First up, inspecting the batteries. You can see the other half hiding behind the speakers (that I found in the trash; they work wonderfully). The 1500W+ CC/CV power supply (charger) is sitting on top of the green PVC battery enclosures. The goal of this inspection was to make sure nothing was damaged and to upgrade the sense wires to handle 26 Amps in order to fast balance.
Found this short during inspection. This line only carries voltage, but it mashed up against another cell and poked through. There were still two strands left, so I read voltages just fine.
To address this hazard, I rerouted the wires to go between the bank wires and put several layers of electrical tape at each voltage crossing. Here's the final product:
Way back when I first took the DeWalt packs apart, there were two dead cells in the lot of 200. I wanted to know how A123 makes their cells, so after sufficiently overheating the cells by charging them at 26A for a long time; they never got above 3.4 volts, which means all the energy after that was turned into heat. Eventually, the A123 cell let the magic smoke out, which for LiFe04 is a unique, distinctive smell. After letting the cell cool, I opened it up by pulling on the negative side with a vise grip until it let go. I then unwrapped the cell like you would if you froze an aluminum coke can and then peeled the aluminum off.
Observation: The positive and negative terminals are separated from the chemical substrate inside by a 1/8" air gap on either side. This leads me to believe that you can solder directly to the A123 cells without immediate risk of overheating the cell material.
It's hard to tell in the picture below, but there are actually 5 copper traces that come out of the battery on both the anode and the cathode. This is one of the major reasons why A123 cells can provide such high current throughput.
Once open, the battery easily unravels:
The copper and aluminum provide a ton of surface area for the energy storing LiFeO4 (black). The layer is uniformly thick and no more than a few sheets of paper thick. The aluminum and copper are both thinner than standard kitchen tin foil; I'd guess 1 mil max. The battery just keeps on unrolling:
Until it's about 40 inches long.
That's around 120 square inches of storage per battery
8Wh/cell/120 in sq = 66mWh/in sq
120 sq in * 192 cells on bike = 23,040 sq in = 160 sq ft
23040 sq in * 66mWh/sq in = 1520Wh nominal
Which is almost exactly the capacity of this bank... nominally. I've had problems with banks 4 and 6 dropping faster than the others, which is currently limiting me to around 1170Wh per charge. More on this on another day...
Please note that I'm wearing gloves. I hardly ever leave cautions, so heed these words well:
Lithium reacts with water (sweat) and will leave bad burns if you touch it. I learned this the hard way when I took apart a small lithium battery with a wire cutter when I was 10. It started to itch so I washed my hands... which caused the lithium to react. In short, be careful!
I'm going to start riding my regular bike more until my legs hurt, and then I'll ride this guy. I never meant for this bike to supplement true bike riding and I'm missing the joy of real cycling. I rode to work and downtown and all over the place Friday and today until I was sufficiently tired and then decided to take the electric bike downtown for the octopus project concert (which was great).
Thus far, I've been able to leave the bike locked up without people messing with it, so that's working well :).
