My 4s6p A123 M1 car starter battery

[wb9k]

Thanks for pointing that out, because humid salt air soaking into the paper never crossed my mind. I still have lots of cells with the paper wrappers. If I was building for marine use, which would you suggest, painting the paper, or duct tape (or similar) as extra insulation between each series level, or both?

I've seen these things get salty and gone looking for this issue and always come up empty, but I was told this risk was demonstrated in a lab well before my time. I believe it's one of the main reasons they went to the PET sleeve. I don't want to overstate the risk here because my experience has shown me it's pretty darn low, but you don't want salt crusting up on the aluminum cans no matter what is wrapped around them, so the issue transcends the wrapping material, IMO. For real marine use, you definitely want to keep splashes out. Salt will attack the cans. In severe cases, it could corrode through a can if given enough time.

I think what you did for the car battery is pretty good for making it splashproof. Salty splash isn't really a risk there anyway unless you're driving in a place that salts roads in the winter. Chemical splash, maybe from a car wash or some such. Anyway, the presence of salty sea air is enough to cause accelerated failures in automotive parts sometimes, even without splash. I'm sure you're aware of this and have thought about how to protect things. As far as separating cell groups in a pack, painting is an interesting idea, but I would stick with the kinds of things you would do with PET-wrapped cells--put a layer of Mylar or similar between them, or put a little physical space between them. Pay special attention to creepage distances on the negative terminal side. Negative weld strap-to-can clearances can get too small if there's a nick in the can's corner insulation. Be careful not to damage the plastic disc that surrounds the anode tab when disassembling and reassembling packs.

That should about cover it...I think...

 

[dmwahl]

How is this working ~2 years later? I need a new starter in my 4runner and was thinking about putting one together with 4S2P 15Ah BMI cells that I have sitting around.

 

[John in CR]

How is this working ~2 years later? I need a new starter in my 4runner and was thinking about putting one together with 4S2P 15Ah BMI cells that I have sitting around.

I just saw the response. Since I installed the pack you could probably count the number of times I checked balance on one hand, and that was kind of meaningless unlike lipo due to the significant surface charge voltage range of well used old A123's. Not once have I balanced the pack. The car has always started, and cranked up better than ever using a lead battery. A friend has an automotive shop and after my nearly 2 years of bragging we tested it with his big battery load tester, he was dumbfounded that he couldn't make the voltage sag below 12V.

Today I figured out a meaningful way to look at balance, and that's using a Turnigy 2-8s battery monitor and low voltage alarm with the car running with the radiator fan blowing to know it's charging. One parallel group was going up to 3.75V with the others not too far from 3.4V with the alternator pumping 14V. I figured it was finally time for a balance charge. Since that one group was full and fell back to in the 3.50's with the car off, I single cell charged the other groups to 3.65 with my handy iCharger (one of the most useful ebike tools I own. The most any of the 6p groups took to charge was 580mah, so not too bad with such old cells.

Now that I have a good balance charge, I'll run a couple of cycles with my iCharger to test capacity tonight. Overall I'm super happy with my A123 car battery, especially considering that it's made from the leftovers of less than 800 cells, of which the best 600 were picked to go in ebike packs and at least 100 were dead. Imagine the car battery I can make with my new and unused A123 AMP20 cells. 8)

 

[liveforphysics]

I used an AMP20 4s pack for a car battery in a few cars. It's critical to keep them dry, but they perform so much better than any lead acid and it weighs just a few lbs.

 

[dmwahl]

My main concern is longevity, although the cells are just sitting around unused anyway so not a huge deal if I burn them out after a few years. LFP, how long have you been using yours for?