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I may not have been clear. You want each cell block (logical cell group), to have the same capacity. Otherwise the pack will be limited by the 2 lowest capacity cells (matched together). So you want to pair cells in such a way that each pair has as close to the same capacity as reasonable...

Depends on your current. High current applications should match against IR, so each cell in the block shares current equally. Lower current applications should pair cells so that each block/group has the same capacity. Your IR values are close enough that contact resistance variance between...

I wish there was a decent auto tilting mechanism out there (for RVs). Haven't found one yet at least. Even 10 degrees would make a big difference!

If you operate within the middle 50% SOC, then it can take years for imbalance to appear. Most of us don't want to spend double on a pack, so we use 90% or so of the total capacity when needed. Which is why it's a bit disingenuous/ confusing to make some broad claims when operating a system...

Agreed. In fact due to cell to cell variance, in the middle range two cells of the same soc can have 1-2 mv of difference as well. Which is why attempting to balance in this range can actually create a worse imbalance. This imbalance can be unseen until the pack is taken to high or low SOC...

If the pack is operated continuously in the flat area of voltage curve, no balancer, active or otherwise, can counteract differences in self discharge. This is why regular top ups to the knee area are often required to avoid significant SOC drift with small parallel cell count packs. EVs...

I don't think two separate batteries with solve your drift issue. The primary issue causing the drift after an extended period without a top balance or float, is due to differences in self-discharge between the cells. This is due to manufacturing differences but also due to temperature...

Obviously these cells were likely damaged at the factory. But it can't hurt to remind everyone. These "blue" aluminum cased prismatics are a component, designed to be built into a well designed battery. They have the bare minimum of case thickness, and insulation covering for that purpose...

It is also possible that the cells case has a higher resistance short through the jelly roll at the corner. This causes current to flow through that short location, corroding the case from the inside. This would make sense as the corner is showing signs of mechanical damage.

I believe the cell cases need to be electrically isolated from each other, and from ground. If you short the case to ground, their is a complete galvanic corrosion circuit. This may be what is driving the corrosion. I haven't seen any research on this topic though, so its speculation on my...

Indeed. In the early days of EVs, most of us were running lead acid batteries for cost reasons. I was too cheap to buy a new pack every time a battery died, so having a 6A active balancer running on the pack (each battery was 6v, so it wasn't cell level) allowed me to keep the charge rates up...

Yes, the marine systems I have worked on were all equipped with at least one load shed programmed to leave some reserve capacity. Folks like to throw around the 50% DOD limit for lead, but thats not very accurate. If you look at the total amp hours delivered from a lead battery vs DOD...

Its a very nifty feature of the chemistry. It also makes them less efficient when charging unfortunately. Back when lead acid was used in industrial vehicles, we would occasionally use balancers to keep individual cells (200lb+ 2V cells) in balance. This was typically due to difference in...

On a boat, the best approach is to have a charge and discharge bus with separate BMS driven control. Depending on the battery schema (single dual, triple independent banks) a separate mission critical bus can be implemented. This can drive things like radio, nav gear, bilge pumps etc. Ideally...

The major difference is that a lead acid battery can self balance its cells during absorb through the shuttle reactions. Lithium batteries cannot do this. So balancing is needed, and a BMS can perform this. Lithium cells do not self limit their voltage during absorb. So if a single cell...

A properly fused system would blow a fuse. Not to mention the BMS should drop out. Its a moot point, if you have more than one battery, the same thing can happen with two LFP packs. I have over 20 years experience with every type of lead acid out there. There is no single design spec for...

Engineering for failure courses are a goldmine, and they teach very differently. A lead acid battery cannot disconnect from the bus. They can gradually fail, or become discharged. No matter what you do to a LFP pack, it will always have a disconnect system which relies on digital logic...

Depending on the design some PV controllers can be damaged be repeat disconnect at higher loads. There are a myriad of different designs for PV controller schematics. Check the manual for details. Some are totally fine with this, while others will experience an inductive/back EMF kick, which...

The most common method is to set all the chargers to use a absorb timer. When the absorb setpoint is hit, they all start counting down. You will need to verify that all their reported voltages agree (not all units are calibrated well). Also ensure a reasonably low voltage drop between the...

I can do the math for you, but I don't have the time or motivation right now. We are talking about a small lead acid battery, which by their basic characteristics, are current limited. Even if one of was totally dead, internal resistance, and wiring resistance, will easily limit current. Now...

I am sure there is a reason for that spec, but its not the be-all or end-all of design considerations. Several authoritative sources I have encountered over the years break down the details of such a configuration, and even recommend it for systems where redundant battery packs are not...

There are quite a few marine applications where a modest sized lead acid battery in parallel with the LFP (after the disconnect BMS), can provide significant protection from unexpected disconnect, without the cost of a redundant LFP pack. They don't carry any of the load generally though...

Since LFP doesn't need fancy charge profiles, you can build a basic and effective charger this way. Dumb single voltage power supply (with integral current limit). Set it to whatever you want your final termination voltage to be. Programmable voltage sensitive relay. Set the rely to open when...

Changing the cell resistance range is pretty simple in the Orion software. Assuming your resistance values aren't too tight, then it could be a poor connection on that cell.

Generally speaking, about 85% of the torque on a fastener goes to overcome friction, and the remainder goes to adding clamping force. Friction is split between friction between the nutface (or bolt face if tightening the bolt side), and thread friction. Clamping force (pullout force), is...

Any chance the terminal spun? Probably not worth it, but you could cut the can off the cell if you still have it. BTW the electrolyte is toxic when it comes into contact with moisture, so wear gloves, and use copious water to wipe down any surfaces.

Thanks for posting, thats good info for all of us, though its an unfortunate turn of events. If I am ever drilling something sensitive like this, I make a drill stop from a piece of pvc/pex pipe, or I get a locking collar on the drill bit.

Pack is still rock solid, no balance issues, and the MG paste and nickel plate seems to be doing its job. Might do a capacity test in a bit to see what my degradation has been.

1% per year while cycling is very good, Though your temps aren't southwest like, which helps. Assuming a standard capacity loss acceleration, 15 years should be totally doable, maybe 17 if you don't mind operating with capacity less than 80%. My vans pack has seen more elevated temperatures...

Thanks for the data, very useful! A couple questions, I tried wading through the thread, but gave up after 10 pages. What is your charge voltage? How many months/years has the pack been in service? The reason I ask, is so that I can work out your degradation a function of pack age and cycles.

Looks like nickel plated copper to my eye. I believe the base material is nickel plated copper which is stamped to shape, then they are stacked, and the heat shrink is applied. So the edges will be bare copper. Given how flexible they are, hopefully surface imperfections will flatten out with...

I am a big proponent of having heat generating equipment in a separate compartment from the batteries when in a hot climate. The energy required to keep a LFP pack cool is nearly an order of magnitude less than what is required for inverters, charge controllers etc. In many cases a moderately...

Not sure if it was mentioned here, but these look promising. Basically CALB style laminated tinned copper. I believe they are available in several spacing options. https://www.aliexpress.com/item/1005003616882134.html I have had good like with the MG chemicals carbon paste, that might be...

My initial target was also 3kw of PV. However, looking at my layout options, I could just barely squeeze 4kw of PV onto the roof. Which based on my insulation and AC efficiency, should be pretty much 100% of my needs in summer, which includes a condenser dryer and induction cooktop. Even with...

I'm familiar with the whoosh and related noise that comes when the reversing valve flips. This noise happens a few seconds later as the compressor ramps up and it's almost like someone's playing a horn or instrument inside of my idu. I guess I will see what cooling performance is like in the...