Battery Fault

[nicknorman]

14 minutes ago, WotEver said:

So if a battery is storing no energy, how much ‘charge’ does it have?  If a battery has as much energy as it can hold, how much ‘charge’ does it have? If a battery only has 40% of its original ‘full’ energy available, how much ‘charge’ does it have?

Well it doesn’t really have any charge, but it does have a state of charge. The answers are 0%, 100% and something hard to determine, perhaps around 50-55%.

The same applies to measuring SoC using specific gravity. A battery whose SoC as determined by sg is say 50%, has perhaps 40% or less energy remaining.

The important point in this whole debate is that Peukert predicts “lost” charge in terms of AH, coulombs or whatever. It doesn’t have anything to say about lost energy.

4 minutes ago, WotEver said:

No it doesn’t. It integrates current flow over time. It has no concept of ‘charge’ other than what the user inputs. 

When you integrate current flow over time, you get charge. Or to put it another way, current is defined as the rate of flow of charge. So your point seems weird! You really don’t seem to know what charge is. Look it up!

Edited November 29, 2017 by nicknorman

[WotEver]

1 minute ago, nicknorman said:

The important point in this whole debate is that Peukert predicts “lost” charge in terms of AH, coulombs or whatever. It doesn’t have anything to say about lost energy.

Yes, because that was what he observed.

After observing the ‘lost’ charge he didn’t then go out of his way to calculate how much was due to wasted energy, keep it a secret, then create a formula to calculate only the ‘losses’ that are due to slow dispersion. He created a formula in a form that works to calculate all of the ‘losses‘ that he observed.

We know that Energy (and hence charge) is lost through heating and other effects, so the losses that Peukert observed were an accumulation of everything. He simply (!) discharged a few batteries heavily, noted the changes in available charge, and created a formula that tracks the ‘loss’. 

The fundamental problem here I think is that you seem to think that Peukert did some genius chemistry and maths to work out the equation. He didn't. He graphed the results, randomly threw things at it until it drew a similar graph, then said "That'll do" and went to the pub.

If he’d worked out that the weight of fluff in his pocket multiplied by the length of his shoelaces gave the same result that’s what he’d have used. 

I really don’t know how to describe it any better. 

[nicknorman]

1 minute ago, WotEver said:

Yes, because that was what he observed.

After observing the ‘lost’ charge he didn’t then go out of his way to calculate how much was due to wasted energy, keep it a secret, then create a formula to calculate only the ‘losses’ that are due to slow dispersion. He created a formula in a form that works to calculate all of the ‘losses‘ that he observed.

We know that Energy (and hence charge) is lost through heating and other effects, so the losses that Peukert observed were an accumulation of everything. He simply (!) discharged a few batteries heavily, noted the changes in available charge, and created a formula that tracks the ‘loss’. 

The fundamental problem here I think is that you seem to think that Peukert did some genius chemistry and maths to work out the equation. He didn't. He graphed the results, randomly threw things at it until it drew a similar graph, then said "That'll do" and went to the pub.

If he’d worked out that the weight of fluff in his pocket multiplied by the length of his shoelaces gave the same result that’s what he’d have used. 

I really don’t know how to describe it any better. 

But he didn’t. He didn’t make any attempt to determine losses due to heating. This is why his equation has no dimensions of power and energy. We are back to square one, you say Peukert describes lost energy but this is patently wrong because it has no dimensions of energy. If you understood anything about physics you would see the point. And no, when energy is lost, no charge is lost. Kirchov’s first law, AGAIN! Of course I am talking about proper charge, the property of something that makes it subject to a force in an electric field. As used in Peukert where he talks about current, charge and time. Not Mr Tony’s  personal definition of charge which is something completely different. Oranges, wasn’t it?

Anyway, I’m getting headache and struggling to remain vaguely courteous so I REALLY AM out now. I have provided plenty of discourse on the matter and happy to let anyone who has enough time on their hands to read through it all, make up their own minds based on the evidence.

[Dr Bob]

Phew! Glad that's finshed..........what was the answer?

 

 

.....and will it help my ecofan go round faster?

Edited November 30, 2017 by Dr Bob

[rusty69]

2 minutes ago, Dr Bob said:

Phew! Glad that's finshed..........what was the answer?

 

 

.....and will it help my ecofan go round faster?

42

[Dr Bob]

1 minute ago, rusty69 said:

42

I think I got the bit about Everything and the universe but missed the 'life' bit.

[WotEver]

13 minutes ago, rusty69 said:

42

And a half. 

[rusty69]

Its been going on so long, I've forgotten what the question was!

[Dr Bob]

Just now, WotEver said:

And a half. 

I think you are wrong. I think you missed the bit in post 301 that clearly shows the half is not covered by the theory and you need to keep up. Com'on this is important.

Just now, rusty69 said:

Its been going on so long, I've forgotten what the question was!

....yes I know, but you are right, the answer is definitely 42 and not 42.5.

[bizzard]

Neutral=Neutron bomb. 

Edited November 30, 2017 by bizzard

[frahkn]

3 hours ago, rusty69 said:

Its been going on so long, I've forgotten what the question was!

Yep. You would have trouble guessing it from the answers!

[MtB]

4 hours ago, rusty69 said:

Its been going on so long, I've forgotten what the question was!

 

I think it was why does a nurse need to have a degee, wasn’t it?

[Dr Bob]

48 minutes ago, Mike the Boilerman said:

 

I think it was why does a nurse need to have a degee, wasn’t it?

Was there even a question?

[MtB]

10 minutes ago, Dr Bob said:

Was there even a question?

 

You're right. THAT was the question!

[WotEver]

If anyone’s still awake I find it interesting that in “A critical review of using the Peukert equation for determining the remaining capacity of lead-acid and lithium-ion batteries” by Dennis Doerffel & Abu Sharkh, published in the Journal of Power Sources in April 2006, that they state, in part...

Quote

Peukert’s equation should be interpreted with care. It should not be understood to mean that when a battery is discharged fully at a certain high current discharge rate that it is completely empty. In fact it is well known that a seemingly empty battery discharged at a high current will still have some available capacity at a lesser discharge current. In fact, it suggests that if a battery was discharged at successively decreasing rates, the total Ah capacity obtained from a battery will be the same as that obtained from using a constant low current discharge. However, this paper presents results that suggest that there is a nett loss of available capacity when a battery is discharged at a high rate, followed by successive low discharge rates compared to a battery discharged at a low current rate from the start.

They then go on to explain their methodology.

Interesting, as I say, because from real-life testing they agree with what I’ve been saying all along, which Nick reckons is impossible. 

The paper doesn’t appear to be available free other than on slideshare. 

Edited November 30, 2017 by WotEver
Unexplained paragraph break!

[Dr Bob]

10 minutes ago, WotEver said:

If anyone’s still awake I find it interesting that in “A critical review of using the Peukert equation for determining the remaining capacity of lead-acid and lithium-ion batteries” by Dennis Doerffel & Abu Sharkh, published in the Journal of Power Sources in April 2006, that they state, in part...

They then go on to explain their methodology.

Interesting, as I say, because from real-life testing they agree with what I’ve been saying all along, which Nick reckons is impossible. 

The paper doesn’t appear to be available free other than on slideshare. 

That sounds very logical and fits the chemistry. What is 'Slideshare'. Be interesting to see the full paper. Is there a link?

[WotEver]

Just now, Dr Bob said:

That sounds very logical and fits the chemistry. What is 'Slideshare'. Be interesting to see the full paper. Is there a link?

It’s nasty...

https://www.slideshare.net/mobile/componer/a-critical-review-of-using-the-peukert-equation-for-determining-the-remaining-capacity-of-lead-acid-and-lithium-ion-batteries

[Dr Bob]

11 hours ago, WotEver said:

It’s nasty...

https://www.slideshare.net/mobile/componer/a-critical-review-of-using-the-peukert-equation-for-determining-the-remaining-capacity-of-lead-acid-and-lithium-ion-batteries

Thanks, that looks a really interesting paper. I will read it once we have finished our days cruise.

[Dr Bob]

14 hours ago, WotEver said:

It’s nasty...

https://www.slideshare.net/mobile/componer/a-critical-review-of-using-the-peukert-equation-for-determining-the-remaining-capacity-of-lead-acid-and-lithium-ion-batteries

Thanks Wotever, that is a really interesting paper and provides some useful input. Only word of caution is that 'Papers' are not always right and are only the views of the writers so not always 100% correct. Bit difficult to read on a tablet, so I stopped taking them and read it on my Mac.

The things the paper confirms for me are:

1) Peukert tried to model the total loss of capacity for each cycle and didn't try and differentiate between loss due to the chemistry of loss due to the internal resistance (and hence loss via heat) as you were saying.

2)The loss via Chemistry (the writer says this is “reformation of the hydrated gel zones in the electrode active centres during the waiting period” - which I described earlier as the replenishment of the HSO4- ion on the plate surface at the active sites – I prefer my description but hey...) is transient and can be recovered during the cycle by resting - to replenish the ions on the surface.

3)The loss via internal resistance is lost during the cycle and cant be got back until the next cycle.

4) From the graphs the energy lost by internal resistance – and that is the resistance between the PbO and the grid (interesting) – is circa 3Ahrs in 60Ahrs so 5% of the total capacity at the high load – so maybe 15-30% of the Peukerts loss as you suggested earlier.

Any battery monitor should therefore attempt to include internal resistance losses to give indications of SoC.

In practise however on a narrow boat, none of the above is really that important as we don't tend to discharge at those high rates that cause the 5% heat loss – or at least never for more than a few minutes while running the Nesspresso machine. Sure Peukert's equation is important but maybe charging efficiency is more important and it would be good to read some papers on that.

The surprise from the paper was the text on Lithium batteries. I hadn't realised how important temperature was on efficiency. What then concerns me is what happens with Lithiums at low temperatures, ie when approaching zero – as it has been in the last few nights. I read somewhere else you cannot charge a lithium battery at temps of zero or below and it looks like the energy available when under load is somewhat limited at 1 or 2 deg C.

I would be interested in seeing some similar data for tests done on AGMs where I think I remembered the Peukerts constant was 1.1 (ish). For me, in practice, most of my discharge is done at low rate and I am far more interested in understanding how to get more energy back into the bank during charging. I am currently using cheapo LA's but put off getting Trojans for my next set due to the high voltages needed – and thinking AGM's maybe a better bet for charging efficiency. Thinking through the chemisty and Peukert losses, does a higher Peukert number also means an inferior charging efficiency – ie if energy is temporarily lost due to slow migration of ions during discharge, surely energy will not go in as easily on charge as the ions will build up on the plate surface and slow the recharge reaction. Sounds like AGMs should accept charge much better? Is this right or am I talking a load of 'Muppets'.

[nicknorman]

Looks like it was done by a couple of undergraduates. Normally one would put the qualifications after authors' names. So firstly, it shows that the difference between the fast discharge followed by the slow discharge isn't much compared to the slow - most of the "lost" Peukert charge is recovered later. Most, but not all. There is a small loss. I would say this is likely to be due simply to timing issues. They made the overall discharge times equal but the way in which the discharge was done were fairly extreme. I think it would have been better to say compare discharging at 5A, with discharging at 50 A for 1 minute followed by nothing for 9 minutes, repeated. My feeling is that if they had continued the tests with a further discharge cycle, they would have recovered all the remaining "lost" charge. They didn't go there for some reason, probably it was time to go to the pub.

But all that said, it is a pretty extreme example of fast discharging the battery until it is flat, followed by recovering the remainder after a wait. And even then, the "lost" AH is pretty small. In a more normal boating environment this sort of pattern wouldn't be followed. The loss of charge caused by say us putting the 2kw kettle on for 4 minutes is insignificant (and probably only exists at all as a result of some gassing).

At least they do point out the folly of trying to apply Peukert to an AH-counting SoC gauge.

Finally, they do not adequately explain where the lost charge went. They talk about "increases the resistance of the interface, thus leading to a net loss of capacity". So they imagine that charge or current can be "dropped" through resistance. They are fools and if I had been marking that paper it would have got a D- for breaching Kirchov's first law. As it is, they provide no valid suggestions for the mechanism by which these electrons evaporate and IMO the chances are, they don't.

[nicknorman]

44 minutes ago, Dr Bob said:

Thanks Wotever, that is a really interesting paper and provides some useful input. Only word of caution is that 'Papers' are not always right and are only the views of the writers so not always 100% correct. Bit difficult to read on a tablet, so I stopped taking them and read it on my Mac.

The things the paper confirms for me are:

1) Peukert tried to model the total loss of capacity for each cycle and didn't try and differentiate between loss due to the chemistry of loss due to the internal resistance (and hence loss via heat) as you were saying. There cannpt be a  loss of capacity due to internal resistance. Kirchov's first law

2)The loss via Chemistry (the writer says this is “reformation of the hydrated gel zones in the electrode active centres during the waiting period” - which I described earlier as the replenishment of the HSO4- ion on the plate surface at the active sites – I prefer my description but hey...) is transient and can be recovered during the cycle by resting - to replenish the ions on the surface.

3)The loss via internal resistance is lost during the cycle and cant be got back until the next cycle. No capacity is lost due to internal resistance. Kirchoff's first law. Energy is lost due to reduced terminal voltage.

4) From the graphs the energy lost by internal resistance – and that is the resistance between the PbO and the grid (interesting) – is circa 3Ahrs in 60Ahrs Dimensionally incorrect. AH does not have dimensions of energy and so can't be used to measure it any more that it would be appropriate to use it to measure the flavour of one of Tony's oranges. so 5% of the total capacity at the high load – so maybe 15-30% of the Peukerts loss as you suggested earlier. The graphs don't show the energy lost to internal resistance. Well you would have to integrate the area under the curves to find it.

Any battery monitor should therefore attempt to include internal resistance losses to give indications of SoC. No, SoC gauges work in AH, to calculate the % of AH remaining, not in WH. AH are not lost due to internal resistance. Kirchoff's first law. Of course one could have a WH (SoE - State of Energy) gauge but pretty difficult to take all the variables into account.

In practise however on a narrow boat, none of the above is really that important as we don't tend to discharge at those high rates that cause the 5% heat loss – or at least never for more than a few minutes while running the Nesspresso machine. Sure Peukert's equation is important but maybe charging efficiency is more important and it would be good to read some papers on that. Peukert has nothing to do with losses due to heating/internal resistance. Not that that issue isn't significant, it is. But Mr P didn't attempt to devise a formula to deal with it. Far too difficult and it wouldnt just be a nice exponent.

The surprise from the paper was the text on Lithium batteries. I hadn't realised how important temperature was on efficiency. What then concerns me is what happens with Lithiums at low temperatures, ie when approaching zero – as it has been in the last few nights. I read somewhere else you cannot charge a lithium battery at temps of zero or below and it looks like the energy available when under load is somewhat limited at 1 or 2 deg C. I was thinking about getting a lithium battery for my glider. But then I noticed the temperature issue. Not good for high wave flying when the outside temperature can be -30 or less with no heater except the sun (if you are lucky)!

I would be interested in seeing some similar data for tests done on AGMs where I think I remembered the Peukerts constant was 1.1 (ish). For me, in practice, most of my discharge is done at low rate and I am far more interested in understanding how to get more energy back into the bank during charging. I am currently using cheapo LA's but put off getting Trojans for my next set due to the high voltages needed – and thinking AGM's maybe a better bet for charging efficiency. Thinking through the chemisty and Peukert losses, does a higher Peukert number also means an inferior charging efficiency – ie if energy is temporarily lost due to slow migration of ions during discharge, surely energy will not go in as easily on charge as the ions will build up on the plate surface and slow the recharge reaction. Sounds like AGMs should accept charge much better? Is this right or am I talking a load of 'Muppets'. I think AGMs do take charge faster earlier on. Not sure how much difference there is in the overall fully charged time since its the last bit that takes forever!

 

Edited December 1, 2017 by nicknorman

[Dr Bob]

3 hours ago, nicknorman said:

Finally, they do not adequately explain where the lost charge went. They talk about "increases the resistance of the interface, thus leading to a net loss of capacity". So they imagine that charge or current can be "dropped" through resistance. They are fools and if I had been marking that paper it would have got a D- for breaching Kirchov's first law.

Nick,

I think we were in agreement a few pages back so I am not going to re-open the endless discussion again.

Just a comment though on Kirchov's first law. This was about the number of electrons in a circuit being the same all the way round - ie no electrons can disappear. I am not sure why you keep invoking this law all the time wrt batteries. If there is an internal circuit or in increase in internal resistance for an external circuit, then the same number of electrons will flow all the way round that circuit (therefore preserving Kirchov's first law). The heating effect and therefore the loss of energy in the battery from the increased internal resistance is just from the loss of 'energy' in the electrons flowing in that circuit in the same way that any electrical heater circuit works. I posted something about this 2 pages ago linking to a book that had been linked to (apologies, I forgot who posted it). No electrons disappear so Kirchov's law is not broken.

[nicknorman]

49 minutes ago, Dr Bob said:

Nick,

I think we were in agreement a few pages back so I am not going to re-open the endless discussion again.

Just a comment though on Kirchov's first law. This was about the number of electrons in a circuit being the same all the way round - ie no electrons can disappear. I am not sure why you keep invoking this law all the time wrt batteries. If there is an internal circuit or in increase in internal resistance for an external circuit, then the same number of electrons will flow all the way round that circuit (therefore preserving Kirchov's first law). The heating effect and therefore the loss of energy in the battery from the increased internal resistance is just from the loss of 'energy' in the electrons flowing in that circuit in the same way that any electrical heater circuit works. I posted something about this 2 pages ago linking to a book that had been linked to (apologies, I forgot who posted it). No electrons disappear so Kirchov's law is not broken.

I think points of disagreement often arise due to careless use of scientific terms. Kirchoff’s first law is of course really about preservation of current around a circuit. My bad is that I just say “electrons” in a light hearted way. Current is of course electrons moving, not electrons themselves!

Anyway, this point is an important one, so listen carefully as I shall say this only once... (Yea RIGHT!).

Peukert is only about current and charge - charge as in AH, coulombs etc, the scientific definition of charge.

Current flowing through a resistor doesn’t result in less current flowing out of it than went in. Therefore when you said earlier that charge was lost due to the battery’s resistance, this is clearly wrong and I invoke Kirchhoff to prove it.

So what you say above is entirely correct. The circuit results in a loss of power (voltage drop across the resistor x the current). But you sometimes say that it results in a loss of charge. This is quite wrong as charge is merely the integral of current and if current is not lost in a resistor, nor can charge be.

I suspect it boils down to you using “charge” to mean the energy in the battery when in fact it means ... the charge! Charge is the property of something that causes it to feel a force when in an electric field. AH, coulombs or whatever. The integral of current. The Charge of a battery is on the label, 110AH or whatever. Charge is measured in an AH-counting SoC gauge. Charge, or the temporary loss of it, is what Peukert describes. Charge does not have the dimensions of energy any more than oranges do. 

If you use the wrong term it will always cause confusion. Just as if you said voltage when you meant current, charge when you meant oranges.

If I don’t pick folk up on it each time, a completely false and misleading impression is given.

[Dr Bob]

4 minutes ago, nicknorman said:

I think points of disagreement often arise due to careless use of scientific terms. Kirchoff’s first law is of course really about preservation of current around a circuit. My bad is that I just say “electrons” in a light hearted way. Current is of course electrons moving, not electrons themselves!

Anyway, this point is an important one, so listen carefully as I shall say this only once... (Yea RIGHT!).

Peukert is only about current and charge - charge as in AH, coulombs etc, the scientific definition of charge.

Current flowing through a resistor doesn’t result in less current flowing out of it than went in. Therefore when you said earlier that charge was lost due to the battery’s resistance, this is clearly wrong and I invoke Kirchhoff to prove it.

So what you say above is entirely correct. The circuit results in a loss of power (voltage drop across the resistor x the current). But you sometimes say that it results in a loss of charge. This is quite wrong as charge is merely the integral of current and if current is not lost in a resistor, nor can charge be.

I suspect it boils down to you using “charge” to mean the energy in the battery when in fact it means ... the charge! Charge is the property of something that causes it to feel a force when in an electric field. AH, coulombs or whatever. The integral of current. The Charge of a battery is on the label, 110AH or whatever. Charge is measured in an AH-counting SoC gauge. Charge, or the temporary loss of it, is what Peukert describes. Charge does not have the dimensions of energy any more than oranges do. 

If you use the wrong term it will always cause confusion. Just as if you said voltage when you meant current, charge when you meant oranges.

If I don’t pick folk up on it each time, a completely false and misleading impression is given.

Quite right and in a previous post I identified my use of 'charge' as the noun derived from the verb 'to charge'. Fully agree...but in my last post I did not mention charge, just that Kirchoffs law was being observed despite loss of ENERGY due to internal resistance. I think we are there.

Now given all the above, why do we say 'State of Charge' and use Ahr as the measure? The Ahr of a battery will vary  with discharge rate etc so is not an absolute value. We should really be measuring the amount of 'energy' in a battery ie when you charge it up , you pump energy in which is used to raise the chemicals in the battery up to a higher energy state. You get this energy back when you allow current to run out round a circuit. Problem then is no one would understand what 'energy' meant but it would be absolute. State of Charge relates to this energy but it is confusing as you say in your post.

[nicknorman]

22 minutes ago, Dr Bob said:

Quite right and in a previous post I identified my use of 'charge' as the noun derived from the verb 'to charge'. Fully agree...but in my last post I did not mention charge, just that Kirchoffs law was being observed despite loss of ENERGY due to internal resistance. I think we are there.

Now given all the above, why do we say 'State of Charge' and use Ahr as the measure? The Ahr of a battery will vary  with discharge rate etc so is not an absolute value. We should really be measuring the amount of 'energy' in a battery ie when you charge it up , you pump energy in which is used to raise the chemicals in the battery up to a higher energy state. You get this energy back when you allow current to run out round a circuit. Problem then is no one would understand what 'energy' meant but it would be absolute. State of Charge relates to this energy but it is confusing as you say in your post.

Yes your previous post was fine! But careful with your last sentence in this post as SoC does NOT relate to the energy remaining in the battery. It relates to the charge remaining, AH etc not WH! The clue is in the word “charge”!

SoC as opposed to SoE -I think simply because working out the charge is quite easy. Working out the energy is much more complex.

For charge, there is x kg of chemicals, that produces y amount of AH regardless. Predictable because, in case I didn’t mention it before, Kirchhoff means that no current is lost and hence none of its integral - charge - is lost. If time is of the essence you can apply Peukert to see how much less charge will be available when discharging fast to flat.

For energy, which is of course the product of charge and voltage, it is much harder to work out because the voltage is so hard to predict. Of course the voltage varies through out the discharge in a fairly non-linear way, there is “surface charge” which initially gives an elevated voltage. Temperature has a big effect on terminal voltage under load. And of course terminal voltage varies according to current drain AND SoC. So If you take 50% of the energy out of the battery, how much is left? Really hard to say as it depends on something that is going to happen in the future. If you discharge slowly, you can recover another 50%. If you discharge fast you will only get 40%. So what should the gauge read? 50%, even though I might only get 40% if I discharge fast? Or 40% even though I might get another 50% if I discharge slowly. 

Really difficult to model. But not impossible of course.

As an aside it’s interesting to note that AH-counting SoC gauges calculate CEF (charge efficiency factor) which is the AH out vs AH put back in again to get back to fully charged. Typically around 94% or so. Which makes batteries sound fairly efficient! But if you look at the PEF (power efficiency factor) which of course is the discharge AH x discharge voltage, vs the charge AH x charge voltage, batteries are really inefficient simply because the charge voltage is so much higher than the discharge voltage!

Edited December 1, 2017 by nicknorman