Another Question Regarding Cell Voltages

[Dr. Dickie]

Thanks daromer.

Since I will most likely be doing a 100 or 160 P, I would never be drawing 0.50 Amps or more.

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Ask the question if the IR is of that importance? Are you going tha close to its limits in terms of current?
If you have that many cells i promise that randomizing it will get you close enough and if you happen to end up with all highs in 1 pack and then lows in another you should buy a lotto-ticket...


The IR is of larger significance when you push the limits.

Thanks.

I will not be pushing the limits, not on this first one

I will likely use the manufacturer tolerance as my limit (60m Ohms)

 

[Wolf]

I will not be pushing the limits, not on this first one

I will likely use the manufacturer tolerance as my limit (60m Ohms)

If you have exclusively all LG M26 cells then according to my experience anything over 42m? will be a lower performer.
Again not that there is anything wrong with the cell at > 42m?but it is an indication that the cell is starting to waiver.
Try to stick to cells <42m?. Better yet if possible <39m?.
Just an observation and sharing that experience with you.

Wolf

 

[Dr. Dickie]

I will not be pushing the limits, not on this first one

I will likely use the manufacturer tolerance as my limit (60m Ohms)

If you have exclusively all LG M26 cells then according to my experience anything over 42m? will be a lower performer.
Again not that there is anything wrong with the cell at > 42m?but it is an indication that the cell is starting to waiver.
Try to stick to cells <42m?. Better yet if possible <39m?.
Just an observation and sharing that experience with you.

Wolf

Wow, even if the manufacturer lists acceptable impedance as <= 60 mOhms??
Okay.
When I get my internal impedance tester I will see what I see.
The resistance I am getting from the Mixboxer is generally over 40 mOhms and up to 75 mOhms (I assume this is resistance), but since the AC impedance is generally smaller than the DC resistance (something I currently do not understand, but I will), I am hoping to be okay.
Although to me, it would seem that DC resistance is more important than AC impedance to battery health.
I would think it might be better for me to get a high quality resistor and get some quality measurements of the DC resistance.

 

[Wolf]

Wow, even if the manufacturer lists acceptable impedance as <= 60 mOhms??
Okay.
When I get my internal impedance tester I will see what I see.
The resistance I am getting from the Mixboxer is generally over 40 mOhms and up to 75 mOhms (I assume this is resistance), but since the AC impedance is generally smaller than the DC resistance (something I currently do not understand, but I will), I am hoping to be okay.
Although to me, it would seem that DC resistance is more important than AC impedance to battery health.
I would think it might be better for me to get a high quality resistor and get some quality measurements of the DC resistance.

Dr.

If you have time I suggest reading this thread https://secondlifestorage.com/showthread.php?tid=9471&pid=64601#pid64601 there ia a lot of discussion about AC IR andDC IR. Including my findings and other people's input. I even built an ESP32 DC IR tester.

In a nutshell DC IR is ? 2X the AC IR i.e 80m? DC IR =? 40m? AC IR on a good cell.

AC IR can measure SOH on a cell at < 3.5V whereas DC IR needs the cell to be at least at storage voltage, so ? 3.6 V or above as it works on a v drop and if the cell is not charged enough v dop is dramatic and so is DC IR. Hence some good of the shelf testers won't even check IR if the voltage is too low.

Once you get your AC IR tester you will find out that 60m? on aLG M26 cell is really high and it will not perform up to the standards we need for our powerwalls.

Wolf

 

[Dr. Dickie]

Wow, even if the manufacturer lists acceptable impedance as <= 60 mOhms??
Okay.
When I get my internal impedance tester I will see what I see.
The resistance I am getting from the Mixboxer is generally over 40 mOhms and up to 75 mOhms (I assume this is resistance), but since the AC impedance is generally smaller than the DC resistance (something I currently do not understand, but I will), I am hoping to be okay.
Although to me, it would seem that DC resistance is more important than AC impedance to battery health.
I would think it might be better for me to get a high quality resistor and get some quality measurements of the DC resistance.

Dr.

If you have time I suggest reading this threadhttps://secondlifestorage.com/showthread.php?tid=9471&pid=64601#pid64601 there ia a lot of discussion about AC IR andDC IR. Including my findings and other people's input. I even built an ESP32 DC IR tester.

In a nutshell DC IR is ? 2X the AC IR i.e 80m? DC IR =? 40m? AC IR on a good cell.

AC IR can measure SOH on a cell at < 3.5V whereas DC IR needs the cell to be at least at storage voltage, so ? 3.6 V or above as it works on a v drop and if the cell is not charged enough v dop is dramatic and so is DC IR. Hence some good of the shelf testers won't even check IR if the voltage is too low.

Once you get your AC IR tester you will find out that 60m? on aLG M26 cell is really high and it will not perform up to the standards we need for our powerwalls.

Wolf

Thanks Wolf, as always fantastic info.
I will dive into that discussion as soon as I get a chance. When I don't understand something, it drives me crazy until I do.

 

[Dr. Dickie]

Read through the stuff Wolf, very interesting. Thanks so much.
I am almost to the point of not seeing the reason for testing capacity. As I said, I am using two Opus, one always gives values about 50 mAh greater than the other--with slot 3 and 4 always the highest (at 27xx mAh), And the other Opus, slot 3 is always the lowest (around 259X or 261X).
It is not 100% that, but pretty close to it. My IR tester should be here in a week or so,
I THINK my two MegaCell chargers are coming today. I got notification of a shipment from China coming DHL today, and cannot think of anything else it might be (fingers crossed). If so, I hope for some better (more accurate) numbers. But truth be told, if they are all (as they have been) between 2.65+/- about 50 mAh, I don't think I need to test for capacity. As I have not had it show up any bad cells (capacity wise) with about 1.8K out of 2.2K done so far. I will continue to test, just for the experience, and in case I get a pack that is messed up.
Now I need to start digging in to understanding the available BMSs out there. From what I can see, it seems that Batrium is the about the only "good" option. I just have to understand their different configurations.

Well, the bad news, it was not my Megacell chargers.
The good news is, it was my RC3563 IR tester.
So, tomorrow begins the great IR testing!!

Do have a question. Mine did not come with a manual, is there somewhere on the web where I can get one?
Seems simple enough, but...