I’m trying to build a battery pack, 5S3P. The holes in the BMS for the B+ and B- connections are about 15 mm wide. I’m trying to do a 30 A continuous pack. How can I build this pack using nickel strip? What dimensions do I use for the strips? I’m mostly worried about the B+ and B- connections. Since I’m limited to one cell wide strip of at most 21 mm, sine 21700 cells are 21 mm wide. Need some sort of air gap, so really the most wide I can do 15 mm, and stack as many layers as possible of 15 mm wide pure nickel strip. But how do I know how many layers to stack that can support 30 A continuous? I’m using 21700 cells.
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Hi yes, but how but there’s not a nickel strip that is less than 21 mm wide (likely need something a few mm less than this to have some sort of air gap), that can carry 30 A continuous on this table. So what is a guy supposed to do?
Thanks for any help!
can you post pics or a diagram of the layout you’re trying to achieve.
coiuld be just me but, I’m having trouble picturing what you’re trying to achieve.
are you trying to use nickel for the series connections? for the BMS connection?
you can use wire instead. (particularly if you’re talking the bms connection a nickel connection would be a less usual choice )
stacking nickel for more current is not a common practice anymore either, can do it. but wire might do you better.
Thanks for the help!
Something similar to a power tool battery pack. Except 5S3P instead of 5S2P (as shown in the picture). I’m thinking you might be onto something. For the B+ and B- connections that I want to withstand 30 A continuous, I might want to use copper. Soldering copper wire to nickel strip, and then using the copper wire to the BMS?
Is there ampacity tables for copper strip?
we mostly use coper wire and nickel strip.
coper strip is impossible to spot weld in a DIY sense.
some are playing with nickel plated coper strips. but it’s much less common.
I suggest use nickel to join the pgropus. ideally one big piece of nickel. use coper wire to join th series group and make final attachments. if you can scratch up and “pre-tin” the nickel with solder before you attach it. (avoids heating/damaging cells from soldering heat )
check out the battery builders club thread. It’s giant. so follow it and read the latest. but also jump back randomly some time and read peoples builds and the in particular the critques on them. post your own progress.
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For mass production, or a one-off DIY build?
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Hey thanks. It seems like most power tool battery packs do not have space to attach copper wires. The box is not wide enough, but I can give it a try. Would also need some thick gauge cable. The holes in the BMS are not circular, and intended to be attached to with a strip. It’s a rectangular hole in the BMS for a strip, as opposed to a circular hole for a copper wire. I can give it a try though.
I’m thinking the only way to get a high output power tool battery pack is to use copper strip.
Is there an ampacity table for copper strip I could reference?
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Thanks for the table by the way. What temperatures correspond to the green, yellow, and red colors by the way?
You can get custom shapes of copper strip with nickel windows on AliExpress
You can weld copper if u add a bit of steel or nickel on top to increase resistance and a long thread about it on endless-sphere.
You could extrapolate the current-handling ability of copper based on charts using nickel. Capacity charts can’t be looked at as definite and conditions vary
Have you used these strips before?
This is my reference chart. In the past I have built quite a lot of 21700 power tool battery’s. All with 15mmx0,2mm on positive and negative terminal.
Should be sufficient for 30A continues.
In my experience the do not get hot at that load.
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how do you get from the battery pack array to the BMS? Most power tool BMS only has small hole meant for strip not wire, and it seems like most of these holes are 10 mm wide and not 15 mm wide.
Are you literally repacking a power tool battery?
If you’ve got some copper sheet, you could probably cut it up into chosen shape and solder it onto the nickel.
I kept the lid to my old hot water header tank for this reason after I replumbed. I had a rose bush growing in the tank, until someone come up my driveway and stole the tank but left the rosebush. Now I have an electric gate to help keep the skateboards in, and the munters out.
if the slot in the pcb is to narrow for my liking i double it up with another sheet of nickle from the outside. Not as Clean but it works. if you only pull 30A you might get away with a singel layer of 10mmx0.2mm
Are these copper strips cheaper than buying a spot welder than can spot weld copper?
Yes I am, yea i feel like power tool battery packs are not meant to have copper wire going to the cell array, at least for the B+ and B- connections, not enough space in the pack.
That’s what I’m thinking. But at the same time I’m thinking for the 12 V tools (3 cells) that have a very limited BMS, that essentially allow as much current as the cells want to put out, if you used tabless cells that can output 70 A continuous, at some point nickel will no longer be good enough?
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