John,
First off, this topic is probably more appropriate for an electric
bicycle or dc generator list/forum.
FWIW, I'm not an engineer, so this may be wildly inaccurate, but here is
what I think I know:
Multiply the efficiencies and subtract a few percent to account for
other losses to get an estimate. Assuming 80-85% efficiency for both
the generator and the motor and that the energy generated goes directly
from the generator to the motor, I would estimate that it's around
60-70% efficient (80%*80%=64%). If the generator is only 40-50%
efficient, then it would be closer to 30-40%.
Generators have a peak output within a specific range. They range
pretty much from 0-95% efficiency. If you can keep the rpm in the best
range, the efficiency will be better, but what the % curve will be is
entirely based on the generator. Staying within that optimal range may
be difficult. You will need to spec out the generator motor carefully
and may need to add gearing and a flywheel. An overrunning clutch may
be useful as well.
If the energy is stored in the battery and then used by the motor, that
adds another efficiency hit. If you are pedaling while the motor is
operating, I think most of the juice should be used directly, but don't
quote me on that.
I would try very hard to go direct drive before I even considered the
pedal powered generator option. The generator is probably more trouble
than it's worth.
Hope that helps.
Seth
john fisher wrote:
I am thinking through a high-powered 3 wheel elec-bicycle. For
packaging reasons, using the human-powered drive component through
direct drive is awkward. So what I am wondering is how much efficiency
would I give up by pedalling a generator/alternator and charging the
battery.
assuming:
the human produces about 150W steady
a few pounds of extra weight is acceptable.
the direct-drive efficiency is basically 100%
any opinions? is it a 50% loss? even greater?
John
