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Thread: Question on 18650 Battery Connections

              
   
   
  1. #1
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    Question on 18650 Battery Connections

    Hi all,

    I am building a bike drive system using LiMn 18650 cells. Does anyone have any recommendations on how to make high-amperage series and parallel connections?

    I am building a 72V system, so 20 cells in series. To keep the number of cells down, I wanted to try and use high-drain cells. With 200 cells with 20 in series, I can make parallel packs of 10 cells. Each cell is rated at 35A draw, and I want peak draw on the whole battery to be 200A, therefore I only have 20A PEAK draw on each cell, which should extend the life of the cells.

    However, 20A is a lot of draw for the connections between cells, and I have very little intuition as to what is necessary. I have no spot welder but I can solder.

    Thanks

  2. #2
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    I planning to build a similar battery pack for my e-bike project. Here is some information a had from many research:

    First don't solder, you will damage the cells.. you risk to add resistance in cells and risk to heat more with the current and lose a bit of capacity. Anode (-) is the side that you risk to damage. Many guys do it, but mostly with savage cell for low power use. (like home power wall)

    For the connection, the two main choice i found in forum. 1- nickel tab in multiple layer in the serie connection and make sure to be balance be the current flowing rought.
    2- Tesla style, a busbar between each series with single wire fuse by cell. Nice setup, but need more work and testing for gaging the size of the wire fuse..

    If you found more option, please share, i will follow this tread

    whitch cells are you planning to use? For my project i'm looking mostly samsumg 30q or sony vtc6

  3. #3
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    AQ above is correct, if you try to solder the cells directly you will do them damage - if your cells aren't tabbed then you'll need to make, acquire or otherwise gain access to a tab welder.
    However if you've got tabbed cells then you can solder away to your hearts content. The tabs will take 20A for a short period happily enough.

    In between the cells then precisely how you hookup will come down to the geometry of your pack, but suffice to say don't forget to link all of the tabs coming into and out of any parallels with an appropriate guage wire (only has to handle an amp or so, nothing like the main bus load).

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