A dual cell charger (3-6V 4A in, 8.4V ~3A out) combined with active balancing (1.3A).

• The charging part makes sure to load the battery pack to 8.4v
• The balancing part makes sure to keep both batteries at the same voltage always, by charging the lower one using the higher one (active balancing)

Having these combined will in theory give the perfect 2S bms, so that batteries won't die, charge fast and don't waste energy.

Any buyable bms i have tested so far fails to keep both batteries at the same voltage, so that one is e.g. 4.6v and the other 3.8v, resulting in 8.4v total but leading to damage/death of the overcharged cell, hence this proect to solve the issue and have a reliable, hackable solution.

Still in concept phase, highly experimental and untested. Even the pcb traces are not wide enough to support the supplied current and would probably delaminate or catch fire.

Releases starting with v1 or higher can be used and are tested.

Most parts a salvaged from commercially available modules, which are dirt-cheap on aliexpress:

• Charging module (2S, 4A
• Balancing module (2S, 1.3A, active)

So all parts of those modules can be desoldered using a hot-plate and solder3d on this project's pcb.

Follows the recommendations and schematics of the datasheets

Follows the reverse engineered chinese pcb modules, so they are merged into this pcb to minimize the need of additional components (just move parts over).

Todo

• The status group of the ETA3000 consisting of a red led and a 1k resistor use BatC as one pole and SW as the other. Thus it does not have a real GND but current flows with BatC acting as Vcc and SW acting as GND for the led
• The said red status led connections could also be exploited to power an optocoupler, so the GND stays independent for this part of the circuit and status becomes measurable using e.g. an arduino
• Connecting BIAS or SW of the ETA3000 to the GND, which is the negative side of the 2 batteries connected in series, kills the IC and from there it gets very hot while being powered
• None of the 2 ic's (CN3302 && ETA3000) have a symbol in snapeda, so generic packages are used and pins renamed to match this ic

• Datasheet (EN) of CN3302
• Datasheet (CN) of CN3302

• Writeup on ETA3000
• Datasheet of ETA3000