A quick, ugly "pedal generator" made from an old
3 speed bicycle.
This is a brief page about a simple pedal bike we made
from a 3 speed bicycle. Although none of us really cares to "pedal"
for power, we thought it would be interesting to see just how much power
could be generated this way. It also served to test a low rpm alternator
we built from a single phase 1/2hp induction motor. Although most
folks who live off the power grid probably get plenty of exercise doing
other things, this could provide significant power if used daily.
We built this in about 1 hour, if a person actually had a need, it would
be well worth taking a little more time, and making certain improvements
to the design. The two things are necessary to build one, a
bike, and a low rpm generator/alternator. We used an old 3 speed,
although the gears on a 10 speed might be more appropriate. We removed
the back wheel, and took the sprocket off it.
The sprocket was welded to a hub which fit the shaft
of the generator. A design improvement would probably be to have
a flywheel on the same shaft as the generator. The generator fit
into a bracket which we welded near the back of the bike(approx where the
rear wheel was). We welded "feet" together out of some re-bar left
over from a concrete project. Another design improvement would be
more rigid feet. The feet were welded to the back of the bike so
that it was level, and high enough off the ground to operate. I'll
have to admit...it's kind of wobbly and a little bit scary when pedaled
at full speed. Better feet, and a flywheel at the generator would
help a bunch. Another improvement would be a higher gear ratio.
The gears from a 10 speed would be excellent, at least with the alternator
we used. The generator, is actually an alternator we built from a
1/2hp furnace blower motor. The lower the rpm for this type of motor,
the more poles, so that it generates at lower rpm.
This was a 1200 rpm 6 pole motor. We removed the
armature and cut a slot into which we inserted 6 surplus computer hard
drive magnets, with alternating poles facing outwards. Although the
magnets were not a perfect fit for arc, and diameter, they were more than
close enough. The
gaps between the magnets were evened up by sliding the magnets, fitting
feeler gauges between them, and then using "super glue" to hold them in
place. The magnets are a light press fit into the slot cut.
We then put the armature back into the motor, and it becomes an effective
low rpm alternator. Alternating Current(AC) is rectified into Direct
Current(DC) using a bridge rectifier (4 diodes). Although I have
not tested this alternator for exact speed vs output information, it seems
to start charging 12 volts at approx 80 rpm. When coupled to the
bike, I was able to generate 5 amps(60 watts) in a leisurely way, and if
I pedaled as fast as I could, I'd get about 10 amps(120 watts). This
seems to be in line with claims we've seen for other peoples plans, although
it seems clear that with a higher gear ratio, one could generate significantly
more with this alternator.
In summary, again...none of us really feels the need,
or want to pedal for electricity, which is why we didn't invest a great
deal of time here. Seems like, with a few improvements to
the bike, and a 1 hour workout daily, one could produce easily 100 watt
hours per day, which is significant, and might actually be practical for
some folks who have small power systems. Especially when one considers
the efficiency of new light bulbs and LED's, a daily 1 hour workout could
easily provide lights, and radio for a small, simple power system.
With the use of a welder and a hack saw, it took about 1 hour to make our
bike. The generator took another hour, of course, it required use
of a metal lathe.
©2000 by OTHERPOWER