The Peukert myth exposed

[nicknorman]

1 minute ago, Gibbo said:

 

Throughout the two discharges battery A will have spent it at an average terminal voltage of 12.4 volts. Battery B will have been at an average of 11.1 volts.

The load on the battery A will have benefitted from (converted, consumed, dissipated, call it whatever you want, it makes no difference). 12.1V x 5A x 10 hours = 620 watt hours of energy.

The load on the battery B will have "benefitted" from 11.1V x 50A x 1 hour = 550 watt hours.

Both batteries started at 100% SoC. You agree that they both ended the discharge in the same SoC.

Where are the missing 65 watt hours?

Your schoolboy error appears to be you believing an amp hour to be a unit of energy. It is not.

This thought experiment proves beyond any doubt that higher discharge currents result in less available energy from the battery. The effect is permanent and cannot be "got around" by waiting a bit.

 

 

The missing 65 watt hours have been dissipated as heat into the  battery. And no of course I do not think an amp hour is a unit of energy. By the same token, peukert does not have dimensions of energy or power either, which is why it is not relevant to the points you are raising.

 

Your last statement is of course correct and never in dispute, assuming by "available" energy you mean electrical energy at the terminals. I thought we cleared up available (useful) energy vs total energy earlier. Or is this one of your back-pedals now you have realised your error?

[dmr]

But does  Peukert apply to energy or amp-hours?

Energy (external energy) is different due to the lower terminal voltage but I assume that Peukert is about amp-hours which is why it has to be specified in devices like the Victron BMV and these are amp-hour counters.

 

I think this entertaining argument is confusing energy with amp-hours, though confusion is not a good word as it implies a degree of stupidity. Conflating is a better word but that's a bit too close for newspeak for my liking.

[Gibbo]

3 minutes ago, nicknorman said:

 

The missing 65 watt hours have been dissipated as heat into the  battery.

 

No. They absolutely have not. They were simply never created in the first place. Due to...

 

Peukert's effect. i.e. slow ion migration resulting in less ions available at the plate/electrolyte interface.

 

The Nernst equation defines the voltage generated in a cell and it is proportional to the log of the quantity of ions at the cell interface. Note "log". Hence why Peukert's equation is exponential. They are intimately connected.

 

It has absolutely nothing (well, close to nothing. Close enough that it can be ignored for these purposes) to do with wasting energy into heat.

[nicknorman]

21 minutes ago, dmr said:

But does  Peukert apply to energy or amp-hours?

Energy (external energy) is different due to the lower terminal voltage but I assume that Peukert is about amp-hours which is why it has to be specified in devices like the Victron BMV and these are amp-hour counters.

 

I think this entertaining argument is confusing energy with amp-hours, though confusion is not a good word as it implies a degree of stupidity. Conflating is a better word but that's a bit too close for newspeak for my liking.

 

Well there is certainly no confusion on my part. Neither Amp hours nor Peukert's equation have the dimensions of energy. In order to get energy from amp hours you need to multiply by the voltage at which those amp hours flowed.

The reason why Peukert has to be specified in amp-hour counting devices is only for the "time to run" display. The SoC element should not have Peukert applied, for the reasons I've given.

20 minutes ago, Gibbo said:

 

No. They absolutely have not. They were simply never created in the first place. Due to...

 

Peukert's effect. i.e. slow ion migration resulting in less ions available at the plate/electrolyte interface.

 

The Nernst equation defines the voltage generated in a cell and it is proportional to the log of the quantity of ions at the cell interface. Note "log". Hence why Peukert's equation is exponential. They are intimately connected.

 

It has absolutely nothing (well, close to nothing. Close enough that it can be ignored for these purposes) to do with wasting energy into heat.

You are breaching the first law of thermodynamics (paraphrased as) "Energy cannot be created or destroyed, it can only be converted into other forms of energy".

At the start, the battery had a certain amount of chemical energy that could have been extracted and turned into heat and electricity. By your hypothesis, depending on how rapidly you choose to discharge the battery, this fixed amount of chemical energy is converted into a variable amount of heat and electrical energy. So if you discharge fast, what happened to the part of the original chemical energy that has now vanished? Where is it? Hiding in Spain perhaps? Or been whisked away by your amazing powers of teleportation? No, it is has not because that would be a clear breach of the first law of thermodynamics. Try again.

 

I gues this is one of the differences between us. A degree foundation, that you once scoffed at, provides the tools for this basic gross error checking. Hypotheses that flout the basic laws of physics fail at the outset, never mind the introduction of "logs" or other smokescreens, the hypothesis must be fundamentally flawed.

Edited November 9, 2023 by nicknorman

[nb Innisfree]

If  energy is lost in heat then surely the battery temp will increase in line with amount of discharge* (over and above what what it would normally be if charge rate was at C20) ie the higher the level of charge/ discharge then higher or lower temp will be present and therefore measurable? 

 

*instead of "discharge" spell check inserted "didgeridoo" 🤣🤣🤣

 

Henceforth I shall refer to "discharge" as "didgeridoo", it makes sense 🤔

[nicknorman]

4 minutes ago, nb Innisfree said:

If  energy is lost in heat then surely the battery temp will increase in line with amount of discharge* (over and above what what it would normally be if charge rate was at C20) ie the higher the level of charge/ discharge then higher or lower temp will be present and therefore measurable? 

 

*instead of "discharge" spell check inserted "didgeridoo" 🤣🤣🤣

 

Henceforth I shall refer to "discharge" as "didgeridoo", it makes sense 🤔

Yes the battery does warm up if it is discharged fast. Or discharged at all - just more so when discharged fast. Of course it has quite a lot of thermal capacity (lead and water) so the temperature rise for a given amount of heat is not massive. But it is certainly easily measurable.

Edited November 9, 2023 by nicknorman

[Morris]

41 minutes ago, magnetman said:

A lead acid battery is flat if you can hold a steel ruler across the terminals. 

 

 

 

Just tested one of mine using your method - wasn't flat.

In my head it sounds like 'poy-curt' 

[nb Innisfree]

I have doubts about "laws" of physics having actually seen them being broken (along with 10 witnesses) 

3 minutes ago, nicknorman said:

Yes the battery does warm up if it is discharged fast. Or discharged at all - just more so when discharged fast. Of course it has quite a lot of thermal capacity (lead and water) so the temperature rise for a given amount of heat is not massive. But it is certainly easily measurable.

But has anybody actually measured it? 

[Gibbo]

7 minutes ago, nicknorman said:

 

 

You're waffling again. I am in no way arguing against conservation of energy. But a battery cannot be thought of as an energy store in the way a capacitor can.

 

Google Nernst. I think you're in for a surprise.

 

I have never scoffed at degrees. Though clearly they don't always benefit their owners with wisdom.

 

I have shown quite clearly that higher discharge rates result in a permanent loss of battery capacity, which you clearly stated was a temporary illusion of some sort, and that the apparently lost energy would become available again given a suitable rest period. That is clearly wrong as this thread has shown.

[nicknorman]

4 minutes ago, nb Innisfree said:

I have doubts about "laws" of physics having actually seen them being broken (along with 10 witnesses) 

But has anybody actually measured it? 

 

Yea but that was on Star Trek. Surely you can appreciate that if you discharge a battery fast, it tends to get noticably warmer. It has to, because there is finite internal resistance and with power being the current squared times the resistance, that power is dissipated as heat into the battery. Same as when you pass current through any resistor.

[Tony Brooks]

1 minute ago, nb Innisfree said:

But has anybody actually measured it? 

 

Well, if anyone on here has, it would have been Gibbo when he was developing the Smartguage.

 

Recognising that Peukert has real life implications for boaters has real consequences is, in my view, far more important than the theoretical niceties that as far as I can see have no, or very little real life effect. I have noticed in the past that Nick seem to put theory above practice.

[nicknorman]

2 minutes ago, Gibbo said:

 

You're waffling again. I am in no way arguing against conservation of energy. But a battery cannot be thought of as an energy store in the way a capacitor can.

 

Google Nernst. I think you're in for a surprise.

 

I have never scoffed at degrees. Though clearly they don't always benefit their owners with wisdom.

 

I have shown quite clearly that higher discharge rates result in a permanent loss of battery capacity, which you clearly stated was a temporary illusion of some sort, and that the apparently lost energy would become available again given a suitable rest period. That is clearly wrong as this thread has shown.

You haven't shown anything, you have just repeated your myth with no evidence and no response to my challenge about the breach of first law of thermodynamics, other than to deny it.

A battery is an energy store, the energy being chemical energy. There is a fixed amount of chemical energy in the lead and acid. Your hypothesis is like saying "here I have 2 idencial pieces of coal, if I burn this one slowly I get more total energy from it than if I burn this one rapidly". Pure rubbish.

 

A capacitor stores energy in an electric field which as you say is different, but still an energy store

[nb Innisfree]

Discipline, we all must didgeridoo our duties. 

[nicknorman]

3 minutes ago, Tony Brooks said:

 

Well, if anyone on here has, it would have been Gibbo when he was developing the Smartguage.

 

Recognising that Peukert has real life implications for boaters has real consequences is, in my view, far more important than the theoretical niceties that as far as I can see have no, or very little real life effect. I have noticed in the past that Nick seem to put theory above practice.

 

But what real-life consequences does Peukert have for boaters? Please remember that no-one is denying that fast discharge of batteries gives less useful energy, but that is nothing to do with Peukert. It is only to do with the voltage efficiency of a battery (remember, Peukert has nothing to do with voltage). It is however a source of a lot of confusion and mis-information, and it is that which is my mission to dispel.

You accuse me of putting theory above practice but I would say that if practice is contrary to theory, then that practice is probably wrong even though it may well have been common thinking for decades or centuries. The world is full of such self-perpetuating misconceptions.

[Gibbo]

Yet more irrelevant waffling. 65 missing watt hours.

 

Not heat. Converted into lead suphate. Takes energy.

[NB Alnwick]

We were looking for a bit of comforting nostalgia and here we have it!

All I can say is that the original Smartgauge was probably the most useful item of equipment that we ever purchased for our boat.

The designer also provided helpful advice on how I should wire my 24v battery bank.

In the many years that I spent as a moderator on here, I often had to intervene when armchair 'experts' challenged those who gave considered advice based on real reseach and experience. Thankfully I am no longer required to do this.

I hope Gibbo continues to help others on here in the way that he helped me.

 

Edited November 9, 2023 by NB Alnwick

[Tony Brooks]

18 minutes ago, NB Alnwick said:

We were looking for a bit of comforting nostalgia and here we have it!

All I can say is that the original Smartgauge was probably the most useful item of equipment that we ever purchased for our boat.

The designer also provided helpful advice on how I should wire my 24v battery bank.

In the many years that I spent as a moderator on here, I often had to intervene when armchair 'experts' challenged those who gave considered advice based on real reseach and experience. Thankfully I am no longer required to do this.

I hope Gibbo continues to help others on here in the way that he helped me.

 

Amen to that.

[nicknorman]

18 minutes ago, Gibbo said:

Yet more irrelevant waffling. 65 missing watt hours.

 

Not heat. Converted into lead suphate. Takes energy.

?? Do you have any idea how lead acid batteries work? They convert chemical energy to electrical energy by a chemical reaction between lead and sulphuric acid that creates lead sulphate (yes the reaction is a bit more complicated than that, but that is the outcome). Lead sulphate has a lower energy state than the individual lead and acid. So far from converting into lead sulphate TAKING energy, au contraire it is that very reaction the liberates electrical energy. No more or no less lead sulphate is created by discharging x amp hours if it is done slowly or rapidly.

Just now, Tony Brooks said:

Amen to that.

 

One has to bear in mind that this started on another thread with Gibbo saying he wanted an argument. I am simply obliging. Don't hate me for it, I am just satisfying an old man.

[IanD]

3 minutes ago, nicknorman said:

?? Do you have any idea how lead acid batteries work? They convert chemical energy to electrical energy by a chemical reaction between lead and sulphuric acid that creates lead sulphate (yes the reaction is a bit more complicated than that, but that is the outcome). Lead sulphate has a lower energy state than the individual lead and acid. So far from converting into lead sulphate TAKING energy, au contraire it is that very reaction the liberates electrical energy. No more or no less lead sulphate is created by discharging x amp hours if it is done slowly or rapidly.

 

One has to bear in mind that this started on another thread with Gibbo saying he wanted an argument. I am simply obliging. Don't hate me for it, I am just satisfying an old man.

Two old men, surely? 😉

[nicknorman]

21 minutes ago, NB Alnwick said:

We were looking for a bit of comforting nostalgia and here we have it!

All I can say is that the original Smartgauge was probably the most useful item of equipment that we ever purchased for our boat.

The designer also provided helpful advice on how I should wire my 24v battery bank.

In the many years that I spent as a moderator on here, I often had to intervene when armchair 'experts' challenged those who gave considered advice based on real reseach and experience. Thankfully I am no longer required to do this.

I hope Gibbo continues to help others on here in the way that he helped me.

 

 

Yes the Smartgauge was pretty good, even though he didn't handle the charging side of things well. He used a linear algorithm to increase the SoC according to charge voltage regardless of SoC, whereas we all know that it is not a linear thing. A bit lazy, really. But it was very good on the discharge side of things.

That someone is helpful does not give them carte blanche to deny the basic laws of physics.

And anyway he LITERALLY asked for an argument, so please direct your sympathy elsewhere!

Just now, IanD said:

Two old men, surely? 😉

Actually I have a suspicion that he is younger than me!

[Tony Brooks]

21 minutes ago, nicknorman said:

 

But what real-life consequences does Peukert have for boaters? Please remember that no-one is denying that fast discharge of batteries gives less useful energy, but that is nothing to do with Peukert. It is only to do with the voltage efficiency of a battery (remember, Peukert has nothing to do with voltage). It is however a source of a lot of confusion and mis-information, and it is that which is my mission to dispel.

You accuse me of putting theory above practice but I would say that if practice is contrary to theory, then that practice is probably wrong even though it may well have been common thinking for decades or centuries. The world is full of such self-perpetuating misconceptions.

 

I will just ask how come the amp hour counters drift away from giving a true state of charge over time, and why they seem to need Pukert fiddle factors in their algorithms? Experience suggest it is used for more that time to run.

 

It is also valuable when trying to get your head around battery sizing for a particular application, or how long a bateau of given capacity will "last" from any given state of charge.

 

As far as I can see Pukert is just a way of expressing observed phenomenon.

[nicknorman]

9 minutes ago, Tony Brooks said:

 

I will just ask how come the amp hour counters drift away from giving a true state of charge over time, and why they seem to need Pukert fiddle factors in their algorithms? Experience suggest it is used for more that time to run.

 

It is also valuable when trying to get your head around battery sizing for a particular application, or how long a bateau of given capacity will "last" from any given state of charge.

 

As far as I can see Pukert is just a way of expressing observed phenomenon.

I really commend you to watch the 3 Youtube videos I linked to, this explains the whole thing well, and is quite interesting.

 

The point is that AmpHour counters do not need peukert fiddle factors to display SoC. They only need it to display "time to run" at the current discharge rate, which is not really a useful thing for boaters.

How come amp-hour counters drift? It is simply the slight inaccuracy in measuring current and then subjecting that data to integration wrt time to go from current to amphours. Any process involving integration will suffer from accumulating increasing error unless the input data is perfect, which it is never going to be. That has nothing to do with Peukert.

 

For boaters in particular, who tend to discharge their batteries at a very slow rate overall (20 hour rate or slower), Peukert is not relevant. Peukert only describes the (alleged) loss of Ah, it does not describe the loss of energy from rapid discharge. So in some ways you are correct, it vaguely describes a phenomena but using the wrong concepts and the wrong numbers, and an Ah counter will not reflect the loss of energy as it only counts Ah, and Ah is not a unit of energy.

Perhaps you don't mind using completely the wrong ideas to describe a phenomena if the outcome is satisfactory? Personally I do, although I would agree that it doesn't matter too much in practise so long as you are not someone designing an Ah counting SoC meter. But it just offends me to see incorrect information repeated parrott fashion by so many people, when giving the right information is just as easy. Why not just give the right information?

[Gibbo]

1 hour ago, nicknorman said:

 

 

Nick, you are wrong.

 

65 watt hours. Not in heat.

[nicknorman]

28 minutes ago, Gibbo said:

 

Nick, you are wrong.

 

65 watt hours. Not in heat.

Gibbo you are wrong. The lost energy goes to heat. None of which is related to Peukert, which only describes "lost" Ah, not lost energy.

 

There, can I get on with something more useful now? I am in the middle of a little project for a rotational position sensor, using a diametrically magnetised 5mm rod and my own design 3D printed housing, and my own design 25mm diameter pcb that is being made in china as we speak, with a 2 axis magnetic sensor chip that can send data over I2C. I didn't really know that you could get diametrically magnetised rods but that just has to rotate above the chip and the chip resolves that into angle. All very cheap and simple. And it might even work!

 

3D printers are great by the way, you should get one. It's the sort of thing you never knew you needed until you got one, and then you use it all the time!

Edited November 9, 2023 by nicknorman

[nb Innisfree]

1 hour ago, IanD said:

Two old men, surely? 😉

Oh much more than two

 

Let's face it at the end of the day trying to show SoC/Ah remaining etc is guesswork, even Smart gauge is guessing just that those guesses get increasingly accurate until a working indication is reached. 

Edited November 9, 2023 by nb Innisfree