Wh and Ah and More

[upnorthandpersonal]

About 1 year ago I had 4x 280K cells form SFK and I built a battery it tested to 278.1 AH and 3601 WH with the 150 AMP bms (same as jbd). So is this a pass or fail on capacity? 3601/4 = 900.25 Wh/cell if they are are rated to 896 Wh each. 900.25/3.2 would be 281.3 Ah.

That's the issue: "they are rated at 896Wh each". Where does this come from? By multiplying 3.2V nominal with 280Ah capacity. Eliminate the 3.2V and take your 900.25Wh you measured. Divide 900.25 by 3.2V - awesome, 281Ah per cell yes? But you measured 278Ah. So which one is correct? But SFK said 3.25V is nominal for Grade A, so you should divide your 900.25 by 3.25, so 276Ah - cool you're over that cause you measured 278! All perfect! Well, no, of course not. This is just handwaving around the fact that the cell is rated at 280Ah and doesn't meet this...

That's why Wh aren't used, and why cells are rated in Ah.

 

[EastFalcon]

No more mention of WattHours, all in AmpHours.

my cells both Watthours and Amhours on the label:
https://diysolarforum.com/threads/48-cell-304-pallet-from-sun-fun-kits.72913/#post-925556 I don't think SFK is trying to be shady by including Wh. I also checked the QR code it did not have any signs of sanding.

 

[Steve_S]

Thread Subject = Cell price drop NOT an SFK foollishness Thread...

Start a separate thread: Why do we Love or Hate SFK and all the bafflegab about them in THERE !

 

[hwy17]

my cells both Watthours and Amhours on the label:
https://diysolarforum.com/threads/48-cell-304-pallet-from-sun-fun-kits.72913/#post-925556 I don't think SFK is trying to be shady by including Wh. I also checked the QR code it did not have any signs of sanding.

Everyone seems to be somewhat in agreement that SFK is in the business of attempting to sell decent product. You don't need take it as an assertion that you got bad product.

The bad blood here stems from 1. SFK's responses during the 280K drama with misleading claims about the WH AH interaction. 2. SFK's behavior when interacting with community members and youtubers.

It's basically rehashing an old debate about the claims in point 1. and settling the matter that it is still agreed their previous WH claims are incorrect. Now that EVE is fixing their product, SFK seems willing to move on from the claims in 1. and stand by AH again, when their product passes.

 

[hwy17]

@Steve_S The people want the drama and more importantly newcomers deserve to know the backstory behind the SFK controversies, especially as we see that SFK is going to continue to be a competitive player in the US market.

People deserve to know that if you buy from SFK it comes with the risk of unreasonable attitude from the seller if you're going to portray them badly online.

 

[Sam Cho TX]

That's the issue: "they are rated at 896Wh each". Where does this come from? By multiplying 3.2V nominal with 280Ah capacity. Eliminate the 3.2V and take your 900.25Wh you measured. Divide 900.25 by 3.2V - awesome, 281Ah per cell yes? But you measured 278Ah. So which one is correct? But SFK said 3.25V is nominal for Grade A, so you should divide your 900.25 by 3.25, so 276Ah - cool you're over that cause you measured 278! All perfect! Well, no, of course not. This is just handwaving around the fact that the cell is rated at 280Ah and doesn't meet this...

That's why Wh aren't used, and why cells are rated in Ah.

Rant about Ah and Wh...

Ok, this has been grinding my gears to the point where I'm annoyed with it, so I just wanted to write it down here. I see statements like this all over the net when it comes to cell capacity testing: - "you need to divide the Wh reading by the nominal voltage of 3.2V to get the real Ah...

diysolarforum.com

I'm just going to say this: taking the Wh reading of your measurement and dividing it with the nominal voltage of the cell or battery is just wrong.

Everyone I have asked said its Just Fine. Seems like a personal issue you have with SFK.

 

[hwy17]

Everyone I have asked said its Just Fine. Seems like a personal issue you have with SFK.

If you ask a PHD about measuring gas they will tell you the Therm is an ideal quantifier. But if a propane seller sells you 4.8 gallons and says it's 5 gallons by Therms they are in violation of the department of weights and measures, because propane is sold by the gallon.

Some products are measured certain ways by industry convention and/or regulations and it's not fair to change them out for another one when convenient.

 

[EastFalcon]

Everyone seems to be somewhat in agreement that SFK is in the business of attempting to sell decent product. You don't need take it as an assertion that you got bad product.

The bad blood here stems from 1. SFK's responses during the 280K drama with misleading claims about the WH AH interaction. 2. SFK's behavior when interacting with community members and youtubers.

It's basically rehashing an old debate about the claims in point 1. and settling the matter that it is still agreed their previous WH claims are incorrect. Now that EVE is fixing their product, SFK seems willing to move on from the claims in 1. and stand by AH again, when their product passes.

I purchased there cells based on this video:

The guy showed the AH and WH, also at the time they were the cheapest cells I could find with test reports. So they do show the WH/3.2 is the AH.

If WH / 3.2 is a valid way to get AH then why is this a point of contention? Either its right or wrong.

 

[hwy17]

I purchased there cells based on this video

I'm not saying you acted wrong for your own interest. The WH AH debate is nearly academic. As a buyer you just want good quality unused cells and you probably got that. I don't rule out buying SFK myself possibly in the future, he's out there doing work to make the connections and get cells into the USA to customers. Setting aside the other issues I respect that and your decision to buy them.

If WH / 3.2 is a valid way to get AH then why is this a point of contention? Either it's right or wrong.

It's wrong. That's what we're settling here. Not valid for the purpose the measurement was used. Wrong measurement.

Again, my analogy. Therms is a fantastic and more accurate measurement of propane gas. Therms are wrong though, because propane is not sold by the therm it's sold by the gallon.

 

[Horsefly]

I'm with @upnorthandpersonal on this. When a cell is tested it is measuring the current every second, and summing this up over time to give an Ah measurement. If the tester is also measuring Wh, it is calculating that ever second as well. That all is accurate. But to get to Wh by taking this carefully measured Ah number and multiplying it by 3.2V, is simply ignoring that the voltage of the cell is probably only at exactly 3.2V for a few seconds.

I think most of us engineers may be a bit picky about this, but I've always thought SFK used Wh to try and wave away whatever shortfall they cells had in Ah.

 

[upnorthandpersonal]

If WH / 3.2 is a valid way to get AH

Only in a very specific case under the test conditions where this is true. It's not general. See my post #130

Everyone I have asked said its Just Fine. Seems like a personal issue you have with SFK.

See above, plus I have issues with the facts. I don't care about SFK - I'm not even in the States, they can do whatever they want. I'm still going to point out when anyone represents something wrong, just like I pointed out Docan is wrong by changing the QR codes.

 

[EastFalcon]

It's wrong.

Watt-Hour is much more accurate way of measuring capacity. If you pass watt-hour you passed capacity test IMO, AH is nice but does not override WH I believe.

from Sams thread: https://diysolarforum.com/threads/cell-price-drop.72837/post-950027

That link to quora post explains:

Dieter Ernst
Studied Electrical Engineering at ETH Zurich (Graduated 1981)Updated Fri
Taking the energy measured in Wh, and dividing it by nominal voltage, will indeed give you charge capacity in Ah.
Ampere hours, but also watt hours need either a shunt or a current clamp to measure the current.
Characterizing a battery by its energy content (Wh) is way better than to characterize it with its charge capacity (Ah), but then still need the voltage to have a complete picture.
If you have the charge content (Ah), you can calculate the energy content by multiplying it with the voltage.
Some manufacturers have started to supply only voltage or charge capacity ratings to their products. This is a reason not to buy their products, a sign that they are not sincere and transparent. Again, someone will have to force them by law, which is a petty. Human stupidity leads up to the need for laws for every and any otherwise negligible rational!
I do not know who said it — some attribute it to Einstein — that (paraphrasing it) human stupidity is most probably infinite.
(Finally, it is better to write Wh and Ah, since that is the convention: upper cases for Watt and Ampère being names of prominent scientists, and lower case for ordinary units)

Watt Hour is just a better overall measurement.

 

[upnorthandpersonal]

Watt-Hour is much more accurate way of measuring capacity.

Watt Hour is just a better overall measurement.

Check this vdieo:

Do you understand why it's not? Or rather, why it's very difficult to do accurately?

 

[Horsefly]

Watt-Hour is much more accurate way of measuring capacity. If you pass watt-hour you passed capacity test IMO, AH is nice but does not override WH I believe.

If Wh is actually measured, it's fine. If the device is measuring Ah and Wh, both are fine (but neither is more accurate than the other). However, getting to Wh by simply taking measured Ah and multiplying by 3.2V is very inaccurate. The only way it would be accurate is if the voltage of the cells remained 3.2V for the entire capacity test.

 

[upnorthandpersonal]

If the device is measuring Ah and Wh, both are fine

Actually, no - see the video

Edit: for those who don't want to see the video, here is the results screenshot:

 

[Horsefly]

Actually, no - see the video

Yeah, I should have said that it is very difficult to measure Wh accurately.

 

[hwy17]

Watt-Hour is much more accurate way of measuring capacity. If you pass watt-hour you passed capacity test IMO, AH is nice but does not override WH I believe.

Therms is a much more accurate way of measuring propane. Don't matter though, it's wrong and illegal to use therms for retail sales.

 

[BuffaloTrace]

Couple of reasons:

- For one, measuring Wh means tracking two variables (voltage and current) versus only one (current) over time. Energy is the area under the curve of these measurements over time. However, if you have losses anywhere in your set-up (like connections, wires, etc.) you won't measure those at your instrument due to these losses. AmpHours eliminate these losses altogether, and is the reason why this is chosen for battery testing - have a look at this extreme set-up I did:

- Secondly: a cell that is specified at 280Ah (in addition to whatever other means) means that it should deliver a constant 280A for one Hour. Or, at 0.2C, 56A for 5 hours. This is a very straight forward test, again, because losses don't matter (the current is the same everywhere in the circuit - see video again). If you measure anything less than that, it means it doesn't match the manufacturer specification and everything after that is handwaving.

This is simplified for the user for sure. And it makes sense because one is achieving the specified Amperage over a specified time (voltage a given based on chemistry) and isn't that what really matters? Or does it?

I can also understand why most electrical power applications are rated and billed in kilowatt-hours; a certain amount power and more importantly, therms. This would equate to the actual power being achieved from the cell right?

Is there a way to achieve a test of 280ah+, but not get the factory specified watt-hours or therms(power) out of a cell?

Starts to get overcomplicated and Amps over Time is much easier to understand

 

[upnorthandpersonal]

isn't that what really matters? Or does it?

Well yes, but that's not the argument. The argument is that if you do the test on a 280Ah battery, and measure 277Ah, everything is fine because nominal voltage handwaving.

why most electrical power applications are rated and billed in kilowatt-hours

And that makes perfect sense, including for power audits etc. I'm not arguing against that at all. Just in the specific case of cell testing - and even then EVE is moving towards Wh testing (which will mean more expensive testers if you want to do that accurately) but still specify the Ah rating, which still has to be met in order to match specifications.

Is there a way to achieve a test of 280ah+, but not get the factory specified watt-hours or therms(power) out of a cell?

No, the issue is the opposite: not measuring 280Ah (being below that), but still getting the factory specified Wh (using said handwaving).

 

[Alkaline]

Ah completely ignores voltage drops/sagging in a cell, I believe its popular because it helps grade B cells appear better than they are, this thread I showed you previously:

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

cell 10: 270.4 AH - 865.1 WH
cell 9: 269.7 AH - 859.6 WH
cell 8: 271.4 AH - 868.0 WH
cell 7: 274.0 AH - 866.7 WH
cell 6: 270.4 AH - 864.8 WH
cell 5: 270.3 AH - 863.3 WH
cell 4: 270.5 AH - 866.2 WH
cell 3: 265.2 AH - 851.1 WH
cell 2: 268.4 AH - 845.4 WH
cell 1: 274.0 AH - 880.3 WH

You dismissed it saying wire issues (despite all cells tested on the same equipment), I disagree. Looking at the results cell 1 and cell 7 would appear to be the same 274.00 Ah capacity but when looking at the WH cell 10 has more WH 880.3 vs 866.7 Cell 1 is the superior cell determined not by AH but by WH and its 13.6 WH better.

I have the zke 40 and have run plenty of tests on the same cell multiple times, it varies at most .5 AH between test and 2 WH, there would never be a swing of 13.6 WH. Cell 7 is a weaker cell than cell 1 despite testing to the same AH. This is why people testing with fan testers think they got something better than what it really is.

Watt Hour gives you more overall information than Amp Hour, grade A cells should pass either reading with 1-3% above the stated rating. The shadiness lies with EVE the manufacturer themselves, retailers will put whatever spin they have to do to sell the stock they have. V1/V2 280K failed expectations and previous established industry norms (e.g. 280N).

In the end whoever you deal with make sure they have a test report, make sure you verify that test report form the manufacturer, and then verify one one of your cells physically around the qr code on a test cell.