Re: Collected 12 kj of sweat energy the other day
- From: Doug Goncz <DGoncz@xxxxxxx>
- Date: Sat, 24 Jun 2006 21:13:52 +0000 (UTC)
I wrote:
I will try the local track on a clear day soon. We have rain all
weekend here. :(
Well, this morning was clear enough, so I went to the track, but it was
closed.
On a few small hills the stiffness of the system was impressive. By
changing by only two gears I went from pushing hard uphill to pushing
easily with little change in speed. The transition from storing to
delivering energy is seamless, as expected.
I did a test in Dr. Majweski's lab with a motor and parallel chemical
battery years ago and found the stiffness (watts per delta mph) of that
system unacceptable. Thinking it over, such a curve would have a slope
at the crossover voltage, and less extreme slopes farther from
crossover, due to I^2*R losses. I think I feel those losses.
The 8 cells are charged to 11.74 volts total with a population standard
deviation of 9.6 millivolts on individual voltages, or less than 0.01%.
That's pretty good balance, even though the balancing resistors (one
across each cell) are only 5% tolerance. That's over 20 kilojoules at
that voltage.
Assuming 0.01% standard deviation at any charge, which seems reasonable
given the circuit topology, if this pack were charged to 20 volts, the
probability of any cell exceeding the design limit of 2.7 V is around
2x10^-30. That's important.
Beyond 2.7V any cell would begin to pressurize and could vent
acetonitrile. The cells are mounted in a zippered rack bag on a rack
behind the seat so that in this event, the chance of cyanosis is
lessened.
My brother sold me his 3x7 Sachs hub so I am building a hybrid
transmission (a new wheel, the hub, cogs, and front chain rings) with
almost a decade (1000%) of range. Thanks, bro. Of interest is the
system's ability to redirect pedaling power to storage during a descent
in which the power rate is already high. The goal is to store the
energy of descent instead of warming the atmosphere behind the bicycle
with that energy. It's a large volume of air with a very small
temperature differential, but it's a lot of energy.
Doug
.
- References:
- Collected 12 kj of sweat energy the other day
- From: Doug Goncz
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