New Toys Arrived - ZKE-40 Tester & Sun Fun Kits EVE LF304 cells.

[Alkaline]

No, there isn't for the purpose of capacity testing. If a 1000V battery says on the label it's 10Ah, I should be able to take a tester and verify the 10Ah. That's how batteries are specified, precisely because it takes all the losses of measuring Wh out of the equation.

I'm not sure I can agree here... You can take a 12v battery 100AH battery put a dc-dc down converter to 6v and then violla you now have a 200AH 6v battery, so have I magically double my AH?

Do we even know how eve is testing these cells? The qr codes always say WH on them, on the 280K it is 896 WH not AH. Maybe we need to start looking at WH more closely.

I want to point to this thread:

Poor Docan Experience (Resolved)

Purchased 16 eve 280k from Docan over a month ago confirming the description had them as brand new, full capacity cells. Cells arrived bloated, more than 5mm out of spec at only 3.2v. No grade B QR and had the front labels that they had been "tested" at 280ah and matching IR .19. - Reached out...

diysolarforum.com

see: https://diysolarforum.com/attachments/cell1-274-png.115790/

vs

https://diysolarforum.com/attachments/cell7-png.115796/

I posted about this on October and Both these cells test to 274AH but cell1 is making 880 WH and the cell7 is 866WH and if all you looked at was the 274AH you would say well hey they are the same. The 880 Wh cell has more usable energy than the 866 Wh yet they both have the same AH???
Also the cell 1 average voltage is 3.21 but cell 7 is 3.16

So there is something to look at when it comes to WH and voltage when it comes to AH.

 

[upnorthandpersonal]

I'm not sure I can agree here... You can take a 12v battery 100AH battery put a dc-dc down converter to 6v and then violla you now have a 200AH 6v battery, so have I magically double my AH?

Any conversion you do is no longer the battery itself in question, and you should then indeed have a 6V 200Ah system (and take losses with regard to the conversion into account as well). The battery / battery cell here has a very specific meaning, being the chemical storage entity.

I have an idea what EVE and others are doing: moving away from the Ah rating to a Wh rating because it actually indicates something meaningful when talking about energy. The problem becomes when you put both on the label and try to justify one based on the other with a nominal voltage. That's not the case: because the Wh has to take voltage into account, you have to make a constant voltage measurement and make the multiplication with the current at that time, or for example, keep the load variable to draw the same current with changing voltage. In other words, you have to calculate the integral of the discharge function. Suffice to say, this will lead to wildly different measurements from tester to tester and test set-up (connection issues, cable voltage drop, etc.) especially when you also don't use separate leads to measure the cell voltage so you can account for the voltage drop over the leads, etc.

 

[Alkaline]

Yes down conversion will have a loss... but going back to this thread though: https://diysolarforum.com/threads/poor-docan-experience-resolved.48592/#post-618121

2 cells both testeding to 274AH, 1 has 880WH and the cell 7has 866WH, there is something here and it only resolves the issue if you look at the voltage. Cell 1 is 274AH @ 3.21v and Cell 7 is 274AH @ 3.16

So all I'm saying voltage does have something, I'm not saying its everything but something. ?‍

 

[upnorthandpersonal]

2 cells both testeding to 274AH, 1 has 880WH and the cell 7has 866WH, there is something here and it only resolves the issue if you look at the voltage. Cell 1 is 274AH @ 3.21v and Cell 7 is 274AH @ 3.16

So all I'm saying voltage does have something, I'm not saying its everything but something. ?‍

Yes, that's what I was saying: a slightly different connection, a slightly warmer cable (higher resistance), slight temperature changes, timing, etc. all impact the Wh rating. None of those impact the Ah rating (if ambient at 25C), which is why it's such a useful way to measure capacity.

 

[Alkaline]

meh...the v-sense cables would take those differences out... for me a passing cell should meet both the AH & WH which all grade A cells should meet (expect this 280k...) but as a consolation prize, using the sfk method my ?Luyuan 280ks are now 281 AH instead of 278AH? ?

 

[upnorthandpersonal]

meh...the v-sense cables would take those differences out... for me a passing cell should meet both the AH & WH which all grade A cells should meet (expect this 280k...) but as a consolation prize, using the sfk method my ?Luyuan 280ks are now 281 AH instead of 278AH? ?

The reason why they are higher is because you spend most of the discharge above 3.2V (60% to 70% if I remember correctly, depending on the rate) on a cell. So if you then take Wh reading over the entire voltage range, and then divide it by the 3.2V or thereabout, you will get a higher Ah number purely because you can't treat the Wh number that way. And that's exactly what happens when OP tested, quoting parts of post #33

"316.70 AH and Energy 1026.63" (my note: Wh measured, Ah measured, they're both fine).

"Label on the cell said 320.2583 AH" (my note: this is where I have issues, see below)

--> so just divide the measured Wh by 3.2V and voila: 320.8Ah. Just as the label says, everyone happy. Except it's wrong. It's not a 320Ah cell. It's a 316Ah cell (actually, it's a 304Ah rated cell). Someone is treating the Wh numbers as a constant in function of the voltage, but it's not - 60% of the discharge cycle is above 3.2V.

Look, I know this is going to end up a nit-picking thread, but if they would just have advertised these cells as being 304Ah cells (as per EVE) with perhaps the test capacity measured normally (not the Wh/3.2V stuff) none of this would be written about these cells and everyone would be happy.


As for OP: you've got good cells, put them to work and enjoy!