Battery pack Tetris

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reikiman's picture
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Joined: Sunday, November 19, 2006 - 17:52
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Battery pack Tetris

Following up on two prior postings... My latest e-bicycle build, and My headway LiFePO4 cells keep dying

I ordered a couple more cells to fill the pack out to 48 volts 20 AH and have assembled the pack. Looking for a way to encase the pack protecting it from the weather I've decided on this "Dry Sack" product sold by Topeak. It fits on their MTX racks and has the desirable feature of being large inside, large enough to hold this pack. On the other hand it's easily removable and a thief might make off with the pack. On the other hand easy removability means it can be taken inside easily for indoor charging (like, at the office) ... Plus, on my other bicycle over a year of experience and no thefts with a pack held in a different MTX bag.

Anyway .. due to the size of their Dry Sack it led to a strange geometry conundrum. What fits into the bag best is rows of cells, 7 cells long. But the pack is 16 pairs of cells which would normally be 8 cells per row. That led to having two cell pairs left over and... well ...



The dry sack is in the background. In the foreground is the BMS I got from .. the orange bits are from batteryspace.

The plan is to put the pack into the bag - and I have an MTX rack that is already hacked up and can be bolted onto the bike (haven't chosen a location yet).

After assembling - well - tetris - needisaymore?

BMS is not wired up yet. There are 16 wires in the harness you see - the obvious wiring thing would be one wire per cell pair. The BMS doesn't have a heat sink but there are a series of 16 resistors on the inside.

Photo on 2010-03-14 at 11.56.jpg

That's the innards of the BMS - very simple, a set of chips with three pins each but only two connected, 12 of them. On the other board 16 resistors and a layer of epoxy spread over the board. The boards are very sturdy and the whole thing is very well assembled.

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