My gf's car car battery died a couple weeks back and as I was replacing it, I thought there MUST be a better alternative to a heavy lead/acid battery. These things are heavy and large!
Soooo, what about A123 cells? They are very robust and the voltage and current characteristics make them ideal IMO.
To get the needed voltage, a 4s pack is required. Then, to get the starting current required for a car on a cold day, I figure an 11p arrangement would suffice. Yeah, a 4s11p pack - a bit pricey compared to a standard battery. But let's forget that for now.
A 4s11p pack would be:
- Dimensions: 4.25" X 11.69" X 2.5"
- Weight: 7.28lbs without bus bars/wires/etc.
- Capacity: 25.3Ah
- At 30c, that's 759A. At 60c burst, that's 1518A.
This is how I figured it could be wired up (I know there's a problem with the wiring, but you get the idea):
- "Alt" is the alternator. Since 4s is 14.4v @ 3.6v/cell, might have to bump the output to 15v for proper charge operation.
- "Load" is the starter and other car electronics.
- The charger would have to be a special unit that auto powers up and is pre-set to do a CC/CV charge at ~40A.
- The diode would have to be quite large to handle ~100A, but certainly do-able. This prevents the battery from back-feeding into the charger when the car (and alternator) is off. The ~0.7v drop would also keep the alternator voltage (bumped to 15v) closer to the 14.4v rating that today's vehicles use.
However, even at $100 for a 10 cell DeWalt pack on eBay, this would be an expensive car battery at $500 plus the charger, diode, etc! Too bad A123 didn't have larger capacity cells since so many are needed to get the Ah rating a car should have.
Anyway, just a fun thought...