Help with surplus prismatic cell specs

[Sparky_SC]

I am in the process of getting a large quantity of prismatic Lifepo4 cells and the spec sheet has me confused.
It lists 4.25V as max charging voltage. This seems wildly above the norm for this type of cell.

Long story but they are going to be free.

Any comments much appreciated!

Spec sheet attached.

 

[houseofancients]

they look nice cells, much like the earlier syno or calb cells

 

[houseofancients]

only thing you can do is test them 1 by 1.

have these been in production somewhere, or where the in a warehouse "forgotten" ?

 

[Sparky_SC]

Here is what I have coming, total rack is 300KWH, 30 modules in the rack. Unknown yet how many prismatics in each module.

 

[houseofancients]

holy mozes, you might just have hit the motherload
if these cells spec out at 80% of their original capacity, you could light up a village with this

 

[Sparky_SC]

only thing you can do is test them 1 by 1.

have these been in production somewhere, or where the in a warehouse "forgotten" ?

A power-on-demand system in a company that went bankrupt within a couple months of the system being installed. I friend bought the entire system, he only wanted the solar panels and inverters. The system was to reduce their peak demand and thus lower their bills.

 

[Sparky_SC]

holy mozes, you might just have hit the motherload
if these cells spec out at 80% of their original capacity, you could light up a village with this

Or burn one down ! LOL

 

[houseofancients]

Or burn one down ! LOL

that why i suggest you test, and test well

 

[Sparky_SC]

that why i suggest you test, and test well

Absolutely, that is the plan. I am just doing the preliminary investigating and that's how the 4.25V question came about.

 

[KauaiMolokai]

I am in the process of getting a large quantity of prismatic Lifepo4 cells and the spec sheet has me confused.
It lists 4.25V as max charging voltage. This seems wildly above the norm for this type of cell.

Long story but they are going to be free.

Any comments much appreciated!

Spec sheet attached.

Spec sheet looks clear and legit. Congratulations, great score! Free!!

 

[toms]

4.25 was what the original winston (thundersky) cells were specced at.
I wouldn’t take them over 3.65V though

 

[Sparky_SC]

4.25 was what the original winston (thundersky) cells were specced at.
I wouldn’t take them over 3.65V though

Good info, Thanks !

 

[Sparky_SC]

Finally got a bunch of the batteries in-hand last week. The battery modules are 32V with 10 prismatics in each battery module. Unfortunately, many of the cells are down between 1.1-1.5 volts from being stored for so long. I have not been able to find much information on refreshing LifePo4 cells that are deeply discharged, only hints to charge them at very tiny milliamp rates until they rise above 2.5V then charge them normally.

Anyone have more information on a procedure/specs to attempt refreshing a over discharged cell? I have a bunch, they were free so nothing to loose in trying even if they turn out useless.

I tried one cell, at 1.1V, charged it a 50 mills until it rose above 2V then increased current to 100ma, 150ma in steps until above 2.5V, then charged it at 20A. It appears to have taken charge and holding it but no load tests done yet.

Just looking for some data on currents / procedure to refresh over discharged cells if anyone has knowledge on the subject.

 

[ericgrand]

From experience, it seems recovered cells are just behaving as if nothing happen... I had Valence U27-12XP batteries that were below 2V (4 cells serie...) that just recovered and behave perfectly: full capacity. They may have lost few cycles, but given the price paid, who cares!

 

[Sparky_SC]

From experience, it seems recovered cells are just behaving as if nothing happen... I had Valence U27-12XP batteries that were below 2V (4 cells serie...) that just recovered and behave perfectly: full capacity. They may have lost few cycles, but given the price paid, who cares!

Reassuring to hear that. Did you perform any special recovery process first or just charge them normally?

 

[ericgrand]

To be honest, I just connect a 5A power supply initially and the battery quickly jump above 2.5V/cell...but I learn after that I should have charge initially at less than 0.5A, which I did for the other batteries.
They are all behaving the same.

 

[Sparky_SC]

To be honest, I just connect a 5A power supply initially and the battery quickly jump above 2.5V/cell...but I learn after that I should have charge initially at less than 0.5A, which I did for the other batteries.
They are all behaving the same.

Its pretty hard to find any info on the subject. We all know not to discharge below 2.5V/cell but what if it happens my accident? You would think some of the manufacturers would publish a emergency recovery procedure.

We have some real battery guru's here on the forum, thus my post with the question.

 

[ericgrand]

In the Valence battery manual, they say than when the battery display a red flashing light, the OEM should be contacted to assess if battery can be recovered or not...except for undervoltage. It is described that if the battery reach 2.3V per cell in less than a minute at 0.5A, then the alarm will disappear.
So I think in Valence case, they consider that it is a minor problem if the battery recover quickly.
But there is no rules for that, and considering you didn't pay for the cells, I would just charge them with a low current initially and build a battery with a BMS.
I would avoid connecting multiples cells in parallel until you are 100% sure they are behaving properly. It may be problematic that good cells get drained by bad one in a pack.

 

[Sparky_SC]

In the Valence battery manual, they say than when the battery display a red flashing light, the OEM should be contacted to assess if battery can be recovered or not...except for undervoltage. It is described that if the battery reach 2.3V per cell in less than a minute at 0.5A, then the alarm will disappear.
So I think in Valence case, they consider that it is a minor problem if the battery recover quickly.
But there is no rules for that, and considering you didn't pay for the cells, I would just charge them with a low current initially and build a battery with a BMS.
I would avoid connecting multiples cells in parallel until you are 100% sure they are behaving properly. It may be problematic that good cells get drained by bad one in a pack.

I have been doing initial tests for a few days being very conservative. The cells do recover from the low voltage pretty quick, I hook a few in parallel and charge at 500ma/cell first, they quickly rise to above 2V. At around 2.3 or so v/cell I go to 1 amp per cell because the rate of rise has slowed considerably. After I get to 2.6-2.7 I step up the current again, about 3-5a/cell. Once I get to about 3.1v/cell I remove the bus bars and let them set a while, then check voltages. They seem do be balanced at that point at just over 3V/cell. Then, I do a 4S config with BMS and charge fully. I have a 20V 45A bench supply used for the charging utilizing the current limiting.

The process I am using seems pretty gentle on the cells. Considering I have 180 cells on-hand and more coming in a couple weeks, efficiency of testing is very desirable.

Have not done any real load tests yet, played a bit and there seems to be plenty of power in a charged 12V 4S pack so I am optimistic. Turned out my 700W 12V inverter that I had on the shelf was no good so I picked up another one yesterday. Also, I have one of those import battery monitor meters with a hall effect current sensor that reads AH, current, volts etc... The instructions are horrible and todays goal is to sort out that meter and get it calibrated and reading correctly so I can get good numbers while testing.

 

[ericgrand]

That's a huge number of cells! Testing them one by one will be tricky! I would simply charge them up to 3.65V and connect them 16 by 16 to built a 48V battery, with a BMS. Then running a load like an inverter, I would check if there is any runner on the pack and replace it.

It all depends what you want to do with them. If you plan to use them as 48V pack, then I would use one BMS per 16 cells, just to monitor cell by cell and not a bunch of cells in parallel...