Li-Ion battery pack without bms!?

How do you know the cells are balancing themselves? It could be just that the cells have very litttle difference brotha. :kissing_heart:

On multiple occasions I have measured each cells beginning voltage before charge and re-measured after charge. It shows that there is up to a 0.6v per cell deviation. After charge there will be, typically, a 0.25v deviation per cell. After sitting overnight the deviations is typically .1v at most.

Strange. The cells seem to have memory of each other. :ghost: you should record every charge over night voltage difference, because we want to see how the cells progress over time brotha. :jack_o_lantern:

I did for about 3 months, got tiring. I do it about once a month now. I will eventually stop recording all together if it stays at the limits I described.

I’m thinking about using a VGA header to make a balance plug and then cooking an enclosure up for a BMS, so I can balance charge multiple packs with a single BMS.

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So If I just use the bms for charging and not for discharging I don’t have to spend 100+€ for a 100A discharge bms. I will say my vesc’s they have to shut down If my batter voltage goes down to 30V (or another Voltage). Theorethically I don’t damage my battery with over discharge. Is this right or I’m just retarted? :sweat_smile: Alex

No, you absolutely can damage a battery with over discharge. You can use the VESC to set the voltage cutoff values, so using a BMS for discharge only is acceptable. Its not the safest, but many people do it because they keep on eye on the pack voltage.

So I have to spend a lot of money for a 120A discharge bms? :slightly_frowning_face:

No dude, if you don’t let your pack voltage get below 2.9 per cell you are fine. So set your cutoffs accordingly in the VESC and it will cutoff voltage when it reaches that limit. You can use a charge only BMS so that the cells are balanced and charged correctly, and discharge directly to the VESC/VESCs.

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Oh okay now I understand, sorry :sweat_smile: Thank you very much for your time

No worries, let me know if you need anything else.

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How are the cells hooked up during charging? Are you measuring directly on the cells or some place along the charge wire?

But the cells do have some recovery, after a heavy current the can take a while to get to resting voltage, that’s the problem with determining state of charge using voltage only, you never know if the cells is at rest or still recovering

@mmaner You mean something like I made ! with a smart configurable BMS

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The charge port is connected directly to the pack POS & NEG. Im measuring the balance leads individually.

Well that’s just cool as hell :). Have you done a write up on it?

Nice, there no is load them, I guess it’s the cells recovering after current in or out

Really neat brotha. :lying_face: Mind spilling how you did the software? :yum:

@mmaner Nah -On my board I have a normal charge socket that connects directly to battery +ve and -ve .

No BMS in board enclosure at all ( one less thing to break down and I don’t need BMS to fail braking down-hill)

My battery has all 11 balance leads bought out to a weatherproof socket ( using 0.75 sq. mm high temp silicon wire) for the external BMS. I put 5A wire fuses in these leads to protect battery ( and prevent a fire) should there be a fault.

So I can charge without BMS directly into normal charge socket on the board ( which I do 99% of the time)

or I can plug in BMS box to monitor only cell voltages during charging through board charging socket

or I can balance charge through BMS box using the 11 balance wires ( which I haven’t done for a month or so.

Ultimate flexibility !

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BMS from AliExpress - with PC uart connection

Even comes with a Bluetooth module for android phone cell voltage monitoring and configuration capacity

https://www.aliexpress.com/item/13S-60A-active-bms-2017-new-Li-ion-smart-bms-pcm-with-android-Bluetooth-app-UART/32821764284.html?spm=2114.search0104.3.89.30717e9as0sSvw&ws_ab_test=searchweb0_0,searchweb201602_2_10152_10065_10151_10344_10068_10130_10342_10547_10343_10340_10548_10341_10084_10083_10618_10307_10131_10132_10133_5711211_10313_10059_10534_100031_10103_10627_10626_10624_10623_10622_10621_5722412_10620_5711312,searchweb201603_25,ppcSwitch_5&algo_expid=d1e41397-3fd7-45fc-8cad-7dd843697eb0-13&algo_pvid=d1e41397-3fd7-45fc-8cad-7dd843697eb0&transAbTest=ae803_3&priceBeautifyAB=0

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Personally I would include a BMS in all my packs that I build, that way they can easily be charged just with a charging brick, however, I generally only use a low rated amp output current BMS, and bypass it for discharge, only using it to charge and balance the cells…

I find this very effective if your ESC handles cutoff voltages such as a VESC derivative.

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Thats quite cool bms and “charge monitoring” box u have made. U should definetely make a sepereate post or tell more info about it.

Looks like u can also configure a few settings or the bluetooth is just for monitoring?

On a side note - to the guy who said his lipos drift in voltage - that is quite true, thats also why li ion tends to be more popular choice, i think, if really high current is not needed, li ion cylindrical cells drift a lot less or almost not at all, if they are from same batch and balanced properly in first place

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