How do I check / charge these batteries?

[chaosdsm]

They are LiFePO4 32700 with threaded posts on both negative & positive side. I've seen these in larger cells, but not 32700's. Pack currently shows 2.15V. I want to disassemble the pack and check / charge the batteries individually, and possibly use them in my Maglite with 3D - 6D Malkoff Drop in LED. I'm guessing that one or two of the cells is bad & I would hopefully have 2 good cells for powering the Malkoff LED.

It came out of 1 of 2 solar street lights I purchased about 3 years ago and is supposed to be a 55Ah pack. Of course they also call the light "10,000 lumens" but my Convoy L6 on high (not turbo) is brighter..... This light stated having problems about a year ago, not as bright, doesn't run all night, though as they days are getting longer, it was starting to get a little brighter, & run a little longer. I was using it as a security light to be able to see the front of my shop clearly at night from inside my house. So I bought a much cheaper & brighter light for temporary use till I can afford a real solar parking/street light...

 

[vicv]

Disassemble the pack and use a hobby charger to check them. I use an imax b6. There are other option

 

[chaosdsm]

Just ordered the SkyRC Imax B6 V2!

Also found a EVE LiFePO4 80Ah prismatic cell for under $50 shipped that will easily fit in the battery cavity of the street light to hopefully resurrect it!!!

 

[chaosdsm]

Just disassembled the battery pack, all 4 cells test on my digital multi-meter at 2.16V

 

[Ocelot808]

All is not lost. LiFePO4 can be discharged to 2V without harm. The maximum voltage (full capacity) is 3.45V. Nominal (50% charge for storage) working voltage is 3.2V.

The critical thing with LiFePO4 is the charge voltage should NEVER exceed 3.65V per cell.

The SkyRC should be able to do that. Just do NOT jumper them to an ordinary lithium ion 4.2V CC/CV charger. No danger of fire or explosion but it will seriously damage the cell.

That EVE cell sounds great 80Ah is huge and $50 is a great deal. 👍

 

[jtr1962]

Just disassembled the battery pack, all 4 cells test on my digital multi-meter at 2.16V

That's just fine. When I capacity test my LFP I discharge them down to 2V all the time.

Also, I made a device to "resurrect" some old A123 cells which I foolishly kept stored at full charge. They still worked, but lost over 1/3 of their capacity over a period of about 12 years. My device held them at 2V for several weeks, as per a paper I read on the subject. Not only were they not damaged by this, but I restored them to nearly full capacity. Bottom line-the voltage on your cells is just fine. You'll obviously need to do a capacity test to see if they're still useful. I suspect they will be.

 

[vicv]

All is not lost. LiFePO4 can be discharged to 2V without harm. The maximum voltage (full capacity) is 3.45V. Nominal (50% charge for storage) working voltage is 3.2V.

The critical thing with LiFePO4 is the charge voltage should NEVER exceed 3.65V per cell.

The SkyRC should be able to do that. Just do NOT jumper them to an ordinary lithium ion 4.2V CC/CV charger. No danger of fire or explosion but it will seriously damage the cell.

That EVE cell sounds great 80Ah is huge and $50 is a great deal. 👍

Actaully lifepo4 cells can be charged to 4.2V. They'll immediately drop to 3.65v or so but they'll be fine. Probably shouldn't constantly treat them to such abuse but from how I understand it, they don't suffer much from it. That being said, I've always charged them on the proper lifepo4 setting

 

[chaosdsm]

I fear that, having been in this state for about a year, there could be some permanent damage. I've seen some studies that suggest that continually discharging below 2.5V can cause internal corrosion.... But Battery University, suggests that permanent damage won't happen unless discharged below 2.0V...

Will see what happens when I get the charger in!!!

 

[chaosdsm]

SO... got the charger in, didn't notice that it didn't come with a power source So I tried my the power adapter from my Opus - 12V 3A which is within spec for the charger.... doesn't fit but then I remembered that I bought an Insignia AC>DC power adapter a while back with multiple charging tips. It maxes out at 12V 1.25A, but should do for what I need till I get a better adapter....

Anyway, tested the internal resistance of all 4 cells, average was 160 milliohm's which is apparently really good as the range for LiFePO4 cells is listed as 0.15 to 0.30 Ohm's or 150 - 300 milliohms, so looks like I should have 4 good cells 🤞

But with the voltage so low, I had to lie to the charger to get the first cell to start charging. When I put it on LiFe charge 1S, it said incorrect voltage. So I put it on NiMH charge 2S @ 1A and it went up to 2.8V in 2 minutes. Then I stopped the charge & changed back to LiFe charge @ 0.5A - wanna take it easy & not stress the battery. 17 minutes in, battery is up to 3.1V, & battery external temperature is at 75F (room temperature) according to my infrared thermometer, so I could probably do 1A easily.

 

[vicv]

Ya you need to trick them sometimes. Nimh is always a good setting!
I'll have to look around more but one aspect of lifepo4 is their incredibly low resistance. 150mohms seems very high. Especially for that size. I have 16340 lifepo4 cells that measure around 100mohms. I'd expect your cells to be below 20 mohms if they were in good shape
Even standard 18650 high drain cells are under 50mohms

 

[chaosdsm]

What Is A Good Internal Resistance For A Lifepo4 Battery?

The internal resistance of common lithium iron phosphate batteries is usually in the range of 0.6Ω-1Ω, but for batteries, the smaller the internal resistance, the better, because it is impossible to achieve zero internal resistance due to the manufacturing process and other factors. Therefore, the internal resistance of a good lifepo4 battery is usually in the range of 0.15Ω-0.3Ω. Source: Harvey Power

Sadly, Battery University doesn't have much on internal resistance for LiFePO4, so I'm having to rely on other sources that may potentially not have good info...

I do know one thing for sure.... there's no possible way that original street light had 55,000mAh battery capacity with just four 32700 cells. The highest legit rated ones I've seen are 7000mAh each (LiitoKala) for 28,000mAh pack.

 

[vicv]

Harvey's numbers match my own then. But even if yours don't match those numbers doesn't mean they're junk. Just means you can only put 15A on them instead of 75A ( I'm just making up random numbers) but if 15A or less is all you need, theyll work. As long as everything else is fine
Ya that definitely isn't a 55000mah pack

 

[chaosdsm]

So far the first 3 cells all showed charging capacity at over 4200mAh, after that initial charge to 3V.

I double checked resistance on this last battery that I just put on the charger. At 2.16V, IR was at 172m ohm. After I charged it to 3V on NiMh setting, it's now reading 42m ohm! I'll check them again after I finish charging this last cell, then I'll do a discharge test.

Definitely looking good at this point

 

[vicv]

What is the plan for the cells?

 

[chaosdsm]

As mentioned in first post, I'd like to put them to use in my Maglite. The old NiMh D cells I used to use in it are long since dead. I'm currently using 1.5V Lithium Ion AA batteries in 3P AA to D-cell adapters to power it.

I'll of course have to custom build a negative tail-piece, a coupler, and a positive cap out of copper to take advantage of the threaded +/- terminals on the batteries, but that should be easy enough!

Since the LED drop-in can handle six D cells, it will have no problems with 2 of these cells!

 

[chaosdsm]

BTW... here's the battery management module that I pulled from the battery pack:

From what I can see, it's designed to manage three 3.7V lithium Ion batteries in parallel with a 3V discharge detection voltage of 2.45V (+/- 0.1V), which seems to have failed since all 4 cells were at 2.16V when I pulled them from the pack.

When charging the cells the first time: First cell at 0.5A, then 1A, then 1.5A (highest my AC adapter will handle) to make sure heat would not be an issue, then the remaining 3 cells at 1.5A I saw capacity values ranging from just over 4000mAh to 4423mAh on the best cell.



But after sitting overnight, all 4 batteries dropped down to about 3.35V (+/- 0.02V), and discharge capacity @ 1.4A was all over the place.... worst one was about 2880mAh, two were in the 3500mAh range, and the best one hit just over 4000mAh.


I also tested all the cells in the 2.8V discharge state for internal resistance and they were all +/- 6m ohms

best cell registered 28m ohms, worst was 39m ohms - quite a difference from the 2.16V results originally reported!!!

I'm still waiting on my SkyRC AC adapter to arrive, was supposed to arrive today, but has been delayed

 

[vicv]

That's not good. But I will say one thing, lifepo4 cells always drop to approx 3.35v after resting. And open circuit voltage has nothing to do with remaining capacity. 3.35 V could be 100% charge, or it could be almost dead.

 

[chaosdsm]

I'm working with these batteries daily, I am getting improved results with almost every cycle. I also picked up a second imax B6, this time I made sure to get the AC version with direct grounded AC plug-in, so now I can work with two batteries at once.

Charge testing, doesn't seem to matter what amperage I charge at, capacity seems to come out nearly the same, though I just charged one cell from 3.18V @ 5A, final charge capacity showed 4080mAh from 3.18V instead of 2.8V.

Still getting some pretty significant differences in discharge capacity, though it seems to be improving. 1.5A was draining the batteries down to about 3V in 10-15 seconds on first to charge/discharge cycles. Now it takes over a minute to hit 3V @ 1.5A. I decided to try 1A discharge which is about what the LED's seem to have been drawing... First battery at 1A discharge is over 180 minutes into discharge cycle and currently sitting at 3.16V / & over 3000mAh capacity. This is the same battery that tested at 2880mAh discharge capacity several days ago.



EDIT: Ending capacity on this discharge was 4724mAh

 

[chaosdsm]

For some reason, neither of these chargers will discharge at more than 1.6A, even though they are supposed to be capable of 2A discharge

Still, the batteries are showing much improvement over last cycle. Seems like they're finally 'waking up' after a bit of 'exercise' The one above ended up at 4662mAh discharge capacity at 1A discharge, and 4320mAh charge capacity at 4A charge after a 10 minute rest.

Current battery is running 1.5A discharge (fluctuates from 1.4A to 1.6A on display), and still at 3.15V after 69min 45sec of discharge time. So seems that the minute or two to 3.15V are now in hours.

 

[chaosdsm]

Finished cycling the batteries, I saw less than 150mAh change between last two cycles.

Didn't think about it till after the fact, but I didn't record the discharge capacities, only the charge capacities



3642mAh to 4367mAh not to bad!

Discharge cycle was down to 2.8V
Charge cycle up to 3.6V

I varied charge & discharge amperage between the first 5 cycles from 0.5A to 5A charging, and 0.5A to 1.5A discharge. Last few cycles I alternated between 2A & 4A charge & 1A & 1.5A discharge, with the last charge/discharge cycle for all batteries at 1.5A discharge / 2A charge.