Charging problem on a custom board. Zenit rocket white pony style

Hello everyone, after months of assembly i finished yesterday my first build. A zenit rocket with elofty like motors and 12s 3p molicel p42a battery.I put all the internals together and did i quick test to check everything and all looked good, i even tested if it was charging and the light turned red on the charger, nice! I didnt give it more importance.
This morning i went to test it and it was amazing but when i tryed to charge it back it wasnt working…
I got crazy and started to test everithing, fuse ok, battery 42 volts charger 50 volts…and when i checked the output (conection between negative cable on the charger and pisitive terminal of batteries)of the bms it was reading 0,02.
My battery is a 12s3p molicel p42a.
I charged my bateries when i got them into starage mode, 3, 7 volt bc i knew there would be some timenuntill i could use them. When i install them yesterday i pared them by groups with same voltage. There was 8 3p group with 3,68v, 1 3p group with 3,69, 1 3p at 3,67v and the last one at 3,66v
After not charging today and removed the bms, i checked the balance wires again, and al 3p groups were at 3,5/ 3,6 v but 2 of them were at 4, so they went up in charge?!
The bms is a chinese brand from aliexpress;daly 12s.
Should i believe that is a faulty bms? Could something fryed it?
Now im stuck with this brand bcaus of the little space i have and that i dont want to remove balancing wires, so i will need same conector.
I was so happy this morning and now im so sad…


Thanks

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Update,
Mesuring current in between consecutive cells through balancing cables is a constant 3,5 volts.
current between battery positive and b- of the bms is 42, 6v and between batery positive and p- of bms is 39, 2 without balanced cables conected. Is that normal or that means bms is dead?
Resistance between b- and p- with balanced cables conected is 0.


That is the bms, is it appropriate for a 12s3p molicel p42a battery?
Please help!

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First off, great looking build!

If your cells are varying in voltage simply after plugging the BMS in it is definitely a BMS issue. If they are deviating during charging you may need to open up you NESE modules and see if there is an issue with some of the cells not making contact. If a cell is not making contact, that group has 33% less capacity and will change faster accordingly. I find daly’s to be very rugged even when i mix up a P wire group they still charge properly after correcting the issue. But i have burned one before when I wired it entirely backwards. I almost immediately knew the issue because it became warm very quickly after finishing wiring before pluggin into the charger. Did you notice it being warm without the charger at any point?

The voltage difference between the battery leads and the bms - to battery + should be very small in my experience, .01V the 3V difference does point to a BMS issue imo.

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Thank you my friend for your response.
No warming issues at all. I test the board for 6 miles and it was delivering amazingly. Didnt went flat out bc the park was crazy full, but acordingly to my hobbywing remote(i know is not the most precise one) i was getting 28mph easily.
I also think is a bms problem, but my concern is that during the assembly i plug it the charger for a second just to know if everything was correctly conected and it worked. Never tryed to charge the board again untill i returned for the test. What could had happened in the test to kill the bms?
If i get a new one, could it happen again?
I learnt my lesson and im going to use bullet conectors to reassemble it again, no more permanent soldering, i might assembly it again with same bms and se what happens

Thanks for your kind words, it has been a hard and learning experience to put this together, but very intersting too
more pictures of the board

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Great build for a first one, I like your approach to simplify and keep cost down for the ESC, especially because it fits so well (just like everything else) inside the battery compartment :slight_smile:

I designed th compartmen with all the components on mind that is why it fits perfect :wink:
I chose that esc mainly because i ride my other board with a hobbywing esc about 15 miles a day to comuto to work and after more than a year i havent had an issue with it. Rainny days included!
I had some regrets bc it limits the capacity of my molicel battery , but it goes perfect with the non very trustfully elofty kind motors, so i wont over power them.
Thanks for your words!!
Any suggestions about my charging problem?

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I think its a faulty BMS, and that you should utilize whatever warranty or Customer Service claim system you can.

Its behavior doesnt make sense to me, unfortunately. My last build used a 10s Daly BMS and it was a piece of cake, no setup beyond plugging things in (in no correct order, as some BMSs require this)… so I think youve got a bad unit.

You might be stuck using another copy of this BMS (due to size constraints), but if you think you can fit another 12s BMS, i think looking around for other options is a great idea.

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New updates.
I decided to put all back together again using bullet connectors so everithing is removable.
Long story short I accidentally shorcuted the charging port while installing it with metal pliers.
The thing is that the fuse didn’t blow off (7.5amp fuse) but this time the bms is dead for good, now measuring the internal resistance between p- and b- is not 0, there is no continuity.
HOW IS THIS POSIBLE?? Shouldn’t the fuse installed in the negative cable of the port have protected the bms?