I have a battery pack from a BH Atom X.

I have a battery pack from a BH Atom X. The electronics failed so I ripped into it. It's a 55 x 16500-35E cell pack with a charge of 44.5V (39.6V, 700WAh) 11x5. Kinda like 36V pack that goes to 11.

The pack, if I decide not to rip it apart and make a 48V pack, will drive a 36V Bafang hub motor. I suppose I may end up with controller issues if run at 39.6V but I'll cross that bridge if I need to.

Am I correct to asume, if I buy a 36V BMS throw it on and use a standard 36V charger (42V) I'll end up with about 620Wh 36V battery that only ever charges to about 89% capacity giving it a long life?

Or.

Find a charger and BMS that will use the potential and make the bike go to 11. How hard would it be to find a 39.6 BMS?

Just a note, I moved this post out of the RC Lipo pack tip thread because you don't seem to be talking about an RC Lipo pack. If you don't like the thread title, just edit the subject line of your post above.

BCBeaver said:

I have a battery pack from a BH Atom X. The electronics failed so I ripped into it. It's a 55 x 16500-35E cell pack

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Is 16500 supposed to be 18650? Or maybe 21700?

with a charge of 44.5V (39.6V, 700WAh) 11x5. Kinda like 36V pack that goes to 11.

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Does "11x5" mean 11 seriesed groups of 5 parallel cells?

Am I correct to asume, if I buy a 36V BMS throw it on and use a standard 36V charger (42V) I'll end up with about 620Wh 36V battery that only ever charges to about 89% capacity giving it a long life?

Click to expand...

A 36v BMS will only work with a pack taht is 10 cells in series (10s). If you use it with an 11s pack, then you have no monitoring or protection for the 11th cell group.

If you use a 36v BMS, you'd need to connect up only 10 of the cell groups to the BMS. If you start with the most negative cell group, then you would leave the most positive cell group's positive end not connected to any wires, including the output wire. The large main positive wire would go on the connection point between that most positive group and the next more negative one instead. Then you'd be using only the 10 cell groups, and the 11th would be unused, disconnected from the circuit, and the 10 groups would charge just like any other 36v pack with a 36v pack charger.


If you use an 11s BMS, then you could do it the way you discuss, not fully charging the cells, using a 36v pack charger.

However, unless you get a BMS that has programmable balancing points, the cells will never be balanced, so they will drift apart over time, and you'll get less and less capacity as the lower-capacity less-capable cells get lower and lower relative to the others. If they're well-matched, that won't be much of a problem, but if they're not (pretty common), it'll happen faster the less well-matched they are.

Yup, 18650 cells.
I hadn't considered the additional cell monitoring.
The pack is not like any other pack I've seen, I haven't ripped it apart so I don't know how it is physically connected. The cells are arranged end to end in 5 rows of 5 and 5 rows of 6. If it's as easy as ripping off one cell in each row of 6 to get a 10s5p pack I might just do that and give it to my daughter.
The other option is to tear it all apart and make a 13s4p pack but that will require a spot welder of some sort. I've got a wire feed welder, I could really frock things up with that.