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21700 Lithium Ion battery pack build

21700 Lithium Ion battery pack build

21700 Lithium Ion battery pack build

I am currently converting a classic motorcycle to electric .
The motor is a 48v DC brushless max power 10Kw but can peak at 20Kw for 14 seconds.
I am building 4 battery packs
Each pack consists of 13 cells in series stacked 5 high and then connected in parallel.Each stack will be connected/ soldered to a copper bus bar at each end( 0.8 by 10mm ) which will in turn connect to 10mm2 copper wires running direct to the motor terminal ( no intermediate connectors ).
I am using cell holders.
I have bought a battery connector /strip welder ( Chinese from Ebay )
I bought the batteries from Frogstar along with a roll of 0.2 by 10mm nickel strip.
I also bought a lot of practice cells.

The welder will not work with the 0.2mm nickel strips ( although these are magnetic so maybe they are iron with nickel coating ).
The welder came with "nickel plated iron" strips of 0.15mm thickness which attach very well.
The cell spacers allow a max 10mm strip to be used.

My first question is whether a 0.15mm by 10mm nickel /iron strip can carry 35 amps at 48 v. I suspect they will but there must be a calculation table although I do not have the resistivity of the 0.2 by 10mm strips ( although the dont work ) but the strips supplied with the welder ( not long or wide enough at 8mm are stated as 11.5mOhm/100mm ).

Is it also advisable to use the cell protector rings at the positive end ?

I then need to move onto what load/cell balancers I need to attach to each pack and where and then get a spec for a onboard ( 3 pin plug as I understand this is the only option )charger.

Any advice appreciated.

I attach a picture of a pack but please note the cells are not in the correct orientation yet , I just needed to check the size of a pack.



RE: 21700 Lithium Ion battery pack build

Did you test the cells first? I would hate to see you weld in a bad cell.
Are you using a charge controller that allows you to measure and control each cell (or cell group) individually?

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

RE: 21700 Lithium Ion battery pack build

Is this thread in the correct area? This is not an electric anything section.

RE: 21700 Lithium Ion battery pack build

Seems you could determine resistivity by measuring resistance at several different lengths with a multimeter. Reistivity per length would be the slope of the plot of ohms vs. mm, for instance. This method would eliminate other considerations like lead and contact resistance. You might check EV fora. A lot of the EV battery information on eng-tips I've seen may not be misinformed, but it's usually not of the 'I've done the same/similar thing before, it worked and this is what I did' sort that presumably would benefit you the most.

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