Most reacted posts

ABYC is great (well, most of the time: their lithium battery working group is struggling to keep up with the pace of the industry), but the wire ampacity standards look pretty normal to me. Those wires, when connected to motors and bus bars and things that are tolerant of some heat, are fine...

I'm not sure which is better, but both seem good. A nice, fat vertical bus bar, or a pair of leads like you've drawn I think would both be fine. With three leads, I'd put them on 1/3/5, but again we're splitting pretty fine hairs. It's going to work great regardless.

You've gotten excellent advice so far. A few additional comments/opinions: You can parallel multiple ATs to increase capacity. Generally two Victrons is the most someone needs in USA RV land. You can also buy or commission a custom AT for your desired power. Depending on the topology you...

Tesla's management system measures cell imbalance at top of charge, calculates the excess energy in the cell, and tasks a bleeder circuit with burning the determined amount off of that cell over time during quiet periods. It still requires the cells to go into the upper knee to make the...

Ah, I see. With some setups, you can control charging based on SOC estimate from a shunt-based integrator/counter instead. That's probably the only option in that range, you're right. (That's also how I control charging when off grid.) You would have to get back to 100% for a counter resync...

You can find a detailed discussion of the balancing strategy on the Tesla forum. It is pretty simple: a computer watches the cell's voltage rise in the knee and estimates a quantum of energy that needs to be dumped. That value is written into a timing circuit that proceeds to slowly bleed off...

I did it the "easy" way, by empirical observation. I gradually increased the CV threshold, a few millivolts at a time, while watching the weakest cell in each string. It turns out I was able to get to about 92% of rated capacity without the weakest cell diverging enough to be an issue. At...

You would need a 48V solar charger to charge the whole thing. You technically could charge each 12V unit separately, but you'd have a lot of imbalance issues. You'll have some imbalance issues anyway, since your new 24V pack would have a different capacity than your older BB 12V packs. The...

Yes, that would be a top balance. Well done.

At the top of charge, when the computer can see the imbalance most clearly, it calculates an amount of energy to bleed off for the cell. The bleeder is just a small, fixed resistance, so the energy burn goal can be turned into a time goal. The time goal is latched into a bleed controller on...

For three separate strings: - 3 BMSes instead of one ($) - 3x overcurrent protection (e.g., fuses) + redundancy if a string drops out (but, other strings have to be capable of taking the increased load); can do maintenance on part of the battery while leaving system up if needed - individual...

Looks good. Why do you think single-phase will be rare? It's super common in a lot of the most interesting places.

I think a simple BMS and a 4s pack are much more practical for a lot of projects. But it can be instructive for any DIYer to understand the range of choices, even if it's likely they'll choose one of the simpler paths. It just became a hobby. I'm a software guy. But they did make me go to...

Sure, no worries; your stance is not unreasonable. You didn't respond to my important clarifying question, though: we are talking about multiple bus bars, not a single one dumping its heat into a massive battery pack. If you're going to leave an order-of-magnitude factor hanging out there...

That certainly seems plausible. There are real issues with chronic undercharging of lead acid, such that I suspect poor paralleling ends up doing a lot of early damage to batteries that are getting the short end of the charging stick. This is almost a non-issue with lithium, except insofar as...

We've heard other reports of Chargery being very sensitive to ripple. I guess something like that is possible. Indeed, just a few controlled loads, all colocated... float it is fine. Well, 250 A DC, yeah, probably big and expensive. I'd just use two fuses, but they're also pretty big and...

I'm using MX14 (a little better mounting arrangement for my setup, and a little more current headroom; my system is a bit larger than yours) with great success. Note that the holding power is 2.0W with the 48V coil; also a rounding error. Speaking of watts, what's your plan for dealing with...

The best way to do it is by titration, because everything is super sensitive to your connection impedances and how your stopping device takes its measurement. Use a coulomb counter to track your battery's SOC (resync it frequently while you're testing) and adjust your voltages until you get the...

I'll have to improve my McMaster-fu; thanks. Yeah, like usual, it's a tradeoff. (ABYC actually specifies 7 inches, btw.) I have long runs, through multiple cabins and areas, between battery packs and the bus up point where they are all joined together. I'm not confident I have perfect...

I don't know any of the numbers, but I can attest that I have already managed to blow out one set of female threads in one of the aluminum terminals on one cell. :(

Yeah, [happiness] = [reality] - [expectations], doesn't it? Even the high end stuff (I'm looking at you, Victron) suffers from over-zealous marketing making its way into the datasheets... it's rampant.

Certainly. Living in both marine and overland environments, ruggedness is important. But volume and mass are also very important. And price is important. I'm not at all convinced that plastic-shell cells are more rugged than the modern alternative. Do you have evidence of this? If...

They use them in submarines.

And, just for reference, Frey aluminum cells, with their fancy plastic separator shells, specifically are not compressed during build. (And they also do not expand at 100% SOC.) So either some manufacturers build in extra volume to accommodate it, or their chemistry minimizes it, or the shell...

Put them in 16s, draw them down to 3.1 or so volts while watching carefully. Put them in 16p, stick them on my powerlab8 in discharge mode, discharge to 2.90V. Let them rest. Discharge again. Let them rest again. Now they are bottom-balanced, but you could do the same thing except in...

Exactly. Now, the comments about low-rate usage not causing heating... are simply not true. There is heating, and there will be a temp gradient across the pack, especially if you wedge them all together. Will tapes his cells together, but he is not building a huge pack for mission critical...

Indeed; there is some Substantially Misguided Writing in this forum at times. Ironically, putting large numbers of mildly-mismatched cells in parallel groups actually improves capacity balance among many of those groups placed in series, because of the law of large numbers.

Mine are exactly the same. Enough that with some of them, it is nearly impossible to get them perfectly aligned in groups of three or four. I have resorted to swapping them around until their various undulations "cancel out" better for squaring up the terminals. There are many other alu cells...

I love that you ran the numbers. I think you've been very aggressive; I would expect the battery being discussed (RV energy storage, not a traction pack) to operate at well under 1C normally and have much lower heating than your worst-case scenario. Here are some counterpoints, to further...