How to recharge an 8s with one plug?

ESK8 Electronics
21

This is certainly not true. I have a 12V lead-acid battery and a AA battery and an 18450 cell and some 5S lipos here and none of those have 5 wires for balancing. Details matter a lot. In fact, it’s all about the details. Whether it works or not will be entirely dependent upon details. Don’t overlook things or assume anything.

If they are two 4S lipo batteries, it’s likely each one has 7 wires coming out – 2 large and 5 small. You may not need to use all of them because some are redundant. When you connect the cells in series you also make one of the balance wires redundant. See another other diagram for an example. (The loop key is wrong in that diagram, but the balance wires are correct — for those batteries and that BMS, not for yours)

Checking with the multimeter will tell you which one is redundant

22

I think I’m not explaining things the right way :slight_smile: My two batteries are in series, so let’s treat them as one battery that is 8s1p, has a big black wire, a big red one and 10 little ones connected to the balance plugs. With a multimeter, starting from the negative side of the battery I have a voltage of 0, 4, 8, 12, 16V on the first 5 little wires. These little ones I have to wire to the balance cables going to the bms’s port, going from b- to b4 (the balance port of the bms is labeled from b- to b8).

On the positive side of the battery (the pack with the big red wire that is my main positive wire) has also 5 little wires: on the multimeter they are 16, 20, 24, 28, 33V. So now I know that I have two of the little ones that read 16V I know one of them is redundant: my question is which one is the redundant one? what have I to do with it? should I connect the two wires that read 16V on the bms or what else?

23

You can leave either one unhooked that reads the same voltage – they are connected together where the big black and red wires meet between the 4S packs. Essentially, they are the same connection. One is the top end of the bottom battery and the other is the bottom end of the top battery.

24

that’s the thing I didn’t understand! thank you! you were super helpful :smiley:

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25

mostly thanks to @b264 I succeeded to build a bmsed 8s limo without perishing into the flames. it worked! I guess the list of ppl to thank in my upcoming build thread grows by the day :slight_smile:

edit: also, thanks to @b264 I earned the “firs mention badge” :smiley:

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