving, the light went out. Most of that didn’t factor into my thinking.
I had the thought that, if I eliminated the ordinary load of moving the bike, and hooked up multiple generators, I could produce a significant amount of power. Seemed like a thing worth doing.
I cobbled up a bike stand, using a bike cargo rack and the wreckage of two old deck chairs. The result was wobbly, but it served to suspend the rear wheel above the ground, and I could mount it and spin the pedals.
I mounted first one, and then another of those bottle generators onto the frame, then hooked them up in parallel. That would be my first test. I breadboarded a series the low power light sockets, and an array of switches. My plan was to switch in the lights one at a time.
I mounted the bike and began pedaling. The first light burned brightly, and I wasn’t even working yet. In fact, by really spinning up the wheel, I was able to burn the single bulb out. After I replaced it, I resumed my experimenting, but a little more carefully.
In short order, I had six of the lights burning brightly, and I still wasn’t working hard. (Of course, the lights did tend to flicker as my speed changed. That got better when I shifted to higher gears and spun.)
I showed the rig to my father. Dad was an electrical engineer by training. He glanced at what I’d accomplished, watched a demonstration, and said, “Impressive. I’d say you’re burning about 50 watts, and with reasonable allowances for losses, probably applying about 75 to 80 watts to the bike. What’s next?”
I told him I wasn’t sure, but I wanted to investigate charging batteries.
“Should be interesting,” Dad said. “Be careful though.”
My plan was to increase the output. I mounted two more generators to the bike, on the opposite from the first two. I’ll spare you the details, but that didn’t work well. You see, these were generators. (A fact which will be important later too!) That meant that they delivered direct current. More important, the polarity of the current depended on which way the generator was spinning. In essence, I’d done the same thing as putting half the batteries into the gadget pointing the wrong way. I produced no light with this rig, but I did let the smoke out of one of the generators. (All electrical devices run on smoke. If one lets the smoke out of an electrical device it no longer works. Q.E.D.)
Once I figured that one out, I simply reversed the output wiring on my second pair of generators.
At that time, my family had an old Gravely Tractor. This was a monstrous ancestor of today’s modern lawn tractors. The thing had an electric starter, but no means of charging the battery. So the battery (a miniature version of an automotive one) had to be removed and charged with a battery charger. I figured this would be a great test of the practical side of my riggery. After all, I had figured out how to produce something like 100 watts of 12-volt electrical power. That should be significant, right? Well… maybe.
I wired everything up, jumped on the bike, and threw the switch. Yikes! To my huge dismay, I wasn’t turning the cranks. They were turning me! In fact, the rear wheel was being spun so fast that the driveline could not keep up with it. The chain jumped off and fowled. The wheel jammed, and the little generators were still spinning hard against it! Before I could reach the switch, more smoke was emitted, and the whole thing came to a stop.
Here’s the thing, without getting too technical, a DC motor, and a DC generator are fundamentally just about identical. If one applies a direct current to a generator, it will act as a motor. In short, it will turn! Another point of interest; a storage battery that is so discharged that it will not start a tractor, will likely have plenty of charge left in it.
The ultimate solution to that problem lay in a bit of electronic rigging. I cannibalized an automotive alternator to get a couple of high power diodes, and I scrounged up a hefty rheostat to limit the current. This let me have current flow in only one direction from my homebrew power plant, and it allowed me to control how much current would flow. If I wanted to charge the battery slowly, but not have a lot of leg strain, I could do so. But the thing was, if I wanted to charge it quickly, I had to work. I mean really really work! At that, the best compromise I could arrive at was about four hours to pump the battery up enough so that it would start the lawn tractor a couple of times.
All this was (pardon the pun) an illuminating experience.
In the years since, I’ve learned a few things. From the standpoint of generating power, a human is a pretty puny engine. Most of us have weed wackers, or leaf blowers that are capable of generating a lot more power than we can.
No comments:
Post a Comment