I am finding it rather amusing that two people with barely 200 posts between them
I find it funny that, there's really nothing lamer than a pissing contest based on the number of posts they've made, or valuing anyone's opinion based on how much they've spoken. Especially on a particular forum with a particular account. Or how old their account is. Or some other clique-y but meaningless measurement. I certainly don't judge anyone that way, seems it's the entirety of how you do.
I care more about how much someone listened than how much they speak.
dtbaker said:
I don't need to a lecture on how those choices were wrong
I haven't seen anyone do that. I don't think anyone's criticizing you for your choices.
I do not have room to create independent 'boosters' for weak cells.
You just need some empty space... anywhere in the car. They don't have to be side-by-side. You can locate them all in another box and just drag wires back to the pack. But, if you don't want that solution, that's okay.
My best bet at this time appears to be to find, or build, a simple cheap way to monitor all cells during charge, and stop the charge if any cell goes above 3.70 before the pack voltage triggers a 'normal' end of charge to the charger.
I don't think your problem is on the charging side, your problem is on the discharging side. Lithiums, especially LiFes, are decently tolerable to over-charging. I've got some I've regularly thrown into normal lithium chargers, (cutting off at 4.2v instead of 3.6) and it's not doing them any harm.
What murders Lithium is the reverse charging that happens when you drain them past dead. That's what you need to be extra sure you're not doing.
The problem with doing what you want is it's probably as much effort to do that, as to actually fix it.
The easiest thing would be the relay trip, you've already got that figured. There's probably already a contactor in there to do that so just hijack it an insert another switch, or, interrupt the input side.
The difficult part is that you need 48 different voltage readings, and some brains overtop that to control it. That's 49 different wires to the cells. If you're building a circuit, that's 48 different circuits to do things to, and you seemed to indicate earlier you weren't even interested in the effort it would take to do a discharge test to find out which cells were low. So I'm trying to picture what kind of solution is cheaper than the couple hundred 18650s you could buy to fix the capacity issue, and also take less time than doing a simple capacity test. There's not much on the table with those conditions.
But in any case...
Maybe something like 48x 3.7v zener diodes, in series with a NC relay? Then when any of them conduct (when any one of their voltage cross 3.7v), it activates the coil and breaks the relay? It'll pulse and flicker, maybe add the few components to make it a one-shot-stop, like emergency pushbuttons on industrial gear?
On the discharge-side, where I think your actual problem is, would you be okay with a human solution? I.E. If you could just occasionally keep an eye on something and manually know not to keep driving?
In that case, I'd drill an 8x6 grid into some plastic and insert red LEDs. Have each of them wired to their own cell with some kind of resistor that yields barely enough current to light the LED when at your minimum voltage is.
So when you're driving you'll see the LEDs brightly lit when charged, they'll all slowly dim (but barely, it's pretty digital for most of its range), until they get near the bottom of their range and then they'll dim much more rapidly and eventually go out. If you ever see one go out, you're done, stop the car.