Eve 280ah Lifepo4 degradation, how much in the first year is acceptable?

[MalBurn]

I had cause to test one of my 12v batteries, made from 4x Eve 280ah Lifepo4 cells.

The battery had been in service for 1 year and has just completed 67 cycles. My usage, as far as discharge amps is concerned is no more than .25c maximum, with the pack running generally much lower than that. Charge rate would be similar maybe .3c on a very good sunny day, but usually much less.

The weakest cell tested at 267.8ah (865.5wh)
Of the other three the highest was 270.9 (884.2wh) with the other two just failing to make it to 270ah

Is this inside normal range, as far as loss of capacity is concerned?

 

[BentleyJ]

So that is about a 4% capacity loss after only 67 cycles, which as you suspected is quite high. However, since there is no historic capacity data from when you initially received the cells, its difficult to determine if they were used or low capacity cells to begin with or have undergone accelerated aging for some reason.

Based on what others have experienced from various less than reputable sellers, my bet would be those cells were out of spec. when you received them. Your usage history does not indicate the cells were abused or operated in harsh conditions.

 

[Aussieguy]

any
balancer
bluetooth to tell you what each cell's values are?

do they even get charged enough to allow the bms to balance?

 

[JeromeS13]

Did you do a capacity test before assmembly? If not, you don't really have an accurate basis of how much you've lost...

 

[Alkaline]

I had cause to test one of my 12v batteries, made from 4x Eve 280ah Lifepo4 cells.

The battery had been in service for 1 year and has just completed 67 cycles. My usage, as far as discharge amps is concerned is no more than .25c maximum, with the pack running generally much lower than that. Charge rate would be similar maybe .3c on a very good sunny day, but usually much less.

The weakest cell tested at 267.8ah (865.5wh)
Of the other three the highest was 270.9 (884.2wh) with the other two just failing to make it to 270ah

Is this inside normal range, as far as loss of capacity is concerned?

Most of the 280s will settle in around 250-260 for quite a while so I doubt it will go down any more.

 

[MalBurn]

Most of the 280s will settle in around 250-260 for quite a while so I doubt it will go down any more.

Thanks for that, these are the among the first bare cells I bought.
I wasn’t really expecting much of a difference from 1st tests last year, but good to know.

 

[SeaGal]

Thanks for that, these are the among the first bare cells I bought.
I wasn’t really expecting much of a difference from 1st tests last year, but good to know.

So what was the value then? This thread is useless without that information

 

[MalBurn]

So what was the value then? This thread is useless without that information

I didn't have that info on hand, it's written down somewhere around here, but from memory the best cell was around 277ah and the worst 275ah. If I can find the details include the wh reading I'll post back.

This time I printed out the test info and stuck it on each cell!

The reason for the post was, I've lost around 7ah capacity from each cell, when my expectation was there would be little, or no difference at this level of cycles and low rates of C.
It concerned me I might have 'relatively' poor performing cells, with possibly not the best outlook ahead.

I expect those who have used Eve cells over longer periods, might be able to reassure, if figures like 267ah from a year old Eve 280ah cell with low cycles and low usage where nothing to be concerned about and it seems that's the case.

So the thread is in fact useful, at least it is to me, but thank you for the reply in any case.

 

[SeaGal]

I didn't have that info on hand, it's written down somewhere around here, but from memory the best cell was around 277ah and the worst 275ah. If I can find the details include the wh reading I'll post back...
...
So the thread is in fact useful, at least it is to me, but thank you for the reply in any case.

My point about the thread being useless was without that info you have now given we have no way of knowing how much, if any the cells have degraded.

But now, let's assume that the worst cell was measured at 275Ah and has now been measured at 267.8Ah...

That's a theoretical degradation of just over 7Ah or around 2.5%.

But tell me, honestly, with what accuracy you can measure those values? It would be quite extraordinary - unless you have professionally calibrated equipment - to be able to measure something like that to less than 1% accuracy. More likely in the range of 2% to 5% with standard equipment. It's more complex than just taking a snapshot of voltage or current.

Then take environmental factors, especially temperature, into account. Not just temperature of the room, but of the wires, cells and measuring device. IIRC the performance of LiFePO4 cells (in terms of extractable capacity) can vary by as much as 10% over a 30 degree C temperature range. So you can see it is highly likely that unless you are using calibrated equipment in an temperature controlled environment then a variance of 2.5% of two measurements, taken one year apart is probably not statistically significant.

 

[Solarcabin Channel]

I would suggest testing again after a completely full charge and allowing the battery to sit and balance.

The cells can show different charge rates until the BMS balances the battery which takes some time.

It is possible you have some bad cells but on average any decent LIFEPO4 will get 3000 cycles to 80% DOD. If you completely drain and recharge every day that would be 8 years or 2.5% capacity loss per year.

 

[SeaGal]

... that would be 8 years or 2.5% capacity loss per year.

.. only if it can be assumed that degradation is linear over time

 

[Solarcabin Channel]

.. only if it can be assumed that degradation is linear over time

Yes and that depends more on how you use and cycle the battery.

Deep draw to empty is going to degrade the cells faster.

"Because the 20% capacity fade and/or 100% internal resistance increase are considered to be the EOL criterion which are widely accepted, almost all of the tests performed in the aforementioned literature are carried out within this battery life span. There are few studies on aging behavior outside this range."

Here is a study of the factors for degradation: https://www.mdpi.com/1996-1073/14/6/1732

ADDED: Ambient temperature and charge source can also affect degradation rates.

 

[MalBurn]

So that is about a 4% capacity loss after only 67 cycles, which as you suspected is quite high. However, since there is no historic capacity data from when you initially received the cells, its difficult to determine if they were used or low capacity cells to begin with or have undergone accelerated aging for some reason.

Based on what others have experienced from various less than reputable sellers, my bet would be those cells were out of spec. when you received them. Your usage history does not indicate the cells were abused or operated in harsh conditions.

Thank you for that, I’m trying to find my data, which is proving a little elusive.
I did have a reason to be a bit general (maybe more on that later), but as you say without historic data it’s not an easy question to answer.

I’ll post again soon with a more detailed account of my findings past, present and methodology used.

 

[MalBurn]

My point about the thread being useless was without that info you have now given we have no way of knowing how much, if any the cells have degraded.

But now, let's assume that the worst cell was measured at 275Ah and has now been measured at 267.8Ah...

That's a theoretical degradation of just over 7Ah or around 2.5%.

But tell me, honestly, with what accuracy you can measure those values? It would be quite extraordinary - unless you have professionally calibrated equipment - to be able to measure something like that to less than 1% accuracy. More likely in the range of 2% to 5% with standard equipment. It's more complex than just taking a snapshot of voltage or current.

Then take environmental factors, especially temperature, into account. Not just temperature of the room, but of the wires, cells and measuring device. IIRC the performance of LiFePO4 cells (in terms of extractable capacity) can vary by as much as 10% over a 30 degree C temperature range. So you can see it is highly likely that unless you are using calibrated equipment in an temperature controlled environment then a variance of 2.5% of two measurements, taken one year apart is probably not statistically significant.

Thank for that I’m going to repost, or edit the original post with more information as soon as I can get it collated.
I’d slightly disagree with you on accuracy of even relatively cheap testers, but more on that later.

 

[MalBurn]

Did you do a capacity test before assmembly? If not, you don't really have an accurate basis of how much you've lost...

I did, but didn’t have data to hand, will be reposting soon

 

[MalBurn]

I would suggest testing again after a completely full charge and allowing the battery to sit and balance.

The cells can show different charge rates until the BMS balances the battery which takes some time.

It is possible you have some bad cells but on average any decent LIFEPO4 will get 3000 cycles to 80% DOD. If you completely drain and recharge every day that would be 8 years or 2.5% capacity loss per year.

The battery was fully charged, cells removed, bought into my home, as my garage where the pack lives, was around 17c. Cells acclimatised to room temp of 23.5c paralleled and top balanced with a 5a bench psu to 3.65v. Left for an hour before first cell tested, discharged down until 2.5v reached.

I’ll repost all the data soon, thank you for the reply

 

[MalBurn]

Ok, my apologies, I've searched and searched, but I can't find my original data on the cells. I was building the system back then and my time spent notating things was a little more disorganised than it would be now.
I know I'm going to get some comments on that, but I do have what I think is a reasonable reference value to allow discussion on this topic.

What I can say as a reference is, these are Fogstar UK Grade B Eve LF280K cells,
Fogstar website stipulates a minimum capacity of 277ah from these cells.

Using that as starting point, after 1yr and 67 cycles my results for a 12v battery I made up using 4x Eve LF280K grade B cells is


Cell No1- 270.971AH (884.252WH)

Cell No2- 267.807AH (865.529WH)

Cell No3- 269.494AH (875.721WH)

Cell No4- 269.736AH (878.418)

Testing:
Before testing I fully charged the battery, removed the cells and took them from my garage into my home.
Let them warm to room temp (23.5c), then paralleled and top balanced to 3.65v using a 5 amp bench psu.
Once fully charged (psu less than 1 watt, all cells 3.65v) I left the cells for an hour, then began the test at 39.3a with cut off set to 2.5v.

Tester is an Atorch DL24, I used the 4 cable method with good quality cables.

Re accuracy of the DL24, I bought 4 more Grade A Eve 280ah cells from Fogstar in July of this year and tested them with the same tester and methodology
they returned between 281.8 and 286AH, so I can't see my tester being inaccurate enough to explain the losses with the B grade cells. I tested the grade A in July with a room temp of 23.5, which is why raised room temperature to 23.5 for the grade B test. I know spec sheets say 25c for optimum output, but I’m from Northern Ireland and sticking 23.5c was bad enough, I’m used to things a mite cooler ?

Usage:
The battery had been in service for 1 year and has just completed 67 cycles. My usage, as far as discharge amps is concerned is no more than .25c maximum, with the battery running generally much lower than that. Charge rate would be similar maybe .3c on a very good sunny day, but usually much less. BMS is a JK B2A8S20P-H

 

[TimE]

Ok, my apologies, I've searched and searched, but I can't find my original data on the cells. I was building the system back then and my time spent notating things was a little more disorganised than it would be now.
I know I'm going to get some comments on that, but I do have what I think is a reasonable reference value to allow discussion on this topic.

What I can say as a reference is, these are Fogstar UK Grade B Eve LF280K cells,
Fogstar website stipulates a minimum capacity of 277ah from these cells.

Using that as starting point, after 1yr and 67 cycles my results for a 12v battery I made up using 4x Eve LF280K grade B cells is


Cell No1- 270.971AH (884.252WH)

Cell No2- 267.807AH (865.529WH)

Cell No3- 269.494AH (875.721WH)

Cell No4- 269.736AH (878.418)

Testing:
Before testing I fully charged the battery, removed the cells and took them from my garage into my home.
Let them warm to room temp (23.5c), then paralleled and top balanced to 3.65v using a 5 amp bench psu.
Once fully charged (psu less than 1 watt, all cells 3.65v) I left the cells for an hour, then began the test at 39.3a with cut off set to 2.5v.

Tester is an Atorch DL24, I used the 4 cable method with good quality cables.

Re accuracy of the DL24, I bought 4 more Grade A Eve 280ah cells from Fogstar in July of this year and tested them with the same tester and methodology
they returned between 281.8 and 286AH, so I can't see my tester being inaccurate enough to explain the losses with the B grade cells.

Usage:
The battery had been in service for 1 year and has just completed 67 cycles. My usage, as far as discharge amps is concerned is no more than .25c maximum, with the battery running generally much lower than that. Charge rate would be similar maybe .3c on a very good sunny day, but usually much less. BMS is a JK B2A8S20P-H

You have these cells in a garage in the UK. No temperature control? Wouldn't they be better in the temperature controlled part of the house? Ideal temperature would be about 25degC

 

[MalBurn]

You have these cells in a garage in the UK. No temperature control? Wouldn't they be better in the temperature controlled part of the house? Ideal temperature would be about 25degC

I keep a close check on the cells, and have a basic method for keeping them from going too cold in the worst of winter.
Upgrading that aspect to something more sophisticated very soon.

I understand capacity drops in lower temps, but unless the cells hit freezing temps and are subjected to charging, low, but not freezing temperatures shouldn’t be harmful.
At least that’s my understanding.

 

[TomC4306]

Check the spec sheet.
The graph that describes the cycles to 80% capacity is the one you want.
Degradation follows the same curve as a discharge curve. Accelerated degradation at first followed by a long flat (ish) slide.