A quick internet search returns many bicycle generators, mostly for teaching purposes. Yet, in spite of this information, there were more than a few people back home that expressed their doubt that a bicycle can create electricity. I am proud to say that today our bicycle produces approximately 12V and 6.5 amps, or 80 watts. To give you a sense of scale, CFL lightbulb that consumes 22-watts puts out as much light as a 100-watt incandescent lightbulb. With 30 watts, my notebook can be powered and also charge the battery, my ancient, gigantic laptop consumes 75 watts, and my cell phone uses approximately 2.5 watts.
The bicycle generator comprises two systems - mechanical and electrical. The mechanical system is built on a makeshift bicycle frame, and uses the traditional front gear by the pedals connected by a bicycle chain to the back freewheel. The freewheel shares a shaft with a large pulley (the flywheel), which is connected to the motor by a v-belt. The first bicycle was built with a larger flywheel and filled with concrete to increase the moment of inertia. This system was connected to a car alternator. There were 2 problems with this system. First, a car alternator really only works for an output of less than 30 watts, so when it was connected to the battery it became impossible to pedal. The second problem was that the belt on the wheel and the motor were not compatible, and there was quite a bit of slippage:
According to the internet, it's possible to get up to 200 watts out of the system, and ours is only producing 80 watts. The technician wanted to try adding another flywheel to the system:
As you might imagine, this extra pulley made it too difficult to bike. The second pulley was taken off, and we reverted to the original system. The electrical part of the system begins with a permanent magnet dynamo, also known as a low RPM DC motor.
When we measured the voltage directly from the motor, it was quite high and fluctuated quite a bit. Our technician spent many days searching in the market for a voltage regulator, only to find the one he purchased was broken and couldn't be fixed. He then purchased another one that eventually worked once we hooked it up to a small light bulb that acts as a switch to prevent the battery from discharging.
At one point, we even tried a charge regulator used with solar panels, but eventually reverted back to the car regulator.
Our next steps with this project are twofold. First, we are currently working with 2 electrical engineers to hook the bicycle up to a computer program called LabVIEW, so that we can see the variation in power over time, and across different users to get a better sense of the capabilities of the system, and how it is used by users. Secondly, we are building a second generator on a mountain bike frame using a gear box. We are hoping to create more power with this system, and hoping that the cost will be kept down by using bicycle frames instead of building our own. Our final prototype will probably be some sort of combination of the two systems. Connecting these systems to the computer will allow us to better quantify the amount of power we are producing, and help identify areas of improvement.