BATTERY SELLERS - THE GOOD, BAD, UGLY -- or Jenny (DOCAN) so far so good ...

[dr.diesel]

Save $100 to lose protection

Much agreed, it goes great until all of the sudden it doesn't, just like the Michael debacle.

 

[NCSolarGarage]

I am half way through testing my 32 EVE LF280K Grade A cells connecting in 4S (12v Nom.) batches. (Bought privately in Australia from Chinese importer)
Ist battery batch 4S 271 A/H
2nd " " " 275 "
3rd " " " 279 "
4th " " " 271 "
Using a TAO BMS @ 110A (roughly 0.4C) (after top balance)
So a bit down on advertised A/H
Am going to compare with Victron BMV712 Smart on next test set up)
Cheers - Leigh

Your numbers are similar to mine. I'm using the A40L, and when I mentioned it to Jenny Wu, she suggested testing at only 30A to get advertised numbers.

 

[S Davis]

Your numbers are similar to mine. I'm using the A40L, and when I mentioned it to Jenny Wu, she suggested testing at only 30A to get advertised numbers.

Are these capacity tests being done at the specified temperature in the spec sheet?

 

[NCSolarGarage]

I am performing the tests in my house which is around 23-24ºC this time of year.

 

[Rossman]

Are these capacity tests being done at the specified temperature in the spec sheet?

What temperature delta do you think would cause this kind of poor performance? ie. Cells rated for 0.5C (140A continuous) and you can't draw more than 30A continuous? sounds sus.

 

[Horsefly]

What temperature delta do you think would cause this kind of poor performance? ie. Cells rated for 0.5C (140A continuous) and you can't draw more than 30A continuous? sounds sus.

I tested eight Eve 280Ah (K series, I think) at 50°F - 55°F and got below 280Ah out of all of them. I moved inside and retested two of them and got over 284Ah on both. I think cells will mostly perform well in cooler temps, but the capacity is affected more than you might think.

 

[Rossman]

I tested eight Eve 280Ah (K series, I think) at 50°F - 55°F and got below 280Ah out of all of them. I moved inside and retested to of them and got over 284Ah on both. I think cells will mostly perform well in cooler temps, but the capacity is affected more than you might think.

I feel like you didn't read my post? I wasn't talking about capacity per se, I'm talking about discharge rates. The EVE 280 cells are rated for 0.5C, so you should be able to withdraw 280Ah at 140amps if they are to spec? Acccording to the original post I quoted, only getting 280Ah out if you discharge at less than 30A seems pretty bad?

 

[Horsefly]

I feel like you didn't read my post? I wasn't talking about capacity per se, I'm talking about discharge rates. The EVE 280 cells are rated for 0.5C, so you should be able to withdraw 280Ah at 140amps if they are to spec? Acccording to the original post I quoted, only getting 280Ah out if you discharge at less than 30A seems pretty bad?

Sorry. I was only trying to say that temperature has an effect on prismatic lfp cells that is greater than people - at least me - might think. Didn't mean to derail your point. My only direct experience is with capacity, but the temps might effect performance otherwise.

 

[S Davis]

What temperature delta do you think would cause this kind of poor performance? ie. Cells rated for 0.5C (140A continuous) and you can't draw more than 30A continuous? sounds sus.

I just remember seeing in the EVE spec sheet discharge performance at different temperatures, see item 3 below.

 

[Rossman]

I just remember seeing in the EVE spec sheet discharge performance at different temperatures, see item 3 below.

Yeah, I just dont understand how what you are suggesting relates to capacity at a given discharge rate. Yes, cells have different capacities at different temperatures, but we were talking about different capacities at different discharge rates.

Like with lead acid batteries you will get a capacity based on a variety of discharge rates, the higher the discharge rate, the less power you can draw from the battery.
F.ex:


Maybe I am wrong here, but I thought the EVE batteries are speced @ 0.5C discharge for their capacity. ie. I should be able to draw 140A for 2 hours and completely exhaust the battery. What Docan appears to be saying is that you can only draw at 30A (0.1C!!!) to get the full capacity. That seems lame and seems to indicate that these are not automotive grade cells.

Not an expert tho so maybe I just dont understand :D

 

[Ampster]

That seems lame and seems to indicate that these are not automotive grade cells.

No they are not automotive grade, whatever that is?
If you are referring to cranking Amps that is an entirely different application than storage. I rarely draw more than .1C from my 42kWh pack. I charge it faster.

 

[Rossman]

If you are referring to cranking Amps that is an entirely different application than storage.

I am not talking about cranking amps. I pasted the specs specifically from a Rolls renewable 2V battery above (not a car battery). It shows that if you discharge at 66.75A you can discharge 1335Ah, but if you discharge at a lower rate, like 15.35A, you will see capacity closer to 1535Ah. (and conversely at a higher discharge rate, less capacity).

I guess I hoped that the Docan EVE batteries could/would perform closer to the battery spec Feels like there should be two spec sheets, one for automotive grade cells and one for the cells that do not meet that standard.

 

[Bob B]

Yeah, I just dont understand how what you are suggesting relates to capacity at a given discharge rate. Yes, cells have different capacities at different temperatures, but we were talking about different capacities at different discharge rates.

As with most things .... 1 factor doesn't stand alone.

I think the caution was just to be aware of the temperature influence ... for instance if you do a capacity test at .5C and 50 DegF .... and another test at .25C at 70 DegF .... don't be fooled into thinking that the different rate was the only possible reason for a difference in the measured capacity.

If you want to measure how the rate affects capacity you need to be VERY careful that the temperature remains the same .... I think that the point that is being made about temperature.

 

[Rossman]

I think the caution was just to be aware of the temperature influence ... for instance if you do a capacity test at .5C and 50 DegF .... and another test at .25C at 70 DegF .... don't be fooled into thinking that the different rate was the only possible reason for a difference in the measured capacity.

I guess I've assumed that the tester isn't doing their tests under wildly varying environmental conditions, and have controlled for this. Perhaps a poor assumption.

 

[Bob B]

I guess I've assumed that the tester isn't doing their tests under wildly varying environmental conditions, and have controlled for this. Perhaps a poor assumption.

I was just answering your question about .... why temperature was being brought into the discussion ... you seemed to be dismissing it as irrelevant .... carry on.

 

[Ampster]

I am not talking about cranking amps. I pasted the specs specifically from a Rolls renewable 2V battery above (not a car battery). ......

I guess I hoped that the Docan EVE batteries could/would perform closer to the battery spec Feels like there should be two spec sheets, one for automotive grade cells and one for the cells that do not meet that standard

I don't know what "automotive grade" is? Do you mean batteries that can only be discharged 50% and suffer frome Peukerts? Those are characteristics of Lead Acid chemistry. Lithium chemistry suffers none of those things. Plus no watering, no long inefficient Absorb cycles and no monthly equalization cycles. Is that is what you call "automotive grade" ?
There are variation among Lithium chemistries. I had some Headways that were capable of high C rate discharge. I used them on an E-bike and did not pay attention to how long they lasted.

 

[Rossman]

I don't know what "automotive grade" is? Do you mean batteries that can only be discharged 50% and suffer frome Peukerts? Those are characteristics of Lead Acid chemistry. Lithium chemistry suffers none of those things. Plus no watering, no long inefficient Absorb cycles and no monthly equalization cycles. Is that is what you call "automotive grade" ?
There are variation among Lithium chemistries. I had some Headways that were capable of high C rate discharge. I used them on an E-bike and did not pay attention to how long they lasted.

Automotive grade is the spec that EVE produces their lifepo4 cells to, to sell to automotive (EV) manufacturers.

See the video in the OP here: https://diysolarforum.com/threads/are-we-all-getting-grade-b-cells.39156/

Cells that meet that spec can be discharged at the specifications indicated in the EVE cell spec sheet (for the newest 280Ah cells, this is 0.5C, or 140A). In the case of the cells from Docan, 0.1C seems to be the discharge rate, so they appear not to meet the EV automotive chinese spec.

 

[Horsefly]

Automotive grade is the spec that EVE produces their lifepo4 cells to, to sell to automotive (EV) manufacturers.

See the video in the OP here: https://diysolarforum.com/threads/are-we-all-getting-grade-b-cells.39156/

Cells that meet that spec can be discharged at the specifications indicated in the EVE cell spec sheet (for the newest 280Ah cells, this is 0.5C, or 140A). In the case of the cells from Docan, 0.1C seems to be the discharge rate, so they appear not to meet the EV automotive chinese spec.

Just to be clear: Docan (or any of the sellers available to us) don't have cells that are for a different purpose. ALL of these cells are manufactured (by Eve in this case) for EV use. I don't know exactly what you are saying, but don't be thinking the Docan cells were built for something different.

 

[Rossman]

Just to be clear: Docan (or any of the sellers available to us) don't have cells that are for a different purpose. ALL of these cells are manufactured (by Eve in this case) for EV use. I don't know exactly what you are saying, but don't be thinking the Docan cells were built for something different.

I'm not sure what about my posts is so hard to understand, sorry if I wasn't clear.

I am not asserting the cells were built for a different purpose.

I am saying the cells available to us from Docan are clearly cells which do not meet the aforementioned EV/automotive spec. Only the cells that come with EVE test reports do, and cells from Docan do not. They are basically EV spec rejects - still new, but don't perform to the spec. Which may be fine for solar but it feels somewhat lame to buy a cell and be told the discharge rate is 0.5C but the cell you get can only be discharged at 0.1C. They should be advertised as such.

 

[sergea]

I'm not sure what about my posts is so hard to understand, sorry if I wasn't clear.

I am not asserting the cells were built for a different purpose.

I am saying the cells available to us from Docan are clearly cells which do not meet the aforementioned EV/automotive spec. Only the cells that come with EVE test reports do, and cells from Docan do not. They are basically EV spec rejects - still new, but don't perform to the spec. Which may be fine for solar but it feels somewhat lame to buy a cell and be told the discharge rate is 0.5C but the cell you get can only be discharged at 0.1C. They should be advertised as such.

Yep, I only got EVE test report with cells coming from Amy W. however I still can use my cells from docan at 0.5 C . it seems you got a bad cell.