You don't need an active balancer or current limiting on the BMS side. A passive balancer is just fine (and is part of most BMSes anyway), as for current limiting; given that LFPs tend to hold their current flat up to ~90-95%, there's no need for that either. You just cut off charging at 3.65V and its going to be fine. Maybe the battery won't be fully charged always, but that's actually a good thing in automotive application.
I think the biggest issue here is cold weather countries. If you're in an area that has regularly temps below freezing and if BMS is properly set, you might end up with a discharged battery eventually, since you can't charge it.
So a heated battery, sane voltage limits and a more relaxed short term discharge current limits would make such battery just fine for an EV application.
There's a chance such battery exists.
I thought the same, get them balanced to start with and a passive balancer would keep them that way ..... By passive, you are of course referring turning a resistor into a heat across that cell if it goes above a nominated voltage, most are set at 3.8v and off at 3.45v.
Even with them mounted on it'd own piece of proper finned heat sink and on the outside of battery, they still got that hot I couldn't touch them.
Even though they were big units, supposed to handle 2 amps, it didn't take long before the first ones failed, turned on but didn't turn off ....
Luckly, the BMS I designed and built, had warns for out of balance between cells and a second unit that did Blue Tooth and over the interweb as well, would send a warning that half the pack voltage was more than 5% out of balance to the other half ..... because the top of the cells were accessible, I could direct the owner on which wires to disconnect and how to put the single cell charger on to bring the cell voltage back up ....
But what about the drop in battery, I know they only use around 5mA load across the resistor as a balancing current capacity draw down ...... but trapped inside that drop in box ..... that heater is mounted to a piece of aluminium, designed to dissipate the heat into the surrounding air ..... but that heat is trapped inside the box, no air movement across the heatsink ..... that voltage sensing circuit relies on a transistor to turn the link to the resistor on or off, and we all know what happens to diodes when exposed to excessive heat .....
Now, there is no warning a cell is dropping voltage in comparison to the others, there is no way to get to the cell wires to disconnect the cell from the balancer and resistor .... the cell just gets pulled low and now has less capacity than the other cells ...... those cells still have the energy to push through the cell that has now dropped to 0V, this is called reverse current flow, instantly that cell dies, killing the whole battery.
The same scenario happens with electric tool batteries, it's only a single cell that went flat and died ..... but the whole battery goes in the bin if you don't know how to repair them.
That was the reason to upgrade to active balancers. Tried the capacitor bank type, maybe ok for 12 mths, if they worked in the first place, but the induction coil balancers seem to work for life ..... although, there are so many copy units sold by every man and his dog, who knows any more.
We used and still use ZHC solar, they have been reliable, just need to ensure some clown, dressed as an auto electrician, doesn't decide he knows all about this stuff, disconnects one of the cables and doesn't immediately wrap it is some form of electrical insulation ..... they can shift 5 amps, but not 100 amps if shorted to ground .....
T1 Terry
