10S BMS on 8S battery?

ESK8 Electronics
#1

Hi guys!

I got a little accident a few days ago (thanks I am fine!) my battery enclosure broke and the battery fall off the board and blocked my back wheels. I had to remove two of the cells from my li-ion pack and have now an 8s battery left.

First crap is: I cannot charge this with my 42V charger… to find an 8S Battery charger is not that easy… :slight_smile: but I found one and bought it (15euro from AliExpress.). Now I want to bring the battery back in nice condition and bought some huge shrink stuff and will connect my old BMS to it. BUT can I connect my 10s BMS to the 8s Battery? I guess yes, just leave the last two wires open… correct?

IMG_5820

Thanks for you help guys! Have a safe ride!!

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#2

Bestech D140 is a small compact bms, if you get a 10s version just leave the 2 wires disconnected and it will work normally, same would be for 12s version. should work in your case too

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#3

I myself have a 10s BMS with 8s batterypack lipos. I use my 10s charger. Works fine

Make sure you leave BMS balance wires 9 and 10 disconnected

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#4

Yes, if you do it properly

Start from negative, and connect up to the more positive cells and leave the last two empty

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#5

And u can also use an 10s(42v) charger?! So tue BMS Tales also care about the right voltage if the batter is connected properly?

#6

As long as it is a constant current / constant voltage charger. It will charge the pack when empty at the appropriate voltage, and once the voltage exceeds the BMS over voltage protection for cell level voltage (4.2 or 4.25 sometimes) it will disconnect from the charger.

If the charger has an indication light on it it should also turn green as it stops drawing current.

Please verify that the BMS has over voltage protection and is able to disconnect. Keep in mind that you MUST charge through the BMS.

#7

On a slightly different note, separate from my explanation above.

Who here is experienced in lithium battery chemistry? I ask because normally when a battery charges it is constant current until the charger reaches 4.2V per cell, and then remains at constant voltage.

This leads to the charger current gradually platouing until it reaches 0.

What happens when you charge at the full 2 amps until full? Is it detrimental to the battery?

Theoretically this should lead to a faster charge time. If I’m using a BMS anyways wouldn’t it be better to use a 12S battery for 10S so I can get a boost charge at the high end of capacity? This is assuming the BMS doesn’t fail of course.

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#8

Awesome! Worked as expected! Green light Showed up, my is saying battery is full. Thanks a lot!

image

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#9

This sounds extremely dangerous, but I’ve wondered the same thing before. I would not want such a thing charging in my home, though.

#10

It definitely is more risky without additional protection circuitry other than a BMS.

But the method is proven. Phone batteries will turbo charge at 9V when the cell itself is only 4.2V.

I’m by no means advocating that you hook up extra voltage to your charge only BMS.

#11

I live in a high-rise so it’s imperative I’m a little more safe than others who only live in single-family dwellings. LoL

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#12

Yes I can imagine a “spontaneous and catastrophic kitchen oil fire” would be a lot more dangerous in a high-rise. :wink:

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#13

when I charging something even slightly risky, I always have a quick disposal plan ‘it can go thru this door/window if it really has too’ not really any way of quick dispose at height, would really worry me!

#14

2022 update:

This doesn’t work on all BMSs, but does work on some.

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#15

2022 update —> [DISCLAIMER THIS IS NOT ADVICE, Do not try this at home]: You can also short cell n–>last [all voltages of cell ports n+1, n+2 will read the same as cell n and should in theory be balanced to it’s 4.2 respectively. only Issue I see is maybe it will be balanced at higher currents which might mess with the cycle life of the affected n cell in this case cell 8 but in reality it shouldn’t matter much.]