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5/21/2025, 6:27:17 AM
>>2918150
>With high currents the claim is blatant nonsense
Do the math. A 2cm-long copper conductor that's 0.25mm thick and 10mm wide will have a resistance of about 130µΩ. In other words, a full 100A across such a relatively lightweight conductor would only produce 13mV of voltage difference. You don't even have to take my word for it, just play with it in Falstad or your SPICE simulator of choice. Pic related. Even the cell with a full hundred-and-thirty times the resistance of the best cell is only 4.7mV lower than it at ~37A of load.
>Moreover, the *currents* won’t be the same.
That's why parallel groups of cells work at all. The weaker cells will experience more voltage drop internally, and supply proportionately less current. Cell wear and internal resistance are directly proportional. Thus, the worse the cell gets (relative to the rest of the parallel group), the less work it has to do.
The problem with cells in _very_ poor condition, however. is that they may just start to fail outright instead of just increasing their internal resistance. At that point, you likely have a small disaster on your hands, because the rest of the cell group will just start to dump a bunch of current into it. I don't think I need to explain why that's bad, and it's the major reason I'd advice against mixing and matching good/bad cells, even if you can get each parallel group well-matched in terms of capacity and average health.
>With high currents the claim is blatant nonsense
Do the math. A 2cm-long copper conductor that's 0.25mm thick and 10mm wide will have a resistance of about 130µΩ. In other words, a full 100A across such a relatively lightweight conductor would only produce 13mV of voltage difference. You don't even have to take my word for it, just play with it in Falstad or your SPICE simulator of choice. Pic related. Even the cell with a full hundred-and-thirty times the resistance of the best cell is only 4.7mV lower than it at ~37A of load.
>Moreover, the *currents* won’t be the same.
That's why parallel groups of cells work at all. The weaker cells will experience more voltage drop internally, and supply proportionately less current. Cell wear and internal resistance are directly proportional. Thus, the worse the cell gets (relative to the rest of the parallel group), the less work it has to do.
The problem with cells in _very_ poor condition, however. is that they may just start to fail outright instead of just increasing their internal resistance. At that point, you likely have a small disaster on your hands, because the rest of the cell group will just start to dump a bunch of current into it. I don't think I need to explain why that's bad, and it's the major reason I'd advice against mixing and matching good/bad cells, even if you can get each parallel group well-matched in terms of capacity and average health.
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