because I have a few cells in my pack that are 'drifting' out of balance after a few charge cycles.
I can't change the capacity either. So, at this point it doesn't do me any good to measure either the capacity or the IR as there is nothing I can do to 'fix' the damaged cells. I cannot replace them at this time, so I am exploring ways to live with them and prevent overcharge as the short capacity cells will doubtless 'drift' higher and higher at end of charge.Not to beat a dead horse, but, again... you do not have cells drifting out of balance. You have pack with cells that no longer have matched capacity due to damage.
Your only solution is to make the capacities match. No amount of balancing will solve a capacity issue.
I know you keep insisting you don't want to measure the capacities because you don't have time, but, that is your only solution.
You can't "balance" a weak cell to be larger again.
Either increase your skillset, reduce your expectations, or spend a lot more money.
This is not a mature area of technology for DIY efforts.
I am hoping that one of the more EE oriented people in the forum can see a way to jigger one of these guys:No one will be more pleased than I, if it turns out that what you are looking for actually exists.
If it turns out my suggestion is the best way to go within your budget, you may find it takes just a couple of enjoyable evenings to figure out how to do it.
I am only motivated by trying to be helpful, and (constantly) climbing my own learning curves.
Sure you can. For quite cheap you could buy some LiFePO4 18650s (or even regular lithiums if they're more available, and just cut your expectations in half) and parallel them to the weakest cells. You could build a little booster box, since presumably you already have some kind of BMS onboard, you'll already have all those sense wires broken out.I can't change the capacity either.
So, what's happening there is quite likely that the degree to which they are unballancing is directly the amount which their capacity is being murdered every single time they're used. The weak cells are continuously being amputated and permanently losing capacity an an accelerating rate.I top balance all the cells, and after a couple charge cycles the damaged cells start finishing significantly ahead of the the others.
It just seems like you're labeling and attempting to fix the wrong problem the wrong way. I kinda feel shitty for you since your solutions are continuing to harm your batteries.Why don't you accept that I am trying to find a way to live with the slightly mismatched cells in situ for now?
I do not have room to create independent 'boosters' for weak cells... What I am after is how to use the pack I have a little longer without adding or replacing batteries.Sure you can. For quite cheap you could buy some LiFePO4 18650s (or even regular lithiums if they're more available, and just cut your expectations in half) and parallel them to the weakest cells. You could build a little booster box, since presumably you already have some kind of BMS onboard, you'll already have all those sense wires broken out.
exactlyAll the shunt-type BMSs will overcharge your good cells because they can't handle full charging current in the rebalancing (they can't bleed off enough of the power going to the full ones).
I certainly do not put myself in a class with either Major or Tesseract... but I find the noise to signal ratio high in the responses to my recent posts.dtbaker, I am finding it rather amusing that two people with barely 200 posts between them are lecturing you on what you should do and how to do it. That seems a bit like someone trying to tell Major he doesn't know motors or Tesseract that he really should stop talking about controllers until he learns a thing or two. But that's just my opinion...
I use the CellLog8M to shut off my charger when the first cell reaches 3.500 volts.Hi !
rwaudio has his Cellog8 breakout boards for sale again.
That could be an idea.
But be aware of the unbalaced load of the Cellog8.
Or, take a JLD404, which every conversion should have, and set the alarm for VOLTS and set the number for (3.7) (45) 166.5 volts. Trim the volts as required a little down until the first cell hits the 3.7 volts. The alarm relay contact of the JLD can be wired to latch a power relay to shut off the charger.You could build up 45 little circuit boards with an LM431, a FET opto isolator, a small transistor and 3 resistors. Daisy chain the boards like the Clean Power setup and when any cell hits your 3.7 volts, the opto opens and latches a power relay to shut off the charger. Pretty simple but sort of a PIA to make up 45 units.
That's how I would do it.
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 am finding it rather amusing that two people with barely 200 posts between them
I haven't seen anyone do that. I don't think anyone's criticizing you for your choices.dtbaker said:I don't need to a lecture on how those choices were wrong
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.I do not have room to create independent 'boosters' for weak cells.
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.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.