How to identify chemistry of 26650 battery cells

[ingko]

I am a new member but I have already been making my own battery packs. I am currently building a new battery pack for my 500W 48V hub motor.
I have an old battery pack probably 3 years old from a Chinese electric scooter that was given to me. This electric scooter was never used and I planned to use its battery pack for my new E-Bike project. I tested this old battery pack and it reads 51 Volts, so I assumed it is still good. I even tested it with the hub motor and it works fine. I began to open the battery pack because I intended to change the enclosure in place of a custom fiberglass enclosure. But upon opening, I notice that there is no BMS or any circuit present for battery protection. The battery terminals is wired directly to the negative and positive side of the pack.

I can install a BMS, however, I cannot identify what chemistry the cells in this battery pack. The battery pack has 5 parallel cells and 14 series cells. The dimensions of one cell is 26mm diameter and a height of 65mm. Some of the cells has a label indicating "AZ-0531" while some has label indicating "AZ-0622". My only assumption is that it is 26650 cells.

My problem is that I can't identify the chemistry if weather it is LiFePo4 or Li-ion because BMS for LiFePo4 or Li-ion has different min/max cut-off voltages and I have to use the right one.

Is there a way or a method to determine battery chemistry?
Can I still use the cells of this never used 3 year old battery pack which ever chemistry it is?

I have in my shop a 16S LiFePo4 BMS and I plan to use this. Of course I will have to rearrange the cells to have 4 parallel and 16 series. This means I will have 6 cells spare.

 

[redilast]

If the pack is at 51v and its 14s and it hasn't been charged in the last hour or two, then it is 100% NOT LiFePo4. Because that would be 3.64v per cell. LiFePo4 even if overcharged to 4.20v will settle down to around 3.4v after a few hours. As for what chemistry it is, its probably some kind of LiMn hybrid cell. That is very suspicious that it would not come with a BMS, unless there are some protection features built into the motor controller. Even then it still should have a BMS. Even with perfectly balanced cells they will likely become out of balance eventually due to uneven wear due to temperature differences between inner and outer cells and other minute internal cell differences.

I'd be interested to see a picture of the pack.

 

[ingko]

Thanks for replying redilast.
I think you are correct. The battery has not been charged for more years. I already removed some cells out of the pack and they measure between 6.5 to 6.65 volts.
I am still wondering as to why it did not have a BMS. Although, there was a small tab attached to one of the cells and it seemed to be a temperature sensor of some sort.
I also notice that the solder tab is connected in series only and not in parallel which means, even with BMS, it would only work on one series groups.
The photos only have 4 cells in parallel because I removed the 5th cell.

 

[amberwolf]

The battery has not been charged for more years. I already removed some cells out of the pack and they measure between 6.5 to 6.65 volts.

I think you might want to check the battery in your multimeter, because that is an unlikley voltage--even if they ahd been severely overcharged at one time, I doubt they would have retained that for years.

If they did, then all the cells are toast; you'd be safest to drain them down to zero volts and recycle them.

 

[redilast]

6.5 to 6.65v? Are you sure you are not measuring 2 cells in series? Try to measure one individual cell. 6v+ shouldn't be possible. Or like amber said maybe your multimeter batteries are bad and its giving false readings.

 

[ingko]

Apologies. I wrote the wrong numbers in my last reply. The voltage measured was 3.5 to 3.6 volts. It was a typographical error.

 

[Peter.bp]

According to your last update, this battery is definitely not LiFePO4...
BTW, have you ever open the LiIon battery for Makita power tools? The BMS measures only one cell voltage, it even have any balancer. For example, Hitachi batteries have balancer...
It is not first time that somebody sells LiIon batteries without proper protection...