first time building a tab welded 18650 battery any advice?

[phillmoorewot]

First off sorry for the long message but I'd like to give a massive thanks to everyone on the sphere and the facebook group :wink: I've learnt so much and continue to learn more everyday plus all the banter is absolutely brilliant and I wouldn't be where I am with my ebike an electronics/battery knowledge without the sphere and the people within it

Recently I repaired a few ebike's for a friend of my missus who turned out to be a ceo of an electric trials bike Company and was rather impressed by my work so he asked me if I had a project thread to show what else I've done...after talking and showing him my projects I've documented so far he offered me a part time job

After helping out here an there he's tasked me with refurbing 2 battery packs of tab welded 18650 cells with bms's into 1 fully working pack with a new bms...now I've never tab welded before but I've built a few packs of lipos, sla's etc with and without bms's an I feel I'll be confident enough to be able to refurb the battery as I've seen a lot of people documenting their battery builds an I have an idea of where to start and what I'll need to do but I also know I'll need to step my game up and it's gonna challenge me but tbh I'm really looking forward to it so any advice or tips would be highly appreciated

The Plan

I'm thinking I'll need to strip the pack down to separate cells as the parallel strings are unbalanced an I suspect a few dead/dying cells may be to blame (I've asked but they have no idea when the battery's were last charged or used)

Then identify which cells are good an which are bad/dying and match up the useful cells into groups to see what I've got to build with

Then start working out what size, configuration an shape I'm building the pack

Workout any parts I'll need and order them like nickel strips etc

Double check I've got everything worked out an test my tab welding on the unused cells first or just plain metal

Then when I'm happy I'll start tab welding parallels first then series while adding the balance leads of the bms etc as I go until I've built the pack

I have no time limit on this as the packs were gonna be thrown if I can't fix them so that helps a lot but I'd like to get it done in a respectable time to a high enough standard to show what I'm capable of and hopefully secure my foot in the door of a job I'd love to do for a living

Thanks in advance for any advice, ideas , opinions or links

 

[Wheazel]

Your workflow plan seems sound, but its not the only alternative.
How are you keeping the cells together and how are you packaging them?

When I built my most recent pack from 18sx26p 18650 cells, I used nickel strip that was wide to span over 2rows of cells and stamped to fit the 18650 holders I had bought.
Thus making both the parallell and series connections with the same strip. This saved me alot of time compared to cutting all small nickel parts individualy.
The only unforssen obstacle was that I had to stretch the tabs slightly to make them fit over long rows of cells. (made a simple jig for this)

I think the most timeconsuming part of your task ahead is the testing of the cells.
How many cells are we talking really?

 

[dnmun]

do not assume. you should test the cell groups that are present now to evaluate their capacity and internal resistance before proceeding. do not tear them apart.

there are no pictures so no idea of what you have.

 

[phillmoorewot]

Your workflow plan seems sound, but its not the only alternative.
How are you keeping the cells together and how are you packaging them?

When I built my most recent pack from 18sx26p 18650 cells, I used nickel strip that was wide to span over 2rows of cells and stamped to fit the 18650 holders I had bought.
Thus making both the parallell and series connections with the same strip. This saved me alot of time compared to cutting all small nickel parts individualy.
The only unforssen obstacle was that I had to stretch the tabs slightly to make them fit over long rows of cells. (made a simple jig for this)

I think the most timeconsuming part of your task ahead is the testing of the cells.
How many cells are we talking really?

Cheers Wheazel and I didn't make the pack but its made up of 16sx7p with packing foam and pieces of pcb board by the looks of it , I need to measure the bike it'll be going on before i choose what size/shape it'll be then work out how im going to connect everything but thanks for the heads up on how i could do it :wink:

 

[phillmoorewot]

do not assume. you should test the cell groups that are present now to evaluate their capacity and internal resistance before proceeding. do not tear them apart.

there are no pictures so no idea of what you have.

that dnmun is exactly why I have left the pack whole til I got a more experienced opinion from the sphere to make sure I do it right so thank you , i'll start with testing the groups first and i'll post some pictures in moment so you can see what I've got to work with

 

[phillmoorewot]