Advice when constructing 18650 battery pack

Challa

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Joined
Dec 5, 2020
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2
I am building an electric longboard, I've calculated that I'll need 96 batteries, in a 12s8p configuration to deliver 80A at 44V. I have experience with LiPo batteries for UAVs, but I am not sure about batteries on this scale. I am UK based, and so far the best option seems like Sanyo NCR18650GA 10A batteries at €4.10 each.
For starters showbox.bio/ tutuapp.uno/, I saw someone getting told off for using a soldering iron when wiring cells, what is the recommended method?
Secondly, I know wiring in series without balance leads is bad, but what about parallel? And to charge this behemoth I doubt my 300w Turnigy charger will cut it.
Right now my thoughts are constructing 12 sets of 8 batteries in parallel, and making a harness for use on the skateboard, then another that connects all 12 sets in parallel for charging.
Is this right?
Thanks for any advice/help! :)
 

OffGridInTheCity

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Dec 15, 2018
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>12s8p configuration to deliver 80A at 44V.
80a @ 44v in an 8p would be 10a per cell. Cells rated for 10a.. its pushing it right to their limits and either won't quite deliver that much or will wear out quickly. I'd think in terms of using 15a cells to get 10a/cell 'actual'... but then my applications are low a/cell - so others may comment with more info that me.

Solder vs Spotweld - several threads. Here's an example - https://secondlifestorage.com/index...dering-technique-part2.9667/page-3#post-69164 You might search a bit. Many of us have soldered many many cells and its worked out OK. I use 100w iron. The general consensus is that spot-weld is preferred but you need to buy / learn to use a spot welder. Personally - I think either way is OK for your situation.

>Right now my thoughts are constructing 12 sets of 8 batteries in parallel, and making a harness for use on the skateboard,
The 12 sets (of 8 cells) would be connected in series

>then another that connects all 12 sets in parallel for charging.
This implies all 12 'packs' can be disconnected from series configuration in the skate board and then reconnected in parallel for charging up to 4.1Xv. Typically, instead of doing this, you would charge the overall battery as it is (e.g. while its connected in series) and you have a 12 BMS as or at least a hobby/balance charger with sense leads to each of the 12 packs.
 

DiggsUt

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Oct 30, 2019
Messages
64
The other problem you will face pulling so much current is if you pull hard on the pack and the voltage dips below the cutoff threshold of the BMS it will shut down and leave you stranded even though the pack may still be 75% charged. Most BMSs will not reset until they see a charge current. I've faced this several time on ebike builds where I used either a controller or BMS that allows too much current to be drawn from a pack.

@add - Ahhh, I see no reference to a BMS in the original post. My bad.... Not sure why no BMS is being used but you may want to rethink that.
 
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Overmind

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Jan 16, 2019
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412
Try putting samsungs 30Qs which are 15A; that would fix your current problem; or add more rows in parallel.
Alternately, try to find 26650s that also support higher current.
 
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