battery charging some up to 3.99 some at 3.3

[jvbutter01]

Have new cells purchased in forum group buy, watching some of the vids out there about top balancing. I will lay them all in parallel, get the voltages the same. Some I had to hook up the mini cell tester @Will Prowse recommends in one of his vid to get the cell back so its matched to the others...
#1@ 3.35
#2@ 3.33
#3@ 3.35
#4@ 3.34
when I hook them back up in series 4s config, and put the charger, the 1 positive and now 1&2 pos climb up above #3&4 cells
#1@ 3.82
#2@ 3.37
#3@ 3.37
#4@ 4.16

I put the cell tester back on the cells and got them down to same voltage
#1@ 3.35
#2 @3.33
#3@ 3.35
#4@ 3.34

I broke down the pack and swapped the #1 &2 cell and #3&4 cell in the position in the back. now put back on charger starts out 42a charging, within 20 min shuts off ( they are probably high SOC) and I check the voltages and we have
#1@ 3.9
#2 @3.33
#3@ 3.45
#4@ 3.35
seems where ever I move this cell it keeps charging up to 3.9x. Is there anything to do about this? I cant get the pack to charge up to 3.65 as i have read about.

thx

 

[snoobler]

Not sure what you've read, but it's wrong. Please read the document in the Top Balancing post in Resources.

You have a cell that is at a higher state of charge. Of course the problem is going to move with the cell. The ONLY way to top balance is to parallel and charge them to 3.6-3.65V. Any other efforts require luck.

 

[Bob B]

You are letting your cells get too high when in series and are risking ruining them .... are you trying to charge in series without a BMS?

 

[BarkingSpider]

Try discharging that cell at few 10ths of a volt, to bring the state of charge in line with the others, then charging the whole pack.

Or remove it from the pack, and charge up the remaining cells to the same level.

if that does not work out, that cell simply has a lower capacity than the other cells.

 

[jvbutter01]

thanks for the info... @snoobler i will read that. I hadn't read that, only watched wills vid and was working off that. @BarkingSpider yes I have done that a few times, dropped it down to match the other 3 and when in series and back on charger, it peaks first again, shutting off the BMS.

 

[MisterSandals]

Yea, that cell may never be compatible with the other 3. Putting them in parallel, i think preferably at a lower but equal voltage ~3v, then charging in parallel (as snoobler instructed) up to 3.6-3.65 is you beat chance.
Charging in series at 42A (pretty high current) will be more prone to revealing cell capacity differences.
And, even a balancer will have a hard time keeping up with a 42A charge.
Perhaps after to balancing, a super conservative charge strategy will make it more manageable. Try charging up to 13.4v for example and see if all cells stay within safety bounds (2.5v-3.65v).
If good, try 13.5v...
Thee will be some charge/discharge range that will work without the rogue cell being overcharged. Maybe thats enough for your use.

Worst case is you replace that cell.
Maybe your cell can be replaced now if recently purchased (best case scenario).

 

[Steve_S]

That cel;l is more than likely a RUNNER. Meaning it has a differing Internal Resistance and that is why it is taking charge so much faster. Without an IR Tester to compare the cells, you will not know what the internal resistance of the cells are.

You set the cells into Parallel and charge them to 3.50V and allow the amperage to drop to 10% of the charge rate being applied. IE if charging with a start of 40A, then allow cutoff at 4.0A. You can safely charge at 0.5C, so for a 100AH Cell that is 50 Amps. You can push cells up to 3.60V but note that once you reach 3.55 the cells will take charge at a much slower rate. You can do one cell @ 3.50 @ 40A or groups of cells as well, of course with groups the speed of the charge will be reduced. A higher rate of charge will also help "out" runners. These will CAP the high side of your battery assembly, as they will take a charge to a certain point and then run to High Volt Disconnect point.

Low Runners: You have yet to see which, if any cell is a Low Runner. During discharge, you will find the cells will stay fairly even until close to 3.100V. At this point the weakling will appear and it will drop voltage faster then the rest causing LVD (Low Voltage Disconnect). That one will be the limiter for your bottom. These will act out faster, the higher the rate of discharge.

Bottom & Top Balancing can help flush out the Hi/Lo Runners and in some instances, with a few deep charge/discharge cycles they can be levelled up a bit more.

This is not uncommon with Bulk Commodity Cells which are not Matched & Batched.
Measuring Voltage & IR when the cells are at storage voltage is not an indicator the cells are matched.

More info in my Signature See the thread on ESS Systems.

 

[Sojourner1]

That cel;l is more than likely a RUNNER. Meaning it has a differing Internal Resistance and that is why it is taking charge so much faster. Without an IR Tester to compare the cells, you will not know what the internal resistance of the cells are.

You set the cells into Parallel and charge them to 3.50V and allow the amperage to drop to 10% of the charge rate being applied. IE if charging with a start of 40A, then allow cutoff at 4.0A. You can safely charge at 0.5C, so for a 100AH Cell that is 50 Amps. You can push cells up to 3.60V but note that once you reach 3.55 the cells will take charge at a much slower rate. You can do one cell @ 3.50 @ 40A or groups of cells as well, of course with groups the speed of the charge will be reduced. A higher rate of charge will also help "out" runners. These will CAP the high side of your battery assembly, as they will take a charge to a certain point and then run to High Volt Disconnect point.

Low Runners: You have yet to see which, if any cell is a Low Runner. During discharge, you will find the cells will stay fairly even until close to 3.100V. At this point the weakling will appear and it will drop voltage faster then the rest causing LVD (Low Voltage Disconnect). That one will be the limiter for your bottom. These will act out faster, the higher the rate of discharge.

Bottom & Top Balancing can help flush out the Hi/Lo Runners and in some instances, with a few deep charge/discharge cycles they can be levelled up a bit more.

This is not uncommon with Bulk Commodity Cells which are not Matched & Batched.
Measuring Voltage & IR when the cells are at storage voltage is not an indicator the cells are matched.

More info in my Signature See the thread on ESS Systems.

There really needs to be sticky at the top so new folks can get a grasp on what's happening and how to top balance their cells.

Yes, there is the resource section but it seems not a lot of folks go digging, seems to be a common theme of I watched Wills videos.

 

[snoobler]

There really needs to be sticky at the top so new folks can get a grasp on what's happening and how to top balance their cells.

Yes, there is the resource section but it seems not a lot of folks go digging, seems to be a common theme of I watched Wills videos.

Agreed. Done.

 

[texskeet]

Will a good top balance fix cells that run some of the time? most of the time? When do you give up and change out the cell?

 

[Steve_S]

After some very hard and abusive testing involving deep hard discharge up to 200A and hard charges up to 150A per single pack the Hi Runners I have calmed down a bit and do not run as fast. As for the bottom end, the lazies still tap LVD far too soon. This is after 5 Extreme Runs with a few lighter uns (lower amp charge/discharge runs). I have two cells which will not play nice and will be swapped out. Enough time wasted, they will goto a 12V pack I am putting together which will only have low to minimal demand and non-critical.

A full out Bottom to Top Balance can help with lazies but not with weak runners.
NO device (BMS or Balancer" can or will fix any of this) An Active Balancer, however, can help with the top and levelling up if the cells are healthy even if a little weak or slightly inclined to run.

 

[texskeet]

Thanks any more people want to chine in?

 

[MisterSandals]

Have new cells purchased in forum group buy

Are those the 280AH cells?

There are so many of them around, i wonder if they could be tested and regrouped, particularly the runners, into usable packs?
It would likely produce “lower than 280ah” batteries but maybe usable.

This does not help those replacing runners and it sounds like replacements are unavailable.

 

[jvbutter01]

A full out Bottom to Top Balance can help with lazies but not with weak runners.
NO device (BMS or Balancer" can or will fix any of this) An Active Balancer, however, can help with the top and levelling up if the cells are healthy even if a little weak or slightly inclined to run.

isn't this just like new cars off assembly line... most engines are good long running, some last for ever no matter what punishment's they get put through, and some are just crappy from the start and have short life.

@MisterSandals yes they are 280ah recently bought. Its more important for me to get all cells that charge up the same vs 1 that runs up and hits HVD and the other 3 in the pack are only 3/4 charged. 3 cells not fully or 90% charged are lowering overall capacity. For my RV application, I think this is important to keep off the generator for charging later vs sooner.

 

[MisterSandals]

Thanks any more people want to chine in?

I think Steve_s covered everything: there is no “fix” but maybe they can be prepared/conditioned as well as possible and make them manageable.

 

[Steve_S]

LFP Nominal Power Point is 3.2V.
Majority of the power curve is 3.450 to 3.000
Above 3.5 to 3.65 only represents a FRACTION of the power. LFP will always settle to 3.55. This is also a "Hard Climb Charge" meaning very slow from 3.5V up.
Below 3.0 is a "Cliff Fall" and also only represents a fraction of the total stored capacity.
Most people reserve off the top & bottom anyways.

 

[snoobler]

LFP Nominal Power Point is 3.2V.
Majority of the power curve is 3.450 to 3.000
Above 3.5 to 3.65 only represents a FRACTION of the power. LFP will always settle to 3.55. This is also a "Hard Climb Charge" meaning very slow from 3.5V up.
Below 3.0 is a "Cliff Fall" and also only represents a fraction of the total stored capacity.
Most people reserve off the top & bottom anyways.

Based on my experience with many dozens of data points, the above bolded statements are not true. LFP will settle to below 3.35V. Here's an example:



The above chart follows a charge of a CALB cell to 3.65V with a 0.05C cut-off. It drops below 3.50V before 3 minutes have elapsed. After about 5 hours it settled to 3.34V.

If you have logged data documenting different results, I'd love to see it.

 

[MisterSandals]

LFP will settle to below 3.35V

3.35v is my settle point to the 40+ cells that i work with. I am rather surprised by the consistency of this across 22ah cells up to 206ah cells.

 

[Steve_S]

Based on my experience with many dozens of data points,

Why not setup an About My System page and show us your gear & setup with a list of the goodies you use to test all of this ?

All my cells settle to the same point, the 280's & 175's. and it is very consistent.

 

[MisterSandals]

LFP will always settle to 3.55

I wonder if this is because, from what I have seen, you charge and discharge at high C rates?

I am more of a trickler compared to the amps i have seen you talk about!