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Hi Will, Buy a relay rated for purpose. They are more expensive. :) The good relays most of us use have back EMF suppression built in. They cost a little bit more. :) I'm not sure this is true. Larger systems simply have higher complexity; there is no way around the physics. Even...

It's entirely possible that some of these large format prismatics actually undergo a capacity change during their initial few uses (and during their long passive period sitting on the pallets and boat). It stands to reason, if there are mechanical changes (electrolyte expansion, case-widening...

The problem with 'normal' ampacity ratings is that they allow for huge temperature deltas -- 50C is pretty common. +50C over ambient is a very hot busbar to have in direct contact with a lithium cell terminal that is attached to a battery that we know doesn't enjoy getting much over 35C in...

Well, I certainly appreciate your rigor, in a very selfish way.

Yes, for most of us, our design peak currents will not be continuous and/or may never be achieved in real life. And many of us will just overkill since we are not often cost-engineering here. Yes, but radiative losses are not the dominant heat transfer mechanism in most wire (unless it is...

I agree with most of what you've written in these threads, but this is simply not true in my experience. You can slowly charge LFP to 96 or 97% SOC at 3.40Vpc, any day of the week. (And it might well take all day, because the rate will be quite low at that CV.) I don't think it's fair to say...

Getting similar wiring resistance is a good idea for maximum pack efficiency, but in real life the paralleled batteries (strings) have other factors that affect their current flow much more, in my experience. On top of that, there are LOTS of battery installs where people are just paralleling...

Yeah, float them at lower voltages until you see the SOC you’d like to achieve. Don’t listen to the folks advocating for holding packs at 100% all the time. It makes sense to take simple steps to (maybe) get even longer life out of the cells.

Running cells at 131F, or even 100F, for long periods is a great way to cut their lifespan way down. Even a small amount of internal heating can amass a large heat reservoir in a big block of dense metal and liquid. Some packs are installed in locations without active climate control...

When networked, the BMV voltage should be being used as the reference.

Larger modern cells seem to be performing better than older ones did years ago. Hopefully the internal mechanical stability has been improved over time. More important today for mobile setups, in my opinion, is how feasibly you can brace the cells and how sturdy the terminals are. The cells...

I don't use a BMS on eight 16s packs, some for nearly three years now. They work fine. You have to commit to managing the charge and discharge voltages carefully at first, along with a robust initial balance and cell capacity validation phase. You must accept that you are not going to be able...

I was suggesting that, if you’re willing to accept the consequences of storing at 30%, you might as well store at 70%.

I'm going to disagree, again, here. I use this exact strategy. My smallest cells (which are 3Ah smaller than the largest) are not being damaged. Have you actually tried this? Please share your actual data... because I have mine, and I'm curious what you're doing differently (and whether I...

I've carried around a few spare 100Ah cells for several years now. They're within 10% of the SOC they started with (~70%).

Yes, it is normal. There's a meaningful gap between the voltage when charging and when discharging. As much as 300mV at the very top of the capacity curve, and roughly 100-175mV in the middle. (The actual delta depends on how much current you move.)

I don't mean to sound like I'm quibbling with your terminology. But I have lived full time off of my battery for 2.5 years now, and I have a lot of incentive to charge fast, to not run my generator longer than I need to, and to harvest all the solar I can get. And those desires are not...

On a Multiplus, if the AC input is powered, the buffer capacitors are charged immediately. On a Quattro, that is true only for AC input 1. I can't think of a reason to avoid connecting the battery when the unit is powered up on AC. I suspect during a restart procedure that you're overlooking...

Yeah, the exact voltage is really dependent on the things in the circuit between your battery and the thing measuring the voltage (e.g., wires, fuses, relays, BMSes), and then the thing measuring the voltage has some error in it, too. Since even a few millivolts can yield a pretty different...

Bingo. These cells are a bargain. Qualifying and then replacing a few at 96% of specification might feel good, but it is a Pyrrhic victory that places the value of our time at something like pennies per hour, for that little extra. Just assume they’re 90% of rated, or buy 10% more than you...

The extended cycle life with clamping is estimated in the context of a "standard charge," which in their definition is 0.5C, ramped to 0.05C at 3.65V. That's running these cells up reasonably fast to a pretty high SOC. Observed results suggest that charging to a slightly lower SOC (say, 90 or...

Very cool. Thanks? Thanks.

What I ended up doing is placing a large bus bar (with a 6mm hole) on the battery first. Then I put the MRBF on top of that bar, wherein it has a large contact patch. I also made a shim to keep the 10mm hole from floating around on the 6mm post. No meaningful heating issues observed under...

The data are sparse, but it's very clear that carrying higher temperatures AND holding high SOC will dramatically accelerate capacity fade in LFP. Interestingly, NCA seems to do about as well, and NMC totally falls off of a cliff. The best paper I've come across is Keil, 2016, JECS. It would...

Good idea, do some math. But I think you may have missed some important things. First of all, in a uniform wire, length is irrelevant. A longer 4/0 will have more resistance, and a shorter 4/0 will have less resistance, but also each will have different mass and different radiating surface...

I measured the current on the parallel versus series links in a pack I am building this week. The series links carry most of the current. The parallel bars mostly carry rebalance current. The pack is a 4p4s topology. The rebalance current, within the time resolution I could measure with my...

2.1V one time only is not a problem for LFP cells. Those cells will probably be okay, if you want to use them. You do need to figure out the source(s) of your errors so you can get back to a stable setup and start to gain confidence. You are learning the semi-stressful way, but hang in...

Both of these last two posts by Luthj match my understanding/experience exactly. One thing I would add is that the overcurrent cascade failure risk is reduced when there are more strings in play. Then, the contribution of a string that suddenly drops out can be distributed across more sibling...

I would marry them at your balancing "side" of the voltage curve. For example, if you top-balanced both strings, join them up at a high voltage close to the balancing value you started with. You won't get much power inrush if the voltage is pretty close, because discharging LFPs drop in...