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I think he's wrong about one thing. A good BMS not only monitors cell voltages, it has the ability to bypass some charging current around individual cells. Not a lot, but enough to balance the charge of all cells over a cycle. That capability can do wonders for the reliability and life of a pack.

While I worked in EVs for 6 years, I have no knowledge of the Tesla BMS - they were not our customer and I worked mostly in motor control anyway.

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Here is the spec sheet for the main square chip on that board. http://www.ti.com/lit/ds/symlink/bq76pl536a-q1.pdf You're right. It does have a cell balancing feature.

Where is the actuation mechanism for that that though? There does not appear to be any circuitry for that here. At a minimum you'd need something that would engage/disengage the cells, either a FET or a IGBT. (the voltage drop on other devices would be too large).

Take a look at http://files.wizkid057.com/teslapack/update2/Tesla%20BMS%20M...

For cell #1, my guess is that the 4 parallel resistors (R3) are the balancing resistors and that Q1 is a small logic level MOSFET which enables cell balancing. On a BMS project I'm working on balancing current is only 250mA, so a small SOT-23 MOSFET is all you would need.

Good eye. There are exactly 6 of those so yes, you are very likely right!

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