Why cant I run more than 4 lifepo4 batteries in parallel?

[time2roll]

As I said there's no magic number "4", but the more you throw at it, the more you need to protect it, monitor it, and know how to react to it when things go wonky

I think four is from the lead-acid world. Such that if one battery has a shorted cell the other parallel batteries will dissipate their energy into the shorted battery and boil off the electrolyte and potentially cause an explosion.

 

[Bobert]

That too, but no. Batteries in parallel will self balance over time, this is true, but it is the over time that can get you if the power being pushed into the different batteries is done so unevenly, or even when the individual batteries in the string absorb / provide power unevenly. Having run multiple banks in in parallel, and even used mixed chemistries in series/para mix I've watched it happen, I've adjusted for it, and I've remediated it.

Top that off, with the fact that unless you're staying with 12-volts these are series connections as well and the need to just know what your in for becomes priceless

As I said there's no magic number "4", but the more you throw at it, the more you need to protect it, monitor it, and know how to react to it when things go wonky

Ah yes I wasn’t thinking about high continuous c rates. In my application the charge and discharge rate is relatively low and I have a large amount of time every day that the batteries are virtually idle.

 

[eabyrd]

Yes sir. all batteries have monitors on them. They stay within .1 to .2 volts of each other.

And there you go, if your willing and able to put forth the oversight then any configuration is doable. Within reason

 

[good4politics]

Bingo! I have run four, but now only three for that reason. I have no problems with three but have had an issue with four. I see guys with up to eight batteries in parallel, but they have more money than sense and a lot of high-tech goodies to monitor them.

I have not found this to be a big issue. I am running 48v/550ah. Now... All my BMS are JBD programable ones. They are all set to cut of charging if any one cell exceeds 3.4v for more than 2 seconds. There is very little energy above 3.4v and even less below 3.0v but your batteries will have a much longer life if they stay between those voltages. Both are well inside the absolute minimums and maximums so it's a non-issue.
These are not even the same kind of cells. One set is 4s2p 75ah per battery. 2 are 4s1p 100ah per battery, 2 are 16s1p 48v batteries but each cell is made of 20P 5ah 26700 cells.

It all works fine if you stay between 20% and 80% of the cell voltages. All of them are attached to a single pair of 800a bus bars all the charge controllers are attached to those same bus bars too. Charge controllers -- 100v|20a, 150v|40a, 150v|60a, 150v|70a

I would contend that the more batteries that are in parallel, the less likely any battery will have a voltage significantly lower than the others. If they do, there's something wrong with that low battery.

Lifepo4 batteries in parallel balance. They really have no choice unless one is defective, having a significantly higher resistance than the others.
Lifepo4 batteries in series do not balance. a 4 battery balancer would be a good idea.

If I had 16 batteries that are exactly the same, I would place 4 each in parallel, then put the 4 parallel sets in series with a 4 battery balancer attached to each parallel set. (one pair of wires per parallel set).

If you have ever top balanced a set of cells this should not be news to you.

 

[hclarkx]

Not true. While the op was talking a out batteries not cells, even with cells there is risk in placing them in parallel. The BMS is not designed to sense the state of or to balance a group of cells with each lead. It will not know the condition ofthe individual cells at each point in the series. Yes cells and batteries will eventually self balance. The problem is the differing rates of charge and discharge. 2 is fine. Up to 4 manageable with care. more than that is problematic

Lifeblue uses 12 parallel 25 Ah cells (per "cell") in their 300 Ah batteries.

 

[Bop]

This would only be true if you were actually trying to pull 600A from the batteries. Assuming 12V batteries that would mean over 7200W. No one should be attempting to such usage. Just because 6 such batteries in parallel could support 600A of discharge current, that doesn't mean they will be subjected to anything anywhere near that much.

Someone using a 12V setup might, at most, have a 3000W inverter which could pull up to 300A if pushed to its limits.

Looks at the 12v 8kw inverter in the corner running this computer...
They don't???
Bugga- seems I am imagining my life here...

Coupled to a 4S4P 16x 400Ah cell battery bank currently...
(stayed with 12v at this point as I a: had the inverter (been in the back of the ute for camping and work since 2014- hence the battered appearance) and b: the caravan runs off 12v for its lighting, waterpumps for the shower and sink, and the inbuilt TV- so 12v made more sense for this setup- once the house is finished, it will be reconfigured as a 16S 48v system (would have preferred 96v, but I got the 48v 12kw LF inverter cheap as it was 'old stock', nobody here is installing 48v anymore for offgrid housing

 

[pollenface]

Some manufacturers state "unlimited" parallel connections.