A few days ago I got all of the cells in balance, every single cell reading the same 2.75 volts. So today when I finally started joining them in series as a pack. In these few days they had all crept to 2.76 volts, but I called this “close enough” and started attaching them together. The whole pack measured exactly 69 Volts (2.76 volts per cell again). Good enough. As you can see I’ve decided to make two separate packs. The bigger pack, measuring 35cm from aft to front, will be inserted below gas tank, inside a fabricated battery box. And the smaller one will be inserted in front of the motor (the motor will be placed where the old gear box used to be), both just below the bigger pack.
The beauty of bottom-balancing – no spaghetti BMS wire mess!
Then the wires for the charger were attached to the pack and the first charging started. In just a few minutes the voltages had gone up some 6 volts (at first the battery voltage climbs the steep curve’s end from “empty” to more operational voltages) and it just kept on going up. In the end, after some 8 hours (with the 6A current), the charger should end up with 87.6V for the whole pack (which would make 3.5V per cell). I left the charger doing it’s thing for the night, so it will be interesting to see tomorrow how the individual cells measure. I’m hoping they will end up pretty close to each other, around the 3.5V, so that there would not be too much deviation.
Here’s some insulated tools I used for the battery connections, wrapping some heat shrink tube on the handles (didn’t want to cause any unneccessary sparks). For the pack connectors I used ones for 40Ah to connect them sideways and the ones for 60Ah (a bit longer) to cover the end to end connections. They’re just the perfect fit.
Update 29/06/2013: The pack is charged full and everything went fine. Charger works as it should. The whole pack measures 83.6V and individual cells are all at 3.33-3.35V. So very minimal deviation. Fabulous!