So much for perfection - JK bms

[Skypower]

After having a pretty good run with two JK bms’s, I added a third bms & battery for 16 cell batteries. The first two are are models JK-B2A24S20P (24cell version) and the only issue I can see is some strange occasional “Abnormal release of current sensor” in the log file but doesn’t seem to have any affect in functionality nor alarm so I ignored it, also with the third battery it seems to be gone. The new, and perhaps problematic is the JK - B2A20S20P (20 cell reference now on). The first two took about 5 cycles to learn what 100% full SOC (state of charge) was. Curiously, the new 20 cell read 100% on the first charge. Things looked great for the first week then I started to notice it’s divergence from the first two and up to 12% deviance. Now I understand that the batteries can charge and discharge at different rates but full is full and when they are all at the same voltage at the top, I’d think that, that would be the only time that they’d be having the same readings of 100%. None of these bms’s have ever seen anything more than the full, bulk, end of charge 55.2 volts. They all get to full charge at least once every 3 days. All are nicely balanced charging and contributing perfectly. The only thing that is a problem is my OCD when I don’t ever see the Solar Assistant get to 100% because it uses the average of the three batteries. I’ve re checked the voltage and current adjustment in the app to reality and it’s correct. The only thing I can think of is the new bms has a different algorithm that wants to see more absorption time (that it’s not gonna get). Typically it runs up the knee, current drops off, holds at 55.2V for 15 to 20 minutes, releases and drops to 54.4 float as long as the sun can hold it there. Rinse and repeat every day. Already ordered a new 24 cell JK. At least the layout in the apps will look the same since data is presented in different order between the 24 vs the 20 cell. Any ideas? I wish that JK offered a “set state of charge” like other brands.

 

[timselectric]

At 55.2v you're only getting the cells to 3.45v. That's barely touching the upper knee of the charge curve. There's no way to know if you're cells are balanced. Because they will always be close in the flat part of the curve. I don't even start balancing until 3.45v. Because there is no balancing required, yet.

 

[LydMekk]

I have 2 pcs. 24 versions 200a.
I prefer to bulk with 3.55V and float with balancing at 3.45V.
Works very well here.

I think I set the balancing to begin from 3.3V and upwards.
The active balancing is very nice and one of the main purchase points for me.

 

[Skypower]

At 55.2v you're only getting the cells to 3.45v. That's barely touching the upper knee of the charge curve. There's no way to know if you're cells are balanced. Because they will always be close in the flat part of the curve. I don't even start balancing until 3.45v. Because there is no balancing required, yet.

I’ve been watching others and Andy, Off grid Garage and they typically don’t go any higher. I’ve noticed that voltage shoots up like a rocket once it gets past 3.4vpc and I don’t believe there’s much capacity to be gained up there. All three batteries balance to .003 or better and usually stop balancing before the bulk charge is released. My delta is beautiful though out the flat even with a heavy load. Float 3.4 , balance start 3.42, bulk 3.45. So you’re saying the new bms is confused because I’m not going higher?

 

[Skypower]

When you zoom in on the voltage/time, you can actually see a flat top or dwell time where it has ample time for balance along with some of the time ot the sides. The points aren’t exactly pointy.

 

[timselectric]

I’ve been watching others and Andy, Off grid Garage and they typically don’t go any higher.

I'm not saying that you have to go higher. If you float long enough, you can get to better than 95%.

I’ve noticed that voltage shoots up like a rocket once it gets past 3.4vpc

that is because you are getting into the upper knee. Which is where balancing is needed.

and I don’t believe there’s much capacity to be gained up there.

Correct
Only about 5% or less.

All three batteries balance to .003 or better and usually stop balancing before the bulk charge is released.

That's easily done because you are still in the flat part of the charge curve.

My delta is beautiful though out the flat even with a heavy load.

It should be, unless you have a bad cell.

So you’re saying the new bms is confused because I’m not going higher?

Not at all.
I was only commenting on your statement that your cells are well balanced. And that you wouldn't know that, if they never get to the point where they would need to balance. You don't need to charge that high regularly. But you should occasionally get them in the upper knee. So that they can balance. Or at least once in a while, to see how well they are actually balanced.
I also use the JK BMS's. (Wouldn't use anything else)
I started with the 24s, and liked them a lot. But they became impossible to find. So I started getting the 20s. While I wouldn't trust any BMS to report accurate SOC. The 20s aren't even close.
If you want accurate SOC monitoring. A shunt is the best option. I use a Victron Smart Shunt. (Again, wouldn't use anything else)

 

[Skypower]

If I charge them up higher, wouldn’t all the bms’s think that’s the regular full state of charge or does it take more ventures to that level to learn? That 20s just seems different, newer I think, but different. Yeah, I’m kinda holding out on that shunt, no argument that it’s not the “last word” of accuracy. The irony is that when I first ordered the first two bms it was for the 20 cell and they asked to substituted them for 24 because they were out, I said sure. I hope they don’t substitute it around the other way this time lol.

JK Smart BMS with 4S 8S 16S 100-350A LiFePO4 Battery Protection Board with Bluetooth Module 1A 2A Active Balance (JK-B2A24S-20P)

https://a.co/d/1z9cJGY

 

[timselectric]

That's not a bad price, either.

 

[timselectric]

If I charge them up higher, wouldn’t all the bms’s think that’s the regular full state of charge or does it take more ventures to that level to learn?

It's hard to say. The 24s's don't report 100% until one of the alarms are triggered. My 20s's report 100%, while still charging at 40a. lol

 

[Skypower]

It's hard to say. The 24s's don't report 100% until one of the alarms are triggered. My 20s's report 100%, while still charging at 40a. lol

Humm, there is a difference, but not on the outside unless you can read chicken scratch. The color bar I posted was a bit misleading, the two at 95% do regularly get to 100%. I just grabbed screen to show the spread to the other. The one doesn’t get over 92% and usually less.
The price isn’t bad but there’s still shipping and tax. On the other side, there’s the Amazon guarantee so I know I get what I pay for. Unlike the 40 thieves.

 

[timselectric]

Oh no, the price just got too high for me.
I'll stick with 18650batterystore.

But before I click post, let me check current prices. lol

Well, Crap......
Looks like prices have gone up, everywhere.

 

[Skypower]

Just wait till you see the new price for your cereals

 

[timselectric]

Hopefully things will get better, after the next election.

 

[Skypower]

Oops ?
So I took you advice…..
Don’t worry ?
So I charge them to 58V and within minutes all three batteries alarmed and disconnected charge ?
The new one, over voltage exceeded (forgot I had set it at (3.6v) delta was fine @ only 10mv.
The two older ones had high cells and disconnected (3.65) but both balanced within minutes.
Observation; very soon after passing the original absorption voltage, the new cell reset to 100%. I guess it just needed a kick in the ass.?
Now the other batteries are reading 98% @ 55.2 so I guess it’ll be a few cycles for them to relearn?
Next time;
Just turn off the charge/discharge on the older batteries. Limit the solar charge current and bump the new one till it resets SOC. Then bring everything back to square one.
It’s not lookin bad at float. I’ll take it?

 

[Skypower]

Now I got a Spare JK Lol not a bad thing

 

[timselectric]

I keep a spare.
Always one ahead of the next order.

 

[Skypower]

When you’re prepared, you’ll never need it.

 

[740GLE]

Or if it ends up burning a hole in your pocket reach out I may be able to take it off your hands ?

 

[Skypower]

And this is why I don’t want a Frankenstein battery. The new one is a 280 Eve and the two others are 2 year old 305 CATL’s. They all play hard together and sometimes the new one outpaces the old so it makes up for the reduced hunger into the knee. Just different subtleties in design, but imagine trying to balance a battery with this mix! Monster NEEY $$$$.

 

[timselectric]

It all works out on its own.
Right now I have 5- 280ah diy and 1 - 100ah server rack running my system. They are all happy to do their share.