BMS (Battery Management System) || DIY or Buy || Properly protecting Li-Ion/Li-Po Battery Packs

I always dream if the BMS, that just can take anything. Like you pick up any battery, hook it up and it just works.

Great video and nice explanations. I'd just like to add that, today, if it were just for the "extra" monitoring and balancing features, there are plenty of inexpensive (<30 USD) and high-quality commercial BMSs that have these features, including cell phone apps via Bluetooth, even with higher voltages and higher currents. But it's still great to learn how BMSs work, and your video really helps to illustrate this.

I enjoyed the video, but for a small limited use charger, I will go online and buy one. Thanks for helping with the decision.

Use ESP32 to for its BLE (much less power hungry than wifi) and deep sleep features.

Buy turned out to be cheaper for me

Never trust these small BMS boards. I have bought & tested one of them (4S, with 16.8V - 18.1V supply voltage) and they did not even protect my cells against over voltage. My 18650 Li-Ion cells have reached 4.5 Volts each. 😠 They are totally trash. If you know any other reliable and cheap alternative; please let me know. Thanks.

Can one connect an Imax B6 AC battery charger to the negative and positive contact pins on the battery pack to charge the battery pack?

Hi brother
I have 6s bms 24v
And I need 5s 20v bms what can I do to convert it 5s bms please a little help

DIY has become a lot easier. There are several custom IC solutions that only require some passives and FETs. Nice project to get into designing your own PCBs

The E-Bike makers need to convert them to use LiFePO4 batteries. Repairers need to help convert the existing bikes to safer designs, & promote/use safer manufacturers.
The nom ~3.7v, max ~4.2v type Li-ion/Li-Polymer are not safe in these sizes & environments.

Can a BMS for 18650 cells used for 21700 cells? Someone answer pls 🙏

Hello brother, I have a 3s 40A bms setup for my batteries, yesterday they worked fine but today as soon as i connect a load the Output voltage of the BMS drops to 6V from 11V making the load inoperable. This board is even new already threw one 3S 25A board for facing similar issue. Pls resolve or guide me if u know.



when load gets disconnected BMS shows Op again to 11V...each battery has 3.78, 3.79 and 3.80V

Great video, very informative, can I ask you a question. I have a 60v battery i am working with at the mo that has the 2+1+5 discharge connector I can't seem to get power from or only low power, the ground to the discharge side of the bms is 70v so I'm guessing one of the other wires must go to ground to make the circuit or a resister, I can not get a diagram for the board 2 power feeds then a 6 pin connector with 5 wires, first 2 wires are twisted together one goes to a resister, fz, the second is marked lock the third is rcst then dport then toot then pim_iso 🤷‍♂️ any help would be much appreciated

Can you explain lifepo4 battery bms and lithium ion battery bms to lifepo4 battery to charge can you make

good explanation, Thanks for sharing.

i was planning to use it to charge my drone batteries.
But ended up buying 4ch 4s charger for 60eur.
Im glad i did, at the end.

Jordi Motorway

Sorry but after years of working with ev power trains I can only state one thing:
I'm absolutely baffled by stupidity of people NOT to understand that BMS shall disconnects all it's connections to the battery cells when it recognises that cell voltage fell WAY to low, and only readable it self when charging is provided and slowly retest the battery and figure out whenever battery is dead or safe to charge !
That stupid mistake is causing more fires than people think !

well done

But Scott where is balance discharging feature??

can we charge every string of batteries by e 4.2 charger module by Connect them individually with 3 modules for 3s and charge it with a single port typ c ???

But my system uses lifepo4....

At the end in couple of shots it shows voltage calibration value exceeding 4.4v and you mentioned the charge exceeded the set 4.1v and boards balanced them out. So does that mean they got as high as 4.4 and then the DIY BMS brought them down back to 4.1v? Was did it allow to charge that high in the first place?? That is really bad / high voltage for battery life.

hi it is very good to find you here. could you tell me wat is dual stack motor and how does it work?

if you pay more you get better bms.

To confirm, does the voltage/cell monitoring function use the same cables as the balancing?

You didn't do a good job of measuring the resistor in the current limit. Measurement with two wires can never be accurate because the resistance of the cables themselves is also introduced. In order to take an accurate measurement, 4 wires must be used. The value of the current limiting resistor is 0.0013 ohms, not 0.05 ohms. The protection activation voltage is probably 50mV

So some of the BMS you find that look like yours and are sold on several platforms (amazon, ebay, or aliexpress) do not actually do as they claim. I bought one almost identical to your only 3s version... it almost ruined my pack. I have a nearly perfectly balanced pack (50mAh variance out of 30 000 mAh total). The issue is that is somehow managed to make 2 of my cell banks (3s16p battery) were discharged to 0 volts and one was at 4.3 volts... Not good. None of my cells had any measurable self discharge before this happened, and I have been attempting to find out what is now causing the self-discharge, whether it's the BMS or if the cells now have a self discharge. I didn't even get one charge out of the pack. Only the initial charge was usable (I charged each cell to full to test for self-discharge and so they'd all be the same SoC for assembly).

I saved the pack with a small active balancer, and thankfully the over charge and over discharge protections all worked on the BMS or it would have started my pack on fire.

Maybe mine is defective, but I'll have it investigate later. In any case I would recommend an active balancer on any large pack. They actively balance at any voltage so they can be used even you limit the charge to between 20% and 80% to extend cycle life... and they're a LOT faster than bleeding off the cells since every amp you drain from the highest cells goes to the lowest cells so it's almost like balancing twice as fast... while making less heat. Though some of them have low current so I just get one that has low drain ( less than a miliamp) and leave it connected so it can just always balance and I never have to worry about it. Realistically, the DIY BMS with the 1 amp bleeder resistors is faster than cheap active balancers because of that giant 1 amp of current... the bleeder resistors in most commercial BMS boards are way way smaller and are thus going to be slower than active balancers and are only going ot activate at a set voltage which is set by the BMS circuit rather than programmable software.

https://youtu.be/_8yEHdrNCVI?si=nCNqeNZIU2nQ9PEH

Hi great scott, kindly help in arduino programming

Looking into a project that will require a 128s BMS, great info!

There are no microcontroller in the BMS?

Nice.

Does this board draw current when the pack is supposed to be shut off?

Very nicely done. Has anyone made this "universal" - capable of supporting any voltage and any battery chemistry?

Why do you bother with a Mickey Mouse Arrangements

4:30 In this BMS case, could the output resistors be increased to charge the battery not to 4.20-4.25V, but to a maximum of 4.1volts, in balanced mode????

This modd, would significantly increase battery life, and it would be very important to change this! 4.1V = + 30-40% charge cycle lifetime! If anyone knows, please let me know here!

That purple marker completely smudging the ink of the numbers and letters really pissed me off more then i would want to admit. For esthetical reasons please consider an alternative.

How do you make a 400V battery management system with 108 3.7v batteries with 6 in parallel and 18 batteries in series?

I have a 36v battery pack. It's a seperate port bms. It charges to 42v however when I test the neg and positive out it reads 20v. This is an older lithium battery pack that came from a scooter. What components could cause the output to read 20v? Everything is factory made. The pcb board and batterys work before. But no longer can discharge becsuse the bms read 20v and the battery at its neg and pos ends read 42v. Is it a bad mosfet?