On 17/02/13 12:34, John Rumm wrote:
On 17/02/2013 06:31, The Natural Philosopher wrote:
On 17/02/13 02:51, John Rumm wrote:
On 17/02/2013 00:25, Grimly Curmudgeon wrote:

http://www.upworthy.com/see-the-scie...-battery-l?g=2




Dribble as usual was extrapolating too far without actually thinking
through the implications.

While a high capacity super cap would be good new for all sorts of
electronic gadgets, it would simply bring a different problem should you
apply it to (longer range) transport.

If you have a 50kWh battery and want to charge it, what charge rate do
you need to use to charge it in a minute (or even ten)?



(there are actually some even more interesting developments using hybrid
LiPoly batteries with carbon nano tubes to increase capacity)


NOT to increase capacity. To decrease internal resistance. faster
charging, no more miles per charge.

That statement seems mutually contradictory...

Even just a reduction in internal resistance would make more of the
stored energy usefully available, and result in less dissipation in the
cell itself.


Not significantly. WE get about 20% capacity loss from the 10 hour rate
with models draining them in 5-10 minutes. travelling for a couple of
*hours* they are already as good as they need to be.

The key things is *recharge* losses when being banged full of electrons
in a hurry. They get hot and that's where you lose power and edge up
towards 'unsafe'..

realistically a safe if not especially efficient charge is 20 minutes or
so on existing technology.

I've seen prototypes quotes as being safe for 5 minutes.


However what I was reading also suggested an increase in capacity as well:

http://www.scientificamerican.com/ar...ithium-battery



Boost of power is not boost of capacity.

As I said, power is not that hard. model aircraft batteries are edging
towards at 3 minute discharge times something like a horsepower per
pound weight, or more.

giving an overall performance level with airframe and motors stuff of
around 500bhp-800bhp per tonne. Which is formula one (fuelled up)
levels of performance. The problem is that its a wild ride, but it only
lasts a couple of minutes.







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