Help connecting bms to battery for charging.

To keep it clear and simple,
I received my charger today, and attempted to charge my battery for the first time.
I had presumed that I should plug the bms into the battery before connecting the power charger to have a load for the charger and perhaps prevent a spark.
But, that didn’t happen.
I plugged the bms balance leads into the pack, and then the main negative in preparation to charge. I got smoke out of the first resistor on the bms within the first few seconds before I had even attached the charger.


I figure that my resistor is dead on my bms, but I want to know what I did wrong, and how I can prevent it for next time.

Here is the wiring diagram for the bms;

I was thinking that if the bms shorted the positives and main negative of the pack, why would it only destroy one balance resistor? Maybe an inrush of current to balance only the first cell?

And yeah yeah I probably made some dumbass mistake but I have never seen anything mentioned regarding importance in order of connection to your battery for external bms, and this can help others not make the same mistake.
(I can elaborate with more pictures)

I’m very noob to this but one thing every one told me is that you should always insulate the cable you’re not working on.
At first glance I think your diagram is ok. But I’d let the gurus double check it

From what I’ve now seen and heard I simply should have connected the pack negative first :roll_eyes:
Good news is I think I disconnected quick enough for me to only need to replace a 5¢ resistor

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Your supposed to connect B- first, or else resistor blows

Happened to me too, i plugged in the balance wires before B-

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So if I replace the blown resistor all should be good?
It seems to be a 100Ω resistor.

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Not sure, i just dumped my bms, something else could be blown


:expressionless:

I’m always interested in a good story…

what is you’re strategy for removing that resistor from the PCB?

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Simple soldering. Got it off in like 6 seconds.


It’s a 2512 chip size, and a 100 ohm resistor. Did a little searchin and boom.

So now I can blow it up 49 more times :grin:

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Had to replace 3 resistors, and I finally got my multimeter and found out that I… had wired my battery in reverse :laughing:
My ‘#1’ pin was testing at 46.2, not the 3.3v like it should.
Which is wierd, because I double checked that my cells series started from the negative of the pack, and I numbered them as I assembled them… nevertheless I then realized that it was reverse the whole way through the pack (#14 pin testing at 3.3v). So, that was also probably a reason why my charger wouldn’t work lol. I have to make an adapter now to flip all the pins order

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