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The 100Ah "fortune" cells actually come from Jiangsu Frey.

Usually the ampacity tables are built based on an assumption of "still air", which means convective flow is allowed. The air around the wire will heat, which will make it float away to be replaced by more ambient air at the "constant" 70deg. If your wires are in a small compartment that's...

I like your idea of just running three sets of cables. It also makes it easier to grow or shrink the system without redoing the wiring every time.

There are definitely chemistries that require priming, or warmup cycles, before they deliver their full reversibility. There may be a small factor with LFP as well. It is the kind of detail that might not be interesting enough to make it into the public body of research knowledge. Only...

20A is not much; that's weird. I'd check your wiring at those two cells first.

It's really system-dependent. Fuses, bus bars, wire cross section, wire length, and current of course are the main variables. But low-rate charging to a low CV threshold might also mean the current stays high the whole time (mine does). I have a drop of somewhere around 40mV per cell under...

Your RV would become a parallelepiped (and a writeoff) in a rollover, so that safety bar may not be too important.

The best aging study I've seen is written up in Calendar Aging of Lithium-Ion Batteries by Peter Keil. I posted a graph from it above.

On the one hand, it's good that more humans are getting together and talking about batteries. On the other, the signal to noise ratio is clearly falling, so there is a lot of stuff to wade through.

Sounds good. I do have a drill press, but I live mobile full time and rarely have access to a shop like this. I'm afraid I don't have time to procure stuff and fix this cell, but I bought extra cells knowing something like this might happen. For now, I've swapped in a fresh cell. I'm kind of...

My (wild) guess is that maybe the electrolyte wicks down out of the jelly roll membrane a little bit, reducing the active surface area. I say that because new cells sometimes make a sloshing sound when you first handle them, but after a while they don't really seem to make as much noise.

That doesn't sound quite right. Your counter should be at 100% when your bank voltage is 56.8. (What was it at when you started, and what was the voltage then?) Have you configured it to sync to 100% at a specific threshold voltage and current? Most BMSes are going to want to balance at the...

That sounds like a solid approach. Yeah, I mean, it's the only other thing left to test given the video (I know, you're only showing us a subset of what you've done). If one or more is running out low, and you re-charge and they balance, then for sure you have a capacity issue. Doing it that...

Also, if more people try, it might send a message.

I guess my points are, a) the binning mechanism that a manufacturer uses may not align with anyone else's simple rubric for "A, B, and C," and their quality thresholds may even vary over time; b) the manufacturer may choose not to disclose their own reason(s) for putting cells into a...

Yeah, that sounds like basically 100%. You need to calibrate your counter so that it resets itself to 100% at that point (or do it manually, at least, for now). If you've no choice but to charge that high, I think you will get better longevity with top balancing. (I personally bottom...

I've been using these in a large mobile ESS pack for a couple of years now. AMA...

No, it’s not showing SOC divided by starting SOC. At the conclusion of the 9 month test, they re-measured the cell capacity and compare it to the initial capacity. It’s capacity fade that is being plotted versus temp and storage SOC.

I'm making a 3p16s "on end," so the parallel/cross bars have three holes each. The series bars are all 2-hole spans but the "long way". I fortunately don't need to cut any 4-hole bars, but I do need to set up 3 jigs/stops for the various configs I have. I'm planning on drilling ~M8 holes to...

Yes, draw your (entire) circuit please.

I am skeptical of this, mostly because electrically it's not really possible for them to "tell" that they're in parallel with some other BMS in the first place. Can you link to the BMS docs that describe this limitation? (I'm not suggesting you should do 3 or 1 BMS, in particular, by the way.)

Outback makes good stuff, and it might be fine, but I would definitely check with them and try to get something in writing if you plan to run 18s and go all the way up to 64V. My experience with Victron is that they don't always behave at the very edges of the voltage spec. Counting on that...

I would leave an air gap. Use an insulator for spacing so they don't experience any conductive leakage over time.

Ooh, great minds think alike/post at the same time? :D

Looks reasonable to me, if you can fabricate it. One other thing I noticed on mine: the bus bars are going to add a lot of rigidity to the top of the pack after you torque them down. You want to make sure your spacers do a good job of holding the cells in place, themselves, so the bus bars...

Indeed, they dump the heat into the battery for sure. But... that is going into the one cell. Not a "100 pound pack." Right? A 2.5W LED bulb has a huge surface area for your hand to soak heat out of. Try holding a 2.5W LED running at rated power. It will be blazing hot. Now, put one of...

While I agree that it is unlikely that many DIY packs today will use a BMS with this strategy, there definitely exist BMSes that actively rebalance while the pack is in every state (charge, discharge, at rest). Tesla uses this approach. It has a certain degree of elegance to it, if balancing...

Don't be so declarative. There are a variety of solutions for many different scenarios. Choices make the world go 'round.

I know you’ve moved on from this idea already, but for posterity: it’s totally fine to have different interconnect between different cells (or cell groups) in series. I would use bus bars when possible, because physical wires and lugs are a huge hassle (and space hog).

Yeah, I think the main issue comes when using a 120V generator. You can't feed a single phase from one of those generators into both inverters if they are in split phase, so people in that scenario only end up able to use "half" of the generating capacity. I went up thread to look at this...