The Peukert myth exposed

[chris w]

Well, you’ve awakened a third old man. I’m back from my time travels and….. I agree with Gibbo!

 

Furthermore, there is another loss which hasn’t been considered quantitatively. 
 

Take the 2 identical lead acid batteries in the earlier example. One discharging at 5A for 10 hours and one discharging at 50A for 1 hour. 
 

Let’s assume the batteries’ initial internal resistance is 5mohm (a typical fully charged figure), though the actual figure is not relevant to the argument.

 

The energy lost through heat in the first battery will be:

i^2Rt = (5^2)(0.005)(10) = 1.25Wh

 

The energy lost through heat in the second battery will be:

i^2Rt = (50^2)(0.005)(1) = 12.5Wh

 

ie: the second battery will dissipate 10 times the energy compared to the first battery, owing to its internal resistance. This energy (in both cases) is unrecoverable. 
 

Further, the internal resistance of the second battery will actually increase at a faster rate than the first battery as it becomes discharged more quickly. So, in reality, the second battery will dissipate even more energy owing to its internal resistance’s increase. 
 

However, this is not what Peukert is about. Peukert is analogous to a car, whose fuel consumption is quoted by the sales person, when asked, as “30mpg”. 
 

Now, we all understand implicitly that means, driven steadily, our fuel consumption should be as quoted. 
 

We also understand (implicitly), that if we were to drive the car for an extended period at 80mph (where permitted!), we would not expect to obtain 30mpg. 
 

Peukert is a mathematical way of describing those “high speeds” in a battery. 

[nb Innisfree]

AAARRRGGGHHH!! 

[nicknorman]

14 minutes ago, chris w said:

Well, you’ve awakened a third old man. I’m back from my time travels and….. I agree with Gibbo!

 

Furthermore, there is another loss which hasn’t been considered quantitatively. 
 

Take the 2 identical lead acid batteries in the earlier example. One discharging at 5A for 10 hours and one discharging at 50A for 1 hour. 
 

Let’s assume the batteries’ initial internal resistance is 5mohm (a typical fully charged figure), though the actual figure is not relevant to the argument.

 

The energy lost through heat in the first battery will be:

i^2Rt = (5^2)(0.005)(10) = 1.25Wh

 

The energy lost through heat in the second battery will be:

i^2Rt = (50^2)(0.005)(1) = 12.5Wh

 

ie: the second battery will dissipate 10 times the energy compared to the first battery, owing to its internal resistance. This energy (in both cases) is unrecoverable. 
 

Further, the internal resistance of the second battery will actually increase at a faster rate than the first battery as it becomes discharged more quickly. So, in reality, the second battery will dissipate even more energy owing to its internal resistance’s increase. 
 

However, this is not what Peukert is about. Peukert is analogous to a car, whose fuel consumption is quoted by the sales person, when asked, as “30mpg”. 
 

Now, we all understand implicitly that means, driven steadily, our fuel consumption should be as quoted. 
 

We also understand (implicitly), that if we were to drive the car for an extended period at 80mph (where permitted!), we would not expect to obtain 30mpg. 
 

Peukert is a mathematical way of describing those “high speeds” in a battery. 

 

The first half, I agree with of course. The second half once you start referring to Peukert, is a bit confusing but ultimately Peukert describes "lost" Ah as a result of discharging fast. This is only applicable if you intend to continue the discharge until the battery is notionally flat.

 

What both of you seem to be doing is conflating Peukert, which describes lost Ah (Ah not in any way being a measure of energy), with useful energy lost during fast discharge from internal resistance (including reaction rate). These are two entirely separate concepts, one of which is wrong in the context of an Ah counting SoC meter, and the other of which, whilst correct, is also not applicable to an Ah counting SoC meter since that does not measure energy.

 

[nb Innisfree]

Nurse nurse, my head hurts, 

[chris w]

Nick

 

You clearly didn’t read my post correctly. 
 

Particularly that sentence, after my calculations, where I specifically stated,

“However, this is not what Peukert is about.
 

My calculations were to show that it can never be the case that all the energy in a battery is available as useful energy, whereas you were pushing the opposite view.

Edited November 9, 2023 by chris w

[Rebotco]

Tell you what ..........  Let Nick be right on Mon Tues Weds and Gibbo on Thurs Fri and Sat.

.......................................................................... then we can all have Sundays off!!!

[chris w]

I’ll take Sundays, as I’m an atheist. 

[Tony1]

13 hours ago, nicknorman said:

 

Lots of people talk about Peukert because they heard it from the bloke in the pub...

 

 

So you get it as well? 

The blokes in the pub are always trying to get me talking about Peukert.

We're a pretty wild crowd.

 

 

[IanD]

Just now, Tony1 said:

 

So you get it as well? 

The blokes in the pub are always trying to get me talking about Peukert.

We're a pretty wild crowd.

 

 

Do you talk about LFP batteries instead? 😉

[Tony1]

Just now, IanD said:

 

Do you talk about LFP batteries instead? 😉

 

Nobody dares to say the L word when I'm around. Last time they got me going, it went on till 4am. 

 

[IanD]

Just now, Tony1 said:

 

Nobody dares to say the L word when I'm around. Last time they got me going, it went on till 4am. 

 

 

The pub stayed open until 4am? Sounds like my kind of pub, where was it? 😉

[nb Innisfree]

It must have been fascinating listening to Pukehurt as he quaffed his ale. 

[PeterF]

A question, if you take the 2 identical 100Ah batteries fully charged then discharge A at 5A for 10 hours and B at 50A for 1 hour. Leave them to settle and the fully recharge them. How many Ah do the 2 batteries take to fully recharge. Has this been measured. Peukert states that B will have less Ah to deliver, but is this because the Ah are consumed or that they become unavailable.

 

I have some sympathy with Nick's point that the chemical energy is fixed, i.e. there is a fixed number of moles of lead to react and if they are not reacted then they should count towards the remaining SOC.

 

However, I have my own experience as a Chemical Engineer designing large chemical reactors that at times if you makes things react faster, the progress of reaction is not necessarily uniform and the faster you go the more this is the case especially with solid/ liquid or solid/ gas reactions. Does this apply in this case, as you discharge the battery faster, the lead reacts to lead sulphate in a more chaotic manner and results in not all the lead being available for reaction, in some reactions the solid reactant becomes encapsulated in reaction product rendering it unavailable. It is still theoretically available for reaction but on a practical level it is not available. In the case of batteries, if this effect occurred then you should count is as reducing the available SOC because you could no longer call on this.

 

Just musing on this, I may be way off in my thoughts but the question about recharging would be interesting to have an answer to.

Edited November 9, 2023 by PeterF
Spooling

[nicknorman]

30 minutes ago, chris w said:

Nick

 

You clearly didn’t read my post correctly. 
 

Particularly that sentence, after my calculations, where I specifically stated,

“However, this is not what Peukert is about.
 

My calculations were to show that it can never be the case that all the energy in a battery is available as useful energy, whereas you were pushing the opposite view.

Ok fair enough on your first point.

On your second point, absolutely not - as I have repeated said, it is definitely the case that far less useful energy is available from a battery when discharged fast, than when discharged slowly.

8 minutes ago, PeterF said:

A question, if you take the 2 identical 100Ah batteries fully charged then discharge A at 5A for 10 hours and B at 50A for 1 hour. Leave them to settle and the fully recharge them. How many Ah do the 2 batteries take to fully recharge. Has this been measured. Peukert states that B will have less Ah to deliver, but is this because the Ah are consumed or that they become unavailable.

 

I have some sympathy with Nick's point that the chemical energy is fixed, i.e. there is a fixed number of moles of lead to react and if they are not reacted then they should count towards the remaining SOC.

 

However, I have my own experience as a Chemical Engineer designing large chemical reactors that at times if you makes things react faster, the progress of reaction is not necessarily uniform and the faster you go the more this is the case especially with solid/ liquid or solid/ gas reactions. Does this apply in this case, as you discharge the battery faster, the lead reacts to lead sulphate in a more chaotic manner and results in not all the lead being available for reaction, in some reactions the solid reactant becomes encapsulated in reaction product rendering it unavailable. It is still theoretically available for reaction but on a practical level it is not available. In the case of batteries, if this effect occurred then you should count is as reducing the available SOC because you could no longer call on this.

 

Just musing on this, I may be way off in my thoughts but the question about recharging would be interesting to have an answer to.

 

It may be the case that the way in which the lead sulphate is deposited changes slightly, and it is certainly true that the reaction rate slows right down at the end. However having discharged your battery fast until flat, when you leave it for a while the battery recovers and more charge can be taken out because the reaction, although slow, can still occur.

So I could accept "rendering it harder to react" but not "rendering it unavailable to react".

But I think the key point of interest is your recharging one. Having taken out 1/2 the Ah at the two rates, allow settling time, and then recharge both at a fixed rate, the Ah required to recharge will be the same (other than a tiny difference caused by increased gassing at the faster discharge rate).

[nb Innisfree]

In Quantum reality it seems that the act of observation causes events to occur, and the level of observation will affect how that event will occur, so the act of observing and measuring Peukhert effect the results will vary. 

 

The further we go down the rabbit hole the more complex it gets, surely as we learn more things should become clearer not more obscure?

 

Curiouser and curiouser... 

[GUMPY]

44 minutes ago, PeterF said:

A question, if you take the 2 identical 100Ah batteries fully charged then discharge A at 5A for 10 hours and B at 50A for 1 hour. Leave them to settle and the fully recharge them. How many Ah do the 2 batteries take to fully recharge.

How do you decide when they are fully charged? 😉

[PeterF]

15 minutes ago, GUMPY said:

How do you decide when they are fully charged? 😉

I am not sure that it matters a great deal in the context here as long as it is consistent because you are seeing if there is a 50% difference between the 2 cases, so charged up to 1% tail current or similar would suffice.

Edited November 9, 2023 by PeterF

[Guest]

This is great, just like the old times!!

Edited November 9, 2023 by M_JG
Add missing word.

[cuthound]

1 hour ago, nb Innisfree said:

It must have been fascinating listening to Pukehurt as he quaffed his ale. 

 

Yes, but did he quickly down his pint in one or make it last all night?

 

Edited November 9, 2023 by cuthound
Clarification

[rusty69]

2 minutes ago, cuthound said:

 

Yes, but did he quickly down it in one or make it last all night?

 

Tis obvious. The faster he quaffed it, the smaller the flagon of ale became. 

[nb Innisfree]

12 minutes ago, rusty69 said:

Tis obvious. The faster he quaffed it, the smaller the flagon of ale became. 

Not only that, the ale would eventually disappear leaving the flagon empty, but in reality it wouldn't have disappeared it would have gone into Pukehurt's stomach and reappeared later, in an altered state, as puke. 

Edited November 9, 2023 by nb Innisfree
Edited for punctuation, very important.

[rusty69]

3 minutes ago, nb Innisfree said:

Not only that, the ale would eventually disappear leaving the flagon empty, but in reality it wouldn't have disappeared it would have gone into Pukehurt's stomach and reappeared later in an altered state as puke. 

But what of the elephant in the room? Schrodinger's cat!

Not to mention Pavlovs pavlova

[carlt]

2 hours ago, chris w said:

Well, you’ve awakened a third old man. I’m back from my time travels and….. I agree with Gibbo!

 

Furthermore, there is another loss which hasn’t been considered quantitatively. 
 

Take the 2 identical lead acid batteries in the earlier example. One discharging at 5A for 10 hours and one discharging at 50A for 1 hour. 
 

Let’s assume the batteries’ initial internal resistance is 5mohm (a typical fully charged figure), though the actual figure is not relevant to the argument.

 

The energy lost through heat in the first battery will be:

i^2Rt = (5^2)(0.005)(10) = 1.25Wh

 

The energy lost through heat in the second battery will be:

i^2Rt = (50^2)(0.005)(1) = 12.5Wh

 

ie: the second battery will dissipate 10 times the energy compared to the first battery, owing to its internal resistance. This energy (in both cases) is unrecoverable. 
 

Further, the internal resistance of the second battery will actually increase at a faster rate than the first battery as it becomes discharged more quickly. So, in reality, the second battery will dissipate even more energy owing to its internal resistance’s increase. 
 

However, this is not what Peukert is about. Peukert is analogous to a car, whose fuel consumption is quoted by the sales person, when asked, as “30mpg”. 
 

Now, we all understand implicitly that means, driven steadily, our fuel consumption should be as quoted. 
 

We also understand (implicitly), that if we were to drive the car for an extended period at 80mph (where permitted!), we would not expect to obtain 30mpg. 
 

Peukert is a mathematical way of describing those “high speeds” in a battery. 

Not him again!

 

Where do they dig these old dinosaurs up from?

[nb Innisfree]

1 minute ago, rusty69 said:

But what of the elephant in the room? Schrodinger's cat!

Not to mention Pavlovs pavlova

He was too busy eating and packing his trunk to open the box

[rusty69]

3 minutes ago, nb Innisfree said:

He was too busy eating and packing his trunk to open the box

I always find Shrodingers batteries to be both full and empty at the same time.