Introduction: Bike Generator Made From Scavenged Parts

About: I love experimenting with science and physics, especially projects that involve electromagnetism, energy conservation and audio.

My bike generator is built out of an old exercise bike, and uses a chain and sprocket drive that turns an automotive windshield wiper motor. The drive train has a gear ratio of 1:30, meaning a complete revolution of the pedals spins the windshield wiper motor 30 revolutions. The electricity generated is governed by a regulator robbed from the charging system of an electric start riding lawn mower. The regulator allows you to pedal as fast as you want and still output a constant 12-14 volts of direct current. When the generator is not connected to a circuit of any kind, very little effort is needed to pedal. However, when a circuit is made and you begin to push electrons through it, pedaling becomes more difficult. The amount of electricity you produce is limited only by how hard you can pedal. I haven’t done a lot of testing to see how much power I can produce, but I will throw out a couple of numbers. While I believe that it’s possible for someone to put out over a hundred watts, I don’t think anybody would do it for very long at all. 70-80 watts would be more reasonable, though still not easy. It really depends on what kind of shape you are in and how efficient your bike generator is. Pedaling a bike generator can really give you a sense of how much power 100 watts of electricity really is, and can make you realize how cheap and plentiful electrical energy is for most of us.

Made almost entirely from salvaged or scavenged parts, my design is relatively (compared to most designs utilizing a real bicycle) compact, efficient, and permanent. I can keep mine outdoors as long as it is out of the rain, although if it did get rained on now and then it probably wouldn’t suffer any damage.

Most of the parts, with the exception of the exercise bike, can be acquired from broken or inoperative bikes, cars, and lawnmowers. So, if you are a scavenger like Rey in the new Star Wars movie (or a jawa like me) you shouldn't have too much trouble.

For example:

The bike sprockets and chains were salvaged from broken bicycles.

The windshield wiper motor was salvaged from a junk car.

The regulator was salvaged from the husk of an electric start riding lawn mower.

The bearings were salvaged from the front wheels of a riding mower.

One thing I wish I had known before I started:

When trying to select a DC permanent magnet motor to use for your generator, I suggest connecting the motor you are considering to a car battery and watching how fast it spins. The speed it spins is a good representation of the speed that you will have to spin it to make it produce 12 Volts DC. You want a motor that spins at a modest or relatively slow speed. Actually, the slower the motor spins the better. One of the major difficulties of designing a bike generator is generating enough voltage, namely 12 volts, while pedaling at a comfortable pace. A motor that produces this voltage without having to be spun blazing fast will make this much easier to achieve.

Step 1: Build the Chain Drive

I thought about using belts and pulleys, but pulleys require tension to keep them from slipping. This tension creates a resistance that has to be overcome. Chains don’t require tension, and are therefore slightly more efficient, but they are a bit noisy.

The critical moving parts are the two sets of sprockets; each set is a big sprocket connected to a little one spinning together on the same shaft. To make them, I welded the sprockets onto short pieces of steel pipe. The pipe has just the right inside diameter to allow the bearings to be inserted into the ends. The whole assembly is then slid onto a fixed shaft that is attached to the exercise bike frame. When mounting these assemblies, remember that mounting your moving parts onto plates with slots in them is a real luxury. It enables you to make fine adjustments on the tension of your chains. Very small differences in the distance between two sprockets can make a big difference in the tension of the chain that runs on them. The difference between a loose chain and a chain that is too tight to run can be as little of an eighth of an inch.

If you choose to weld the sprockets to the pipe, beware that the heat can warp the sprockets, especially the big ones. This happened to me and I had to pound mine flat again; it was a real pain. I used a stick welder, but brazing or other welding techniques might cause less warping and save you some headaches. Also, some of the small steel sprockets I worked with were hardened or tempered steel, and I couldn’t file or drill on them! Heating them up until they glow red hot and then cooling them slowly should cause them to lose their temper and make them soft enough to machine.

You can find the gear ratio of a set of sprockets, even before you put them in a drive system like mine. Just count the number of teeth on each sprocket. Say you intend to run a chain around two sprockets, one with 8 teeth and one with 32. The ratio of the two sprockets is 8:32, which we can simplify to 1:4. This means that every time the 32-tooth sprocket makes a complete revolution, the 8-tooth will make four.

The chains are from old bicycles, and I had to adjust their length to suit my needs. Normally all the links are the same except for a special link which joins the two ends of the chain together, making it a loop. These special links are called master links. They should be obtainable from bicycle shops, but I really wouldn’t know because I don’t live near one. I had to make do with what I had: parts of chain links I had taken apart along with little pieces of steel rod to join the pieces together. Salvaged chains that are very rusty and have many frozen links can still be used if they are soaked in penetrating oil. After soaking, manipulate each link back and forth to free it up. Keep in mind that a rusty chain can lengthen significantly once you get it in use, as a tiny amount of rust is ground away from in between each of the links!

Step 2: The Motor-Turned-Generator

I used a windshield wiper motor for my generator, robbed it off an old ’81 Ford Escort. These motors typically have an integrated gear box, and the end of the motor shaft is a worm gear. They vary in size however, depending on how big the vehicle is. I had to completely disassemble the motor (if you faint at the sight of motor guts, this project might not be for you), and cut the gear box off with a hacksaw.

Next, while you have your motor apart, you have to rewire it internally. The ground connection, or negative electrical connection, of the motor is actually the motor’s own metal casing. This means that one of the brushes inside is wired to the case. You will have to find which one it is and disconnect it from the case, then attach it to one of the other wires that leads out of the case. My motor has four wires leading out of it. On mine, the white is the low speed and the blue the higher speed. The red and black are connected to a switch inside the motor that gets tripped when the motor reaches the end of its windshield wiping arc. These latter two are of no use to us, so disconnect one of them and wire it to the brush that you disconnected from the case of the motor. Make sure you insulate the connection so that it doesn’t touch anything it’s not supposed to, and make sure it won’t get in the way of the armature (or rotor) of the spinning motor.

The next step is file down the worm gear on the end of the shaft. You will have to reassemble the motor, then clamp it in a bench vise horizontally and connect it to a car battery. With the motor turning (I used the slow speed) take a sharp file and hold it against the worm gear on the end of the shaft, filing it down. Try to file the ‘screw threads’ of the worm gear down evenly. You will have to file them down until they are almost completely gone, and the shaft is about 6mm, or at least enough that you can run a die over the shaft and cut male threads into it. To cut the threads, clamp the motor in the vise vertically. Clamp a vise-grip (locking pliers) with small jaws onto the shaft near the motor itself. This will allow you to keep the motor shaft from turning while you cut the threads.

The sprocket that I attached to my motor shaft is a nylon sprocket from a bike derailleur. I cut a short piece of pipe that would slide onto the shaft first; it slid on until it hit the point where the shaft begins to thicken. Then I slid a washer, the sprocket, another washer, and two nuts to squeeze it all down tight, tight enough that the sprocket now turns with the motor shaft.

The white wire mentioned above, which runs the motor on its slow speed, is the one I connected to my regulator along with the red wire which is my ground. Note that the polarity of these wires is actually determined by the direction that you spin the motor; if I reversed the direction of spin the polarity would be reversed, making the white wire the negative or ground wire.

The motor is bolted onto an aluminum plate, which in turn is bolted to a slotted piece of steel that is fixed to part of the bike frame.

Step 3: The Regulator

I took my regulator from the charging system of a riding lawn mower that featured electric start. Any lawn mower that uses electric start will have an onboard charging system to recharge the battery as the engine runs, and will have a regulator to regulate the current. A generating coil is mounted on top of the engine underneath the flywheel, and as the engine runs a ring of magnets mounted on the inside of the flywheel induce a current in it. Because the engine runs at different RRMs, the current produced will vary accordingly. That is why the wires coming from the coil next travel to the regulator. Mine has two connections labeled AC, this is where the coil is connected. The label AC implies that you could run DC of any polarity into it, but I found that mine only worked when connected one way. If yours doesn’t work, switch the wires and see if that helps. The middle connection of mine is labeled B+, and of course is positive and should be connected to the positive battery terminal. Where is the B- , you ask? The metal body of my regulator is actually the B- or ground terminal.

Step 4: Do Something With the Electricity

The energy you produce can be
stored in a car battery, but keep in mind that about a fourth or fifth of the energy that you put into a car battery won’t be coming back out. That is because at best, most lead acid batteries are only about 80 percent efficient. To charge a battery, simply connect the positive terminal of the regulator to the positive post on the car battery, and the negative terminal to the negative post of the car battery.

Inverters account for some loss of energy as well, mostly dissipated in the form of heat. Good inverters may have an efficiency of around 90 percent. Some that are easy to come by cheaply are “power packs”. These are emergency power supplies that have a built in battery. Once the battery inside will no longer hold a charge, usually due to neglect, most people don’t want them anymore. But they are still very useful if you can find a way to connect them to a working battery. I can use mine simply by taking the cables on the sides, which were originally for jump starting a car, and connecting them to 12 volt source like a car battery, my bike generator, or my personal favorite: both. Mine has a 5 volt DC USB port for charging cellular phones, a 120 volt AC outlet courtesy a built in 120 watt inverter, and a 12 Volt DC cigarette lighter socket. I even opened mine up and took out the dead internal battery, which made it about 5 pounds lighter as well. It also helped electrically, because the “dead” battery would sap some electricity from whatever it was connected to, because it was trying to charge.

The first thing most people try to run is some kind of light. The incandescent light bulb is a model of inefficiency, however. Heating a filament until it is white hot to produce light is very wasteful from the prospective of energy conservation. Thankfully there are other options. Fluorescent light bulbs are one option, but they require AC and most inverters don’t work well with them. Your best option by far is to use light emitting diodes (LEDs). Arrays or spotlights meant for automotive uses like offroading can be run directly with 12 volts DC. In fact, I have an LED brake light that fell off of a school bus that uses 3.5 watts and puts out a surprising amount of light. It had been run over by a car but I was able to disassemble it and bridge the cracks in the circuit board.

If you want to learn more about electronics and 12 volt power, I recommend these books. By their titles, they don’t sound like they would be of much interest, but they are packed with practical, hands on instruction, and are written in plain English by a couple of guys who know from firsthand experience what they are talking about.

Do it Yourself 12 Volt Solar Power by Michel Daniek

Hacking Electronics by Simon Monk

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