Aliexpress BLS LiFePo4 cells problem

[Bhupinder]

Reference please!

I highly doubt anyone on this forum would agree with that and I stand ready to be corrected.

Sure. There are many, just putting ones on hand:

How to charge Lithium Iron Phosphate lithium ion battery packs including packs with high current and High Capacity.

High capacity LiFePO4, Lithium Iron Phosphate batteries.

www.powerstream.com

How to Charge Lithium Iron Phosphate Rechargeable Batteries - Planet Analog

Lithium Iron Phosphate batteries are safer than Lithium-ion cells and are available in a range of huge cell sizes between 5 and 100 AH with much longer cycle life than conventional batteries

www.planetanalog.com

Then there's this whitepaper which states some observations:

Charging Method Research for Lithium Iron Phosphate Battery

Conventional charging methods and possible problems of lithium iron phosphate (LiFePO4) battery have been analyzed, and a large number of experiments …

www.sciencedirect.com

Hope this helps.

 

[MisterSandals]

I am thinking of Top balancing individual cells till 3.5v any of these days and call it a day.

I think this is a necessary first step. I suspect doing them together rather than individually is an important part of this.

Please chime back in with anything you learned.

I will read the article about max voltages with interest. Thanks for sharing it.

 

[JoeHam]

Thanks for the scientific papers. I still would never charge nearly that high.

For real world experience see this thread where @fhorst ruined a cell going above 3.65v just the other day:

Balance or not to balance... 24V 8S 280Ah

Hi, I put together my 8S, 280Ah 24V battery (LiFePo4). All cells when they arrived were a perfect match and are still now at 3.284V each cell. I wonder if I should just connect BMS and be done with it or I should bottom balance them before use. Any opinions on that? Thank you.

diysolarforum.com

 

[Bhupinder]

Yes, no point going beyond 3.5v in real terms.
One cell out of the pack going to 3.9v was an accident and nothing intentional.
Most cells are indicating resistance beyond 3.35 as said in the other post.
So may be if 3.35V indicate 90% of cell capacity, its prudent to let them sit there.
For top balance I think pushing them all to 3.5v once in a while should be fine. Nothing beyond.

While its difficult to gauge SOC from LiFePO4 voltages, I found this chart very Handy.
Its pretty accurate from what I experience in my tests, sharing it here for anyone's reference and further check:



Cheers!

 

[Jake]

What is your final thought/decision on the BLS batteries? Good or Bad?

 

[Sierravans]

Yes, but when you start out with a knee charge across all the cells, you don’t know how close to full each one is, so some could be nearly empty, and some could be totally full at 3.4xx so, pumping constant current into an unbalanced set will exceed most BMS ability to manage...

I think this is what I'm seeing, could you advice on my post?

 

[Supervstech]

I think this is what I'm seeing, could you advice on my post?

I am not sure what post you are referring to, but the advice in this thread after my post you quoted is very good.
If you will regularly have your bank depleted, bottom balancing is best. Pull all cells individually to 3.0 volts.
If your bank will be regularly full, then a top balance is in order, tie all cells together, and charge them up to 3.65volts...

 

[Carlos Carrapiço]

What is your final thought/decision on the BLS batteries? Good or Bad?

Hard to tell as due to the covid-19 I have put my boat batteries DIY upgrade on hold.
Meanwhile, I was looking for a good power source to do a top balancing and put in practice what I learned here.
I guess considering the price I payed, the weight savings vs lead acid, if I get 90AH of the 100AH rated batteries it's a deal.

 

[Carlos Carrapiço]

From my experience with 206AH cells, this has been my exact experience. They tend to settle down to 3.2v and then stay there for days on end.

But first you need to do either a top balance or a bottom balance. My understanding is that you should balance nearest where your batteries will mostly operate: are you running the batteries down most of the way everyday or will you have the batteries mostly topped (fully charged).
I intend to be mostly fully charged or as much as possible so i top balanced (3.65v).
Hooked them all in parallel overnight then charged to 3.65v (from roughly 3.2v).

At this point, my cell difference REALLY tightened up to 10-20mV all the time.

So choose your balance point (top or bottom) and get that taken care of first.

Regarding testing internal resistance, i think its a waste of time. I tried many different tools and methods. My results showed that the position of the cell in the battery made the most difference in how my tools (ISDT, Tenergy, HobbyMade Duo Pro...) calculated IR. Maddening i say.

<EDIT/> I meant to say/type:
They tend to settle down to around 3.32v...

Thank you Sir.

In my case I do think top balancing is the correct way as the batteries will most often be fully charged.
Concerning the internal resistance, I realised that the uncertainty on the resistor and multimeter was comparable with the calculated resistance and therefore all results were meaningless.

 

[Jake]

Have 6+KWH installed on my RV while priMarilyn charging is with solar. I did a good “bottom balance“ when I first installed the batteries about 2.5 months ago and there hasn’t been a single problem so far. Naturally I’ve checked them around 50 times to make sure all is good. Tried living in the RV for the first three weeks to give them some discharge and charge Cycles and only moved back into house when the nights got warmer (Texas)? So far the cells (all 16) are within .015 volts of each other. Total power from Solar reached 70KW two days ago! ???

 

[MisterSandals]

about 2.5 months ago and there hasn’t been a single problem so far. Naturally I’ve checked them around 50 times

Only checking them 50 times in 2.5 months shows a lot of restraint. I think i checked about 50 times the first few days i set mine up.
Very happy to hear your system is working well!
I have not done a bottom balance so have 0 data points and certainly nothing to compare with my few top balances. Thanks for the vicarious data point though!