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Large quantity, low voltage
#1
Hi guys.

Newcomer here. Building a large power wall.

I have harvested cells from around 450 batteries. All batteries were Lenovo, and they have been disposed because the computer refurbished didn’t want to resell the computers (not worth refurbishing) many batteries have been tested from the refurbisher to grade ‘a’.

That means that they were not thrown out because they were dead.

Anyway, got 2700 Sanyo / LG cells rated at 2500-2600 mah.

I purchased two chargers from the battery doctor.

So to the question. If I take 100 cells, maybe only 30 of those are above 3.0 volts. I’ve read that cells below 3,25 volts have too much internal resistance and should be thrown out(recycled)

The batteries have been in storage for servers years before I got my hands on them.

Question 1.
So what do you suggest? Charge to 4,2 and test in two weeks, and dispose all below 4 volts ?

Most of the cells are 2,25 to 2,7 volts.

Question 2.
I noticed that if I charge them up, within the first 5 minutes they will all be in high voltage, like 3,6 volts. Why is that so quick? The whole charge process takes a long time, 3 hours or so. What’s the reason for the quick voltage jump?

Greetings from Denmark.
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#2
(11-16-2019, 02:17 PM)M1kkel Wrote: I have harvested cells from around 450 batteries. All batteries were Lenovo, and they have been disposed because the computer refurbished didn’t want to resell the computers (not worth refurbishing) many batteries have been tested from the refurbisher to grade ‘a’.

That means that they were not thrown out because they were dead.

Anyway, got 2700 Sanyo / LG cells rated at 2500-2600 mah.
Nice!
(11-16-2019, 02:17 PM)M1kkel Wrote: So to the question. If I take 100 cells, maybe only 30 of those are above 3.0 volts. I’ve read that cells below 3,25 volts have too much internal resistance and should be thrown out(recycled)
Where'd you get that information? Here on SLS, we quite often recover cells that are <1V into working order. Also, most cells, if not all of them, have a full discharge voltage according to the datasheet <3V, most around 2.5V and some even down to 2.3V.
If these cells have not been overused/abused, then 3V would be perfectly fine to use.

(11-16-2019, 02:17 PM)M1kkel Wrote: Question 1.
So what do you suggest? Charge to 4,2 and test in two weeks, and dispose all below 4 volts ?

Most of the cells are 2,25 to 2,7 volts.
Always fully charge and test the cells unless they are purchased brand new. There could still be SD's or ones that just don't want to go to 4.2V. Those cells set aside (I wouldn't necessarily discard right away) and give them a second test through and use them for something else.

(11-16-2019, 02:17 PM)M1kkel Wrote: Question 2.
I noticed that if I charge them up, within the first 5 minutes they will all be in high voltage, like 3,6 volts. Why is that so quick? The whole charge process takes a long time, 3 hours or so. What’s the reason for the quick voltage jump?
Voltage curve for LiIons is fairly flat, and LiFePO4's are even flatter (almost horizontal). So yes, after a few minutes the voltage can jump that high. Most of the capacity is held above 3.54/3.5V anyways.

(11-16-2019, 02:17 PM)M1kkel Wrote: Greetings from Denmark.
Welcome!! Smile
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#3
Just to add one thing - when you charge them - just check them for overheating - its often case with sanyo cells when they reach 3.95 - 4.1V.
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#4
Okay, the charger measures temperature for each cell, and i only discharge at 500milliamps for now, but i heard they are called "heaters" Smile

(11-16-2019, 02:32 PM)Korishan Wrote:
(11-16-2019, 02:17 PM)M1kkel Wrote: I have harvested cells from around 450 batteries. All batteries were Lenovo, and they have been disposed because the computer refurbished didn’t want to resell the computers (not worth refurbishing) many batteries have been tested from the refurbisher to grade ‘a’.

That means that they were not thrown out because they were dead.

Anyway, got 2700 Sanyo / LG cells rated at 2500-2600 mah.
Nice!
(11-16-2019, 02:17 PM)M1kkel Wrote: So to the question. If I take 100 cells, maybe only 30 of those are above 3.0 volts. I’ve read that cells below 3,25 volts have too much internal resistance and should be thrown out(recycled)
Where'd you get that information? Here on SLS, we quite often recover cells that are <1V into working order. Also, most cells, if not all of them, have a full discharge voltage according to the datasheet <3V, most around 2.5V and some even down to 2.3V.
If these cells have not been overused/abused, then 3V would be perfectly fine to use.

I got it from some flowcharts i saw on how to sort the cell's - but im really glad i dont have to toss them. I wasnt aware of the full discharge voltage, great info!

(11-16-2019, 02:17 PM)M1kkel Wrote: Question 1.
So what do you suggest? Charge to 4,2 and test in two weeks, and dispose all below 4 volts ?

Most of the cells are 2,25 to 2,7 volts.
Always fully charge and test the cells unless they are purchased brand new. There could still be SD's or ones that just don't want to go to 4.2V. Those cells set aside (I wouldn't necessarily discard right away) and give them a second test through and use them for something else.


(11-16-2019, 02:17 PM)M1kkel Wrote: Question 2.
I noticed that if I charge them up, within the first 5 minutes they will all be in high voltage, like 3,6 volts. Why is that so quick? The whole charge process takes a long time, 3 hours or so. What’s the reason for the quick voltage jump?
Voltage curve for LiIons is fairly flat, and LiFePO4's are even flatter (almost horizontal). So yes, after a few minutes the voltage can jump that high. Most of the capacity is held above 3.54/3.5V anyways.

Okay, i noticed that a short while after they are charged to 4.2 they drop to 4.1 or even 4.05 if thats okay, i will measure in a few weeks to see if they are above 4.0 volts still. If they are not, whats the next step? Charge to 4.2 and discharge to 3.2 and then back to 4.2 and wait two weeks again?

(11-16-2019, 02:17 PM)M1kkel Wrote: Greetings from Denmark.
Welcome!!  Smile
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#5
Some Sanyo's become heaters, yes. But not all. This is why they should be tested regardless. Only those that were manufactured within a certain set of years had the now bad chemical electrolyte. I'm not sure of the years, tho.


The flowcharts may have been made by someone who was going for "very" high grade cells, like B+/A grade cells. Please read the threads on IR posted by completelycharged, Wolf, and a few others. This one has several pages of good info: https://secondlifestorage.com/showthread.php?tid=6575

It's normal for cells to drop from 4.2 down to 4.1V. Some drop to 4.15, others all the way to 4.1V. Give them a few cycles and they usually "wake up" and start holding a charge properly again. Some electrolyte starts to separate or settle or something if they aren't cycled regularly and giving them a few cycles will help realign or what ever it does to them. I'm not a chemist Tongue
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#6
(11-16-2019, 02:17 PM)M1kkel Wrote: Most of the cells are 2,25 to 2,7 volts.

2.25v should still be mostly fine, but many sources recommend charging such low voltage cells very very slowly (typ. 50mA) until they reach 3.0v or so.  I use a laboratory power supply to trickle charge at 30mA.  Some people on here built dedicated slow charging rigs.


(11-16-2019, 02:17 PM)M1kkel Wrote: I noticed that if I charge them up, within the first 5 minutes they will all be in high voltage, like 3,6 volts. Why is that so quick? 

Lithium Ion cells have a "knee" or "cliff" around 3.5v~3.3v where voltage drops off rapidly.  The same applies in reverse when charging.  The voltage of cell at 3.0v will shoot up to 3.5v with very little charging.
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#7
Usaually i test for ir first, every cell that is more then 10% of from the optimum factory ir is out.
Example if a cell has a factory optimum ir of 26mohm and i read 30mohm he is out
Example 2: if a cell has a factory optimum of 54mohm and i read 58mohm, i keep, above 60mohm he is out
Then i charge every cell up to 4.2v leave them for 4 weeks.
Every cell that dropped below 4.0 volt is out.
After those 4 weeks i do a discharge test, every cell that has more than 90% left of his original capacity i keep, the rest is out.

But you must decide for yourself where you draw the line, my bar is set very high.
Big plus on Korishan.
Some must wake up, and yes with a second "test round" you will be able to keep more good cells.
I discovered this a bit to late. Sad
Some cells are below 2.8v, they need some special (not difficult attention) charger, the best for this purpose in my humble opinion is a simple buck converter.
Then charge them normal(can also be done with a buck converter)

Most around here only charge to 4.2 wait 2 to 4 weeks and do a discharge test and keep all cells above 80%

Best, hope this was helpful, good luck with hunting and welcome to your journey to forever! Cool
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