Well, as mentioned previously, I decided to go with a 12S 3P (12 cells in series and 3 of those in parallel, for 36 cells total) LiFePO4 chemistry battery, cells courtesy of an A123 donation to the MIT Electric Vehicles team. I started off just grabbing a big pile of battery cells and metering them to ensure they were at or close to their nominal 3.3V potential, then running hot glue down the sides and sticking the pack into the shape I wanted. Next, I started glomming solder down on the ends of the cells where I'd be connecting them.
|I hot glued everything down to prevent it from shifting around|
|You can see the gray wires equalizing the cells in parallel|
Half an hour later (okay, maybe a slight exaggeration...) with a small heat gun:
Only... it turns out I forgot the middle power outputs, which basically break the battery up into two separate packs that can be charged individually at half the voltage of the entire pack, enabling balancing by most hobby chargers. Oops. Time for some battery-surgery.
|Here's the heatshrink cleanly separated at the top|
Finally, I applied a new section of heatshrink, charged it up (in something on the order of 20 minutes. Turns out this ~6.6 Amp-hour pack can happily charge at 15-20A within ratings), and was possibly a bit over-eager to ride around with the extra power. The result?
|Notice how the brake no longer looks functional? Yeah, the brake was no longer functional.|
In the meantime, I actually received my slightly more powerful shady Chinese brushless motor controller in the mail, and immediately proceeded to snip off most of the useless cables on the box (powered brakes? side-lighting? Hah!), disassembled the case, and stuck a nice new coating of solder across the built-in current limiting resistor, halving its resistance and drastically increasing the output of the controller.
|Current limiting resistor circled red|
That's all for Part 1, but I'll throw in a sneak peak for next time right here:
Expect Part 2 to come in the couple weeks or so!