On Friday last week, a fellow Spitfire converter helped me pick up the next big change for my EV. $7200 in lithium batteries.
I bought them from CALB’s warehouse in Pomona, CA. They’re close enough that I could drive over with my helpful friend and pick ’em up. This also means that if I find something wrong with them I can more easily get service. Well, I’ll at least have someone I can yell at.
Last night, another friend stayed late with me after work and helped me set up the batteries for testing. He set me up with a battery management solution and helped me wire everything up. We hooked it up to our in-house testing equipment and started the first charge.
Connecting all of those wires is quite a bit of work. It’s also a bit dangerous, as one slip of the ratchet could turn the batteries into a ball of plasma. We wrapped our metal tools in electrical tape for good luck.
Once we debugged our monitoring software we started a 10A charge. Things were going pretty smoothly, so we stepped it up to a 50A charge. We took the time to feel the heat of our connections to make sure things were properly hooked up. Sure enough, many of the connections were getting warm, but only on the positive side. The way the batteries are constructed, the positive terminal is aluminum and the negative terminal is copper. Aluminum isn’t a horrible conductor, but Aluminum Oxide is a disaster. The tiny bit of Al2O3 that forms a layer on the metal is enough to create a resistive barrier. It’s just milliohms, but that’s enough to heat up the connectors on a modest current draw. Luckily, we found that it’s relatively easy to sand off. A great lesson to learn before installing the batteries into the car. We’ll also apply a product called Noalox to the terminals, which prevents further corrosion.
Full testing will begin on Sunday. We’ll exercise the batteries and determine their true capacity and internal resistance. I can’t wait to drop them into my little car!