More battery talk

lw395 said:
.....I think if it matters whether my battery is 95 or 98% charged after 10 hours, then I probably need a bigger battery or a good look at the loads....
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95% is considered a cruising charge that most people can get to quite easily, but every two weeks, or less if possible, they should do all they can to get back to 100%. The best way is an overnight shore power charger.

So why is that last 5% is so important?

As part of the chemical process of batteries discharging Lead Sulphate crystals build up on the plates. As batteries charge the reverse happens and the Lead Sulphate Crystals turn back to Lead Oxide and Sulphuric Acid. Temporary sulfation remains on parts of the plates when the battery is not fully charged and these Lead Sulphate Crystals will harden and become permanent sulfation. After 3-4 weeks even high voltages from Equalisation cannot remove these crystals and restore Ah capacity, so the batteries eventually die.

Sulfation is the biggest killer of batteries.
 
lw395 said:
At the end of the day, what do we actually want from our chargers?
My view is that I want it to get my battery to a high state of charge reasonably quickly.
But I also want it to give the battery a long useful life.!
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Ask not what what our batteries can do for us but what we can do for our batteries.. :)

Which for me is long life, how fast they charge isn't that big a deal so long as they do get to full charge as often as possible. Anyway, over 80%ish SoC the charge rate tails off so rapidly is doesn't matter I you have a large power station attached, the battery doesn't care and will just let the last bit trickle in ever slower as it gets towards full.
Which in the real world means trying not to go much below 80% SoC and keep the solar panels clean and pointing roughly to right way - then they can usually keep up.

Measured (before Mr legend starts banging again about how solar can't charge fully) by low current going in with high volts backed up by SG readings. Also, no float, solar regulator set to 14.8v. I strongly suspect an hour or 2 longer at absorption with a tiny loss of electrolyte is actually much healthier long term than the real risk of not getting fully charged by dropping down to float early. And an hour or so from a Honda genny on the mains charger in the winter when solar struggled.
There was what sounded like a major study done a number of years ago now sadly offline looking at off the grid best charging practices, from memory of occasional quotes on US off gridders it found it better to charge high, 15v, to get best life from batts where getting back full was not always happening every day.
Also, I reckon one of the best diagnostic aids y9u can get is a fiver on an eBay voltmeter connected straight to the terminals and visible from your favorite lounging place down below :cool:
 
GHA said:
Ask not what what our batteries can do for us but what we can do for our batteries.. :)

Which for me is long life, how fast they charge isn't that big a deal so long as they do get to full charge as often as possible. Anyway, over 80%ish SoC the charge rate tails off so rapidly is doesn't matter I you have a large power station attached, the battery doesn't care and will just let the last bit trickle in ever slower as it gets towards full.
Which in the real world means trying not to go much below 80% SoC and keep the solar panels clean and pointing roughly to right way - then they can usually keep up.

Measured (before Mr legend starts banging again about how solar can't charge fully) by low current going in with high volts backed up by SG readings. Also, no float, solar regulator set to 14.8v. I strongly suspect an hour or 2 longer at absorption with a tiny loss of electrolyte is actually much healthier long term than the real risk of not getting fully charged by dropping down to float early. And an hour or so from a Honda genny on the mains charger in the winter when solar struggled.
There was what sounded like a major study done a number of years ago now sadly offline looking at off the grid best charging practices, from memory of occasional quotes on US off gridders it found it better to charge high, 15v, to get best life from batts where getting back full was not always happening every day.
Also, I reckon one of the best diagnostic aids y9u can get is a fiver on an eBay voltmeter connected straight to the terminals and visible from your favorite lounging place down below :cool:
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My sterling ultra pro charges my 24v domestic bank to 29.4v ( so 14.7v on 12v batteries) before it goes into absorbtion mode. This seems higher than lots of people have quoted as the switching voltage for their chargers but we are on open cell batteries if that makes a difference. Even with this high voltage we dont gas excessively
 
If you're trying to fully charge before the sun goes in, then that's an additional constraint.
You can pump more charge in by raising the volts, but at a price of raising temperature and losing electrolyte.
Losing electrolyte is not such a big deal with open cell batteries.
But it's what kills a lot of sealed batteries.

Some of those off-grid people have interesting, controversial views. Some firmly believe that charging with clean steady DC is wrong.
But then, they have different priorities to what I need from a yacht or motorbike battery, or what people in industry want from a UPS or battery backup system.
People designing yacht chargers are to some extent guessing about how the system is going to be used. People use their boats quite differently and one charger is not optimum for everyone.
Dead right about voltmeters.
 
GHA said:
Measured (before Mr legend starts banging again about how solar can't charge fully)
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I arrived at the boat at 2000, been out all day. With no load, my domestic bank is showing 13.01 volts.

I'm calling that nicely charged, by nothing but solar. In fact, as i said earlier, my mains charger hasn't been on for two months and i've been onboard all of that time.
 
PaulRainbow said:
I arrived at the boat at 2000, been out all day. With no load, my domestic bank is showing 13.01 volts.

I'm calling that nicely charged, by nothing but solar. In fact, as i said earlier, my mains charger hasn't been on for two months and i've been onboard all of that time.
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Well......, I'm a bit wary of volts alone over a few hours to judge SoC with the trojan t105's as I've seen just how long they can hold the voltage high after a lump of charge even with the laptop on when I know they ain't got all the way up there ...

To regroup thoughts here a little... - determining SoC ain't easy, SG seems to be the best there is and even that is hardly precise peering at a little float and trying to remember which way the temp corrections go... So I would suspect a lot of us are seeing SoC rather more optimistically than it might be in reality. :)
 
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PaulRainbow said:
I arrived at the boat at 2000, been out all day. With no load, my domestic bank is showing 13.01 volts.

I'm calling that nicely charged, by nothing but solar. In fact, as i said earlier, my mains charger hasn't been on for two months and i've been onboard all of that time.
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This is the bit where I can get confused !
the 13.1v your reading , is that reading 13.1v because the solar is keeping up the volts i.e. If you blank off your panel would it stay at 13.1 or would it suddenly drop to say 12.8 v
Mine stays at around the same volts as yours white the sun out ,
but once it goes in down she goes the volts to around 12.7 after a while ,admit the fridge is still working and by then lights are being turned on .
 
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sailaboutvic said:
This is the bit where I can get confused !
the 13.1v your reading , is that reading 13.1v because the solar is keeping up the volts i.e. If you blank off your panel would it stay at 13.1 or would it suddenly drop to say 12.8 v
Mine stays at around the same volts as yours white the sun out ,
but once it goes in down she goes the volts to around 12.7 after a while ,admit the fridge is still working and by then lights are being turned on .
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I got in at 2000, the solar controller was off. The fridge had been on all day but was off at the time, so no loads at all. If the panels had still been charging id have expected a higher voltage. I'm not sure how long the controller had been off and i doubt the batteries would have stayed at that voltage for too many hours, if left standing.

I was up just after 0600 this morning, just before the solar controller started charging. With no load the batteries were at 12.4 volts. My night time load is very light.
 
sailaboutvic said:
This is the bit where I can get confused !
the 13.1v your reading , is that reading 13.1v because the solar is keeping up the volts i.e. If you blank off your panel would it stay at 13.1 or would it suddenly drop to say 12.8 v
Mine stays at around the same volts as yours white the sun out ,
but once it goes in down she goes the volts to around 12.7 after a while ,admit the fridge is still working and by then lights are being turned on .
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Hi Vic

I think what Paul is saying is that batteries continue to show a higher voltage than they are theoretically capable of producing for some time after a charging voltage has been removed, which is why you can only assess the level of charge accurately once the battery has been "rested" for at least 12 hours with no inputs or outputs.

I think (I might be wrong on this though) that even a battery which is not fully charged will show an artificially high voltage if tested as soon as charging is removed, although in this case the artificially high voltage will drop down to the actual voltage (clearly below 12.8V) more quickly.

Similarly, if the battery is actually connected to something which is drawing a current, the drop down to the "actual" voltage will be much quicker in the case of the both the fully or the partly charged battery, once the charging source is removed. In this case the further complication, depending upon the current being drawn, is that the voltage will actually overshoot below the "real" voltage and show an even lower voltage than 12.8V (fully charged) or 12.?V for the partly charged version.

The only way to accurately establish the actual voltage is, as before, to disconnect the drain current and allow some "resting" time before taking a reading.

As Paul's solar panels can fully charge the batteries and satisfy the drain requirements at the same time, when the sun goes down his voltage will be above 12.8V although it will soon drop, depending on the load current, to a level below the actual maximum voltage which would only be seen if the batteries could be "rested" after sunset.

Richard
 
RichardS said:
I think (I might be wrong on this though) that even a battery which is not fully charged will show an artificially high voltage if tested as soon as charging is removed, although in this case the artificially high voltage will drop down to the actual voltage (clearly below 12.8V) more quickly.
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I think you're right. All we're talking about here is 'surface charge'. as I understand it lead batts are clunky old beasts which cannot snappily convert free lead sulfate to lead and other compounds. As a consequence the charging activity is initially concentrated on the plate surfaces, which in turn results in what is known as surface charge on the plates' outside layer. A small load for a few mins shld clear most of this after which one can better measure the true state of charge.
 
dom said:
. A small load for a few mins shld clear most of this after which one can better measure the true state of charge.
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Looks unlikely to be practical in the real world.... So in addition to a charger going in to float we can add using voltage to ascertain battery SoC for a lot of us, unless you can let your batt do nothing for 24h... Or much longer when it's cold..

http://www.pbase.com/mainecruising/battery_state_of_charge



EDIT 2/13/11: As an update I have since applied many different loads to remove the surface charges or about 6 or seven different batteries, ages and types.. 5 amps, 10 amps 20 amps etc. etc., and all for varying times.


The problem is that none of the surface charge removing loads give me an accurate reading that agrees & matches up with a 24+ hour rest. I suppose you could do some rather lengthy experiments and find the exact load to remove a surface charge, that works for your bank, at a certain state of charge, but this would be complicated at best. The closest I got was within 8-10%. A 10% variance on a 400 Ah bank is 40 Ah's or nearly a days worth of power for us. Having & interpreting my bank, reading the equivalent a whole day off, can be and would be rather frustrating.


TEMPERATURE: I have also experimented at length with resting voltages and temperature. At 95F a battery can come to rest in as little as 12 hours. When cold during the winter this can take 10+ days!! Temperature plays a huge role in when you will achieve a "resting" voltage.

​


​
 
GHA said:
Looks unlikely to be practical in the real world.... So in addition to a charger going in to float we can add using voltage to ascertain battery SoC for a lot of us, unless you can let your batt do nothing for 24h... Or much longer when it's cold..

http://www.pbase.com/mainecruising/battery_state_of_charge
Click to expand...


Very interesting -- especially at low temps lead acid batteries truly are slow, imprecise old beasts !!
 
GHA said:
Looks unlikely to be practical in the real world.... So in addition to a charger going in to float we can add using voltage to ascertain battery SoC for a lot of us, unless you can let your batt do nothing for 24h... Or much longer when it's cold..

http://www.pbase.com/mainecruising/battery_state_of_charge



EDIT 2/13/11: As an update I have since applied many different loads to remove the surface charges or about 6 or seven different batteries, ages and types.. 5 amps, 10 amps 20 amps etc. etc., and all for varying times.


The problem is that none of the surface charge removing loads give me an accurate reading that agrees & matches up with a 24+ hour rest. I suppose you could do some rather lengthy experiments and find the exact load to remove a surface charge, that works for your bank, at a certain state of charge, but this would be complicated at best. The closest I got was within 8-10%. A 10% variance on a 400 Ah bank is 40 Ah's or nearly a days worth of power for us. Having & interpreting my bank, reading the equivalent a whole day off, can be and would be rather frustrating.


TEMPERATURE: I have also experimented at length with resting voltages and temperature. At 95F a battery can come to rest in as little as 12 hours. When cold during the winter this can take 10+ days!! Temperature plays a huge role in when you will achieve a "resting" voltage.

​


​
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That's all fine in theory, but for our purposes what do we really want to know?
If you are trying to make decisions based on whether our battery is 80% or 70% charged, then you need some way of repeatably indicating this.
It does not have to be accurate, just repeatable.
E.g. if the real question is 'can I run my fridge overnight without plugging in?', then you need an indication good enough to tell you that.
A voltage and a bit of knowledge of what the battery has been doing for the previous day, together with a bit of history of monitoring voltage with typical loads, will enable the decision.

A battery charger is trying to evaluate the state of charge in terms of the question 'is it beneficial to keep charging?'

The % charge under some arbitrary lab conditions is all very interesting, but the lab conditions are out of the window on a boat.
 
PaulRainbow said:
I got in at 2000, the solar controller was off. The fridge had been on all day but was off at the time, so no loads at all. If the panels had still been charging id have expected a higher voltage. I'm not sure how long the controller had been off and i doubt the batteries would have stayed at that voltage for too many hours, if left standing.

I was up just after 0600 this morning, just before the solar controller started charging. With no load the batteries were at 12.4 volts. My night time load is very light.
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Just curious, Paul, what do you reckon your daily usage is in amps ? You seem to be living aboard but not a liveaboard as in cruising - yes ?
 
Wouldnt a good indication of how well you are charging the batteries be the voltage in the morning? Over night there will just be the fridge running and a few LED lights for most people so before the sun comes up the resting voltage less a bit for the fridge would give you a pretty good idea of where you are at. We regularly see a morning voltage of 25.4v on our 24v battery bank so equivelent to 12.7v. I have checked this voltage on the digital panel meters with a seperate volt meter and it is the same so pretty sure thats our morning voltage. It rarley changes.
If you had a very low morning voltage you would either have a battery problem or insufficiently charged batteries from the night before or insufficient battery capacity ( that means you are cycling the batteries hard so not far away from a future battery problem). So for the sake of arguement, a battery voltage of less than 12.3v would suggest cycling to about 50% or one of the others above. Does that make sense?
 
RobbieW said:
Just curious, Paul, what do you reckon your daily usage is in amps ? You seem to be living aboard but not a liveaboard as in cruising - yes ?
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The battery monitor isn't helpful with daily ah figures, it gives lowest and total, but no average and doesn't say how many days the total is for. But, it looks to be something like 25ah. During the night the only thing that is on is the fridge. At the moment the Eber comes on for a couple of hours around the time the alarm goes off, it's also on in the evening for a short time. Lights are all LED, water is electrically pumped, FM radio on most of the time i'm onboard. The laptop is currently charged via mains, as the previous solar panels couldn't keep up, but this will be changed to 12v in the next few days.
 
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