I have to say that with other batteries charging even at 1A, or discharging at 500mA, nothing got hot. It was only this 1 time. I will test the rest of the cells and let you know what happens. And i will make sure to only use this cells when i can afford for them to burn. Thank you for all your help so far !
I have a question. I charged quite a few of the batteries from old laptops and i found out that certain batteries simply start to heat up dangerously. And that heating always happens at about 4.19V. It charges normaly from start to 4.19V and stays at about 25C. When it reaches 4.19V it starts to heat up and reaches 40 or 50C, that is when i stop charging them so i remain on the safe side. It is interesting that it doesnt heat up during 1A discharge. And i dont understand why it heats up when charging when it reaches 4.19V, it makes no sense. If anything, it should heat up when voltage of battery is lower and more amperage is flowing into them.
edit: i did some more testing and might have found the problem. I am charging a cell and it is showing 4.20V on charger. But when i put the battery out of the charger, its voltage is 3.7V. It has 0.5A flowing into it. Is it possible that the cell simply isnt capable of reaching 4.2V anymore and stops at 3.7V and basicly all the charge that is flowing into it, isnt charging it anymore but instead heating it ?
Can you test the internal resistance of these problematic cells?
The IR values provided by your Lii-500 charger cannot be trusted.
I made a very simple thingy for testing internal resistance. I used this formula:
Resistance = (volt_no_load - volt_at_load) * load_resistance / volt_at_load
I tested 1 battery that doesn’t heat up and 1 battery that heats up:
1) good battery: 0.155Ohm
2) heated battery: 0.6175Ohm
I would love some input about which internal resistance for a battery is ok and over which value, it is to high. Also, since i noticed that some cells only heat up the first time i charge them, is it possible that internal resistance drops and they become ok then ?
1 final question. Since all this cells are salvaged. If they charge without heating and hold good charge for about 10 days, can i say that those cells are ok ?
IMO, the first IR value is OK. The second one is too high.
Those are both quite bad in terms of 18650 performance, which is usually in the 0.020 to 0.060 Ohm range when new.
Chargers usually have problems showing the resting voltage of a cell that is charging, for obvious reasons. Even a short pause in the charging current isn’t enough to detect what the real resting voltage is.
What you’re likely seeing is the charger entering the CV phase of the CC/CV algorithm, but the cell’s true voltage is still very low. This would imply the cell has very high internal resistance, which is why the voltage difference is so great.
You have to charge high IR cells very slowly, as well as use them in applications that demand low current.
Try setting the charger to use 300mA as the charging current. You might get better results, and certainly less heating.
Yup, that heater’s IR is really high! IMO, I wouldn’t use it. You could try very slow charging, but if it still heats up it’s not good for anything.
Yes, that indicates they’re decent. I’d also measure the discharge capacity, to get an idea of how much they have.
Thank you for your replies, i have a seperate thingy for measuring discharge capacity, i start at 1A, as voltage drops, so does the current. The last thing i wrote as to if they hold the charge for 10 days and dont heat up they are good, does this apply also to cells that have been as low as 1V or even 0V during their life time ? So when i revive them, if they dont heat and hold charge, can i say they are still ok ?
Personally, if I found a LI Ion cell that was down to 0V or even 1V at rest, i would immediately toss it. I would not try to charge it.
Thats just the thing, i hate throwing away anything that could still work. I will use those batteries for my powerbank, maybe even for my bluetooth speaker. Obviously i will implement thermal fuse (to stop everything if cell is 60C or more) and i will make sure i only charge it when i am at home.
Btw another question. I tested many laptop bateries that are a few years old and basicly all of them, if they even took a charge, only lasted a few minutes. Basicly its not usable for laptops anymore. But when i take the cells out, basicly all the cells i tested had at least 2.000mAh per cell left (testing cutoff voltage 2.80V). So what is happening to laptops that it lasts few minutes there when cells still have 2.000mAh left ?
0v - 1v is lower than I’d trust. They might still be okay, but you can’t be sure. Over 1v, I might use them. Over 2.5v is often sited as the safe point, though.
It’s possible that the cells (or one of the cells) have developed very high internal resistance. In that case, the laptop draws a moderate amount of current, which causes the cell’s voltage to plummet. This causes the laptop to think the battery is depleted.
At a low discharge (perhaps what you’re testing it at), the cell’s voltage doesn’t drop as much, so you get its full capacity.
It’s even possible the BMS has something built-in to its circuitry that stops the battery from being used much if it’s old or can gone through many cycles. More likely it’s the internal resistance of one or more cells.
I am thinking of converting my drill ni-cd charger to lithium. Its not a highend drill, but its fine for what i need. It uses 14.4V battery, it charges quite fast, so i think voltage of charger is about 19V. I was thinking of how i would do this:
1) 4 cells in series, 3 in parallel. That is 12 batteries altogether. Since i got 3 batteries in parallel, each has to only output 1/3 of current.
2) use 4S BMS for this
3) use ni-cd charger for that
So my question is, what would happen if i used ni-cd charger to charge lithium with BMS ? Lets say that i would always be home when charging. Or would it be better to just buy a dedicated cheap 4S charger (without balance charging thing). Also, do you think my drill would handle it ? It has 10 batteries, lets say fully charged nicd battery is 1.5V, that together comes to 15V, if i use 4 lithium batteries it comes to 16.8V.
Don’t.
are the cells that get hot red sanyo’s?
they are bad for this sort of failure.
long discussion on secondlifestorage about this.
Do you have a link to that discussion?
Most of them are red, but it doesnt say anything on them except some numbers. I did notice that if i charge/discharge them a couple of times, they dont heat up anymore. I think i will still use them for my projects and install heat fuse on them to prevent them overheating.
2,000mAh at low load is no problem, problem is internal resistance
modern Laptops draw 5-6A from a battery when they get stressed with CPU and GPU
as a bit more up he measured a cell with 0.65Ohm internal resistance
so even with a moderate load of 2A that cell is dropping 1.3V so even full its already dropping to 2.9V which is about where the Laptop shows you like 5% battery left
a healthy cell has then only 600mAh more but its internal resistance is like 50mOhm so 0.1V drop at 2A
so if you want to know if the battery is good do a capacity test with 3-5A
still a cell which got recovered from overdischarge is not safe even if capacity and internal resistance looks OK
> i would immediately toss it.
You mean recycle, of course, since bad li-ion batteries are explosives on indefinite delay timers, inappropriate to put in the trash system.
“Last year, 65% of waste facilities fires in California began with lithium-ion batteries…. ”
I decided i want to impement thermal protection to this charger. And i am wondering, if i connect all 4 grounds to the thermal fuse, will that do something bad ? I have a backup plan if it isnt good, but still i would like to know.