Mixing high and low drain/IR cells in packs

Wolf said:

If you you are unable to get a steady supply of these high drain cells then my suggestion is to go with the standard ICR low drain chemistry as there are many more sourcesfor those. Personally I would not mix high drain and low drain cell in a powerwall as the IR difference is too much and there would be an imbalance between the cells.

Wolf

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If someone were to make 80p packs and they put 70 low drain and 10 high drain cells in each pack, would thier packs all behave the same way and remain in balance?

Taking this idea further:
Should IR of each cell be measured and totalled in packs that will be used in strings together to build matching IR packs - the same way that capacity of cells is measured to build matching capacity packs?

Firstly, thanks for creating a new thread to ask a different question

Secondly, it depends on the difference in IR between the cells. However, generally speaking, if they are matched per pack, the impact will be minimized. IR from pack to pack should be close to each other as the capacities are if high currents are required.
So if each cell will see 1A or more, then you do not want to mix IRs of more than a 100 mOhm difference. This is even so if they are high drain cells, but the current limit would probably be closer to 5A or more (depends on the C rating of those cells)
If each cell will be seeing <500mA, especially <250mA, then IR isn't "as" big of a deal.

Remember, IR is kinda like trying to wade through water. If you move slowly, you can barely tell you are in the water and can walk even miles before getting really tired. However, if you try to run in water, you will become exhausted "very" quickly. And just as if you have a group of people moving together, let's say they are pulling a raft, then if everyone is walking, they will keep the same pace as each other. But if they all try to run, people will drop off at different times increasing the pulling load on the remaining pullers until they are all exhausted.
So goes with the cells of differing IRs with high draw. As more cells start to be exhausted, more current will start to flow through the others, and potentially start popping fuses (if you have cell level fusing) best case, or start overheating, worst case.

Korishan said:

Firstly, thanks for creating....

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Awesome!

I was going to ask if it's ok to mix regular and high drain cells on a power wall; I'll avoid that and keep it simple. Thanks a lot!

Cheers!

metalorn.

It is fine as the lowest performing cell determines the max limit.

This Said you need to have same amount of each type of cell in each pack. Doing this then yes you can mix whatever ir or type you want. Note that the first Line in My response is important.
.its like when you add a capacitor to a car stereo.... Its the high drain cells basically....

Korishan said:

Firstly, thanks for creating a new thread to ask a different question

Secondly, it depends on the difference in IR between the cells. However, generally speaking, if they are matched per pack, the impact will be minimized. IR from pack to pack should be close to each other as the capacities are if high currents are required.
So if each cell will see 1A or more, then you do not want to mix IRs of more than a 100 mOhm difference. This is even so if they are high drain cells, ............................................

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Just a side note on this subject.

100m? difference my my what IR tool are you using to measure IR?
Any 18650 with 100m? IR is either a heater or a SD or both.
Anything over 80m? is already a suspect to be binned. Especially highdrain notwithstanding low drain cells

High drain cells rarely have an IR of over 30m? and if they do there capacity is in the toilet.
All low drain cells that have any respectable capacity left that I have found have an IR of 35m? to 75m?.
Unless you are talking about the Sony US18650GR G* series then > 80m? is sometimes acceptable.
But as I stated before I wont be using the Sony GR series in my powerwall anyway. Unless I inherited 3000 of them.
So the maximum difference that I am going for is 40m? and I'm still trying to narrow that down a bit.

Wolf

Wolf,
You are going to have a pw based on IR, oke mine is also(+ soh%, min 90%).
Thanks to you i weed out some bad and ugly ones :exclamation:

But there are cells that are testing around 70mohm at average.
I have around 800 pcs of one kind: the only ones i keep are between 63and 77mohm

The same for cells that are testing around 30 mohm.
I keep only 25 to 35 mohm
Those numbers are also around the 1000.

So al thosenumbers are in your borders, but a cell that has a good average at 30 mohm is alsogood at 70 mohm?
Or the other way around?
Or i missing a point somewhere and i wasthrowing away to many cells?

Those are the most extreme, from 25 to 77mohm
i keep the onesbelow 20 and above 77separate.
If there aremore than 100 cells of each spec (below 20 or above 77)and testing good in soh(more than 90%), i will make a test wall(brick/pebble wall) with it.
Lets see what happens to them or you got a clue? because i don't have one about them.
Will test them in a separate system with some peltier elements.

I test per manufacture and the same type of cell, if i have below 100 cells per manufacturer and same type, the wont be in my powerwall, first a steady average IR test.
Why per 100, only unknown IRcells to get a known IR.

Thanks and best.

100kwh-hunter said:

Wolf,
You are going to have a pw based on IR, oke mine is also(+ soh%, min 90%).
Thanks to you i weed out some bad and ugly ones :exclamation:

Well actually my testing of cells is based on IR the Power Wall is just the recipient of a good harvesting strategy.

But there are cells that are testing around 70mohm at average.
I have around 800 pcs of one kind: the only ones i keep are between 63and 77mohm

Yes there are some cells esp theLGAAS31865,LGDAS31865, andLGEAS31865 never mind the Sony US18650GR G* series
that perform good all the way to 80m? and above. As most of my cells average around 50m? I decided to make my cut off75m?.

The same for cells that are testing around 30 mohm.
I keep only 25 to 35 mohm
Those numbers are also around the 1000.

The cells that are <30m? are more than likely high drain cells such as those found in powertools. Mostly INR chemistry cells.
I keep those separate as they will make a great high drain battery for lots of power in a short period of time.

So al thosenumbers are in your borders, but a cell that has a good average at 30 mohm is alsogood at 70 mohm?
Or the other way around?
Or i missing a point somewhere and i wasthrowing away to many cells?

I think you will find that the low m? cells are INR or IMR chemistry the added manganese and or nickle in the chemistry make them very low IR and high drain.
I have some brand new INR18650-25R cells with an IR of 13m? to 14m?. I have gottensome from power toolpacks andonce their IR goes over 25m? they die and are generally SD cells. But just because a cell has low IR does not mean its bad its just a different chemistry.

Those are the most extreme, from 25 to 77mohm
i keep the onesbelow 20 and above 77separate.
If there aremore than 100 cells of each spec (below 20 or above 77)and testing good in soh(more than 90%), i will make a test wall(brick/pebble wall) with it.

Exactly the low IR ones you can use especially if they test goodand build a nice ~12V battery with them.
The high IR ones you can build a great backup battery to some led lighting that doesn't need gobs of power.

Lets see what happens to them or you got a clue? because i don't have one about them.
Will test them in a separate system with some peltier elements.

See above

I test per manufacture and the same type of cell, if i have below 100 cells per manufacturer and same type, the wont be in my powerwall, first a steady average IR test.
Why per 100, only unknown IRcells to get a known IR.

That is why I have my database and it can be searched by all type of cells that I have processed. Its up to 6058 recorded cells now.
And that's how I built the IR by part number sheet to guide my what is an acceptable IR for each cell manufacturer and part number.

Thanks and best.

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Those are my answers to your comments

Wolf