14s50P capacity variances

ShortcutShawn

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Dec 18, 2019
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I am in the final stages of building my first Power Wall, its a 14s 50p. I have assembled the packs and have been capacity testing them with the icharger X6, and have picked up variances from 91Ah to 102Ah between the packs.

They have been assembled using re-packer, and according to the Litokala's they are all rated at about107540mAh (107Ah)
I understand that the Lii-500's can be off by as much as 10%, but a pack as low as 91Ah and another as high as 102Ah is quite a variance?

Is it a potential issue?
Should i be adding cells to them to balance them out ?
Should i be stripping them down and re-testing ?

Thanks any feedback is greatly appreciated.
 

OffGridInTheCity

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There's a few angles here.

Practical side - once the battery is in operation and you charge/discharge over a few cycles- it may behave better than you think. Your BMS should help you with this - e.g. do they easily stay in balance once they've settled in. I think an 'initial'10% difference is noteworthy but not alarming. If it doesn't balance OK after you put it into operation - then it needs attention. Oreven before you put it online - you canjust add (or disconnect) a few cells on the extreme packs - perfectly reasonable - to bring them closer.

*For me, I leave extra slots on my base packs and have added a few cells to bring up the low ones after I see how they perform in about 20% of my packs. I just put them online and use Batrium 'balance info' to see where I need to tweak things. Most required a 3% adjustment but 1 of them (out of 80) required a 15% bump - not sure why :)

On the more technical side I think you'll get better info here than I can provide - but there are some basic causes:
- maybe you have some self-discharging cells in the low packs - e.g. did you let the cells sit for a few weeks and check for this before building the packs?
- cells/packs will test differently on each charge/discharge in the same tester - to be expected. Is 10% too much to expect - not surebut as I said above, its not out of relm of possibility. You don't mention your pack test procedure - maybe that introduced some differences as well.
- mixed cells / mixed chemistries / mixed IR can cause differences in charge/discharge performances compared to other packs - even if the original test mah all add up the same.

My electrical engineer friend says he just doesn't like batteries because they are 'messy'.. and yes batteries can be messy, so its good to focus on the goal - e.g. do they stay balanced under charge/discharge operations and deliver the power you designed for :)
 

daromer

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Repaclr is not magic... It doesnt compensate any errors. It can actually r error instead. Best is to use random based on a grouped value. Like 50mAh ranges. Also note that you egen having assembled packs you need to test with same current.

Lii do 0.5a so you need 25a current now.

Smaller packs r also more prone to this error. Can be seen IF you use a scattered diagram and document it.
 

Wolf

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Several questions need to be asked.

  1. Did you check the IR of each cell? With a 4 wire kelvin 1kHz m? tester.
  2. What is the lowest and highest mAh of cells used.
  3. What manufacturers are they.
  4. What is the SOH of each battery, i.e. 80% of capacity,lower or higher?
  5. Are the cells used mixed chemistry, i.e. ICR, INR, NCA, etc.
If you want to build a successful pack from used cells the IR needs to be within a window (I personally use 40m? to 55m?) and cells should be within a 400mAh difference of each other. As in 2250mAh to 2650mAh.

I personally use another repacker that was developed by Nemo and can be found on this board.
The results of following those rules create a very balanced pack.

image_agxyta.jpg



I'm sure there will be a bunch of people that will pu pu this technique but the results are in the pudding.
The procedure takes a bit more time but is well worth it.
So far the pack I have builtisshowing very good balance charged and discharged. The variation at max I have seen is 0.06V andthat is mostly withmoderatedischarge or charging. Batrium very rarely needs to go into bypass at the top of the charge.

image_dndqki.jpg


image_yvvnvh.jpg

image_zvgqkt.jpg


So my advice is check the IR of each cell, stick to an IR window and keep all cells within that range.
Stay within a mAh range,use daromers method of random picking, or use either nemos repacker or SLS repacker does notmatter.

That should give you a relatively balanced pack.

Wolf
 

ShortcutShawn

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Thanks for all the insights. I see that i have a few issues that i did not take too seriously, that could come back to bite me in the A$$.

I did not measure internal resistance.
I have a mix of 18650 cells with a range of 1800 to 3000 mah, but did not take into account the original capacity, and therefore the state of health is not going to be 80%+ overall

All the cells are salvaged from laptop batteries exclusively, and they are all capacity tested and then self discharge tested at around 4 weeks.

Am i in trouble, or will i just have a system that will be higher maintenance ?
 

ajw22

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My approach is a bit different.
Capacity testing, sorting, building packs according to Repackr takes way too much time. And after all that there still is some capacity spread, since there are so many variables that can affect the capacity tests.
I build my packs pretty much randomly, then during actual use I see which packs have too little/too much capacity. Then swap low/high capacity cells until the packs are balanced.
 

ShortcutShawn

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Wow, so you use all cells untested ?

ajw22 said:
My approach is a bit different.
Capacity testing, sorting, building packs according to Repackr takes way too much time. And after all that there still is some capacity spread, since there are so many variables that can affect the capacity tests.
I build my packs pretty much randomly, then during actual use I see which packs have too little/too much capacity. Then swap low/high capacity cells until the packs are balanced.
 

Walde

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In my opinion you should test and sort properly. Also look 4 weeks after the test what the battery can still do or whether it has discharged itself (I sometimes have batteries here that after 2 months only have 0-3 volts that go into the garbage can)
 

OffGridInTheCity

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ShortcutShawn said:
Thanks for all the insights. I see that i have a few issues that i did not take too seriously, that could come back to bite me in the A$$.

I did not measure internal resistance.
I have a mix of 18650 cells with a range of 1800 to 3000 mah, but did not take into account the original capacity, and therefore the state of health is not going to be 80%+ overall

All the cells are salvaged from laptop batteries exclusively, and they are all capacity tested and then self discharge tested at around 4 weeks.

Am i in trouble, or will i just have a system that will be higher maintenance ?
I wouldn't get discouraged :) You have a range of 91 - 102. You don't give the count - e.g. are most of them the average of 96.5? or 7 of them 91 and 7 are 102?
5-10% of 50cells is 2.5 - 5 cells. So worst case... add 3 cells to the low ones and/or disconnect 3 cells from the high ones.

But really, if it works for your project, just balance them out (hook in parallel for a week) and then see how it performs. If your load is small and you don't have a largeDOD - it might just be fine.

>Am i in trouble, or will i just have a system that will be higher maintenance ?
I would guess'worst case' is higher maintenance
 

ajw22

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ShortcutShawn said:
Wow, so you use all cells untested ?

ajw22 said:
Capacity testing, sorting, building packs according to Repackr takes way too much time.

Badly worded. I still test for capacity, but just to make sure it has at least ~75% of the original capacity. Then I put them in a dated box and store them for 2 weeks ~ 3months, depending on my schedule.
I then take cells from the oldest box, check voltages tomake sure they've not self discharged, then put them straight into my 14 newpacks in a round robin fashion (like a card dealer). That tends to mostly spread cells from one source over all 14 packs.
With avg 2000mAh,100 cells/pack, the capacities end up remarkably close at the end. I don't keep statistics, but I'd say 10packs don't need any adjusting, the other 4 need maybe +/- 3000mAh adjustments.

Also, the cells degrade at varying rates, unless you have fairly new perfectly matched cells from the same manufacturer. What's the point of spending so much time on getting it perfect, when it's going to go out of balanceafter a few months~year of use anyway.
 

OffGridInTheCity

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ajw22 said:
ShortcutShawn said:
Wow, so you use all cells untested ?

ajw22 said:
Capacity testing, sorting, building packs according to Repackr takes way too much time.

Badly worded. I still test for capacity, but just to make sure it has at least ~75% of the original capacity. Then I put them in a dated box and store them for 2 weeks ~ 3months, depending on my schedule.
I then take cells from the oldest box, check voltages tomake sure they've not self discharged, then put them straight into my 14 newpacks in a round robin fashion (like a card dealer). That tends to mostly spread cells from one source over all 14 packs.
With avg 2000mAh,100 cells/pack, the capacities end up remarkably close at the end. I don't keep statistics, but I'd say 10packs don't need any adjusting, the other 4 need maybe +/- 3000mAh adjustments.

Also, the cells degrade at varying rates, unless you have fairly new perfectly matched cells from the same manufacturer. What's the point of spending so much time on getting it perfect, when it's going to go out of balanceafter a few months~year of use anyway.
Yes sir - @ajw22's approach is similar to what I use / similar philosophy. My oldest packs are 2 years with652 charge/discharge cycles. They're #15 - #42 below and still don't need balancing / appear to be perfectly healthy:)

image_wfwdvw.jpg
 

daromer

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I dont test ir. I dont use repackr. I use a bucket variance and sort it accordingly. My walls have almost 5 years without an issue. You dont have to test ir if you test with a proper current since that itself test the ir.

With that said lower current per cell afterwards including larger packs do alot.
 

Wolf

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As I said I may be p-u p-ued with my technique and thats OK.
I do agree it is a bit more labor intensive and probably not as necessary for some.
ajw2 3dprinted cell holders are ingenious and easy to replace a bad cell or add a higher mAh cell.
Perfect design for maintenance
Offgridinthe citybuilds extra space into the pack to add cells if necessary to balance the packs
Daromer has his packs running almost5 years without a hitch.

Everyone has their way of building the packs they want and so do I.

In my case by using the cell level fuse sheets and my buss bar design it would be very difficult to add subtract or change a cell in my packs.
So I opted to be very picky with the cells that made it into my packs. I wanted to have a relatively maintenance free battery for as long as possible.
Balanced from the get go and stay that way for quite a while.
If daromers pays little mind to IR as long as the cells have a good mAh result at a 1A CDC then it will be randomly chosen to go into his packs.
Perfect!
Just means that if I take a couple more miniscule steps my packs should run maintenance free for at least 5 years if not 10. Im good with that.
Although Im not sure what Im going to do with my spare time. Oh Yea build another pack.

So as far as I am concerned all the advice given is good advice with the proven methods of building a successful power wall with 18650 or at least cylindrical cells.

In the final analysis the choice is yours.
Best of luck with your build.

I personally would put the packs together and see how it all plays out. You may need to do a little fine tuning here or there.
But it would be a great learning experience to see how your packs work.

Wolf
 

OffGridInTheCity

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Wolf said:
As I said I may be p-u p-ued with my technique and thats OK.
I do agree it is a bit more labor intensive and probably not as necessary for some.
ajw2 3dprinted cell holders are ingenious and easy to replace a bad cell or add a higher mAh cell.
Perfect design for maintenance
Offgridinthe citybuilds extra space into the pack to add cells if necessary to balance the packs
Daromer has his packs running almost5 years without a hitch.

Everyone has their way of building the packs they want and so do I.

In my case by using the cell level fuse sheets and my buss bar design it would be very difficult to add subtract or change a cell in my packs.
So I opted to be very picky with the cells that made it into my packs. I wanted to have a relatively maintenance free battery for as long as possible.
Balanced from the get go and stay that way for quite a while.
If daromers pays little mind to IR as long as the cells have a good mAh result at a 1A CDC then it will be randomly chosen to go into his packs.
Perfect!
Just means that if I take a couple more miniscule steps my packs should run maintenance free for at least 5 years if not 10. Im good with that.
Although Im not sure what Im going to do with my spare time. Oh Yea build another pack.

So as far as I am concerned all the advice given is good advice with the proven methods of building a successful power wall with 18650 or at least cylindrical cells.

In the final analysis the choice is yours.
Best of luck with your build.

I personally would put the packs together and see how it all plays out. You may need to do a little fine tuning here or there.
But it would be a great learning experience to see how your packs work.

Wolf
Personally - my hat's off to you! What's not really very clearis the 'life span' of these packs/batteries. It may indeed turn out that your methods extend lifespan = less maintenance/replacement over time. For me, I'm just too lazy to take the extra steps you do - but doesn't mean I don't admire your work :)

>Oh Yea build another pack.
Finished my 6th (14s100p) battery a few weeks ago and tidy'ed up my remaining 700misc cells...but then, late night, just ordered hundreds of RingBatteries for the 7th one. It was the 0.50c / cell + the apparent COVID 'run' on cells supplies that did me in - I must get more cells before they are all gone! Please help me stop!! :dodgy:
 

Wolf

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OffGridInTheCity said:
>Oh Yea build another pack.
Finished my 6th (14s100p) battery...............................................t COVID 'run' on cells supplies that did me in - I must get more cells before they are all gone! Please help me stop!! :dodgy:

This warning should help you stop!
Right, in a pigs eye. Or when pigs fly..........


image_mwfcrn.jpg


Now Offgid be a good boy and listen to the goverment and the lawers. (There is a pink floid song about that. At least trusting the government.)

Don't play with things that have warnings on them.
If that was the case none of us would have done anything like we have.

Another good case for re-wraping cells

Wolf
 

507PowerWall

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Jun 6, 2020
Messages
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Wolf said:
In the final analysis the choice is yours.
Best of luck with your build.

I personally would put the packs together and see how it all plays out. You may need to do a little fine tuning here or there.
But it would be a great learning experience to see how your packs work.

Wolf

Believe me, there are a quite large number of newbies learning from your styles, experienecs and tips.
Thanks for your lessons and guidance, specially answers noob Qs and some repeated questions cuase some of us are lazzy enough to search properly

Thanks again!
 

zerberfert

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Apr 14, 2020
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507Powerwall +1

I have learned a lot from Wolf and appreciate all his advice and help. He is the reason I bought a good IR tester.
 

gauss163

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Jun 28, 2020
Messages
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Wolf said:
This warning should help you stop! Right, in a pigs eye. Or when pigs fly..........


image_mwfcrn.jpg

LG's lawyers are on a roll - see below.


image_jtpjum.jpg


Can you imagine the label design discussion: injuries alone hasn'tstopped 'em so we should notch it up with"disfiguring".

I don'trecall ever seeing warnings about disfiguring injuries. But a google search revealed it is discussed much by ambulance chasers looking to make a cheap buck on butt implants gone wrong. I suppose LG's lawyers had to start out somewhere... (or maybe they readBetter off dead than disfigured? the challenges of facial injury in the pre-modern past- life would be boring without wackygoogle search results).

What's next? Maybe they'll resurrect the old this is your brain on drugs campaign, e.g.

As if we don't have enough to worry about nowadays given recent reports that covid-19 may turn us all into zombiesjust like zombie ants(it even sprouts analogous creepy tentacles). So, hurry, finish yourpowerwalls before the covid zombieapocalypse. Surely a little disfigurement beats being zombie food! So, back to the drawing board LG...

We don't need no label warnings​
We don't need no cell control​
Hey lawyers, leave my cells alone!​
After all it's just another cell in the wall
 
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