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!
At the moment I’m in the final stages of “bottom balancing” the pack. I’ve sucked every single cell way below 3 volts with my Graupner Ultramat 16S computerized charger and now I’ve begun the second pass, as the voltages have bounced up again as expected. But this time the time required to drop the voltages (again) is much lower than the first pass and the amp hours remaining that are drained, are very minimal. The cells are nearing empty. So it’s only the fine tuning left. The charger I’ve set to discharge with 5A current, and all the cells had pretty even 20Ah of juice in them before I started. So it took about 4 hours per cell to discharge them below targeted value. But once the charger stops, they bounce up again within next day, as “lithium ions find their places”. So I need to repeat this until all cells read pretty much the same, 2.75 volts.
So far, looking good…
Things have been on the slow side with the motorcycle lately. Lot’s of planning but not much actual progress. But that’s intentional, as I haven’t scheduled too much work in June as last friday our family became a family of four, as my lovely wife delivered a little baby boy into this world. And in the following couple weeks my priorities are clear (family, if you have to ask)… So not too many posts.
But that’s not to say there’s no progress, as today I had my last driving lessons, and in the next week I’ll have my first (and hopefully last) attempt to achieve the driver’s licence for a motorcycle. Some of the slow speed handling tasks are pretty hard, but I’m feeling quite positive. I think I’m getting the hang of it. And it’s fun! The “funny” thing is that I have to learn to shift gears etc. (the hardest part about driving a gasoline motorcycle in my opinion) which I will never have to do with my own electric motorcycle.
I also went to measure the voltages of my CALB cells. What was pretty great was that the other 24 cells all measured precisely 3.29 volts and only one had 3.28 volts (close enough!). Not bad. So not much deviation. I took one of the cells home as I want to try out my Graupner Ultramat 16 RC-charger (it has also charge/discharge programs for LiFePo4 chemistries) to discharge the cell to 2.75 volts, which is the bottom balance level I intend to aim for each cell (if you’re interested about the “bottom balancing” method you might want to check out the kwsaki blog, as Jake has written pretty good instructions there). After this they are pretty much “empty”, ie. bottom balanced. Then the pack will be joined in series and will be charged to 87.6 volts (approx. 3.5 volts per cell) which is the charger’s cutoff level.
FedEx also brought the Cycle Analyst instrumentation, which I will be using to monitor the battery pack charge level and the energy consumption in use etc. So it will be my main main instrumentation, in addition to a regular speedometer/odometer. I still haven’t decided if I’ll keep the original speedo/tachometer cluster with all the “idiot lights” or will I replace it with a simpler unit with just the basics (speedometer, odometer). We’ll see.