14.2, 14.4, 14.6 - seems like there is no agreement on charging voltage

[John Frum]

I had not tried charging individual cells, it was easier to take one or two down.
Time2roll gave me the same solid advice, my pack is happily balanced now.

Started here…



Finished here…

We can't tell from the second picture if your pack is balanced as all the cells are in the flat part of the curve.

 

[Pierre]

We can't tell from the second picture if your pack is balanced as all the cells are in the flat part of the curve.

Why ? There is no charge current flowing and the total capacity indicates 99% full .

 

[John Frum]

Why ? There is no charge current flowing and the total capacity indicates 99% full .

Because all the cells are in the flat part of the curve.
They usually don't diverge until they in the high knee.
Especially when they are receiving charge current.
That is why its good practice to only balance above float voltage and only during charging.

Weird analogy but its like when a hair dresser pulls the hair away from your scalp to see the cut line.

https://www.wikihow.com/images/thumb/5/5f/Cut-Your-Own-Hair-%28Men%29-Step-12-Version-5.jpg/aid4095407-v4-728px-Cut-Your-Own-Hair-%28Men%29-Step-12-Version-5.jpg.webp

A pack can be far out of balance at the top and appear fine in the flat part of the curve.

 

[John Frum]

@pierre did I convince you?

 

[John Frum]

This is my charge termination from last night.
Boost voltage = 27.75 volts
Float voltage = 26.75 volts
The log doesn't show it but <10 minutes after we transition from boost to float the cells will settle to ~.006mv delta.

BTW I don't consider this pack particularly well balanced either.

2023-01-22 05:05:32 Tail_current < 9A
2023-01-22 05:05:32 Boost=off Balance=10000010 Delta=0.039V Min=3.434V(cell1) Avg=3.452V Max=3.473V(cell0) Cell=26.6C Ambient=25.8C Rate=8.9A
2023-01-22 07:00:41 Power=off Balance=00000000 Delta=0.006V Min=3.336V(cell6) Avg=3.339V Max=3.342V(cell1) Cell=26.2C Ambient=25.6C Rate=0.0A

 

[Pierre]

@pierre did I convince you?

Yes I agree now. The cell voltages should have been around 3,55 to 3,6v. I was only looking at the cells delta and % charge ( which can be manipulated in the settings ) @Browneye is happy with his battery and I had to do the same because of a runner cell.

 

[hwse]

Opening the case and adding charge or load to individual cells is a very quick way to balanse a pre-built pack but there is still hope for those of us who have sealed, non-cervicable packs.

This is where I started. This is actually not the worse case given that this pack had been held at 13.9v for a week for balancing before I took this screen shot which was after the first full capacity test. I did not get a screen shot of the worst delta which was almost 300mv.

1/2/23
Bottom delta @ UVP = 398 mv



12/27/22
Top delta @ OVP = 262 mv




1/22/23
Top delta @ OVP = 68 mv



This is a huge increase in the balance of the pack. I did it by turning off charge balance and charging it slowly until cell #3 got to OVP cutoff. I then turned off both charge and discharge FETs and let the pack balance for 24-hours. rinse and repeat. I saw gains in the max pack voltage I could charge to and reduced delta each day.

 

[sunshine_eggo]

Opening the case and adding charge or load to individual cells is a very quick way to balanse a pre-built pack but there is still hope for those of us who have sealed, non-cervicable packs.

This is where I started. This is actually not the worse case given that this pack had been held at 13.9v for a week for balancing before I took this screen shot which was after the first full capacity test. I did not get a screen shot of the worst delta which was almost 300mv.

1/2/23
Bottom delta @ UVP = 398 mv



12/27/22
Top delta @ OVP = 262 mv




1/22/23
Top delta @ OVP = 68 mv



This is a huge increase in the balance of the pack. I did it by turning off charge balance and charging it slowly until cell #3 got to OVP cutoff. I then turned off both charge and discharge FETs and let the pack balance for 24-hours. rinse and repeat. I saw gains in the max pack voltage I could charge to and reduced delta each day.

Yep. This is pretty much the standard way of doing it. Float the battery at the maximum voltage it can sustain without triggering BMS cut-off. A typical JBD/overkill can balance about 0.5-1.0Ah/day, so it may take awhile.

However, I'm a proponent of holding the cheap-os accountable. If the battery can't be charged to recommended voltage, it does not meet spec. They're using the customers as the final step for quality assurance. An as-received imbalanced battery means they are making no effort to match or balance cells, which means they're of lower quality and may indicate reduced service life.

 

[hwse]

Yep. This is pretty much the standard way of doing it. Float the battery at the maximum voltage it can sustain without triggering BMS cut-off. A typical JBD/overkill can balance about 0.5-1.0Ah/day, so it may take awhile.

However, I'm a proponent of holding the cheap-os accountable. If the battery can't be charged to recommended voltage, it does not meet spec. They're using the customers as the final step for quality assurance. An as-received imbalanced battery means they are making no effort to match or balance cells, which means they're of lower quality and may indicate reduced service life.

I did not hold the pack on float. I charged it up and the isolated it from all charge and loads. The balancing was with charge balance "off".

I agree that it would be good do "hold the seller accountable" but given that it takes 2-months each way and I would need to pay for the shipping, for me, it was better to see if i could get the pack to balance and save the trouble. In the next week or so, I should have it balanced and able to charge to +14.5v and then will do another capacity test.
In the first test, this battery only gave 445Ah out of the rated 460Ah. The other more balanced pack (80mv @ OVP) gave me 475Ah so I am very confident that this pack will now exceed specifications.

 

[sunshine_eggo]

I did not hold the pack on float. I charged it up and the isolated it from all charge and loads. The balancing was with charge balance "off".

I agree that it would be good do "hold the seller accountable" but given that it takes 2-months each way and I would need to pay for the shipping, for me, it was better to see if i could get the pack to balance and save the trouble. In the next week or so, I should have it balanced and able to charge to +14.5v and then will do another capacity test.
In the first test, this battery only gave 445Ah out of the rated 460Ah. The other more balanced pack (80mv @ OVP) gave me 475Ah so I am very confident that this pack will now exceed specifications.

Yes, you want to turn charge-only balance off. The issue with not keeping a float voltage applied is that the slight current from the balancers often pulls the cell voltage down below the balancing threshold pretty quickly, so balancing stops.

I understand that there are other factors at play in the "return or salvage" decision. Important to procure from sources that provide free returns as a company sending you a product that does not meet specification is their issue, not yours.

How did you maintain 13.9V for a week if you didn't float it?

Had you continued to hold it at progressively higher voltages rather than the on/off approach, it would have balanced faster.

 

[KITROBASKIN]

If a tier 1 battery supplier guarantees 100Ah and a 10 year warranty within spec, and a tier 2 supplier does essentially the same for quite a bit less money, is it right to initiate a somewhat expensive process (return) because we want a tier 1 product for a tier 2 price? Realistically how much better (capacity and longevity) is having a very matched set of cells compared to the product SOK seems to be offering these days. 2%? Less? If a person was buying a large quantity of batteries, would it still be more cost competitive to get SOK and live with the single digit decrease in value?

Those members here who have or currently run a business like currentconnected know that there will be compromising in manufacturing to offer a competitive price, that SOK may very well be allowing a greater variance in their cells in order to utilize more efficiency, while still meeting spec.

Is the admittedly imperfect Bluetooth feature more bane than boon? It certainly can yield ruffled feathers, but for most users, thinking they are just going to go fishing, and the few finicky will have to be addressed (wanting a tier 1 product for a tier 2 price) with service tech time and possibly returns.

One opinion.

 

[hwse]

The two 460Ah batteries that I got were from Basen Green and cost $1200 with all fees and shipping, delievered to my house. When I receieved them one produced 480Ah on the capacity test (20Ah more than advertised capacity) in spite of the 80mv imbalance. The other only produced 445Ah on the capacity test (15Ah less than advertised capacity) with an imbalance of 300mv at the OVP and 400mv imbalance at UVP.
The actual tested capacity of the two batteries was 925Ah or 5Ah more than advertised so I got what a paid for.

Now that I have taken the time to get them balanced, I expect both batteries to have somewhere around 485Ah or 970Ah total (12,416wh) for $2400. That comes to $2.47/Ah ($0.19/wh) and I cannot get FLA golf cart batteries for that price assuming 50% SOC max discharge.

Yah, I am pretty dang happy with them.

Basen 12V 460ah Battery LiFePO4 Pack 5000 Cycles Cells

Basen 12V 460ah Battery LiFePO4 Pack High Capacity Deep Cycles Home Stroage Energy System HOUSING: ABS CASE SIZE: 520*269*220MM BMS: 200A BMS WEIGHT: APPROX. 41KG TERMINAL: M8 CYCLE LIFE: 5000+...

www.basengreen.com

 

[hwse]

Yes, you want to turn charge-only balance off. The issue with not keeping a float voltage applied is that the slight current from the balancers often pulls the cell voltage down below the balancing threshold pretty quickly, so balancing stops.

I understand that there are other factors at play in the "return or salvage" decision. Important to procure from sources that provide free returns as a company sending you a product that does not meet specification is their issue, not yours.

How did you maintain 13.9V for a week if you didn't float it?

Had you continued to hold it at progressively higher voltages rather than the on/off approach, it would have balanced faster.

That first weed I did float them at 13.9v but did not like having the constant high voltage with even the tiny charge current that went with it. During that time, I had charge balance turned off because most of the time, there was 0w going or coming from the Magnum, so I was not using the charger for anything other than holding steady at 13.9v

It is true that I might have had a bit faster result by just leaving the float at the highest voltage that I could set without tripping the OVP but felt that the charge and isolate method was safer and gave me a way to see how much progress was made each day. I have two of these 460Ah packs so even though one battery was offline, the other one was always available to run my daily loads. I am currently living in my motorhome so needed to have at least one battery on-line but am currently in a full hookup site so have shore power to charge the other pack.

 

[archjeb]

So, i balanced it by putting a load on cell 3 and have them a little more equal now. But CMOS is still tripping once the cell voltage gets high enough. Makes me wonder if the charger (2Amp Noco) is actually going higher than 14.6 volts.

 

[John Frum]

So, i balanced it by putting a load on cell 3 and have them a little more equal now. But CMOS is still tripping once the cell voltage gets high enough. Makes me wonder if the charger (2Amp Noco) is actually going higher than 14.6 volts.

View attachment 131055

I would call that good and get on with life.

 

[Jennifer]

That first weed I did float them at 13.9v but did not like having the constant high voltage with even the tiny charge current that went with it. During that time

Well that's one way to make the time balancing pass faster, count it in terms of the doobies you burn through while doing it. ?

 

[Browneye]

We can't tell from the second picture if your pack is balanced as all the cells are in the flat part of the curve.

They are always balanced there. Past 3.5Vpc or so usually bms will start balancing one.
To show balance at that voltage I would have to plug in and fire up the charger. RV is in storage mode, I just let the SCC trickle it and keep it around 3.30 to 3.35Vpc.

Perhaps in the next few days I'll capture cell state at high knee with the battery charger. Wouldn't hurt to exercise them a little. It's been sitting for months - last trip was first of October.

 

[hwse]

So, i balanced it by putting a load on cell 3 and have them a little more equal now. But CMOS is still tripping once the cell voltage gets high enough. Makes me wonder if the charger (2Amp Noco) is actually going higher than 14.6 volts.

View attachment 131055

It appears that you have your charging set to 14.6v which means that your pack needs to be perfectly top balanced to 3.65v and even then, will still shut down due to OVP. In normal charging conditions it is best to not charge that high. down around 14.2 - 14.4 is fine.

 

[hwse]

They are always balanced there. Past 3.5Vpc or so usually bms will start balancing one.
To show balance at that voltage I would have to plug in and fire up the charger. RV is in storage mode, I just let the SCC trickle it and keep it around 3.30 to 3.35Vpc.

Perhaps in the next few days I'll capture cell state at high knee with the battery charger. Wouldn't hurt to exercise them a little. It's been sitting for months - last trip was first of October.

On one of my packs, I had a 300mv delta with cell #3 was at 3.65v. Even with that huge delta, the cells were all within 5mv when the battery was between 12.8v and 13.3v. After that, the delta would just go off the chart.

 

[MarcoWasRight]

Please cite a LFP cell specification that permits this.

I know what you're saying, but it's old information, and it shouldn't be perpetuated.

The old A123 ANR26650 M1 specification stated it but I'm having trouble finding a copy of the old datasheet. HKJ copied the info and put it on his website
This site also talks about it

Technical Information LiFePO4 Care Guide: Looking after your lithium batteries

LiFePO4 Care Guide: Looking after your lithium batteries - Technical Information LiFePO4 Care Guide: Looking after your lithium batteries

www.evworks.com.au

Then there is also a couple on YouTube that put lithium in their RV a decade ago and the distributor was telling them (per manufacturer) to charge up to 3.8 or 3.9V
Yes, this is "outdated" information as we now know that there is no benefit above 3.65. That might even change to 3.60 one day
Just because it's old information does not mean it is incorrect. It is the max safe charging voltage. You have nothing to gain and you have no body parts to lose but cycle life is something you will very likely lose.
I had thought this was well known information on this forum.