fechter wrote:I think the silver plating is key here, along with adequate contact pressure. Silver maintains a nice low resistance connection even when tarnished.
The proof will be in the time slip.
rwaudio wrote:Hi Ron,
Nice to see you on this forum, I love your packs, but I have to agree with hillhater.
In my testing of A123 pouches my first design was a block between every tab in a 3P pack (I used aluminium but I'm going to peak at 1000A not 4000A, you may have seen my crappy pictures on diyelectriccar) the voltage drop was much higher than expected, the cells were doing just fine, but it was the hundreds of extra connections each one has a tiny resistance but you add them all up and it's significant.
This was a big enough problem in my testing that I redesigned my connection method. Instead of 7 blocks making up a 3P series connection, I now have 3 blocks, two of them being outside clamps and now only one block is between the series groups, the tabs in each 3P set are all sandwiched together.
I'm not saying your method won't work, it's going to work, and it's going to work pretty well, but I think it could work better. (not from theory, from testing)
I know you don't like A123 cells, but laser welding has nothing to do with the issues that hillhater is trying to point out.
When you get the car on the track make sure you have a logging method for the battery voltage, I would suggest something at the + and - battery terminals and not at the Shiva terminals (or the shiva itself) as there will be so much noise and ripple there it's hard to say how accurate the voltage reading would be. I'll bet you a cold Canadian beer that you experience higher sag at the battery terminals than you are expecting, and it won't be the fault of your cells it will be all of the series connections contributing to significant sag at peak current.
jonescg wrote:But hillhater, every cell tab will need to be connected to a bus somehow, and that connection will have the same issues you describe. Granted there will be fewer problems with the primary series circuit, it just means some cells won't be working as hard. If there is a problem this way, it will be very obvious and easily fixed. Depends on the application really. It's probably as good as you will get for this app. at least.
That's incorrect. It's not an issue of improperly welded connections between cells. The problem was with a welding machine that was used to build individual cells.EVDragRacer wrote:A123 has a 50 million dollar recall because their welding machine did not properly connect the cells, all their modules shorted out!
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