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Old 03-01-2012, 11:22 PM   #12 (permalink)
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Originally Posted by sendler View Post
Bigger starts to get too big and heavy to put in a car or motorcycle.
We do seem to be right on the edge of usable for automotive use.

Lead-acid has low cost for the capacity, but the weight means that you can only build a slow or short range vehicle. A 30 mile range at highway speeds means that you are at a 2C discharge rate (at best). That drives the cycle life and efficiency way down. Adding battery capacity dramatically increases weight, requiring bigger everything, eliminating much of the range gain.

Current LiFePO tempts us with a possible life of 5000 cycles, but only if we discharge at a 0.3C rate. That means a car with at least 3.3 hours of range, which means batteries are more than half the vehicle weight. Most builders compromise with a 1 hour range and a significant discharge with every drive, accepting a likely sub-500 cycle life.

A 3x increase in capacity at the same weight would be a game changer. You could put in enough capacity to not do a major discharge with a short trip, or stress the battery at highway speeds. And once a normal range battery is no longer more than half the vehicle weight, you can increase range without doubling the size of everything.

That said, I haven't seen enough details to believe that this is really a breakthrough in power density.
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