Voltage meter on House batts? necessary?

[halcyon]

My Lifeline AGM manual says 0.5% of capacity at 14.3v.

The problem is you can't set up an Ah meter to this value because the charger will have dropped down to a float voltage long before the current reaches 0.5% of capacity at 14.4 volts. That is why this has to be manually controlled if you really want to check when your batteries are back to 100%. Let them stay at a float voltage for another 12 hours to get fully charged, but don't say your solar panels have fully charged your batteries by lunchtime because you controller has dropped down to float mode!


When my SmartGauge tels me, or when they've been on shorepower for 24 hours which I do once every 2-3 weeks.

12 hours @14.4 volt will not improve capacity unless the previous charge up to 14.4 was bad, with a correctly charged battery charge current will fall to milliamps.


How does your smartgauge know the battery is at 100% capacity ?


Brian

 

[sailinglegend420]

....The 1897 Peukert model is an empirical equation (which is a mathematical way of saying a rule of thumb).......

Yes you are right, but calling it a "rule of thumb" devalues it, in your view I suspect, to a worthless, pointless formula. I you really want to understand the importance of his formula see this SmartGauge link: http://www.smartgauge.co.uk/peukert2.html

If you can understand all of this you are a better man than me!

 

[sailinglegend420]

12 hours @14.4 volt will not improve capacity unless the previous charge up to 14.4 was bad, with a correctly charged battery charge current will fall to milliamps....

I didn't say you should leave it at 14.4 v for 12 hours only that as soon as it goes to float switch back to 14.4v to see what the charge current is and then let it fall back to float again and leave it to fully charge. Leaving it at 14.4v too long will cause too much gassing which is why a multi-stage charger falls to a float voltage way below the battery's gassing voltage.

How does your smartgauge know the battery is at 100% capacity ?...Brian

How does SmartGauge work at all - that is a good question? If you were watching your voltmeter 1100 times a second you'd soon get an idea of the state of charge from the rate of the rise and fall of the voltage. I'm sure to some people it's a worthless, pointless empirical formula that the inventor "Gibbo" has developed, but it works.

 

[GHA]

but don't say your solar panels have fully charged your batteries by lunchtime because you controller has dropped down to float mode!

Don't have one, hasn't been an issue so far and with a manually adjustable regulator on the way I think it will be easy to do much better than a very conservatively programmed controller getting confused with amps going into loads as well as the battery.

Do you have no way of knowing how many amps have been used overnight? The Smartgauge says it measures SoC of the battery capacity, not the data sheet Ah. I think of the state of charge in the monitor onboard as an add on, the most useful bits are live amps in/out and voltage, the SoC readout might drift quickly which is yet another good reason to make sure the batteries are getting close to fully charged as often as possible.

 

[Amulet]

Yes you are right, but calling it a "rule of thumb" devalues it, in your view I suspect, to a worthless, pointless formula. I you really want to understand the importance of his formula see this SmartGauge link: http://www.smartgauge.co.uk/peukert2.html

If you can understand all of this you are a better man than me!

I can understand it, and actually the spreadsheet they built is very like one I built. I understand that Peukert's equation is a valuable tool, and as far as I can see it's critics don't offer anything better. Too many things going on. I saw an experiment quoted that showed that if you take a notional 30 amp hours out of a full battery two different ways: 10 amps for one hour then 20 amps for one hour, or the reverse, 20 amps for one hour and then 10 amps for one hour the remaining capacity differs quite markedly.

However I had not taken into account the live-aboard requirement of making all this work in a complex charging environment with umpteen charging devices and wanting to really get all the way to 100% if any amps are to be had. As far as I can see, you have every charging source ever invented, so I apologise and bow to your practical knowledge and experience.

 

[sailinglegend420]

...Do you have no way of knowing how many amps have been used overnight? The Smartgauge says it measures SoC of the battery capacity, not the data sheet Ah. .....

I use my old Battery Monitor which is still installed as a test to see if I can reprogramme the parameters to get it to match more closely the Voltage and current readings I see, and of course to match the SmartGauge, which I believe to be much more accurate. I haven't managed after 18 months of changing the Capacity, the Charge Efficiency and Peukert's to get it looking any closer. My real interest is knowing what capacity my 10 year old Lifelines AGMs have fallen too. Lifeline say they can fall to 50% of original capacity before they need replacing, whereas other manufacturers say at 70-80% of original capacity.

As I mentioned in a previous post Enersys, who make Optima batteries, said the SmartGauge was very accurate. I can give you their figure which was an unbelievable 0.1% inaccurate. If the SmartGauge was 50 times worse than that at 5%, I would still be happy.

....I understand that Peukert's equation is a valuable tool, and as far as I can see it's critics don't offer anything better. Too many things going on. I saw an experiment quoted that showed that if you take a notional 30 amp hours out of a full battery two different ways: 10 amps for one hour then 20 amps for one hour, or the reverse, 20 amps for one hour and then 10 amps for one hour the remaining capacity differs quite markedly.....

Which Peukert critics are you talking about - what problems do they have with Peukert's Exponent? It's a fact of battery life and difficult to measure, or sometimes even find the real value from your battery manufacturer. That's not a criticism.

The experiment you quote could do with a link! Beware of anything you read on the Web! As you know it is very difficult to measure the capacity remaining in a battery without very expensive equipment. If you did the experiment with a battery monitor and used it's Ah readings then that just proves my point that battery monitors can be very inaccurate, or not programmed properly.

The bottom line of this post should be that every boat needs a Battery Monitor, but beware of it's limitations and make sure it is installed and programmed properly.

A much easier to install option is a SmartGauge, but do also fit an Ah count meter to monitor charge and discharge currents.

 

[GHA]

I use my old Battery Monitor which is still installed as a test to see if I can reprogramme the parameters to get it to match more closely the Voltage and current readings I see, and of course to match the SmartGauge, which I believe to be much more accurate. I haven't managed after 18 months of changing the Capacity, the Charge Efficiency and Peukert's to get it looking any closer. My real interest is knowing what capacity my 10 year old Lifelines AGMs have fallen too. Lifeline say they can fall to 50% of original capacity before they need replacing, whereas other manufacturers say at 70-80% of original capacity.

As I mentioned in a previous post Enersys, who make Optima batteries, said the SmartGauge was very accurate. I can give you their figure which was an unbelievable 0.1% inaccurate. If the SmartGauge was 50 times worse than that at 5%, I would still be happy.

Still confused how you estimate the capacity if Smartgauge just gives you state of charge.


0.1%? Is it even possible to measure that accurately? Cadex did a test of 91 batteries and found up to 15% discrepancies under identical conditions, even if it's possible what good does 5% SoC accuracy when a manufacturer of test equipment can't get better than 15% inaccuracies in testing capacity?
http://www.buchmann.ca/article45-page1.asp

 

[AngusMcDoon]

0.1%? Is it even possible to measure that accurately?

Any gauge is only as good as its sensors. Temperature compensated repeatedly accurate digital to analogue converters that measure to that level consistently over time would make any product containing them a lot more expensive than the SmartGuage, so anyone claiming this level of accuracy either been mislead or is not telling the truth.

 

[halcyon]

I didn't say you should leave it at 14.4 v for 12 hours only that as soon as it goes to float switch back to 14.4v to see what the charge current is and then let it fall back to float again and leave it to fully charge. Leaving it at 14.4v too long will cause too much gassing which is why a multi-stage charger falls to a float voltage way below the battery's gassing voltage.


How does SmartGauge work at all - that is a good question? If you were watching your voltmeter 1100 times a second you'd soon get an idea of the state of charge from the rate of the rise and fall of the voltage. I'm sure to some people it's a worthless, pointless empirical formula that the inventor "Gibbo" has developed, but it works.

But 14.4 is not a fully charged battery, depends on type, but 90% would be closer.


The voltage you see on your voltmeter varies, alter the current voltage for a given battery level changes, alter battery temp and the voltages changes, it varies with age of battery. The change in voltage between 60F and 80F degree battery temp is 0.05 volt or 5% of capacity.

As said voltmeter / ammeter allows you to monitor the point when engine running is not generating useful charge, thus your systems optimum capacity, it then allows you to monitor battery volts for load applied. Which if you charge at 12.3 volt no load, and 11.9 - 12.0 volt with 5-10% of battery capacity load, you recharge at around 45 - 55% battery level.

You free to fit what you are happy with, it's your money, just trying to balance the thread.
Brian

 

[sailinglegend420]

Still confused how you estimate the capacity if Smartgauge just gives you state of charge.

0.1%? Is it even possible to measure that accurately? Cadex did a test of 91 batteries and found up to 15% discrepancies under identical conditions....

Sorry I didn't explain that the SmartGauge doesn't tell you the capacity only the % State of Charge. You don't need to tell it the Ah size of your bank - only what type it is. All battery monitors only tell you the capacity gained or lost as the batteries charge of discharge. The actual capacity is not important only the SoC.

Your link to Cadex proves that electrickery is really all "Fuzzy Logic". Their 91 batteries tests were for capacity measurements not Soc. My 0.1% inaccuracy is purely related to measuring SoC not Capacity. I agree that this is surely an un-measurable value, which is why I didn't quote it in my earlier post.

 

[ghostlymoron]

Nothing I've read on this thread so far has convinced me of the value of any device telling me how long I have till the lights go out. Ammeter and voltmeter are useful but anything else is speculation and changes with the deterioration of any battery (it seems to me).

 

[AngusMcDoon]

My 0.1% inaccuracy is purely related to measuring SoC not Capacity. I agree that this is surely an un-measurable value, which is why I didn't quote it in my earlier post.

... and is complete unmitigated baloney if you or anyone else is claiming that accuracy, and I don't care who told you, it's codswallop.

I've stayed out of this thread so far because I know how defensive of your SmartGuage you are, but I can't let a claim like that pass.

When I was working at Alstom a few years back there was a research project ongoing by colleagues in my team on estimating state of charge of lead acid batteries because they are used in remote sub-stations when the line power is down and cause continual problems. Many types of battery monitoring systems were investigated, including current shunt types, specific gravity measurements, and a voltage only one that claimed whizzy unpublished algorithms in their software, all across a wide variety of temperatures (sub-stations are installed from tundra to hot deserts). This was an exhaustive long term project using a wide variety of batteries of different ages and in different simulated environments. The batteries were on long term test and then tested for real capacity by driving a real load. None of them had repeatable results within even 10%. So 0.1% - marketing drone's dreams only.

 

[sailinglegend420]

... and is complete unmitigated baloney if you or anyone else is claiming that accuracy, and I don't care who told you, it's codswallop.......

OK - my mistake for quoting it.

Let me give a bit more background to SmartGauge. The figure that came from Enersys of an accuracy to 0.1% was given to me personally by the MD of Merlin Equipment who bought SmartGauge and is now developing it for high end use in US and UK military applications. They have now opened US offices and Gibbo, who invented SmartGauge, is locked in a room and not allowed out anymore - but he's the kind of geek who will enjoy that.

The MD, James Hortop, told me that he never believed SmartGauge could work - until he did extensive tests. The reason you haven't seen it marketed heavily is that Merlin have given up on the yachting market to concentrate on other areas because they know it's just not worth the effort, especially with the kind of responses they were used to seeing on this kind of thread. James should be a familiar name because he used to be a Technical Editor on PBO magazine, and used to post on theses forums. He know's how difficult it is to change yachties deep-routed opinions of what's good and what's baloney.

It now appears that Balmar are now selling SmartGauge with a Balmar logo and they are now using the Enersys tests results, but they quote an accuracy to 0.3%, so they must be very confident the these results. Check out their website.

 

[AngusMcDoon]

The figure that came from Enersys of an accuracy to 0.1% was given to me personally by the MD of Merlin Equipment ...

As I said, I don't care who told you. Let me give you a bit more background from my career in engineering - the claims are electronic homeopathy. Just because it's on a fancy website with logos doesn't make it true.

Have you ever tried to get a 0.1% repeatable accuracy from multiple samples of analogue to digital converters and voltage references across a wide temperature, humidity and age range? Any device that can achieve that will require regular calibration at an approved test lab, and will cost a big wad in the first place. And that's just measuring a bog-standard voltage before all the variables, weird behaviour and unknowns of lead acid batteries come into it.

The reason why SmartGuage are on to a winner here is that they can claim these values obtained by their secret whizzy algorithms, but no-one can disprove them because battery state of charge is such a slippery ephemeral value.

A technical editor of a magazine is a journalist, not an engineer. PBO articles in the past on electrics have shown a misunderstanding of Amps and Amp-hours, which says to me that they are not going to have the first clue about engineering concepts like this...

http://en.wikipedia.org/wiki/Accuracy_and_precision

 

[Amulet]

Which Peukert critics are you talking about - what problems do they have with Peukert's Exponent? It's a fact of battery life and difficult to measure, or sometimes even find the real value from your battery manufacturer. That's not a criticism.

The experiment you quote could do with a link! Beware of anything you read on the Web! As you know it is very difficult to measure the capacity remaining in a battery without very expensive equipment. If you did the experiment with a battery monitor and used it's Ah readings then that just proves my point that battery monitors can be very inaccurate, or not programmed properly.

I actually don't remember all the articles I scanned. I started with this one:
D. Doerffel, S.A. Sharkh, A critical review of using the Peukert equation for determining the remaining capacity of lead–acid and lithium-ion batteries, Journal of Power Sources, 155 (2006) 395–400
and then followed citations back and forward. I'll see if I can dig the other one up again for you. Since I was following journal citations not web links it probably wasn't too iffy, though the peer-reviewed literature isn't necessarily that much better than the web. I used to run a scientific web site with 7 million hits a day, so I have an unfortunate relationship with web rot - probably was responsible for some of it!
Having become aware of the depth of my ignorance, I'm trying to find a web version of the original Peukert article:
W. Peukert, Über die Abhängigkeit der Kapazität von der Entladestromstärke bei Bleiakkumulatoren, Elektrotechnische Zeitschrift 20 (1897)
If anyone can find it I'd love to see it.

The basic point is that, in its way, the Peukert Vergliechung tells you that you cannot predict remaining capacity because it tells you that capacity depends on load. So, without knowing what the load is going to be you are just in the business of estimating. My reading of the literature is that one way of estimating is based on averaging the recent load over some period and assuming it will stay steady. Apparently users have found this disconcerting because, following a drop from a high load to a small load, a monitor can up it's estimate of % remaining even though there has been no charge.

However, all this is from reading literature, not practical experience, apart from my very limited stuffing boat data into a Peukert spreadsheet, so I'm willing to believe that it works well in the hands of real users like yourself.

 

[sailinglegend420]

....Have you ever tried to get a 0.1% repeatable accuracy from multiple samples of analogue to digital converters and voltage references across a wide temperature, humidity and age range? ....

I totally agree with you about the SmartGauge accuracy claims - I am only passing on the info, so please don't shoot the messenger.

This is where you show your ignorance. James Hortop is one of the most respected Electrical Engineers in the marine and land based electrical management industry. His wife Vicky is also an engineer, so if you were to phone Merlin with a technical question and she answers don't ask to speak to an Engineer.

 

[sailinglegend420]

...The basic point is that, in its way, the Peukert Vergliechung tells you that you cannot predict remaining capacity because it tells you that capacity depends on load. So, without knowing what the load is going to be you are just in the business of estimating. ....

I'd never thought of Peukert's exponent as a way of predicting remaining capacity, but I suppose it could. The way it's used in a battery monitor is to measure the Ah capacity removed or input and deduct that value from the known Ah capacity of the battery. The trouble is the "known" capacity reduces over time which is one of the reasons why SmartGauge consistently produces more accurate results.

 

[GHA]

The trouble is the "known" capacity reduces over time which is one of the reasons why SmartGauge consistently produces more accurate results.

Which seems like a problem for the Smartgauge, even if it does give accurate results you don't know what they are. Not a lot of use knowing the cup is 60% full when you don't know what size the cup is.
For a cruising boat it looks like it would be not that much use long term on it's own. Maybe handy with a battery meter as well if you have money to spare and don't mind wiring more kit.

 

[ghostlymoron]

Which seems like a problem for the Smartgauge, even if it does give accurate results you don't know what they are. Not a lot of use knowing the cup is 60% full when you don't know what size the cup is.

I like your analogy. I'm definitely going off the idea of battery monitors even more.

 

[sailinglegend420]

Not a lot of use knowing the cup is 60% full when you don't know what size the cup is......

It doesn't matter what size the cup is, what you want to know is when you must charge your batteries as they should never get below 50% State of Charge or their life cycle will be reduced.

If you want to keep a watch on your batteries then all you need is a digital current meter for about £40 and a digital voltmeter for about £5. Use some brain cells and you can get an idea of when you need to charge your batteries.

It would seem you and ghostlymoron don't really understand why this is important. If you don't spend much time cruising away from shorepower then none of this really matters - I'm going back to the Liveaboard Forum.