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

[MalBurn]

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.

Thank you.

I'm not overly concerned about being limited to 267ah, I try to operate between a max 90% and a min of 20% soc, so full capacity doesn't really matter.
My concern was that my pack might be degrading faster than it should and I might find a similar drop again year on year.
If a faster fall at the start of usage, becomes a more gentle curve, then that puts my mind at rest.

Another contributor said similar, so thank you both.
I'll go and look up those graphs

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.

My cells were amongst the first offered by this supplier, since then I believe they test and label the cells with capacity, wh and resistance data.
Perhaps these early non labelled ones weren't as well QC'd
Anyway, thanks to everyone for the help.

 

[740GLE]

Even if the testing shows unacceptable loss of life over a years usage, what are you gonna do? Demand a buy back from the vendor? Throw it in the trash?

The more and more I’ve seen people run “tests” being concerned about every AH/Whr, the more and more I’m happy with my head in the sand running an over capacity system with no testing.

 

[Solarcabin Channel]

Even if the testing shows unacceptable loss of life over a years usage, what are you gonna do? Demand a buy back from the vendor? Throw it in the trash?

The more and more I’ve seen people run “tests” being concerned about every AH/Whr, the more and more I’m happy with my head in the sand running an over capacity system with no testing.

Agreed, unless you have an absolutely constant load and ambient temp all that testing is meaningless and just guess work. The manufacturers of todays LFP probably won't still be in business and the tech will be much improved by the time my LFP need replaced.

 

[TimE]

Agreed, unless you have an absolutely constant load and ambient temp all that testing is meaningless and just guess work. The manufacturers of todays LFP probably won't still be in business and the tech will be much improved by the time my LFP need replaced.

My cells were made by CATL. Thr largest lithium battery manufacturer in the world. Do you really think they won't be in business?

 

[Solarcabin Channel]

My cells were made by CATL. Thr largest lithium battery manufacturer in the world. Do you really think they won't be in business?

The cell manufactures may be in business but probably won't be making those same types of cells.

The technology is changing so rapidly that todays LFP will likely radically change before your batteries wear out.

 

[740GLE]

My cells were made by CATL. Thr largest lithium battery manufacturer in the world. Do you really think they won't be in business?

100% promise they won’t answer your emails or calls.

As for the OP and his tests, I’d put it back in service and then compare again next year, then the year after that. If a time comes either usage increases of AH seems to be not enough but another battery add it to the system and motor on.

 

[TimE]

100% promise they won’t answer your emails or calls.

As for the OP and his tests, I’d put it back in service and then compare again next year, then the year after that. If a time comes either usage increases of AH seems to be not enough but another battery add it to the system and motor on.

That's wasn't the question. May be if you spoke Chinese ?

 

[sunshine_eggo]

Answer to subject:

1-3%/year combined calendar and cycle life degradation. People forget that these deteriorate just from sitting there even if doing nothing. That degradation rate doesn't go away if you use them. It gets compounded by cycle life degradation.

End of life is typically 70-80% rated capacity. IIRC, for the EVE 280K cells, it's 70%.

 

[740GLE]

That's wasn't the question. May be if you spoke Chinese ?

Oh yeah sorry I was too busy reading your post as if Jeremy Clarkson was saying it. “In the world”!!!

Yeah They will prob be around if not merged with a few other companies, but they still won’t care about anyones small DIY build using cast off cells bought on the third party market.

 

[MalBurn]

Even if the testing shows unacceptable loss of life over a years usage, what are you gonna do? Demand a buy back from the vendor? Throw it in the trash?

The more and more I’ve seen people run “tests” being concerned about every AH/Whr, the more and more I’m happy with my head in the sand running an over capacity system with no testing.

If you read my 1st post, I said I had cause to test this battery, it's not that I lie in bed at night wondering if millamps are running away from home in the night.
I completely agree, running tests every 5 minutes is completely unnecessary and given how long it takes ( in my case 4 days, before I could get the battery tested back in the pack and the whole thing re-balanced) it's a pita.

The 'cause', turned out to be an soc error created by my JK bms'es going out of their tiny minds, but that's another story.
I thought I had a bad cell, hence testing which produced an unexpected result, hence question here.
I asked the vendor, but they seem to be ignoring the question, no doubt they get bombarded with stuff like this.

I have another 12v battery made with the same grade B cells from the same source, it's likely it's results would be poor too, but I'm not wasting another 4 days finding out, nor going to worry about it.

What I would "gonna do" to an unacceptable battery, would be replace the poor cell, if it was bad enough that it would cause uneven wear to the battery it was in.
If my battery is following the natural curve for LFP chemistry it's capacity drop should slow down and not take a nose dive, that is all I wanted to know.

Thanks for replying, it's fair comment

 

[MalBurn]

100% promise they won’t answer your emails or calls.

As for the OP and his tests, I’d put it back in service and then compare again next year, then the year after that. If a time comes either usage increases of AH seems to be not enough but another battery add it to the system and motor on.

I'm not going to bother with any more testing, unless something unusual occurs to warrant it.

 

[MalBurn]

Answer to subject:

1-3%/year combined calendar and cycle life degradation. People forget that these deteriorate just from sitting there even if doing nothing. That degradation rate doesn't go away if you use them. It gets compounded by cycle life degradation.

End of life is typically 70-80% rated capacity. IIRC, for the EVE 280K cells, it's 70%.

Thanks for the reply,

I knew the battery would lose capacity, just wasn't aware that like a brand new car, it loses most in the first year and then levels off a little
Just seemed to be quite a lot of loss on the number 2 cell in the pack

Before somebody says it, I don't mean exactly like a new car in % terms

 

[740GLE]

If you read my 1st post, I said I had cause to test this battery, it's not that I lie in bed at night wondering if millamps are running away from home in the night.
I completely agree, running tests every 5 minutes is completely unnecessary and given how long it takes ( in my case 4 days, before I could get the battery tested back in the pack and the whole thing re-balanced) it's a pita.

The 'cause', turned out to be an soc error created by my JK bms'es going out of their tiny minds, but that's another story.
I thought I had a bad cell, hence testing which produced an unexpected result, hence question here.
I asked the vendor, but they seem to be ignoring the question, no doubt they get bombarded with stuff like this.

I have another 12v battery made with the same grade B cells from the same source, it's likely it's results would be poor too, but I'm not wasting another 4 days finding out, nor going to worry about it.

What I would "gonna do" to an unacceptable battery, would be replace the poor cell, if it was bad enough that it would cause uneven wear to the battery it was in.
If my battery is following the natural curve for LFP chemistry it's capacity drop should slow down and not take a nose dive, that is all I wanted to know.

Thanks for replying, it's fair comment

Ahh seems like a bit of this information was missing from your first post. Thanks for adding it to paint the full picture.

Was this your first hiccup with the Jk BMS and SOC?

Do you have an external shunt? That you can cross check to the BMS readings?

I hope you many more cycles in your battery

 

[MalBurn]

Ahh seems like a bit of this information was missing from your first post. Thanks for adding it to paint the full picture.

Was this your first hiccup with the Jk BMS and SOC?

Do you have an external shunt? That you can cross check to the BMS readings?

I hope you many more cycles in your battery

Agreed, my first post was too general, I'll take that onboard in future.

Re the JKs, yes this is the first time in a year running them I've had SOC issues.
I did have a shunt connected, but disconnected it during install of my 3rd battery in July this year, with the intention to reattach when I upgrade my inverter cables, which I was just about to do!

The JKs had always followed the shunt SOC fairly well, so I thought they could be relied on.
It seems that's far from the case, as battery 2 (the one I'm posting about) went from a approx 35% to zero in just a few minutes.
Cell 2 appeared to be the cause at first glance, hence the testing, but it just happened to be the worst performing cell, so bottomed first.

I self impose a low limit of 20% SOC on the pack, so I better get the shunt back on pronto!
When it happened, the cells were a few days away from the end of their warranty, which didn't help my critical thinking at the time.

Thanks for your reply, appreciated and all the other member replies too