The Peukert myth exposed

[Guest]

9 minutes ago, carlt said:

Not him again!

 

Where do they dig these old dinosaurs up from?

 

Bloody Nora Carl - good to see you...

[magnetman]

Yaaay! 

[mrsmelly]

19 minutes ago, M_JG said:

 

Bloody Nora Carl - good to see you...

Indeed so. The forum is suddenly getting back to normal as a result of the in memoriam thread 🤪

[chris w]

Nick

 

Out of courtesy to you, I did watch the 3 YouTube videos you highlighted. 
 

First of all, my initial reaction is that what the author has produced is very much a “Janet & John do batteries; chapter 1.” It’s extremely basic.

He also lets himself down, by his saying, “I studied High School chemistry so I guess that makes me qualified to talk about this subject.” (!!)

 

However, having said that, I don’t disagree substantially with what he is saying about the chemistry. 

As a graduate in Electronics, and with over 30 years of boat owning, I feel I’m at least as qualified as the next guy to espouse my views. 
 

There is much made in these videos as, in this discussion, of leaving a “discharged” battery to rest and then being able to recover more capacity from it. 
 

I agree this is the case. However, that doesn’t mean Peukert’s Law is incorrect as the video author asserts. 
 

When we use batteries in a high discharge situation, such as with an inverter, Peukert’s Law will give an extremely good guide to the amount of capacity we can draw out of the battery, before, say, the inverter cuts off. 
 

We don’t, however, in real use, think “I’ll now rest the battery for 6 hours and then I can drain it some more.” We recharge it, as soon as is practicable. 
 

In the real-world, Peukert is a very good predictor of useable SOC and that’s why it’s important to ensure one does set the correct Peukert Factor in AH meters etc. 
 

I suspect the author of the videos does not have much practical experience in using batteries in real-life situations. He’s just trying to belabour a theoretical point that has no practical use. 
 

 

 

[nb Innisfree]

33 minutes ago, rusty69 said:

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

Now you're being silly

 

 

[bizzard]

I had a battery hen called ''Ever Ready'.

[dmr]

So are there two levels of Peukert?

1 A genuine loss of amp-hour capacity due to rapid discharge

2 A ficticious loss of capacity due to the on-load volt drop when discharging down to 10.5volt.

 

2 is ficticious and I agree with Nick on this.

1 is more difficult and that is for Nick and Gibbo to resolve 😀

 

When battery suppliers (or amp-hour counter suppliers) give figures for Peukert which one are they measuring????

[Cheshire cat]

This thread has made my day!

[IanD]

1 hour ago, rusty69 said:

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

But you can't find that because they're unobservable (in a closed box) -- it's not until you open the box and look at (or measure) the batteries that they become full or empty... 😉

[rusty69]

18 minutes ago, IanD said:

But you can't find that because they're unobservable (in a closed box) -- it's not until you open the box and look at (or measure) the batteries that they become full or empty... 😉

Nah, they're not in a closed box, they're in the engine room connected to a smartgauge.

[nicknorman]

1 hour ago, chris w said:

Nick

 

Out of courtesy to you, I did watch the 3 YouTube videos you highlighted. 
 

First of all, my initial reaction is that what the author has produced is very much a “Janet & John do batteries; chapter 1.” It’s extremely basic.

He also lets himself down, by his saying, “I studied High School chemistry so I guess that makes me qualified to talk about this subject.” (!!)

 

However, having said that, I don’t disagree substantially with what he is saying about the chemistry. 

As a graduate in Electronics, and with over 30 years of boat owning, I feel I’m at least as qualified as the next guy to espouse my views. 
 

There is much made in these videos as, in this discussion, of leaving a “discharged” battery to rest and then being able to recover more capacity from it. 
 

I agree this is the case. However, that doesn’t mean Peukert’s Law is incorrect as the video author asserts. 
 

When we use batteries in a high discharge situation, such as with an inverter, Peukert’s Law will give an extremely good guide to the amount of capacity we can draw out of the battery, before, say, the inverter cuts off. 
 

We don’t, however, in real use, think “I’ll now rest the battery for 6 hours and then I can drain it some more.” We recharge it, as soon as is practicable. 
 

In the real-world, Peukert is a very good predictor of useable SOC and that’s why it’s important to ensure one does set the correct Peukert Factor in AH meters etc. 
 

I suspect the author of the videos does not have much practical experience in using batteries in real-life situations. He’s just trying to belabour a theoretical point that has no practical use. 
 

 

Certainly the videos are a little patronising but then it is hard to aim at just the right level for every audience. I took the bit about "High School chemistry" as a joke.

 

Yes I would agree that Peukert gives a good idea about the amount of capacity an inverter delivering a fairly high load can draw from the battery before it cuts off. As I said, Peukert definitely has a place in "time to run to flat" display.  But is that really a scenario that most boaters want to be a part of? Most boaters don't turn on a high inverter load and want to run that until the inverter trips off due to under-voltage.

 

What is a more realistic scenario IMO, is short bursts of high inverter demand, followed by long periods of low demand. For example we normally use an electric kettle, so that is 200A from the battery for 4 minutes. That will knock off about 14 Ah. Then we will revert to a modest 5 -10 amp load to run the TV or a phone charger for the next several hours. So the question is, should those 14Ah have Peukert applied, thus knocking say 20Ah from the displayed remaining capacity, or should it just knock off the 14 Ah. I say it is the latter.

 

So as you say Peukert is a good predictor of usable SoC IF the present circumstances of high load continue until the battery is flat.  But in reality, boaters don't use their batteries like that. Or those that do, find they have a very short battery life!

 

Of the course the whole issue of displaying SoC is fraught in the first place, because if the SoC meter says you have 50% left out of 100Ah, whilst you do have 50Ah left if you discharge slowly, you have less than that left (before the battery is notionally flat) if you discharge quickly. Since the SoC meter cannot predict the future - the rate at which the battery will be discharged -  it's display of usable remaining capacity is just a guess and assumes a slow rate of discharge.

 

All the above of which reminds me how glad I am that we no longer have Lead Acid domestic batteries!!! Life is so much simpler now!

Edited November 9, 2023 by nicknorman

[IanD]

29 minutes ago, rusty69 said:

Nah, they're not in a closed box, they're in the engine room connected to a smartgauge.

So until you open the engine room door and stick a DVM on them -- or look at the Smartgauge result -- they're neither charged nor flat. Observation is the key... 😉

Edited November 9, 2023 by IanD

[rusty69]

1 minute ago, IanD said:

So until you open the engine room door and stick a DVM on them -- or look at the Smartgauge result -- they're neither charged nor flat. Observation is the key... 😉

They are usually flat when Mrs R is onboard. I don't need to enter the engine room to determine that.

[IanD]

Just now, rusty69 said:

They are usually flat when Mrs R is onboard. I don't need to enter the engine room to determine that.

How do you know they're flat? 😉

 

If you try and turn the lights on and get a dim orange glow, you've just observed their state...

[rusty69]

1 minute ago, IanD said:

How do you know they're flat? 😉

 

If you try and turn the lights on and get a dim orange glow, you've just observed their state...

By association. Mrs R is onboard, ergo they are flat. QED innit.

[pig]

34 minutes ago, rusty69 said:

Nah, they're not in a closed box

BSS fail

[rusty69]

Just now, pig said:

BSS fail

Not all boats are subject to the BSS

[chris w]

44 minutes ago, pig said:

BSS fail

Not having them in a closed box is not a BSS fail. 
 

1. Your batteries are required to be prevented from moving (eg: a closed box or strapping) and

 

2. Must be covered to prevent something falling on the terminals. (eg: a closed box or a covering like rubber mats). 
 

So, a closed box is sufficient, but not necessary. 

2 hours ago, dmr said:

So are there two levels of Peukert?

1 A genuine loss of amp-hour capacity due to rapid discharge

2 A ficticious loss of capacity due to the on-load volt drop when discharging down to 10.5volt.

 

2 is ficticious and I agree with Nick on this.

1 is more difficult and that is for Nick and Gibbo to resolve 😀

 

When battery suppliers (or amp-hour counter suppliers) give figures for Peukert which one are they measuring????

The Peukert Factor quoted by battery manufacturers, tells you how many hours you can discharge continuously, at a certain current, before the battery voltage drops to (usually) 10.5v. 
 

There is no ambiguity in that. 

1 hour ago, nicknorman said:

 

Certainly the videos are a little patronising but then it is hard to aim at just the right level for every audience. I took the bit about "High School chemistry" as a joke.

 

Yes I would agree that Peukert gives a good idea about the amount of capacity an inverter delivering a fairly high load can draw from the battery before it cuts off. As I said, Peukert definitely has a place in "time to run to flat" display.  But is that really a scenario that most boaters want to be a part of? Most boaters don't turn on a high inverter load and want to run that until the inverter trips off due to under-voltage.

 

What is a more realistic scenario IMO, is short bursts of high inverter demand, followed by long periods of low demand. For example we normally use an electric kettle, so that is 200A from the battery for 4 minutes. That will knock off about 14 Ah. Then we will revert to a modest 5 -10 amp load to run the TV or a phone charger for the next several hours. So the question is, should those 14Ah have Peukert applied, thus knocking say 20Ah from the displayed remaining capacity, or should it just knock off the 14 Ah. I say it is the latter.

 

So as you say Peukert is a good predictor of usable SoC IF the present circumstances of high load continue until the battery is flat.  But in reality, boaters don't use their batteries like that. Or those that do, find they have a very short battery life!

 

Of the course the whole issue of displaying SoC is fraught in the first place, because if the SoC meter says you have 50% left out of 100Ah, whilst you do have 50Ah left if you discharge slowly, you have less than that left (before the battery is notionally flat) if you discharge quickly. Since the SoC meter cannot predict the future - the rate at which the battery will be discharged -  it's display of usable remaining capacity is just a guess and assumes a slow rate of discharge.

 

All the above of which reminds me how glad I am that we no longer have Lead Acid domestic batteries!!! Life is so much simpler now!

I use 3 Victron Battery Monitors, on my boat, to monitor various battery banks, including the SOC. 

 

The SOC indication, for the main batteries, in my experience, tracks their actual SOC based on (no load) voltage really well. On recharge, the battery monitor resets the SOC to 100% based on tail current. Tail current is the only sure way to know that your batteries are really charged. 

[dmr]

14 minutes ago, chris w said:

Not having them in a closed box is not a BSS fail. 
 

1. Your batteries are required to be prevented from moving (eg: a closed box or strapping) and

 

2. Must be covered to prevent something falling on the terminals. (eg: a closed box or a covering like rubber mats). 
 

So, a closed box is sufficient, but not necessary. 

The Peukert Factor quoted by battery manufacturers, tells you how many hours you can discharge continuously, at a certain current, before the battery voltage drops to (usually) 10.5v. 
 

There is no ambiguity in that. 

I use 3 Victron Battery Monitors, on my boat, to monitor various battery banks, including the SOC. 

 

The SOC indication, for the main batteries, in my experience, tracks their actual SOC based on (no load) voltage really well. On recharge, the battery monitor resets the SOC to 100% based on tail current. Tail current is the only sure way to know that your batteries are really charged. 

 

So in that respect I am 100% with Nick, that's wrong.

[nicknorman]

16 minutes ago, chris w said:

Not having them in a closed box is not a BSS fail. 
 

1. Your batteries are required to be prevented from moving (eg: a closed box or strapping) and

 

2. Must be covered to prevent something falling on the terminals. (eg: a closed box or a covering like rubber mats). 
 

So, a closed box is sufficient, but not necessary. 

The Peukert Factor quoted by battery manufacturers, tells you how many hours you can discharge continuously, at a certain current, before the battery voltage drops to (usually) 10.5v. 
 

There is no ambiguity in that. 

I use 3 Victron Battery Monitors, on my boat, to monitor various battery banks, including the SOC. 

 

The SOC indication, for the main batteries, in my experience, tracks their actual SOC based on (no load) voltage really well. On recharge, the battery monitor resets the SOC to 100% based on tail current. Tail current is the only sure way to know that your batteries are really charged. 

I am not seeing anything to disagree with. Which rather defeats the object!

[Paul C]

8 hours 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.

 

 

Given that amp-hour counters reset themselves to 100% when they've observed tail current charging for a period of time.........doesn't the "drift away" also coincide with what is generally thought of as abusing batteries, by never really fully charging them and leaving them days/weeks in some <100 percentage of SoC?

[Wanted]

5 hours ago, carlt said:

Not him again!

 

Where do they dig these old dinosaurs up from?

Blimey! Hello chap! Hope all is well! 

[pig]

3 hours ago, rusty69 said:

Not all boats are subject to the BSS

Is this a five minute argument or the full half hour?

[rusty69]

1 minute ago, pig said:

Is this a five minute argument or the full half hour?

It depends at what rate you argue. 

 

The c20 rate will get you the full half hour. 

Edited November 9, 2023 by rusty69

[nicknorman]

Anyway, I think I may have killed Gibbo, which is a shame.