noob question- BMS for charge as balance/not discharge

Spamh8r

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May 19, 2022
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Hi all, I've been reading for hours, and I've found a number of answers to questions I have had, and read a bunch of messages about similar things I want to ask, and even searched some but nothing quite like what I was hoping for, so here goes:

I purchased 4 used battery packs which are 36V nominal, 21Ah 10s x 6p, 748Wh each. LG cells rated at up to 10A discharge, and they've all charged and balanced very well. These are extremely well made and have a charge port with an XT30 connector, and a discharge port with an XT60 connector. The BMS on these is 'locked out' because these are supposed to communicate via CAN with a dashboard unit I don't have, so I've bypassed the BMS for discharge. Now I was thinking that I could probably parallel them easily enough with something like the product linked below, which probably results in some losses, but is using a MOSFET I presume to watch draw on both packs in order to keep them at the same level:

https://www.amazon.com/CONHIS-MOTOR...&pd_rd_wg=FNYtN&pd_rd_i=B099F2QGTF&th=1&psc=1

I believe that this would allow me to charge them individually while connected through the device above through the XT30 as long as power wasn't on- does that make sense?

Next, what I'd really like to do though is to set these up in 2s 2p for 42Ah and 72V. Perhaps there's something like that available for running packs in series? Or maybe this as simple as creating a series connection between two of these. I know it's probably a bad idea-- but I've already bypassed the BMS on discharge, and I plan on setting the current well below the cell max, as well as not abusing it on discharge. I'm looking at the Flipsky 75100 for a controller which is limited to 100Amp draw.

I know I'd be better off removing the BMS, installing a 20s BMS and repackaging the batteries, but the whole thing is so nicely put together and the quality of the board is obvious, I'd rather trust this BMS for charging than getting some junk. I know it does work in series, because there's at least one person who has a video of it on YouTube. I guess I'm trying to justify a charger and BMS and rewiring vs, letting them do their thing. Should someone talk me out of it? Probably...
 
Spamh8r said:
I purchased 4 used battery packs which are 36V nominal, 21Ah 10s x 6p, 748Wh each. LG cells rated at up to 10A discharge, and they've all charged and balanced very well.
Maybe your "Spam" name is why no one has responded yet or maybe you live in Austin, MN ... home of SPAM. Anyhow, i'll bite :wink: hopefully others can follow with some meaningful meat.

Have you checked the voltage of each of the ten p-groups of each of the 4 used 10s6p battery packs via the BMS leads? Until then don't assume they are ... "balanced very well".

Not a good idea to leave them sitting for any length of time (days) FULLY charged. Best not to charge more than 90% (41.0V - 82V in series) before powering your e-bike or whatever.
Spamh8r said:
... maybe this as simple as creating a series connection between two of these.
You could first make up the four into two paralleled (2 Packs) into one battery (10s-12p). Then connect these 2 combined packs into one large series battery (20s-12p).

Being they are used packs you need to FIRST check the voltage of all 40 p-groups via the BMS wire leads. Until then you can't assume they are "balanced very well". My guess off-hand (to be on the safe side) is that 1 or 2 of the p-groups in at least two of the four 10s6p USED batteries are sub-par. If so you may want to use just the two best 10s6p and wire them in series (20s-6p).

If i may ask what are you planning to power with a 20s battery (possibly 4 combined 10s6p) ?
 
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