Generator (V1)
Motivated by riding my bike to/from work, I am building a generator for my Bike Light. I’ve been riding with a brick of a lead-acid battery hanging from the frame for long enough. Besides, I need a new project.
A while back, a piece of expensive equipment blew up at work and was not fixable. So I tore it apart and got all the good stuff out of it, which included a number of really nice Pittman gearhead motors. A DC motor will generate electricity if you spin it. So I figured it might work to power my 12 volt Bike Light. I made some assumptions about the performance of the motor:
- The motor’s maximum output should be similar to its current draw if stalled at its rated voltage.
- The motor’s optimum output should be similar to its current draw with a light load at its rated voltage.
It’s a 24 Volt DC motor and it draws about 1.2 Amps when I stall it with a pair of Vise Grips. So I expected around 25 Watts of output. After more testing than I really had patience for, I mapped out the output efficiency of the generator up to the maximum speed of my power drill which was about 20 MPH. I was elated to discover my generator produces roughly 10 Watts @ 10 MPH and 20 Watts @ 17 MPH!
In my typical fashion, I built the unit out of aluminum and pop-rivets. It attaches to the crown of the bike’s forks by a sandwich plate and bolts. I accomodated the cantilever brakes by extending a single beam from the mounting plate and expanding from that. The construction is surprisingly rigid. The down-force of the generator to the front wheel is adjusted from the bolts in the mounting plates. As an after-thought, I mounted the lights to the generator to see what an all-in-one design might resemble.
Version 1 works pretty well. At around 10 MPH, the 10 Watt bulb is at full brightness. Above that, I manually switch to the 20 Watt bulb. This is a pain to keep track of when I’m riding and I sometimes just leave one of them on all the time and ride appropriately. Also, I regularly ride at 25-40 MPH (lots of big hills in my area) and I’m afraid of burning out the bulbs at higher speeds.