21700 14s2p the right cell and bms config

Bejerholm

1 µW
Joined
May 12, 2022
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Wanting to build my first diy battery. My goal is a light 14s2p configuration in a saddle bag for smaller rides. My bike is fitted with a bafang bbs02b 48V 750W (newest version). The controller is rated at 25 amps I have two cells in scope:

LG INR21700-M50LT 4890mAh - 14.4A discharge

Samsung INR21700-40T (40T3) 4000mAh - 35A discharge

Price is about the same, only 0,5 euros difference per cell. LG is nice because of capacity (pack will be almost 10Ah) and would be ideal in a 3 or 4p config, but I'm not sure if I'm pushing it with the controller amps being so close to the max draw on the cells in this 2p config. Samsung cells are well proven in 2p configuration and the packs 70A max draw will be well within my needs, but capacity is 2aH less. What cell would you go with?

Also, is it enough to go with a 30A bms or should I go for 40A (only for Samsung cells)?

Thank you, let's go cycling 🚴‍♂️💨
 
Bejerholm said:
What about the bms - should i go for a 40A?
71jU7KshMUL._AC_SL1500_.jpg


40A is only 48mm wide ... only $6 more than 30A ($25 vs $19 -- Amazon)

71N+MOJzdLL._AC_SL1500_.jpg


What is perplexing is why 30A dimensions are greater than those of 40A ???
 
Thank you for your input. I have one more question. Since I'm doing a 2p config I will be pulling around 12-13 amps out of each cell at peak. I'm guessing my usual 10x0,15 nickel strip won't do the job and my spot welder wont go any higher. Can I just tack on a double layer of nickel strip, welding each layer one by one?
 
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