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Does internal resistance matter?
#51
(06-10-2019, 10:41 AM)Wolf Wrote: .../...
Staying below 90mΩ has virtually eliminated any hot cells "heaters", vamp cells (ones that never finish charging) and SDs. Although an occasional SD sneaks in there once in a while.

Wolf

Hi Wolf, and all

I'm new here, and unaccustomed to certain specific terms used by locals Wink

So, what is a "SD" cell ?

(Also, sorry for my clumsy english.. I'm French, wasn't really diligent in studying foreign languages at school (looong time ago), and I didn't have the opportunity to practice english IRL...)
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#52
SD = Self Discharge
Proceed with caution. Knowledge is Power! Literally! Cool 
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#53
(09-11-2019, 06:45 PM)Kna Wrote: So, what is a "SD" cell ?

(Also, sorry for my clumsy english.. I'm French, wasn't really diligent in studying foreign languages at school (looong time ago), and I didn't have the opportunity to practice english IRL...)

A "SD" is a cell that self discharges.

This could happen relatively quickly or over a period of time.
We usually consider a cell a SD (Self Discharger) if it loses more than .05V in 30 days.

Wolf
If 18 X 650 = 2200+mAh then we have power! 
May all your Cells have an IR of 75mΩ or less Smile
Last count as of 8/7/2019
Total Number of Cells Recorded and processed                 6149
Total Cells required for PowIRwall                                   2856
Total Cells ≥2200mAh, ≥80%, ≥35mΩ, ≤75mΩ, ≥4.12V   2760
For Info Google Drive
Not your average Wolf       
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#54
Thanks Korishan and Wolf

it seems so simple, I could have thought of that.
I'll probably have to open a new thread about it, but I still have a lot to read and learn before Wink
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#55
(12-11-2018, 09:04 PM)batteryq Wrote: Sorry, I just realized I didn't phrase my question properly, there are actually two questions. But I think you guys guessed what I meant:
Question 1: How much resistance is too much at what discharge level? e.g.:
At 1C, IR should be < 300mOhm
At 2C, IR should be < 250mOhm
Question 2: How much variance of IR among the cells should you tolerate? e.g.:
At 1C, all cell's IR should be within 50mOhm from each other
At 2C: all cell's IR should be within 20mOhm from each other

I don't fully understand the impact of the 2nd question, what would happen if I pair two cells with very different IR? Is the smaller IR one going to be empty much sooner and then start sucking power from the larger IR cell?
So the best I can say at this point is stay tuned and some definitive best practices will come of this I am sure.
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#56
(09-12-2019, 10:36 PM)YAILIYA Wrote:
(12-11-2018, 09:04 PM)batteryq Wrote: Sorry, I just realized I didn't phrase my question properly, there are actually two questions. But I think you guys guessed what I meant:
Question 1: How much resistance is too much at what discharge level? e.g.:
At 1C, IR should be < 300mOhm
At 2C, IR should be < 250mOhm
Question 2: How much variance of IR among the cells should you tolerate? e.g.:
At 1C, all cell's IR should be within 50mOhm from each other
At 2C: all cell's IR should be within 20mOhm from each other

I don't fully understand the impact of the 2nd question, what would happen if I pair two cells with very different IR? Is the smaller IR one going to be empty much sooner and then start sucking power from the larger IR cell?
So the best I can say at this point is stay tuned and some definitive best practices will come of this I am sure.
@Wolf (and some others) have detailed/in-depth info and will probably weight in, but in the meantime I can tell you that IR is delicate to measure - so it can easily vary 40mOhm between testers BUT in general, recommended mOhm should be <50-80mOhm kind of thing.   200-300mOhm is not good!.     

In one of my 14s batteries, I had 10packs averaging 80mOhm'ish and 4 averaging 200mOhm.  One problem was that the 4 200mOhm packs had 'wild' voltage swings during charge/discharge compared to the other 10packs and I could not keep them in close balance.

Suggest reading in detail this and similar threads.
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#57
For those interested in the kind of charts Wolf has been putting out there, check out my google drive (link in signature) and look at the file "Cell IR Database". It is an excel 2016 file. This is almost entirely Wolf's data, but I reformatted it so that anyone can use to review the latest in Cell IR vs Capacity trends.

In the sheet the "IR & Cap chart" tab has a drop-down menu in the top left where you can select cell types. The results are automatically graphed. Below the graph you can enter in values for the IR you have to get a capacity estimate, or enter a desired capacity to get an IR estimate.

If you like this and are interested in helping build the database, send me your data. I'll take information in any format so long as it includes cell model number, measured capacity, and IR measured with a YR1030 or equivalent YR device.
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Cell count as of 10/10/2019
234 Cells >2000mAh, >80% Rem. Cap., 14 day resting voltage >4.12V
191 Cells of Everything Else
68 In progress
 
Aiming for 8 cells tested a day
More info on my Google Drive
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#58
(09-11-2019, 07:47 PM)Korishan Wrote: SD = Self Discharge

SD means self-destruct in my dictionary.
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#59
Soo.. Wait, did the original post get answered?

How much variance between IR on cells should be allowed per pack? It seems like the general consensus is IR should be below 80mOhms ideally - but I haven't seen if it's OK to have cells with an IR of 15mOhms along with cells in the 70 range in the same pack
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#60
My THEORY (and this could be wrong, so feedback from others is welcome) is that mixing 15mOhm cells with 70mOhm cells is ok IF
1. There is only low current per cell
And preferably
2. The mix of IR is similar between your cell packs.
ie. If you have 10 x 15mOhm cells and 70 x 70mOhm cells in a pack, then your other packs also have the same configuration. This would mean that IR of each pack would end up the same so they should behave the same. Of course the normal "packs should all have the same capacity" rules apply.
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