Quote:
Originally Posted by tcaud
Battery Junction is selling 3.7v Li-on batteries with 0.7ah each for about $5 apiece.
To get to Tesla level you'd need 100 of those, which would produce 70ah at 370 volts for 26khw (about 80 miles).
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You can make your pack in series or parallel, or some combination thereof.
A series string raises voltage. A parallel string raises current (amps).
If you make a string of 100 3.7v cells, you get 370 volts as you describe. This does NOT raise the amperage capacity. The resulting pack will deliver 370 volts at 0.7 amp-hours. You could ostensibly draw 0.7 amps for an hour, which would yield 0.26 kW-h. NOT the 26 kW-h you state. In order to generate sufficient power to move a car, you would have to pull power at a MUCH higher rate than that, on the order of five amps at minimum just to get the car moving. Most commercially available cells cannot sustain a draw that high for very long, and we already know what some of the risks are of overheating a Li-Ion cell. You would have to restrict its maximum draw to something less than its stated maximum in order to provide a bit of overhead for safety's sake. But all other things being equal, such a pack would provide sufficient power to move an idealized, featherweight car about three miles before gasping its last. I'm not pulling that guess out of thin air, I'm doing the math against the Delta 11 prototype in EM's own garage, consuming 95 w-h per mile - and that is a crazy good result. Compared to other, more realistic and yet still excellent cars like Planetaire's modified Prius (as little as 175 w-h/mile, an amazing result for a non-purpose built road legal car), you would get about a mile and a half (and not at any kind of high speed, either) before your batteries crapped out.
And of course, resistance being what it is, real world results will almost certainly be less. Non-idealized cars being what they are, real world results will be less again.
My dad once told me that you could start a car with a stick of flashlight batteries, but it would be the last thing those batteries ever did. The cells in EV and hybrid packs are serious, heavy duty hardware, designed with heavy load and recharge currents in mind. It doesn't matter how cheap consumer grade cells are, these are NOT consumer grade cells.
[edit]
Oops, I see others beat me to it.