Quattrohead
Solar Wizard
Yeah because holding your tongue against the terminals of a 51.2 volt battery tends to make one fidget some ......
Rant about Ah and Wh...
- Thread starter upnorthandpersonal
- Start date
Rednecktek
Solar Wizard
Nevah Wick da Wed Wire!!
timselectric
If I can do it, you can do it.
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- 18,766
If your vendor says that your test results are wrong, because you are wearing the wrong color socks.
Don't believe that either.
Don't believe that either.
There's a bit of 'angels dancing on a pin head' to this discussion.
I tested all my cells with the Ztech tester and I've just done a multiply Ah by 3.2 comparison to the measured Wh figures on 15 off 304Ah cells.
The difference ranges from -0.52% to +1.05% with most being less than 0.55% error. Those are completely insignificant in the real world with lots of other confounding variable.
I tested all my cells with the Ztech tester and I've just done a multiply Ah by 3.2 comparison to the measured Wh figures on 15 off 304Ah cells.
The difference ranges from -0.52% to +1.05% with most being less than 0.55% error. Those are completely insignificant in the real world with lots of other confounding variable.
It becomes an issue when someone (a vendor) claims 320Ah, and then the test tells them 310Ah. If everyone just advertises these at 304Ah, it would not be an issue. Trying to claim false/wrong measurements and 'correcting' the measurement with the divide by 3.2V thing is what's my main issue.
Sam Cho TX
Solar Enthusiast
I have asked around some folks at Texas A&M regarding this and this equation: Watts = Amps * Volts is a very reliable means of calculating power and if you have 2 values you can get the third. The same applies to Watt-hours = amp-hours * average voltage.
https://en.wikipedia.org/wiki/Volt-ampere#:~:text=Volt-amperes%20are%20usually%20used,⋅A%20%3D%201%20W).
So if you have any 2 values you can get the third.
Problem is having a testing standard that all adhere to. Take for instance a vehicles MPG (miles per gallon or kilometers per liter if you are metric) rating. Without an EPA in the US you could have rather divergent claims for what any vehicle had. This can be a big deal when people shop for a car.
When shopping for a battery people place a lot of emphasis on claimed ah or wh ratings. However many have only a hazy understanding of what either term means as it relates to a chemical device. I think the battery merchants mostly do a fair job of rating capacity.
That's only true if the voltage is constant over the period of time you do the measurement, or if you actually measure the average voltage. Just taking the nominal voltage is not correct since the nominal voltage is only equal to the average voltage at 0.2C.
That's the reason batteries have mostly been rated at amp-hours - and because you can check this easily with relatively basic equipment. If you for example have one of these:
Your Wh test will be way off, but your Ah test will be pretty spot on.
Again, my main issue is that if you test with the above meter and come to an Ah rating, that the vendor then tells you that your measurement is wrong.
Alkaline
Solar Wizard
Every car battery I have see is rated in KW and same for large battery banks, utility bills, I don't think anyone uses AH. For some reason its all over the place with 12v batteries.
For me I found WH to be way more useful, and yes only using the wh/3.2v method did my Luyuan 280K cells meet listed capacity as they were 278 AH and 900 WH.
So for me I look at both, but to me WH is more important it tends to be more accurate and I have seen, I keep going back to this thread:
diysolarforum.com
2 cells both showing 274 AH but cell 1 makes 880 WH and cell 7 makes 866WH
I know enough that an inverter needs watts to run so if you had a 3v inverter cell 1 would run it longer than cell 7.
So for me I don't look at AH as much as WH. Not 100% on the Wh/3.2 yet but it is starting to make sense a bit to me.
For me I found WH to be way more useful, and yes only using the wh/3.2v method did my Luyuan 280K cells meet listed capacity as they were 278 AH and 900 WH.
So for me I look at both, but to me WH is more important it tends to be more accurate and I have seen, I keep going back 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
2 cells both showing 274 AH but cell 1 makes 880 WH and cell 7 makes 866WH
I know enough that an inverter needs watts to run so if you had a 3v inverter cell 1 would run it longer than cell 7.
So for me I don't look at AH as much as WH. Not 100% on the Wh/3.2 yet but it is starting to make sense a bit to me.
Sam Cho TX
Solar Enthusiast
That's only true if the voltage is constant over the period of time you do the measurement, or if you actually measure the average voltage. Just taking the nominal voltage is not correct since the nominal voltage is only equal to the average voltage at 0.2C.
That's the reason batteries have mostly been rated at amp-hours - and because you can check this easily with relatively basic equipment. If you for example have one of these:
Your Wh test will be way off, but your Ah test will be pretty spot on.
Again, my main issue is that if you test with the above meter and come to an Ah rating, that the vendor then tells you that your measurement is wrong.
That's only true if the voltage is constant over the period of time you do the measurement, or if you actually measure the average voltage. Just taking the nominal voltage is not correct since the nominal voltage is only equal to the average voltage at 0.2C.
That's the reason batteries have mostly been rated at amp-hours - and because you can check this easily with relatively basic equipment. If you for example have one of these:
Your Wh test will be way off, but your Ah test will be pretty spot on.
Again, my main issue is that if you test with the above meter and come to an Ah rating, that the vendor then tells you that your measurement is wrong.
Sorry but I trust my ZKE-40 way more than that little thing...
Well, of course. That was not the point of my comment.
Alkaline
Solar Wizard
How much of a difference are we talking about anyway, 2-4 AH? 5? I doubt its going to make a difference in the real world.
Yes, that's what I'm getting at: is this now a 275Ah (880/3.2) or 270Ah (866/3.2) 'for real'?
My point is that it does not matter, but that you can't use the Wh reading now to get a 'higher' Ah number to satisfy your label.
Anyway, it seems I have a problem getting my point across. It's not important. Never mind, I had my rant.
A battery manufacturer sent me a “110 Ah” battery to test, I ran a .2C load on it through my smart shunt, and it came up 96 Ah, the manufacturer claimed 96 is within the load range of a 110Ah rating, and that is why they are claiming 110Ah. I explained a brand new LFP battery should ALWAYS test higher than the listed rating, as there is always a 5% drop in capacity after a few dozen cycles… I would not recommend the battery, and if they want to reliable the battery 90 Ah, I would be happy to recommend it, but could not in ANY way recommend a battery that tests below the listed rating.
You're right. I assume that you are complaining about inaccurate capacity claims; no doubt if someone measures the energy capacity of a battery and then uses simple arithmetic to find an Ah capacity, then it's likely to be slightly inaccurate. But as far as I can see storage batteries are specified by Ah, I don't see Wh in manufacturers data sheets.
Car batteries aren't specced by energy capacity either, the most important spec is CCA.
Car batteries aren't specced by energy capacity either, the most important spec is CCA.
RV8R
Solar Enthusiast
I get it & agree with you.
Energy Storage Tanks; Batteries, Propane Tanks, Gasoline Tanks, Diesel Tanks ,,, All have this in common. How much energy “capacity“ is stored in these tanks? ,,, the answer is ,,, It Depends
I am fairly new to 12vdc Cabin & Travel Van use electrical systems ,,, roughly around 2016 / 2018 ,,, I have noticed a human phenomenon with batteries as an energy storage tank & health ,,, and the obsession with. I get it, cause the things are not cheap & they are a depreciating assets that do not get healthier over time nor can they do as much as they once could. They are very similar to us.
The battery label is just that ,,, as is the current battery health. If I say I have a 250Ah battery bank & you say do you ,,, My response is actually “no, but that is what the label says”. The capacity is what it is.
RoadTurtle
Solar Enthusiast
- Joined
- Mar 30, 2022
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- 368
I agree with angels on the pin comment. It's all great theoretical discussion, but most consumers aren't going to care if we calculate battery capacity down to the minute or even hours... but what they do care about is, will this get me through TBD time period. Most have no idea how much energy their TV or sound bar or fridge even take to run. Right or wrong, mfg's have settled on AH as the "standard" parameter. Work to 12v and you're going to land "close enough" to real world application. Will has a starter 400ah kit recommendation, and it simplifies the discussion and component shipping.
Interesting and informative thread, and some good points raised by many.
When I started my first DIY CNC build 13 yrs ago reading some posts....to me and from my understanding....the terminology was like learning Chinese through Russian when you speak English...
But here thanks to you guys the battery stuff is easier and its starting to make proper sense to me?
robby
Photon Vampire
- Joined
- May 1, 2021
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I get your point but in the context of home consumers it's just way to complicated.
If your talking about giving specs to the Military or NASA then yes you better have used the Integral in the numbers you present.
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