Well I stuck my big toe into Lifep04

[Grandad]

You discussed this issue a while back somewhere. At the time I recall I came away not being totally sure I understood. But, reading this explanation all was clear.
Was the description different or was my brain tuned in a bit better? Not sure.
The take home message I think I now understand is that if we want to compare batteries we must determine what the 'C' rating is for both. Otherwise the amp/hour description is next to useless. The 'C' rating must be the same, or, we have to do some math to give the comparison some commonality.
And, the lower the 'C' number, the better.
Will I remember that the 'C' number is the number of hours and dividing that number by the voltage will give you how long that battery will last? Not likely. But that what 'Notepad' on my phone is for nowadays.

A couple of things though please. You're using 12V not 13.8V. Is that important?
I'm guessing, its just rounding. Yes? Consistent rather than 100% accurate?

And when you say how many hours to flat, does that assume you're going to go all the way to dead flat? No safety margin for harming the battery?
Again, I'm assuming yes, dead flat. This is for comparison only. Actual usable capacity in AH will be less. Yes?

At the end of the day, I believe you're being too hard on yourself as a teacher. Yes, sometimes people do react with a blank stare but I personally think that only happens when you go beyond what the average consumer needs to know and are trying to explain the background or why something is.
Just a theory.

Jim

[Greynomad]

Jim,

Yes, sometimes people do react with a blank stare but I personally think that only happens when you go beyond what the average consumer needs to know and are trying to explain the background or why something is.
Just a theory.

You could be right, but I remember when I first arrived in Melbourne to start a new job, I was asked by quite a few people,
"Are you related to Peter Nolan?"
(apparently he was a then-popular footballer)...
And when I replied,
"No, but I am related to Sidney." (a joke ) all I got was blank stares from most people.
A very few responded with a wry smile.

[native pepper]

I'm one of the blank stare brigade had discharge rating explained to me many many times, as well as demonstrated, walking away thinking I'd got it. Next day blank stare as for some reason these sort of technicalities seem to make no sense me and it's the same with maths, completely blank understanding no matter what I do. Have had lessons, tried studying computer technology, had my late mate write things down and provide diagrams, yet still read the same explanations and am still none the wiser. Which is very frustrating when I'm so into new technology and in particular, battery technology.

[T1 Terry]

You discussed this issue a while back somewhere. At the time I recall I came away not being totally sure I understood. But, reading this explanation all was clear.
Was the description different or was my brain tuned in a bit better? Not sure.
The take home message I think I now understand is that if we want to compare batteries we must determine what the 'C' rating is for both. Otherwise the amp/hour description is next to useless. The 'C' rating must be the same, or, we have to do some math to give the comparison some commonality.
And, the lower the 'C' number, the better.
Will I remember that the 'C' number is the number of hours and dividing that number by the voltage will give you how long that battery will last? Not likely. But that what 'Notepad' on my phone is for nowadays.


A couple of things though please. You're using 12V not 13.8V. Is that important?
I'm guessing, its just rounding. Yes? Consistent rather than 100% accurate?


And when you say how many hours to flat, does that assume you're going to go all the way to dead flat? No safety margin for harming the battery?
Again, I'm assuming yes, dead flat. This is for comparison only. Actual usable capacity in AH will be less. Yes?


At the end of the day, I believe you're being too hard on yourself as a teacher. Yes, sometimes people do react with a blank stare but I personally think that only happens when you go beyond what the average consumer needs to know and are trying to explain the background or why something is.
Just a theory.

Jim

Will I remember that the 'C' number is the number of hours and dividing that number by the voltage will give you how long that battery will last? Not likely. But that what 'Notepad' on my phone is for nowadays.
Try this one:
The number after the "C" is how many hours you can draw continuously, the max number of amps that equals the advertised Ah capacity divided by the number of hrs shown after the C. Sound confusing?
As an example, a 100Ah battery marked C20 means you can discharge that battery for 20 hrs as long as you take no more than the 100Ah divided by 20hr =5 amps. To stop at a 50% discharge so you have 50% State of charge remaining, you can only take that 5 amps for 10 hrs. If you want more than the 5 amps for the 10 hrs, you need to add 100Ah of battery capacity for each extra 5 amps you want or need.
If you try to take more than the 5 amps for every 100Ah capacity, you can't do that for the theoretical equivalent of 10 hrs ..... another example might help
200Ah battery rated at C20 will deliver 10amp max for a total of 10hrs, but that doesn't mean you can draw 20 amps for a total of 5 hrs and still have only taken 50% of the battery capacity. Discharging at that rate would be called a C10 discharge rate. Looking along the Full River AGM chart shows about 4hrs rather than the 5 hrs before the voltage dropped below 12v or the 50% SOC mark.

A couple of things though please. You're using 12V not 13.8V. Is that important?
I'm guessing, its just rounding. Yes? Consistent rather than 100% accurate?

The 12v bit is nominal voltage and a rounded number, half way between fully charged and fully discharged without damaging the cells. A new in good condition 6 cell 12v nominal battery will be fully discharged at 10.5v (1.75v per cell) and fully charged 13.8v (2.3v). Half way is 12.15v so it is rounded down to 12v for convenience.
Now to throw in a bit of confusion, an LiFeP04 cell is 3.2v nominal, so 4 cells in series = 12.8v. The lower limit the factory specifies is 2.75v (well 2.4v while under a 50 amp load) and the upper 3.6v, (well 3.8v but while charging at 33 amps per 100Ah) but rested around the 3.6v.

And when you say how many hours to flat, does that assume you're going to go all the way to dead flat? No safety margin for harming the battery?
Again, I'm assuming yes, dead flat. This is for comparison only. Actual usable capacity in AH will be less. Yes?

No, I'm not willing to throw that much money away The discharge test will stop at 2.8v in any cell. The telling here will be at such a light load, how many Ah can be drawn out of each battery before a cell drops to what I consider the same limit under load.

Clear as mud eh

T1 Terry

[BernieQ2]

The mud must be thicker in Qld Terry ? confused ..
How much for a drop in 100amp lifo ?
Bernie .

[wayneP]

THANK YOU TERRY!
Do I understand>>>>>>>>>>>>>>>>>>>>>>>>>>>> @#%%%^&*#@$%^^&*$# NO
But the most important thing to me (after the shite you have received from other sources) you still try and help the good people on this forum. I do thank you sincerely as one day, Yes I would like to use this technology. Thank You Bruce (Wendy)and Terry (Margaret) for allowing Terry to help us non techno people to grasp some of the technology information to make some very $$$ decisions.
Many Thanks

[Grandad]

Try this one:
The number after the "C" is how many hours you can draw continuously, the max number of amps that equals the advertised Ah capacity divided by the number of hrs shown after the C. Sound confusing?

No, not at all. I understood that the first time around. Just wrote my response wrong. That's what happens when I respond much later after I first read your post.
I've just copied your last quote to my phone for reference later. Its a better summary than what I had written.

'C' = the number after the letter C in the rating.
'AH' = Advertised Amp Hour
X = number of amps that can be continuously drawn.

Therefore
AH divided by 'C' = X amps that can be drawn for 'C' hours

EG: 100AH battery at C20 =
100/20=5 Amps continuous for 20 hours
Yes?

I still think my take home message was correct. The AH rating of a battery is useless unless you know the 'C' rate. And to compare, you must have the 'C' rate of both. If you don't know the 'C' rating, you basically have no way of knowing just how many AH that battery really is.

200Ah battery rated at C20 will deliver 10amp max for a total of 10hrs, but that doesn't mean you can draw 20 amps for a total of 5 hrs and still have only taken 50% of the battery capacity.

Peukhart effect. not sure of spelling. Yes? Please say yes. Otherwise something else I thought I understood is wrong.

The 12v bit is nominal voltage and a rounded number, half way between fully charged and fully discharged without damaging the cells. A new in good condition 6 cell 12v nominal battery will be fully discharged at 10.5v (1.75v per cell) and fully charged 13.8v (2.3v). Half way is 12.15v so it is rounded down to 12v for convenience.

Thank you. I thought it was supposed to represent the voltage of the battery. as in, we refer to our car battery as being 12V. Its actually 13.8V but we never call it that. Got it. It's halfway between fully charged and effectively dead.

Now to throw in a bit of confusion, an LiFeP04 cell is 3.2v nominal, so 4 cells in series = 12.8v. The lower limit the factory specifies is 2.75v (well 2.4v while under a 50 amp load) and the upper 3.6v, (well 3.8v but while charging at 33 amps per 100Ah) but rested around the 3.6v.

Yeah, now you've confused me.
I guess as a consumer, all I really need to know is max & minimum voltage on each cell
Upper = 3.8V fully charged. Only ever reaches that when top balancing. Recommended = 3.4V from memory. I think I recall you suggesting this as a safe maximum.
Lower = I've got it written down somewhere but can't find it right now. But, exceeding the maximum will kill a cell. Exceeding the minimum will reduce the life but seldom kill it entirely.

Yes?

Clear as mud eh

Only once you got into the LifePO4 examples.

Jim

[T1 Terry]

You are on the money as far as comparing battery capacity you must also be using the same C rate.
Hopefully this bit will help with the confusion between the "C" factor and the CA factor.
The "C" factor uses the number after it to signify the number of hours the discharge will be before the minimum manufacturers specified voltage is reached. In a block type 12v battery, it is an average of the 6 cells because individual cell voltages can not be measured. 1.75v x 6 cells = 10.5v if all 6 cells are *perfectly balanced.
The CA factor has the number before the letters and this indicates the number used to divide the advertised capacity.
An example and how they can both mean the same thing. 0.5CA means the capacity divided by 0.5, 100Ah x 0.5 = 50amps. We can therefore determine that a 100Ah battery should be able to deliver 50 amps for 2 hrs. C2 means the same thing, the capacity drained over 2 hrs = 100Ah divided by 2hrs = 50 amps. CA factor is required when the current can be drawn out in under 1 hr. 2CA means twice the capacity as a load, eg. 200 amps from a 100Ah battery, C0.50 would mean the same but it isn't a recognised discharge rate. The fact quality LYP lithium cells can be discharged at a 5CA rate would cause total confusion referred to as a C0.20 rate, so the C factor stops being used at C1.

The Peukert factor is the effect taking more current than the C or CA rating capacity out of the battery than what it was rated. Just how much more than the rated C factor effects the Peukert factor. Perfect is 1.00, or no losses, 1.25 means roughly 1/4 of the capacity will be lost to heat, electrolysis or the fact there is so little capacity remaining that it can not effect the chemical reaction fast enough to deliver the required current (amps) without the voltage dropping lower than the safe level in a good cell. Some lithium chemistries can be discharged at a 30CA rate. To get your head around that you really need to change the Ah to amp minutes by multiplying the Ah x 60 to get amp minutes. A model plane battery might have a 1CA rating of 5Ah. Multiply that by 60 = 300Amp minutes. 300 amp minutes divided by 30CA = 10 mins. That's right, a 5 Ah battery from fully charged to fully discharged in 10 mins ...... but Peukert does come into the equation even when lithium batteries are concerned when you start to discharge that fast. You wouldn't get 10 mins before the battery became so hot it exploded, in reality probably 5 mins would be about the limit.

They use these things for powered glider competitions, 5 mins to climb straight up, then the motor cuts and the glider pilot rides the thermals for as long as they can before bringing the craft back for a safe landing. If you go too hard to get the maximum climb the battery could explode and burn the glider to ashes as it tumbles to the ground.



Perfectly balanced is an unknown in a sealed top battery
The problem is there is no way of knowing if they are perfectly balanced so the same 10.5v could have a cell much lower than the minimum 1.75v. For example, five cells @ 2v means one cell would be only 0.5v, yet it still adds up to 10.5v. 5 cells at 2.15v means one cell is - 0.25v because it has reverse current flow and this will destroy the cell very quickly, yet there is no warning it is happening in a sealed type battery. In a flooded cell the electrolyte would be bubbling away frantically.
Because a lead acid battery looses its capacity from the first time it is discharged, but never the same in any two cells, the point where any cell drops to the 1.75v safe limit is an unknown so this is why the 50% is based on around 12v so it is safe assumption that no one cell will drop below 1.75v and be damaged. When a 12v lead acid battery suddenly looses voltage at a rapid rate once the 12v point is reached is fair indicator that one cell has been deeply discharged and severely damaged so it no longer has the capacity the other cells have and the voltage has dropped to 0v or even reverse current flow. There is no recovery from that sort of damage, not even with lithium chemistry cells, that is why cell voltage monitoring is so important.

T1 Terry

[Greynomad]

The mud must be thicker in Qld Terry ? confused ..

It certainly is in Rutherglen! I joined the Blank Stare Brigade with T1's first explanation, and things have not improved since!

If it's OK with you, T1, I'll just nod approvingly and leave it to the experts... and hope that, like T1, they're honest and want to help us 'blind reindeer' * customers.



* 'blind reindeer' = No-eye Deer.

[T1 Terry]

Blind reindeer with no legs, still no eye deer I won't do the next line or Dottie will give me another holiday