A123 cells for car battery??

[BrianG]

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...

[MTBikerTim]

I like it. Sucks about the cost though. I wonder if you could remake the standard dewalt A123 charger to charge the batteries.

[jhautz]

Dude!!!! Way to much time on your hands to sit around thinking about this stuff!

You crack me up man.

[glassdoctor]

That's a cool idea... I never thought about that before. I bet a couple Dewalt packs would do it. Heck.. this would be great for a race car/motorcycle, etc where the weight of a lead acid is bad...

I charge my 4s A123 pack straight off my vehicle's "12v" system... about 14.5v.

20 cells.... good for a 5p pack... I can't see how that wouldn't do a good job. Hmmm

But there is also those killer Optima batteries that would be much easier... and cheaper :) http://www.1st-optima-batteries.com They are awesome... but I have never plunked down the $150-200 to get one myself.

Brian... I can get new batteries (either ACDelco or Factory house brand) for $25-30 if you are interested I'll tell you how/where here in town.

[BrianG]

@jhautz: lol, doesn't everyone think about things like this?

@GD: Wow, yeah, my car battery is getting very weak these last few chilly mornings and was thinking about getting a new one for my Mazda 3. I'd appreciate any info you can get at that price! My g/f already got a new battery so it's too late for her.

I've used a yellow-top Optima for one of my previous cars and they work very well. They are lighter than a regular battery, but not as light as a 4s11p A123 pack. Defintely cheaper though! I liked their acid-free design and the pulse discharge characteristics... good for high-powered audio systems.

[lutach]

I was browsing youtube and cam across this video: http://www.youtube.com/watch?v=3olhJKlhOQE. Skip to the killacycle part. I also saw what looked like 2 other sizes of cells that might be good for RC.