Boston Power BMS

I'm building my first battery pack and have a few questions around BMS selection and Solar Charge Controllers

Battery Pack
I have 3 12V 280WH 23.5AH Boston Power Packs. Each of these packs comes with a proprietary system which will need to be replaced. Now my plan is to keep each of them with a separate BMS system and simply connect in parallel for charging. What would be a good fit for a BMS? I'm having trouble finding a good match for the default specs of this battery pack

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Links to Battery Info
Cell Info
Pack Info

Ok, so each pack is a 3s configuration. So it's not really 12V. Even though 4.2 * 3 = 12.6, that's not 12v setup. You have to go by nominal voltage, which is 3.65V. So, 3 * 3.65 = 10.95V

It's hard to take those and connect them up and get anything other than something good in comparison without taking the packs apart. 7s would be ideal as you'd have 24V then. Or take 12s for 36V (which would work as you could take 6 of those and connect them all together in series; really should be 13s, but 12s would work better for 36V than 3s for 12V)

Korishan said:

Ok, so each pack is a 3s configuration. So it's not really 12V. Even though 4.2 * 3 = 12.6, that's not 12v setup. You have to go by nominal voltage, which is 3.65V. So, 3 * 3.65 = 10.95V

It's hard to take those and connect them up and get anything other than something good in comparison without taking the packs apart. 7s would be ideal as you'd have 24V then. Or take 12s for 36V (which would work as you could take 6 of those and connect them all together in series; really should be 13s, but 12s would work better for 36V than 3s for 12V)

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Thanks Korishan, unfortunately that was what I was worried about. Ideally wanted to use these in their original casing....but this is all about learning for me. So I think your 7s idea makes sense. I've mocked-up what I think the battery would look like and picked out a BMS. What do you think?

Yep, both look good. Daromer did a video on that BMS (I think it was that one, they look the same).

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Korishan pid='29870' dateline='1525475335']Yep, both look good. Daromer did a video on that BMS (I think it was that one, they look the same).

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@korishan - First off thanks for your help. It took way longer than I anticipated getting the battery built but I'm finally ready to get the BMS configured and get started using. Can you take a look at my wiring diagram and let me know if this looks correct? I also bought a Digital DC Multimeter but not sure how it should be powered or wired into the battery pack. Lastly, for my input and output cables, I was planning on using 14 gage wire with XT60 connectors. Anything else I'm forgetting? Thanks again for your help, really appreciate it!
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[Edited to upload image of design]

Yep, looks good. The only addition would be your B7+...B1 connections. Each of those connect to the corresponding Pos of each series connection.

So, B1 would connect to the Pos end after your most negative end (in this case, "top" as described above), so that would be the wide blue bar between Row 1 and Row 2. And then B2 is the next, etc, etc. The B7 wire will most likely connect with the most Positive wire as well. This is common as some BMS units can handle other numbered series connection, like 4 or 5 with the same chip.

Actually, looking at your drawing, looks like you connect the Charger+ to C-. That BMS is a Pos Common, so all connections on the BMS will be negative in regards to Charge/Discharge(load) if you go through the BMS for either/or

P- -> Load Neg
C- -> Charger Neg
B- -> Battery Most Neg
B7+ ... B -> Series Connections Pos ends
Load/Charger Pos -> Connected directly to battery Pos.

That's my understanding of the drawing and looking at the BMS units you linked to above.