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Take an educated guess!
#1
*Update: this thread has gone OT with discussion of cells to help in my project. You are still welcome to guess without reading anything! So far we have 26%, 35% and 40%. I harvested 460 untested cells from those 80 batteries.*

I finally have my first 80 laptop batteries to harvest. Who wants to take a guess as to the number of good cells I'll end up with? Good means >2000mah, >80% SoH and IR <5% off spec.

Any other predictions?

 
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#2
Probably less than 40% would be my guess...
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#3
If they are all OEM packs I will take a stab at it.

After recording and testing 6269 cells here is what I came up with:

First a bit of background I first started testing cells with several testers and if the cell was over 2000mAh I was happy and it went into my pile.
Well then I found out just because its 2000mAh does not mean its a good cell if it is a 2800mAh original capacity cell.
So the first 1000 or so cells where tested again but all the <2000mAh cells where not included as I was looking for cells with at least 2000mAh to begin with.
From ~ the 1000 cell mark up to 3500 cells I just looked for ≥2000mAh cells checked the IR and tested them.
Here are the results in percentages with cells ≥2000mAh ≥80% SOH and ≤ 55mΩ.


After cell 3500 I started to take IR seriously and really only tested cells that I believed the IR was good enough to actually test the cell.

Here are the results of that.


So from busting open laptops and just testing cells without an IR test I got ~31% of reasonably good cells.
After starting the IR check the percentage went to almost 50% of reasonable cells. The problem with these numbers of course is I never recorded the high IR cells and have no idea how many I gave away but I am guessing around 3500.
Lets say out of 9500 Cells here are the results of that calculation.


So my guess is 26%

Wolf
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#4
Wolf, what are your personal target IRs ?
Do you consider the official specs for each cell type or you just set a general target and stick with that ?
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#5
i would say 35% is above 2Ah and useable for most of us.
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#6
(06-17-2020, 05:50 AM)Overmind Wrote: Wolf, what are your personal target IRs ?
Do you consider the official specs for each cell type or you just set a general target and stick with that ?

I have an IR cheat sheet that lists the IR of most popular models we see in the laptops that we break down.It was refined to average out the IR of well performing cells. I then took the average of that and 55mΩ was the sweet spot.
I personally built my PW with IR of cells between 40mΩ and 55mΩ
I do consider the Official specs If they are published and I have them incorporated into my spreadsheet  but I do find that some of them are opportunistically high and refer to ≤ XXmΩ a lot.

That being said if you follow my IR cheat sheet you will get good results.



Wolf
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#7
Wolf, I only took a quick glance at your IR test results, but it seems that you consider IR that's within 5% of spec to be okay. Sound right?

If you think 5% is okay for a PW is 10% okay for certain applications? What about 50-100% over spec but still below 100mQ? Maybe low drain or maybe frequent cycling or maybe limiting the number in series or parallel.

Initial cells will go into a 36v 10s3p ebike pack powering a 500w motor. I'm not yet in the packing planning stage of the cells. That's about 13 amps at max draw. That's 4.3 amps per 10s1p cell. If I build my packs with 2200 mAh cells that's, about 2c discharge, right? Anyone have tips for packing for a 2c discharge rate?
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#8
Sed6,

I built my personal spec sheet from experience and have found if I stick to the values that I have in my IR cheat sheet I have good end results.
One thing I have done on occasion is violate my cheat sheet by a couple of mΩ. So if my sheet says ≤55mΩ and I try a cell with 58mΩ just to find out that it does not pass the muster. There are some  cells that have a high IR from the get go and are quite good but the highest IR I have found on those is 80mΩ anything above that is usually either a heater or a sub par cell at far less than 80% SOH. There is one exception I have found ant that is the Sony US18650GR G* series. Just a weird battery and I wont use them unless I have enough to make a pack just with them and never mix other cell in with them.

10% deviation from spec IR is your choice as well as 50-100%. Would I use them in certain applications I don't know as I have given all those with high IR away and someone in Canada and other places are really happy but they are also building 200p to 300p packs so the draw is very low and they can get away with it. I am a little more picky. As I have a great source for cells whenever I need them I can afford to be choosy. I no longer go after laptop packs but am always on the lookout for power tool, medical, scooter, and ebike packs.

If you are going to build an ebike pack my suggestion is going to be power tool packs not laptop packs. Laptop packs generally have ICR chemistry for longer lasting at a low discharge rate. ~500mA tops. Can they do more? Sure but at a price of heat and longevity. Power tool packs generally have IMR INR and sometimes NCA chemistry. This allows for higher discharge rates and still keeps the battery relatively cool. Also you will find that the IR on these cells tends to be in the 12mΩ to 35mΩ range. and added benefit is faster charge times. 
Pulling 13A from a 6600 mAh pack gives you tops ½ an hour of max ride time. More of course if you draw less If you are OK with that great.

Wolf
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#9
Sed6, even a relatively bad shape 3.6V cell / high current cell will handle 4-5A with no problem.

That of course if they are original; if not, they will overheat like hell.
Here's a fake example of HG2s: https://www.youtube.com/watch?v=QqgVVfCLtbI

Basically if they are too cheap they are fakes. They may have the full capacity but will not sustain the stated current and take damage at high current.
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#10
(06-18-2020, 02:58 AM)Wolf Wrote: Power tool packs generally have IMR INR and sometimes NCA chemistry. This allows for higher discharge rates and still keeps the battery relatively cool. Also you will find that the IR on these cells tends to be in the 12mΩ to 35mΩ range. and added benefit is faster charge times. 

Wolf

Great info, all of it! But ugh! I thought I finally had my head wrapped around everything and up comes nickel vs manganese vs cobalt Sad

Sounds like I also need to separate or label the chemistries of my cells if I plan on making batteries for different uses like a PW or ebike battery that have different drain requirements? OR is IR and capacity good enough? Any reason to not mix ICR and IMR/INR cells in a battery if I use packer software and pay attention to IR and mAh?

All my tool batteries so far are low capacity, 1300-1600. Even the 40v, they mostly had 1300's. Best I found so far is a 40v with Sanyo 2600's. Any certain tool packs you've found with higher capacity?

I do have a R2 Recycler around the corner and they are willing to let me dig thru their huge pallets. At $2/lb that's $.23 per cell approx. I'm happy to pay that especially if I can target my haul to appropriate batteries.

Given what you and others have shared; I should target laptop batts for IMR/INR cells for low drain use like a PW and powertool/ebike/scooter batts for ICR cells for higher drain apps like my DIY ebike batt?

Maybe I will get this...
Thanks!
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