DIY Li-Ion Battery pack

EFOIL.builders Electronics (ESC, remote, batteries)
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Hi,

I currently start to build a “foil-assist” powered build for my wingfoiling gear.

In this topic, I share what I done and looking for battery assembly advice.

I choose the 21700 Samsung INR21700-40T (40T3) 4000mAh - 35A (Samsung INR21700-40T (40T3) 4000mAh - 35A - 21700 & 20700 - Li-ion - Piles rechargeables | NKON)

I build a total of 12S8P compose of 2 x 6S8P for better waterproof case organization and the possibility to use my trusted SkyRC RC-Charger (I use it for all my Drone and RC planes without any issues and perfect balance)

I design custom organizer for 21700. Probably not the best - I could have done a better job but will improve it over next iteration.

[place for photos]

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I choose nickel strip 0.20 x 10mm (Amazon.fr)

I use this (expensive on amazon.fr 150€ but 80€ on aliexpress) welder solder that is absolutely perfect
https://www.amazon.fr/dp/B0BTHQ46FS?psc=1&ref=ppx_yo2ov_dt_b_product_details

I have build 2 pack like this one (6s8p)

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[another post for Photos and thingiverse link]

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I would like some advice for soldering the “drain” battery wire. I plan to use AWG 8 but I am not sur how to solder it. I have the idea to solder AWG 8 on another nickel strip on ‘+’ pole and ‘-’ pole.
AWG 8 will be the same length than 8p (so approximate 18cm).

I have copper strip (https://fr.aliexpress.com/item/1005004719059885.html?spm=a2g0o.order_list.order_list_main.20.4ba75e5bDjNUL4&gatewayAdapt=glo2fra the 31mm version) I could use to make connection to assembled pack.

Good or bad idea ? Any advice really appreciate. thanks!

battery
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red and blue: AWG 8 wire soldered on copper strip (step 1)
yellow: copper strip 0.2mm (2p cut in center - welder spot (step 2)

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See the link below how I built my batteries. Built two, the first one I spotwelded the terminal nickel strips first and soldered afterwards. The method for the 2nd one is better, I first soldered 8 AWG to a nickel strip and then spotwelded it to the cels. Less thermal stress.

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super Daniel ! Your advice is exactly what I have in my head. thanks !

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Sorry Daniel @sat_be I forgot to ask where did you find thermoretractable film. My last idea was to use laminate I use on my RC plane wings but perhaps your source is better. :nerd_face:

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From Ali, width 230 is good for 6S, 21700 with my spacers:
Just found this amazing item on AliExpress. Check it out! US $0.68 15％ Off | 1 Meter 18650 Lipo Battery PVC Heat Shrink Tube Pack 85mm ~ 400mm Width Insulated Film Wrap lithium Case Cable Sleeve Blue
https://a.aliexpress.com/_mPosPEW

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