Wiring a 18650 Lithium Ion Battery Pack (12s3p)

Hi all, I am in the process of building an electric longboard & I am currently trying to create a custom lithium battery pack.

My concern/question here, is how exactly to solder/wire my battery.

I will use 36 of these cells SAMSUNG 25R 18650 20A, My pack will be 12s3p. I know that i will need a spot welder, and my highschool has one so that is no problem, but I just dont know which joints to spot weld together and what material to use to do that. I also wanted to maybe add a switch, a battery monitor, a charge port and an XT90 end connector to my battery. Im trying to keep under $250 for it but if i go over its fine.

I will include a picture of a diagram and general information to show exactly what i want to do and in which manner i want to lay out my cells.

Any suggestions or comments on what I am doing would be super helpful thanks!

Use the search function these are easily answered questions, also not sure what highschool has a battery spotwelder so make sure it’s the proper spotwelder for these type of batteries otherwise you will cause a fire

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You want the whole board under $250 or just the battery?

I’m all for DIY and learning but topics like this give me a cold sweat. The first pack you ever make shouldn’t be one you ride, it’s the one you learn how to make a pack on atleast.

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To start you want all of your batteries and pure nickel strips, using your spot welder, because it is 12s3p you need to wire up 12 sets of 3 batteries with nickel strips on both sides across the three batteries with batteries in the same direction on all batteries in one pack. Next, you take the twelve sets and alternate the directions of the poles and wire up the twelve packs in series using the nickel strips again. this will wire the 12 packs in 12s3p like you want. you then want to wire up your BMS or Batter Management System. doing this you will end up with a positive and negative wire. You can connect the xt90 connector to those wires. there are some really good videos on youtube from ebikeschool.com the link for the first video is here I would watch the entire series also linked is a guide on what nickel strips to used. Link for first part: https://www.youtube.com/watch?v=b3eRv_FZjBc link for nickel strips: https://www.youtube.com/watch?v=wdZ_Ca_sAZE . Enjoy