When our our batteries full? 4% at what voltage?

[Richard10002]

Just had a thought - there seems to be a concensus that our batteries are full when charging falls below a small percentage of the bank size. Some say 4%, some say 2%, some say 0.2%, (unless that's a typo?).

 

Whatever the percentage is, what voltage is that at?

 

e.g. I can set my charger at a whole variety of Absorbtion voltages from 14.0V to 15.5V. I usually use the 15.1V setting for open lead acid calcium batteries.

 

At 15.1V, when the charge falls to say 13A, (about 4% of my 330Ah bank), if I switch to the de-sulphate on mode of 15.5V, the charge increases to about 22A.

 

I presume if I charged at say, 14.4V, and the charge fell to 13A, if I increased the voltage to 15.1V, the charge would increase, etc..

 

So at what voltage are these "full" assumptions made., or on what does it depend?

[Chalky]

I would suggest that at 13A you're still charging. I usually recon that when I'm at 14.4V (from the alternator which regulates at 14.4V) and the current is down to 1 - 2 A then they're done. I have 400Ah of AGM - the maximum voltage from the data sheet is 14.8V otherwise they'll cook. If your voltage is too high then you'll boil the electrolyte off the batteries.

 

Ask Gibbo for a definitive.

Edited September 8, 2012 by Chalky

[RobinJ]

Just had a thought - there seems to be a concensus that our batteries are full when charging falls below a small percentage of the bank size. Some say 4%, some say 2%, some say 0.2%, (unless that's a typo?).

 

Whatever the percentage is, what voltage is that at?

 

e.g. I can set my charger at a whole variety of Absorbtion voltages from 14.0V to 15.5V. I usually use the 15.1V setting for open lead acid calcium batteries.

 

At 15.1V, when the charge falls to say 13A, (about 4% of my 330Ah bank), if I switch to the de-sulphate on mode of 15.5V, the charge increases to about 22A.

 

I presume if I charged at say, 14.4V, and the charge fell to 13A, if I increased the voltage to 15.1V, the charge would increase, etc..

 

So at what voltage are these "full" assumptions made., or on what does it depend?

Battery characterics are dynamic, so although you can apply rules of thumb, only by looking at the amount of charge over a period of time and at a particular voltage can you judge accuratley what % charge has been absorbed. This is why the smartgausge works so well!

Edited September 8, 2012 by RobinJ

[Richard10002]

 

Ask Gibbo for a definitive.

 

By posting here, I think that's what I'm doing as well as anyone else who cares to comment.

 

As you say, if it gets down to 1-2A then you're pretty much full.... The concomitant of which is that, at 13A, I'm still charging , but that wasn't really the question.

[smileypete]

Just had a thought - there seems to be a concensus that our batteries are full when charging falls below a small percentage of the bank size. Some say 4%, some say 2%, some say 0.2%, (unless that's a typo?).

 

Whatever the percentage is, what voltage is that at?

 

e.g. I can set my charger at a whole variety of Absorbtion voltages from 14.0V to 15.5V. I usually use the 15.1V setting for open lead acid calcium batteries.

 

At 15.1V, when the charge falls to say 13A, (about 4% of my 330Ah bank), if I switch to the de-sulphate on mode of 15.5V, the charge increases to about 22A.

 

I presume if I charged at say, 14.4V, and the charge fell to 13A, if I increased the voltage to 15.1V, the charge would increase, etc..

 

So at what voltage are these "full" assumptions made., or on what does it depend?

'Tis in The Battery FAQ:

 

'According to IEEE 450-2002 Annex B Recommended Practice, "The pattern of charging current delivered by a conventional voltage-regulated charger after a discharge is the most accurate method for determining state of charge. As the cells approach full charge, the battery voltage rises to approach the charger output voltage, and the charging current decreases. When the charging current has stabilized at the charging voltage, the battery is charged, even though specific gravities have not stabilized." It should be less than two percent of the capacity (C/50) at the manufacturer's recommended temperature compensated absorption charging voltage level of the battery.'

 

http://jgdarden.com/batteryfaq/carfaq9.htm#charged

 

http://www.batteryfaq.org/

 

Probably doesn't have to be super exact. But, more current at a higher voltage doesn't necessarily mean more charging, as the extra current could be going into heat and gassing.

 

cheers, Pete.

~smpt~

[bottle]

Simple answer your batteries are fully charged to there maximum capacity (not what it says on the label) when your three stage charger goes into 'float mode'.

 

If it is a bog standard car battery charger (not recommended) they are charged when the amp reading is at its lowest point, for a period of time and does not move any lower, about two % of battery bank size..

 

15.1v you are boiling your batteries unnecessarily, maximum should be 14.8v whilst in absorption, open lead acid.

 

Check with your battery manufacturer for their figures.

 

Edit: I see Pete has been here before.

Edited September 8, 2012 by bottle

[dmr]

I think you have pretty much hit a battery nail on the head here.

A battery might be fully charged when the current falls to a small amount at the normal charge voltage, but fully charged is a flexible concept.

If the battery is sulphated, or has cell imbalance, or stratification, then its fully charged capacity can be much less than its potential capacity, and using a higher charge voltage, otherwise known as equalisation, will return it to closer to its potential capacity.

This is exactly how batteries get sulphated because the charger goes into float when it thinks the battery looks like it is fully charged, rather than when it really is fully charged. Sadly messing about with acid and hydrometers is the only easy way to establish when a battery is fully charged.

 

.............Dave

[Gibbo]

It's not so much what level the charge current falls to, it's more when it stops changing. That's when they're really full.

 

Problem is, that takes ages (days) so a compromise has to be struck. Picking a certain charge current meets such a compromise in a reasonable way. As to the voltage, you'll get a lot of conflicting answers from people who haven't actually done any real world testing. The true answer is that it doesn't really matter...

 

(this part is to a first approximation)... It looks like increasing the voltage will increase the charge current, and this is indeed the case. But towards the end of the charge cycle it's only temporary. If you're charging at (say) 14.4 volts and getting (say) 5 amps charge current, increasing the voltage to (say) 15.5 volt will indeed increase the charge current, but only for a very short period of time. It will then reduce to whatever it would have been at 14.4 volts. Decreasing the voltage will see the charge current fall, but then it will start to increase back to what it would have been at 14.4 volts again.

 

Going past the first approximation is an effect that almost no one believes. And that is that increasing the charge voltage above the gassing voltage (which changes depending upon the state of charge) might show an increase in measured current, but it isn't charge current. It is merely breaking the electrolyte up into hydrogen and oxygen. That's simply wasting power. The gassing voltage for a fully charged battery varies depending upon battery type but it's around 13.6 volts typically. Charging above this voltage when fully charged will do no good whatsosver. You might measure more current, but it isn't charge current. And the part that people really refuse to believe is that increasing the voltage above the gassing voltage can actually reduce the measured current.

[smileypete]

By posting here, I think that's what I'm doing as well as anyone else who cares to comment.

 

As you say, if it gets down to 1-2A then you're pretty much full.... The concomitant of which is that, at 13A, I'm still charging , but that wasn't really the question.

What batts do you have by the way, open/flooded, sealed/maintenance free, AGM, semi traction monobloc, etc? Also do you have a shoreline, live aboard?

 

cheers, Pete.

~smpt~

Edited September 9, 2012 by smileypete

[Richard10002]

What batts do you have by the way, open/flooded, sealed/maintenance free, AGM, semi traction monobloc, etc? Also do you have a shoreline, live aboard?

 

cheers, Pete.

~smpt~

 

Open lead acid with a label that says calcium. The sterling charger has an option for exactly this type, which charges at 15.1V. The option for open lead acid without calcium is 14.8V.

 

I liked Gibbos answer.

[Keeping Up]

 

 

<snip>

 

(this part is to a first approximation)... It looks like increasing the voltage will increase the charge current, and this is indeed the case. But towards the end of the charge cycle it's only temporary. If you're charging at (say) 14.4 volts and getting (say) 5 amps charge current, increasing the voltage to (say) 15.5 volt will indeed increase the charge current, but only for a very short period of time. It will then reduce to whatever it would have been at 14.4 volts. Decreasing the voltage will see the charge current fall, but then it will start to increase back to what it would have been at 14.4 volts again.

 

<snip>

 

 

One of the reasons I like having moving-needle meters is that this pattern is easily visible at a glance, without having to do any mathematics in your head. It becomes particularly noticeable if you have something like an Adverc which makes step changes in the applied voltage, although the step is down from 14.4 instead of up as Gibbo describes here. I generally assume that if the increase or decrease in charge current lasts for less than a few seconds (combined with the current having already dropped to 2% of capacity) then they batteries must be as well charged as can be expected.

[Guest]

It's not so much what level the charge current falls to, it's more when it stops changing. That's when they're really full.

 

Problem is, that takes ages (days) so a compromise has to be struck. Picking a certain charge current meets such a compromise in a reasonable way. As to the voltage, you'll get a lot of conflicting answers from people who haven't actually done any real world testing. The true answer is that it doesn't really matter...

 

(this part is to a first approximation)... It looks like increasing the voltage will increase the charge current, and this is indeed the case. But towards the end of the charge cycle it's only temporary. If you're charging at (say) 14.4 volts and getting (say) 5 amps charge current, increasing the voltage to (say) 15.5 volt will indeed increase the charge current, but only for a very short period of time. It will then reduce to whatever it would have been at 14.4 volts. Decreasing the voltage will see the charge current fall, but then it will start to increase back to what it would have been at 14.4 volts again.

 

Going past the first approximation is an effect that almost no one believes. And that is that increasing the charge voltage above the gassing voltage (which changes depending upon the state of charge) might show an increase in measured current, but it isn't charge current. It is merely breaking the electrolyte up into hydrogen and oxygen. That's simply wasting power. The gassing voltage for a fully charged battery varies depending upon battery type but it's around 13.6 volts typically. Charging above this voltage when fully charged will do no good whatsosver. You might measure more current, but it isn't charge current. And the part that people really refuse to believe is that increasing the voltage above the gassing voltage can actually reduce the measured current.

A la battery boiler/external regulator on alternator?

Edited September 9, 2012 by Guest

[Keeping Up]

A la battery boiler/external regulator on alternator?

 

I don't believe that any of the commercially available controllers do this.

 

But there are people on this forum who have recommended the fitting of variable "tractor" regulators themselves, and doing precisely that.

[smileypete]

Open lead acid with a label that says calcium. The sterling charger has an option for exactly this type, which charges at 15.1V. The option for open lead acid without calcium is 14.8V.

 

I liked Gibbos answer.

I'd be a bit careful about 100% believing the Sterling manual. There's a table here in the Battery FAQ which is a good starting point, where the batt manufacturers recommendations cannot be found:

 

http://jgdarden.com/batteryfaq/carfaq9.htm#charging

 

If the batt gasses/loses water at 14.8V then it's probably a lead calcium hybrid rather than sealed/maintenance free.

 

Also depends whether charging off a genny or leaving batts unattended on a high power shoreline charger, it pays to be a lot more conservative with the latter.

 

cheers, Pete.

~smpt~

Edited September 9, 2012 by smileypete

[nb Innisfree]

When we used to cc we only did a bulk charge daily and used our Kipor genny on tickover to give an 8 hr absorption approx once a week via our Victron. Only had to leave Victron set to max absorption @ 14.4v (AGMs) We just needed to watch SoC to judge when to do our absorption.

[Richard10002]

I'd be a bit careful about 100% believing the Sterling manual. There's a table here in the Battery FAQ which is a good starting point, where the batt manufacturers recommendations cannot be found:

 

http://jgdarden.com/batteryfaq/carfaq9.htm#charging

 

If the batt gasses/loses water at 14.8V then it's probably a lead calcium hybrid rather than sealed/maintenance free.

 

Also depends whether charging off a genny or leaving batts unattended on a high power shoreline charger, it pays to be a lot more conservative with the latter.

 

cheers, Pete.

~smpt~

 

Conscious of what you say about Sterling, but I have lost almost no water since March when I bought them. I have checked them monthly so know exactly where I'm up to with water losses.. They're open lead acid, not maintenance free - not sure what the calcium means, but they seem to do fine at 15.1V. Having said that, I might try a while at 14.8V, and see how things change, if at all.

 

I use a genny with a high power shoreline charger, but never leave them unattended

[Gibbo]

Conscious of what you say about Sterling, but I have lost almost no water since March when I bought them. I have checked them monthly so know exactly where I'm up to with water losses.. They're open lead acid, not maintenance free - not sure what the calcium means, but they seem to do fine at 15.1V. Having said that, I might try a while at 14.8V, and see how things change, if at all.

 

Lead isn't very strong and tends to fall apart in batteries. Therefore they alloy it with another metal to make it stronger. Antimony is the original and most common. But it tends to substantially increase gassing over pure lead. Calcium is used for the same reason (physical strength) but has a much smaller impact on the increase of gassing.

[nb Innisfree]

Lead isn't very strong and tends to fall apart in batteries. Therefore they alloy it with another metal to make it stronger. Antimony is the original and most common. But it tends to substantially increase gassing over pure lead. Calcium is used for the same reason (physical strength) but has a much smaller impact on the increase of gassing.

 

Is this falling apart due to vibration and general g loading in vehicles and sea going boats? In which case it shouldnt be a prob on canal boats as batts have a smooth ride and no vibration when installed correctly?

[Gibbo]

Is this falling apart due to vibration and general g loading in vehicles and sea going boats? In which case it shouldnt be a prob on canal boats as batts have a smooth ride and no vibration when installed correctly?

 

No. It does it on a battery on test in a workshop that doesn't move at all.

[nb Innisfree]

No. It does it on a battery on test in a workshop that doesn't move at all.

 

Thanks

[Richard10002]

Lead isn't very strong and tends to fall apart in batteries. Therefore they alloy it with another metal to make it stronger. Antimony is the original and most common. But it tends to substantially increase gassing over pure lead. Calcium is used for the same reason (physical strength) but has a much smaller impact on the increase of gassing.

 

So Sterlings 15.1V option for calcium is not unreasonably high?

[Gibbo]

So Sterlings 15.1V option for calcium is not unreasonably high?

 

No. I've seen calciums with recommended (by the manufacturer) charge voltages of over 16 volts. The problem is that some "calcium" batteries are not full calcium and only have a small amount in there along with some antimony and tin. They gas more. Just keep your eyes on the electrolyte level.

 

That's not to say you should keep them at that charge voltage. That really is a charge voltage and it still needs to drop down to a lower float voltage to prevent internal corrosion.