Re: SRAM or nuvinci electric pedal asssist

carlfogel@xxxxxxxxxxx wrote:
On Dec 22, 8:01 am, Peter Cole <peter_c...@xxxxxxxxxxx> wrote:

Ryan Cousineau wrote:

In article <941c1$494a0057$506dc728$4...@xxxxxxxxxxxxxx>,
"G.fried" <radle...@xxxxxxxxxxx> wrote:

Hello,

is there something evolving wih regards to the combination of internally
geared hubs and electric propulsion?
- more power?
- xtra durability?

electric-assist bicycle power is limited, as far as I can tell, by
battery capacity and local laws. The batteries are still getting better.

Batteries may have been just obsoleted. EEstore just received a patent
for their ultracapacitor technology. They claim 52 kW-h in an under
300lb device. That's 10x and 3x the energy/weight density of lead-acid
and lithium respectively. The other things that characterize this
technology is non-toxic & non-explosive chemistry, unlimited recharge
cycles and virtually instantaneous recharge time. If these devices are
for real, they'll completely change the game.

http://www.pat2pdf.org/patents/pat7466536.pdf

Ultracaps have been progressing rapidly. Last year the first commercial
battery replacing product I know of was introduced -- an electric
screwdriver. The bad news was that it could only do 22 screws on a
charge, the good news was a charge takes 90 seconds.

http://www.colemanflashcellscrewdriver.com/


Dear Peter,

Speaking of completely changing the game, how many kilowatt-hours are
there in a gallon of gas (~7 lbs) that takes less than five minutes to
put in the tank?

:-)

"A gallon of gas weighs about 6.3 pounds and produces roughly 35
kilowatt hours of energy."
http://www.american.com/archive/2008/november-december-magazine/why-gasoline-is-still-king

Cheers,

Carl Fogel

Even though that article mentions that almost 80% of the heat energy of gasoline is lost in conversion to mechanical power in a car, it then ignores that, and compares it directly to electrical energy in a battery, which can be converted at relatively high efficiency to mechanical energy by a motor and its drive electronics. The 35 kwh in the article is slightly more than the 117,000 BTU mentioned earlier in the same article, which they say is before the almost 80% wasted.

Gas is still a high-density way to store energy, but their math or thermodynamics is flaky, and their energy-density comparison wrong by a factor of roughly 3.

Dave Lehnen

.

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