Low cost / High performance universal BMS

[DJBecker]

Originally Posted by flores

I'm not an expert at this, but isn't 200mA a bit small for balancing? Is it possible to increase this by decreasing the resistor?

The expectation is that most packs will need only minor tweaks to balance.

The battery management system should be smart enough to track which cells might be out of balance, and gradually pull them back into balance over time and multiple charge cycles.

Attempting to completely balance every charge, during the charge, an overly-simple approach.

[nlc]

Software for the slave board is in very good way, I just needed to change some GPIO placement because of a hardware bug in the PIC !!! Now the first byte of the master frame is directly passed to the next slave board through hardware without software delay. This byte is used for slave board wake up when in sleep mode, for autobaud configuration (to allow operation in the complete -40/+125°c range even with big deviation of the internal clock), and for sample/hold the voltage/temperature value. It permits simultaneous sampling on all cell, very usefull to compare cell voltage under exactly the same current !

[nlc]

DJBecker : I totally agree with you

[nlc]

The communication protocol between master and slave board is finished and work perfectly on the entire temperature range of the microcontroller, even at -40°c




With the auto baud rate configuration on each first byte of the protocol frame, the baudrate always stays below 1% error even with the max +/-6% deviation of the internal clock of the microcontroller.

[nlc]

I just launched a preproduction of 50 pcb

[skeeterb]

sounds great man. I hope you have lots of luck with furthering this project.

[nlc]

Thank you.

I don't received a lot of comment about the symbolic shematic of the Master board I posted some day ago. It is because it is really complete and answer all needs as is !??

[nlc]

Yesterday I received the confirmation for the pcb production, it will looks like this :

[sawickm]

NLC,

Good luck on this project too !!!

I am watching it with great interest. Your BMS mother PCB diagram has a lot of nice integrated options, charger control, display, sounds great !!!

Keep us up to date,

Thanks.

-Mark

[Alcibiades Ramos]

You wrote: "I integrated a balancing of 200mA @ 3.6V and then approx 233mA @ 4.2V (18r resistance). Balancing can be started ON/OFF by the mother board, permitting to optimize balancing algorithm if needed, and thus not just activate them when the cell reach max voltage, which is a terribly bad algorithm if the charger is not able to lower its current under the balancing current value !!"

But, I am only interested in bottom balancing the cells. That is how they get destroyed if don't have control over them. Can you configure the BMS for bottom balancing the cells?