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Old 07-27-2011, 10:44 PM   #11
Luke OP
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Joined: Aug 2004
Location: Idiotville, OR
Oddometer: 4,241
Anyway, since I have some pictures of them, let's start with the batteries.

There are a zillion different kinds available. It turns out, though, that only one type will deliver the sort of power* that I want. They are a lithium cell made by A123. They're the same one used in the electric drag race bikes, and in the lightweight replacement starter batteries. The bad news is that they are only made in a long-C cell size, not a big rectangular pack. So I would have to build a big pack out of a lot of little cells.

*Batteries are usually rated by how much energy they hold, which translates into the range of the bike. Almost as important is the amount of power they can deliver, which translates into the power of the bike.

The cells are expensive, and would be hard to pack into the available space. A little math showed that 100 cells would make a pack that would deliver most of the power that the motor could use. So I paypalled $800 to some guy on ebay and crossed my fingers.

He delivered.

And one pack is filled. It isn't wired yet. The two packs are different sizes due to the way everything mounts on the bike. This one is smaller, a grid of 9 cells in series, 5 parallel. The other is 11 series, 5 parallel.

Lithium cells require management, and I couldn't find anything off-the-shelf that I liked, so I built these:

They limit the voltage to each cell to prevent overcharging, tell the charger when each cell is nearly charged to get the charger to slow down, and tell the bike if the cell voltage gets to low so it doesn't discharge them too much.
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