EVE matched cells, some cells drops very fast

[Just John]

I think you would find that the resellers will quickly say the cells are A- or some such. Logically if a cell met all specs it would not be sold as grey market - there is an almost unlimited demand so why wouldn't EVE sell themselves? Even the resellers are selling them as fast as they can get them in the door by the truckload so they are not going to change their approach unless it increases their profit margins.

I've purchased enough times from that part of the world to suspect how things would go. Westerners are preconditioned to believe marketing but those with some experience tend to consider price as a direct measure of quality. You are not going to get a Tesla Powerwall for 25% of the price.

This is all pretty academic based upon people's perception of if they are being marketed to or lied to. Most consumers would not even bother to test the capacity of a low cost battery purchased and installed in a vehicle etc. as Will is doing. -0.6% on spec is just not relevant. Ever buy a 2.0 liter car and discover it is in fact only 1.96l? Or that the fuel consumption and pollution figures only apply if it is hooked up to a test stand

You guys are going to drive the battery manufacturers crazy, next thing you know you won't even believe how long your cell phone or laptop battery will last.
I don't have any of the Lishen cells, but it seems that their 272AH and the Eve 280AH cells are almost identical in everything except rating. Seems Lishen is more honest in their ratings.
I had always planned on using only 80% of the capacity, so as long as I can get 224AH out of a pack "between the knees", I'll be satisfied that I got good value. Your mileage may vary, and you have every right to expect 280AH out of a cell advertised as 280AH. I suspect that battery manufacturers are not used to having to exaggerate claims, they have relied on cell phone and laptop manufacturers to do it for them.

 

[Just John]

cr1220; this what i put in the 6012w, you also need a power cord. i bought one on ebay etc

Yes, that's correct. To help out, here is the correct clock battery for the 12 amp version I have:
Amazon 1220 battery link
Here is a link to the correct power cord (10 foot no less):
Amazon 10 foot power cord

 

[Gazoo]

I don't have any of the Lishen cells, but it seems that their 272AH and the Eve 280AH cells are almost identical in everything except rating. Seems Lishen is more honest in their ratings.

Or the supplier is not being honest about the Grade of cell they are selling? I am pretty sure new cells bought directly from EVE would meet or exceed their rated capacity.

I had always planned on using only 80% of the capacity, so as long as I can get 224AH out of a pack "between the knees", I'll be satisfied that I got good value.

You should easily be able to get 224ah. Even if all the cells end up being 265ah you would be able to get around 240ah between the knees. The total capacity of my 8 EVE cells in a 24 volt configuration is 272ah's and I get 250ah's.

 

[Steve_S]

I have 2x EVE-280AH: 02YCB66110000H & 2X 02YCB66710000J cells that I am finishing now.
Last one just finished capacity test, they are all coming in 276-278AH. the "H" version at 276, the "J" at 278. starting from 3.60V, they do drop fast from there to 3.450-3.500 and then go into the long flat curve from there on.

These were charged to 3.65V using a bench power supply, starting with 30A Constant Current and switching to Constant Voltage until amps taken reached 1.5A. Each cell done independently. Then allowed to settle for a minimum of 1 hour and then put on a 20A (180) Capacity Tester. With my second round of testing, the disconnect was at 2.50V with starting voltage of 3.600 +/-0.010

My first tests, did not fill the cells as I cutoff charging between 5-7A and I stopped capacity test at 2.65V, which gave erroneous numbers.

Given the power curve is 3.400-3.000 and that the majority of folks prefer to leave a margin at the top & bottom it's quite reasonable to expect 250-255 AH @ 25°C/77°F. Also a factor is that more often than not, there will be one cell in the bunch that will be a runner, meaning at 3.400 +/- a bit, it will run ahead of the others with voltage, forcing HVD by the BMS. That is unless you have properly matched & qualified cells.

 

[Just John]

Or the supplier is not being honest about the Grade of cell they are selling? I am pretty sure new cells bought directly from EVE would meet or exceed their rated capacity.

I found the 2019 Eve spec sheet interesting. Apparently full rated capacity means within one month of manufacturing, and less than 5 cycles.
"Test should be conducted with new batteries within one month after shipment from our factory and the cells shall not be cycled more than five times before the test."

Pretty easy to claim that you didn't meet the defined test conditions. I think the Lishen cells are pretty identical, just rated more accurately. Nobody would be complaining if these were rated at 270AH, but as it is, they should certainly "revise" their spec sheet.

You should easily be able to get 224ah. Even if all the cells end up being 265ah you would be able to get around 240ah between the knees. The total capacity of my 8 EVE cells in a 24 volt configuration is 272ah's and I get 250ah's.

Yes, never having played with LiFePO4 before, I'm experimenting to see what the true capacity is before buying more.
My wife decided getting a new granite countertop for the kitchen is more important, so my cells have sat in the garage since Halloween. Just now starting to capacity test.

Living in the Phoenix area, my aim is to have sufficient battery and solar capacity to run a 12,000 BTU mini split and the fridge all day, every day.
Starting out first by seeing how much battery capacity I need, I'm hoping that 3 batteries at 24v of these 280 Eve cells gets close (starting with 2 to see what I can actually get out of them).

 

[Gazoo]

Also a factor is that more often than not, there will be one cell in the bunch that will be a runner

In my case it's not a runner. It's a slightly weak cell. My delta at the top is less than 100mv's. At the bottom it's a half a volt.

 

[Solarfun4jim]

I have just finished installing the permanent flexible cell busbars and flanged studs...torqued to 4nm...so now the proper testing begins. Discharging my 24v(280AH) pack down at 0.04CA the max cell difference remained below 8mv to 3.2v/cell. By 3.15v/cell it had widened to <20mv, 3.1v <62mv, 3.05v <80mv, 3.00v <101mv, 2.95v <125mv, 2.90v <153mv, 2.85v <197mv, 2.80v <261mv, 2.75v =383mv
At this point the runner cell hit LVD .
Will now take the pack up to HVD and ascertain the upper limits of where the cells diverge, thus establish the practical working range with no cell divergence. This will be done without balancing operating. I will then repeat the discharge/charge cycle with the balancing on during the charge function to see how much it extends the upper limits before the cells diverge. I can then determine whether balancing is worth it or not.
Once i have taken the pack up to HVD, that establishes the 100% SOC baseline. On the next cycle down, i will record the capacity figure on hitting the 3.2v/cell level and similarly on the next charge up.
After that i intend to hook it up to the inverter /charger and conduct similar tests at 0.25CA. (70A)

 

[Gazoo]

Pretty easy to claim that you didn't meet the defined test conditions.

I bought my cells from the group buy and we were told the cells would all be capacity tested. As it turned out some received cells with 265ah capacity. The supplier lied. There is no way they tested anything except the voltage and IR. This was no fault of Michaels. I consider myself fortunate to have received only one slightly weak cell. I didn't, and still don't feel the need to test the individual cells for capacity.

Regarding meeting the defined test conditions, it's possible the cells were sitting around somewhere before they were sold. But even if sitting for two or three years at a half SOC of charge, they should still be pretty close to the rated capacity. Why do some EVE's test at better than 280ah's and some test at 265ah's? I am thinking of @cinergi's capacity tests. From what I have seen the Lishen's tested so far have met or exceeded their rated capacity.

Yes, never having played with LiFePO4 before, I'm experimenting to see what the true capacity is before buying more.
My wife decided getting a new granite countertop for the kitchen is more important, so my cells have sat in the garage since Halloween. Just now starting to capacity test.

Experimenting has been loads of fun for me. I have never built a pack with cells like these. I received my cells in October and my pack still isn't finished. I have assembled it and tested it and I am going to redo it...lol Money is tight here too. I will be interested to know what you find when you test your cells.

 

[Gazoo]

I have just finished installing the permanent flexible cell busbars and flanged screws...torqued to 4nm...so now the proper testing begins.

Awwww man, I'm envious. I love those busbars.

By 3.15v/cell it had widened to <20mv, 3.1v <62mv, 3.05v <80mv, 3.00v <101mv, 2.95v <125mv, 2.90v <153mv, 2.85v <197mv, 2.80v <261mv, 2.75v =383mv

Here is mine just for kicks:

Voltage difference at 25.53 16mv's.
Voltage difference at 25.37 6mv's.
Voltage difference at 25.32 18mv's
Voltage Difference at 25.24 46mv's
Voltage difference at 25.00 102mv's
Voltage difference at 24.55 151mv's lowest cell is 2.969
Voltage Difference at 24.25 177mv's lowest cell is 2.914
Voltage Difference at 24.00 216mv's lowest cell is 2.854
Voltage difference at 23.75 252mv's lowest cell is 2.790
Voltage difference at 23.50 300mv's lowest cell is 2.733
BMS cut off when pack voltage was 22.95 volts Capacity measured 272ah's.

And another one. Cell 7 is the weak cell.

Amp hours remaining at 25.35 volts = 25.24. Voltage Difference = 0.010 Capacity = 9%
Amp hours remaining at 25.30 volts = 21.25 Voltage Difference = 0.020 Capacity = 8% Cell 7 volts lower than others.
Amp hours remaining at 25.25 volts = 19.72 Voltage Difference = 0.033 Capacity = 7%
Amp hours remaining at 25.20 volts = 17.59 Voltage Difference = 0.057 Capacity = 6%
Amp hours remaining at 25.15 volts = 16.98 Voltage Difference = 0.066 Capacity = 6%
Amp hours remaining at 25.10 volts = 16.10 Voltage Difference = 0.079 Capacity = 6%
Amp hours remaining at 25.00 volts = 14.64 Voltage Difference = 0.102 Capacity = 5%
Amp hours remaining at 24.90 volts = 13.57 Voltage Difference = 0.110 Capacity = 5%
Amp hours remaining at 24.80 volts = 12.71 Voltage Difference = 0.122 Capacity = 5%
Amp hours remaining at 24.70 volts = 11.96 Voltage Difference = 0.132 Capacity = 4%
Amp hours remaining at 24.60 volts = 11.20 Voltage Difference = 0.140 Capacity = 4%
Amp hours remaining at 24.50 volts = 10.58 Voltage Difference = 0.150 Capacity = 4%

This was not done in a lab with lab test equipment...lol. The measurements are all taken from the BMS.

I can then determine whether balancing is worth it or not.

I am looking forward to what you think. Thanks for sharing.

 

[Solarfun4jim]

Awwww man, I'm envious. I love those busbars.


Here is mine just for kicks:

Voltage difference at 25.53 16mv's.
Voltage difference at 25.37 6mv's.
Voltage difference at 25.32 18mv's

Looking fairly similar results to mine...so if we only ran down to 3.15v/cell, we should never need bother about divergence.

I'm kinda thinking, that if you top balance to 3.65v/cell, this levels them out at this topline and any 'balancing' at lower levels, either passive or active, is effectively pulling you away from that top balance???
Im wondering now, if i only intend to run the cells up to they diverge, perhaps the 'Top Balance' should be committed at say 3.5v/cell? Would this bring the overall 'balance' more into the middle of the pack, rather than being top weighted? Questions questions questions....lol.

 

[Gazoo]

I'm kinda thinking, that if you top balance to 3.65v/cell, this levels them out at this topline and any 'balancing' at lower levels, either passive or active, is effectively pulling you away from that top balance???

That's what I think too. I don't even think active balancing is necessary unless the cells start drifting between the knees.

Im wondering now, if i only intend to run the cells up to they diverge, perhaps the 'Top Balance' should be committed at say 3.5v/cell? Would this bring the overall 'balance' more into the middle of the pack, rather than being top weighted? Questions questions questions....lol.

I think you will find from your own testing that the BMS's top balancing isn't going to do much. Once you reach whatever voltage you have your BMS to start balancing, there isn't much time for the BMS to balance because the voltage goes up so quickly. You could set your charge current lower to allow more time if your delta doesn't look good at the top. I have set my BMS to start balancing at 3.4 volts. I don't think the delta in the middle of the graph would change because the curve is basically flat between the knees.

When you fully charge the pack let us know what your delta is. Mine is less than 100mv's and I am good with that.

 

[Solarfun4jim]

That's what I think too. I don't even think active balancing is necessary unless the cells start drifting between the knees.


I think you will find from your own testing that the BMS's top balancing isn't going to do much. Once you reach whatever voltage you have your BMS to start balancing, there isn't much time for the BMS to balance because the voltage goes up so quickly. You could set your charge current lower to allow more time if your delta doesn't look good at the top. I have set my BMS to start balancing at 3.4 volts. I don't think the delta in the middle of the graph would change because the curve is basically flat between the knees.

When you fully charge the pack let us know what your delta is. Mine is less than 100mv's and I am good with that.

Gazoo, from your results so far, what would you reckon the capacity is, simply running between 3.2v/cell to 3.4v/cell?

 

[Dzl]

Or the supplier is not being honest about the Grade of cell they are selling? I am pretty sure new cells bought directly from EVE would meet or exceed their rated capacity.

^ This.
EVE's energy storage cell group, should be (1) >280Ah (2) no more than 5.6Ah (2%) spread between highest and lowest cells, but all must be over 280Ah. This is the more relaxed standard, the power cell group, has tighter specs. This is what EVE guarantees/warranties for energy storage group cells bought through official channels (which are not the channels we buy through).

That said, the Lishen cells may be more conservatively rated (though it is still too early to say, tests have been mixed so far--ranging from about 272 to about 285 from what I've seen). If they do consistently hit upper 270's / lower 280's that would put them at 2-5% over capacity which would be welcome but not unusual for a manufacturer to do.

I'm kinda thinking, that if you top balance to 3.65v/cell, this levels them out at this topline and any 'balancing' at lower levels, either passive or active, is effectively pulling you away from that top balance???

I share this understanding, at least I share this understanding if by 'balancing at lower levels' you are referring to the lower part of the voltage range.

Im wondering now, if i only intend to run the cells up to they diverge, perhaps the 'Top Balance' should be committed at say 3.5v/cell? Would this bring the overall 'balance' more into the middle of the pack

I think the value of balancing towards the very top (3.55-3.65 or so) is how sensitive voltage is to SOC up in that range. You are fully in the knee. I do not know if there is any benefit of trying to balance at a lower voltage because you are going to only charge to a lower voltage. I suspect not. Since a balance is equalizing SOC at the top or the bottom. If SOC is equalized at 3.6 or 3.65, it should be virtually equal at 3.5 or so since the differences in SOC between these two voltages should be relatively to neglible. At least this is my current understanding, I'm not sure I have a full grasp of all aspects of this process. Is there anything I am missing/misunderstanding in your opinion?

 

[Solarfun4jim]

^ This.
EVE's energy storage cell group, should be (1) >280Ah (2) no more than 5.6Ah (2%) spread between highest and lowest cells, but all must be over 280Ah. This is the more relaxed standard, the power cell group, has tighter specs. This is what EVE guarantees/warranties for energy storage group cells bought through official channels.

That said, the Lishen cells may be more conservatively rated (though it is still too early to say, tests have been mixed so far--ranging from about 272 to about 285 from what I've seen). If they do consistently hit upper 270's / lower 280's that would put them at 2-5% over capacity which would be welcome but not unusual for a manufacturer to do.


I share this understanding, at least I share this understanding if by 'balancing at lower levels' you are referring to the lower part of the voltage range.

I think the value of balancing towards the very top (3.55-3.65 or so) is how sensitive voltage is to SOC up in that range. You are fully in the knee. I do not know if there is any benefit of trying to balance at a lower voltage because you are going to only charge to a lower voltage. I suspect not. Since a balance is equalizing SOC at the top or the bottom. If SOC is equalized at 3.6 or 3.65, it should be virtually equal at 3.5 or so since the differences in SOC between these two voltages should be relatively to neglible. At least this is my current understanding, I'm not sure I have a full grasp of all aspects of this process. Is there anything I am missing/misunderstanding in your opinion?

Actually DZL, that is a very good opinion you gave. Your point is well made that, if balanced at 3.6 or above, the divergence or need for balancing lower down that knee will be minimal...sometimes you just have to read it from someone else.

 

[Dzl]

Actually DZL, that is a very good opinion you gave. Your point is well made that, if balanced at 3.6 or above, the divergence or need for balancing lower down the knee will be minimal...sometimes you just have to read it from someone else.

Speaking of reading it from someone else (which I totally agree with, sometimes hearing it just makes things click in a different way than when you think something yourself), you should check out the resource filterguy and I (mostly him) put together on the what and the why of balancing. Its a good (I hope) conceptual level overview. Filterguy is a good explainer, and has been working hard churning out resources for the community lately.

 

[Solarfun4jim]

Speaking of reading it from someone else (which I totally agree with, sometimes hearing it just makes things click in a different way than when you think something yourself), you should check out the resource filterguy and I (mostly him) put together on the what and the why of balancing. Its a good (I hope) conceptual level overview. Filterguy is a good explainer, and has been working hard churning out resources for the community lately.

Yeah i have noticed the work you both have done...very commendable.

Just one small niggle...i'm trying to reconcile why, when i have top balanced at 3.65v/cell, why my cell pack when charging thereafter, starts to diverge at 3.43v/cell? You would think they would stay closer together up to nearly 3.65v, but show drastic divergence at the bottom end???

 

[fafrd]

^ This.
EVE's energy storage cell group, should be (1) >280Ah (2) no more than 5.6Ah (2%) spread between highest and lowest cells, but all must be over 280Ah. This is the more relaxed standard, the power cell group, has tighter specs. This is what EVE guarantees/warranties for energy storage group cells bought through official channels.

That said, the Lishen cells may be more conservatively rated (though it is still too early to say, tests have been mixed so far--ranging from about 272 to about 285 from what I've seen). If they do consistently hit upper 270's / lower 280's that would put them at 2-5% over capacity which would be welcome but not unusual for a manufacturer to do.


I share this understanding, at least I share this understanding if by 'balancing at lower levels' you are referring to the lower part of the voltage range.

I think the value of balancing towards the very top (3.55-3.65 or so) is how sensitive voltage is to SOC up in that range. You are fully in the knee. I do not know if there is any benefit of trying to balance at a lower voltage because you are going to only charge to a lower voltage. I suspect not. Since a balance is equalizing SOC at the top or the bottom. If SOC is equalized at 3.6 or 3.65, it should be virtually equal at 3.5 or so since the differences in SOC between these two voltages should be relatively to neglible. At least this is my current understanding, I'm not sure I have a full grasp of all aspects of this process. Is there anything I am missing/misunderstanding in your opinion?

Unfortunately, no, balance is not balancing SOC, it is balancing voltage. Which should amount to the same thing but does not because of channel measurement accuracy.

Most of the BMSes (as well as active balancers) have a channel read precision of +/-5mV.

This means to cells can be off by as much as 10mV and be considered in ‘perfect balance’ by the BMS or Balancer.

10mV way up into the knee past 3.5V represents very little difference in underlying SOC, so voltage-based balancing way up there works reasonably well.

But down in the flats, 10mV of mismatch can represent as much as 20% SOC, so the read-channel accuracy renders to he balance function all but useless used in a 20% / 80% cycle.

This is the reason many charge up into the knee occasionally (monthly or quarterly) - to actually re-too-balance their cells.

I purchased a BattGO passive balancer and it is all but useless for this reason. It drags all cells down to the voltage of the lowest cell, which is usually in the flats. Compounded by the read-channel precision of +/5mV, the pact is totally unbalanced after the balance cycle (unless you can get the weakest cell up into the knee, but even then, all cells will settle below the knee before the balance cycle is complete, so back to being useless.

The only way to get a useful balance function out of a completed battery is to hold all cells above 3.5V while passive balancing or use active balancing while maintaining an average of 3.5V (or more).

 

[Gazoo]

Gazoo, from your results so far, what would you reckon the capacity is, simply running between 3.2v/cell to 3.4v/cell?

Here is what I have found with the total pack voltage. Between 25.35 and 27.25 is the sweet spot for my pack. This is with a delta less than 20 millivolts at the top and bottom. Total capacity measured, keeping between those voltages, was 248ah's. The total capacity of my pack is 272ah's.

 

[Solarfun4jim]

Here is what I have found with the total pack voltage. Between 25.35 and 27.25 is the sweet spot for my pack. This is with a delta less than 20 millivolts at the top and bottom. Total capacity measured, keeping between those voltages, was 248ah's. The total capacity of my pack is 272ah's.

Perfect Gazoo....reckon mine wont be a whole lot different...will find out for sure just directly. 248Ah for trouble free running....sounds just the job for me. Thanks for that info.

 

[Dzl]

Unfortunately, no, balance is not balancing SOC, it is balancing voltage. Which should amount to the same thing but does not because of channel measurement accuracy.

Most of the BMSes (as well as active balancers) have a channel read precision of +/-5mV.

I think you misunderstood what I meant (I probably could've been clearer). Balancing is balancing SOC through balancing voltage
I was referring to the goal, I believe you are referring to the method of achieving it. The higher into the knee you are (within reason) the more sensitive voltage is to small differences in SOC, and therefore the more precise (and I think rapid) the balance can be.

Also in this case, I was referring to an initial (manual) top balance, but most of the concepts should be similar in either case. I may have missed some context.

Soooo, I think we agree on everything. Including most of this:

This means to cells can be off by as much as 10mV and be considered in ‘perfect balance’ by the BMS or Balancer.

10mV way up into the knee past 3.5V represents very little difference in underlying SOC, so voltage-based balancing way up there works reasonably well.

But down in the flats, 10mV of mismatch can represent as much as 20% SOC, so the read-channel accuracy renders to he balance function all but useless used in a 20% / 80% cycle.

This is the reason many charge up into the knee occasionally (monthly or quarterly) - to actually re-too-balance their cells.

I purchased a BattGO passive balancer and it is all but useless for this reason. It drags all cells down to the voltage of the lowest cell, which is usually in the flats. Compounded by the read-channel precision of +/5mV, the pact is totally unbalanced after the balance cycle (unless you can get the weakest cell up into the knee, but even then, all cells will settle below the knee before the balance cycle is complete, so back to being useless.

The only way to get a useful balance function out of a completed battery is to hold all cells above 3.5V while passive balancing or use active balancing while maintaining an average of 3.5V (or more).

 

[Dzl]

Yeah i have noticed the work you both have done...very commendable.

Just one small niggle...i'm trying to reconcile why, when i have top balanced at 3.65v/cell, why my cell pack when charging thereafter, starts to diverge at 3.43v/cell? You would think they would stay closer together up to nearly 3.65v, but show drastic divergence at the bottom end???

I have been wondering about this lately as well, you are not the first person I have seen mention this. What sort of divergence are you talking about? And at what C-rates?

I don't know what factors could lead to this. Any theories?

I wonder if a very slow charge rate or a short rest period would still show divergence?

 

[michael d]

Yes, that's correct. To help out, here is the correct clock battery for the 12 amp version I have:
Amazon 1220 battery link
Here is a link to the correct power cord (10 foot no less):
Amazon 10 foot power cord

I bought the power cord on eBay for $1.58 including shipping; so best to shop around. the batteries can be found almost anywhere.

 

[Solarfun4jim]

I have been wondering about this lately as well, you are not the first person I have seen mention this. What sort of divergence are you talking about? And at what C-rates?

I don't know what factors could lead to this. Any theories?

I wonder if a very slow charge rate or a short rest period would still show divergence?

Divergence of greater than 20mv once above 3.43v/cell at a < 0.05cA rate(and increasing all the time thereafter). Going to be running some tests, so i might have a clearer picture in a few days.
I just struck me odd, that at 3.65 top balance, i can't figure why they would diverge at 3.43v/cell, unless of course my top balance was defective. I will state, that the top balance was not above the 0.05C rate(ie 14A) which gives the recommended cut off. I wonder if charging at rates under this (using 10A bench top power supplies)and letting the current drop to very low values, is simply ineffective and not a true balance....hmmmmm?

 

[Dzl]

Divergence of greater than 20mv once above 3.43v/cell at a < 0.05cA rate(and increasing all the time thereafter). Going to be running some tests, so i might have a clearer picture in a few days.
I just struck me odd, that at 3.65 top balance, i can't figure why they would diverge at 3.43v/cell, unless of course my top balance was defective. I will state, that the top balance was not above the 0.05C rate(ie 14A) which gives the recommended cut off. I wonder if charging at rates under this (using 10A bench top power supplies)and letting the current drop to very low values, is simply ineffective and not a true balance....hmmmmm?

In theory that should be more effective right?

 

[Solarfun4jim]

In theory that should be more effective right?

Thats what i assumed previously, since the cells were getting trickled to maximise the time in getting them to a very close capacity, but my thinking seems to be wrong somewhere...just cant pinpoint where !!!

Fafrd was right when he stated that balancing voltages was not quite the same as balancing SOC, however the difference experienced so far from 3.65v (ie 3.43v/cell) seems to forfeit the point of balancing at all by that method.