Re: SRAM or nuvinci electric pedal asssist

terryc wrote:
On Mon, 22 Dec 2008 15:01:31 +0000, Peter Cole wrote:

They claim 52 kW-h in an under 300lb device.

Sounds a bit like the molten sulphur(?) battery, aka works great if
you are talking about powering a bus and have a power source to plug
into at all other time.

Actually, the 52 kW-h pack is about identical in capacity to the Tesla's, at 1/3 the weight. It would also shorten the recharge time from hours to minutes.

The difference between ultracaps and batteries is that all batteries make use of a reversible chemical reaction. The rate of the reaction limits charge/discharge rates and makes the device sensitive to temperature effects (e.g. loss of capacity in lead-acid, thermal runaway in some lithium chemistries, etc.).

Very few predicted that capacitor storage densities would ever get high enough to challenge batteries. EEstor is claiming to eventually produce storage devices at almost 700 Wh/kg, for $40/kW-h. A 100 kW-h pack would then weigh 140kg and cost $4,000. Although that's the energy equivalent of only 3 gal of gas, the efficiency of electric motors gives at least a 4x multiplier, so that's roughly 12 gal equivalent. With a quick charging technology, electric "gas stations" could be practical, and because of their much smaller footprint and facilities, they could be more numerous.

EEstor may turn out not to live up to the hype, but the fact that ultracap devices are showing up on the consumer market (Coleman screwdriver) and that Lockheed-Martin has reviewed their technology and announced a deal seem to indicate that it's not all vaporware. Even if it falls short of being a battery killer, ultracaps will be an important technology in e-vehicles for power regulation & regenerative braking.
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