More battery talk

[RichardS]

That is maybe what you observe on your boat - but you have Lifeline AGMs - so when the charge settles at 12.8v that is too low as a full resting voltage for Lifelines is 12.9v to 13v - very clearly your batteries are not fully charged.

The reason that batteries need to sit at 14.4v is because it takes time for the charge to diffuse to the deeper parts of the plates. You see this on discharge as well. With a high current load the battery volts might go down to 12.2. but take off the heavy load and the voltage will immediately rise to 12.3 or more. Let the batteries rest for two hours - with no charging - and the voltage may rise to 12.5v

Not the Lifelines on the boat but the standard car batteries in my garage which are fully charged at 12.8V - 12.9V i.e. around 12.8V

The depression of voltage after use is a very well-known feature of lead acid batteries and irrelevant to the fact that the batteries are fully charged if they read this voltage after resting for 24 hours.

Richard

 

[sailinglegend420]

A decent smart charger or solar controller doesn't simply work on a timer. It will have a more complex algorithm whereby it will monitor the voltage and amperage that the battery is accepting. If the voltage is at a given level and the amps have fallen to a predetermined level it will consider that the voltage can be dropped to float level.....

Even Smart chargers don't monitor amperage that the battery is accepting.

I believe you have a Victron charger so maybe you should read what they say:

The End of the Absorption Step
"The absorption step should continue until current through the battery declines to about 2% of battery capacity in Amp–hours. Without knowing what the current is through the battery, you can’t know when it’s full. Just because that fancy charger, (or inverter/charger), has kicked out to float is no sign that the battery is full. . . there is no charger on the market that measures battery current!"

My Victron counts the time to reach absorption voltage and then stays in Absorption for 5 times that duration. So if it takes 1 hour to reach 14.4v it will stay in absorption for 5 hours. If the batteries are fairly well charged they will get to 14.4v quicker, so if it takes 10 minutes to get to 14.4v it will stay in Absorption for 50 minutes before dropping to Float . A battery is fully charged when the current going into the battery is 0.5% of the Ah capacity - at 14.4v - but the charger again will never see this current, and you can't monitor it because the charger will have dropped to Float voltage before that.

 

[sailinglegend420]

Not the Lifelines on the boat but the standard car batteries in my garage which are fully charged at 12.8V - 12.9V i.e. around 12.8V

You can't make generalisations about batteries on a boating Forum by saying at 14.4v they are fully charged and then say - oh no I meant my car batteries.

There's a huge difference in the construction of Deep Cycle and Starter batteries. A starter battery maybe very nearly fully charged when it reaches 14.4v because it has had a very low Ah discharge, maybe less than 1% of its Ah capacity, and the plates are very thin so there is no diffusion problem. A deep cycle battery has much thicker plates and it may discharge up to 50% which is why it needs to stay at 14.4v to fully charge.

 

[RichardS]

Not my experience!
If you leave a battery at 14.0V (or even a bit less) for a long time, it will slowly gas until it is dry.
That's why chargers back off to a lower float voltage.

I'm not sure why you're focussing on a trivial point which I have already covered.

It may well be the case that in some conditions a battery left on charge at 14V will gas slightly ..... but it will take months or years to go dry depending on its size.

We all understand that smart chargers back off to a lower float voltage to avoid over-gassing but I've never owned one that backed off at 14V.

Richard

 

[PaulRainbow]

Even Smart chargers don't monitor amperage that the battery is accepting.

Some do, as do some solar controllers.

I believe you have a Victron charger so maybe you should read what they say:

My charger is a Sterling ProCharge Ultra.

there is no charger on the market that measures battery current!

My solar controller manual states "Additionally, the absorption period is also ended when the charge current decreases to less than 1A."

I can't see why a charger or solar controller cannot see the current that's going into the battery, my solar controller monitor shows amps out, my mains charger does too. My battery monitor shows net amps.

However, i still think a resting voltage of 12.8v qualifies as a fully charged battery.

 

[PaulRainbow]

There's a huge difference in the construction of Deep Cycle and Starter batteries.

Like many (most ?) people on this forum, i don't own any deep cycle batteries.

 

[RichardS]

You can't make generalisations about batteries on a boating Forum by saying at 14.4v they are fully charged and then say - oh no I meant my car batteries.

There's a huge difference in the construction of Deep Cycle and Starter batteries. A starter battery maybe very nearly fully charged when it reaches 14.4v because it has had a very low Ah discharge, maybe less than 1% of its Ah capacity, and the plates are very thin so there is no diffusion problem. A deep cycle battery has much thicker plates and it may discharge up to 50% which is why it needs to stay at 14.4v to fully charge.

I've no idea what you're talking about. Even if your boat doesn't have any conventional high CCA starter batteries, many of us do.

Please start reading the thread again from the beginning and then advise me where it says that we are talking about any specific type of lead-acid battery.

Richard

 

[sailinglegend420]

....I can't see why a charger or solar controller cannot see the current that's going into the battery, my solar controller monitor shows amps out, my mains charger does too. My battery monitor shows net amps....

Your charger may show 10 amps going out - 9 amps could be going into boat loads and the battery could be full and should be dropped to Float. Yes if 1 amp is going out then the battery is probable full - assuming your solar is not in shade and only able to deliver 1 amp.

For all chargers to do their job properly then each would have to have their own shunt to measure the current going into the battery - there isn't a common interface that fits all - unfortunately. If you have shore power and wind and solar then they all need to know what is actually going in to the battery.

 

[sailinglegend420]

I've no idea what you're talking about....

That is very obvious!!!!!

 

[RichardS]

That is very obvious!!!!!

Oh dear SL420 ..... your insecurities are really showing now.

Richard

 

[PaulRainbow]

Your charger may show 10 amps going out - 9 amps could be going into boat loads and the battery could be full and should be dropped to Float.

My controller will vary it's output instantly. If the battery is taking 2 amps and a 2 amp load is turned on the controller outputs 4 amps. It is therefore still putting the same charge into the battery whilst simultaneously running the load, thus not depleting the batteries.

Yes if 1 amp is going out then the battery is probable full - assuming your solar is not in shade and only able to deliver 1 amp.

Don't forget though, according to you "there is no charger on the market that measures battery current!"

For all chargers to do their job properly then each would have to have their own shunt to measure the current going into the battery - there isn't a common interface that fits all - unfortunately.

How will that work ? The shunt could read amps going through it, but it won't know if those amps were used by system loads or if they went to the battery, same as now.

If you have shore power and wind and solar then they all need to know what is actually going in to the battery.

Absolutely and i can't see an easy way for that to happen. Not sure how wind and solar together would work, i don't have a wind gen'. I do know that if i switch the mains charger on the solar controller sees the voltage from the charger and shuts down. So i don't have the mains charger on. My battery monitor has an inbuilt, configurable relay. This is connected to a relay in the consumer unit that has a 12v coil and switches the mains charger on if the voltage of the domestic batteries falls below a pre-set figure. This has only recently been added and has yet to switch in anger.

 

[Uricanejack]

Like many (most ?) people on this forum, i don't own any deep cycle batteries.

Mine are sold as Marine/RV. Deep cycle. Reading up on batteries. Although sold as "deep cycle" The Marine/RV is the giveaway.They are not true deep cycle batteries. They are dual use batteries.

 

[PaulRainbow]

Mine are sold as Marine/RV. Deep cycle. Reading up on batteries. Although sold as "deep cycle" The Marine/RV is the giveaway.They are not true deep cycle batteries. They are dual use batteries.

To all intensive purposes they are starter batteries. They may have slightly thicker plates and would hopefully have better plate support, but they are still starter batteries. My domestic bank has three of these, the engine battery is a heavy duty car starter battery.

 

[lw395]

Even Smart chargers don't monitor amperage that the battery is accepting.

I believe you have a Victron charger so maybe you should read what they say:

The End of the Absorption Step
"The absorption step should continue until current through the battery declines to about 2% of battery capacity in Amp–hours. Without knowing what the current is through the battery, you can’t know when it’s full. Just because that fancy charger, (or inverter/charger), has kicked out to float is no sign that the battery is full. . . there is no charger on the market that measures battery current!"

My Victron counts the time to reach absorption voltage and then stays in Absorption for 5 times that duration. So if it takes 1 hour to reach 14.4v it will stay in absorption for 5 hours. If the batteries are fairly well charged they will get to 14.4v quicker, so if it takes 10 minutes to get to 14.4v it will stay in Absorption for 50 minutes before dropping to Float . A battery is fully charged when the current going into the battery is 0.5% of the Ah capacity - at 14.4v - but the charger again will never see this current, and you can't monitor it because the charger will have dropped to Float voltage before that.

I can't speak for the run of the mill marine market products, but there are plenty of battery chargers that monitor battery current and use it to decide when to switch down to float voltage.
Using timers an so on is fraught with problems if charging is interrupted or loads are drawn from the battery.

Obviously when picking a switch-point current, it helps to know the battery capacity and likely leakage current.

 

[GHA]

Obviously when picking a switch-point current, it helps to know the battery capacity..........

Helps? Isn't it essential, otherwise you're expecting the charger to know when to stop filling the bucket but not telling it what size the bucket is?

Anyway, backing up a little - I think it's fair to say for almost everyone that a charger switching to float is not a reliable indicator of a battery (bank) being at full charge.


In an email from their tech dept trojan said "The finishing rate for a fully charged battery is 1-3% of the total capacity of the battery bank"
And in answer to "Is 6 hours at absorption too long.."

"To verify if 6 hours is too long, take a SG reading at hour 4, 5, and 6 to see where the state of charge is (full charge at 1.277)."

Though suspect they are covering their back sides a bit there, guessing a solar setup staying at absorption rather than switching to float too soon would be better for a batt in the long run even if it means the voltage being high for an hour or 2 after the battery is charged. (Which takes hours from hitting the absorption voltage anyway).

 

[sailinglegend420]

I can't speak for the run of the mill marine market products, but there are plenty of battery chargers that monitor battery current and use it to decide when to switch down to float voltage...

Plenty of chargers use the current and voltage to decide when to drop to Float, but they are not measuring all the battery in/out current with a shunt at the battery terminal. This is the only way to determine the current actually charging the battery.

Expensive Outback Solar chargers have the option of adding a return amps shunt to do this, and the Superyacht Mastervolt MasterBus system has this option, but only works on its brand of chargers so won't monitor and control a Wind regulator or an Alternator.

There is no universal system that will do this at the moment - unless someone else on this forum has specific product details.

 

[lw395]

Helps? Isn't it essential, otherwise you're expecting the charger to know when to stop filling the bucket but not telling it what size the bucket is?

Anyway, backing up a little - I think it's fair to say for almost everyone that a charger switching to float is not a reliable indicator of a battery (bank) being at full charge.


In an email from their tech dept trojan said "The finishing rate for a fully charged battery is 1-3% of the total capacity of the battery bank"
And in answer to "Is 6 hours at absorption too long.."

"To verify if 6 hours is too long, take a SG reading at hour 4, 5, and 6 to see where the state of charge is (full charge at 1.277)."

Though suspect they are covering their back sides a bit there, guessing a solar setup staying at absorption rather than switching to float too soon would be better for a batt in the long run even if it means the voltage being high for an hour or 2 after the battery is charged. (Which takes hours from hitting the absorption voltage anyway).

In practice, it tends to make less difference than you might expect, because the current drops off exponentially.
I saw some worked examples where doubling the battery capacity resulted in switching to float at 95% charge instead of 97%.

Thing may get a bit shaky if you are trying to design for a really wide range of capacities, I think there are Ctek chargers which supposedly cope with 2 to 200Ah or something? But they have a more convoluted multi-step cycle.

 

[lw395]

Plenty of chargers use the current and voltage to decide when to drop to Float, but they are not measuring all the battery in/out current with a shunt at the battery terminal. This is the only way to determine the current actually charging the battery.

Expensive Outback Solar chargers have the option of adding a return amps shunt to do this, and the Superyacht Mastervolt MasterBus system has this option, but only works on its brand of chargers so won't monitor and control a Wind regulator or an Alternator.

There is no universal system that will do this at the moment - unless someone else on this forum has specific product details.

With typical loads on yacht systems, it's probably futile anyway. A yacht battery might be on charge for several hours, but for say 10% of that time be supplying an intermittent load like a fridge. This makes a mockery of the nice graphs published by the equipment makers.

 

[GHA]

In practice, it tends to make less difference than you might expect, because the current drops off exponentially.
I saw some worked examples where doubling the battery capacity resulted in switching to float at 95% charge instead of 97%.
.

Would also depend on SOC at the start of the charge cycle, I still say a charger going into float is far from a reliable indication of the batteries being fully charged for the majority, far too many variables.

Is it possible to even quantify if a chemical process in a battery of unknown health is 95% complete compared with 97% ? (Dunno, but suspect not).

 

[lw395]

Would also depend on SOC at the start of the charge cycle, I still say a charger going into float is far from a reliable indication of the batteries being fully charged for the majority, far too many variables.

Is it possible to even quantify if a chemical process in a battery of unknown health is 95% complete compared with 97% ? (Dunno, but suspect not).

I don't disagree.
The whole charging curve model is a simplification.
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.
That probably means a compromise between banging the last 5/2/1 % of charge in and going into float earlier to minimise loss of electrolyte.
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.

Practically, when my smart charger switches to float, the battery is not fully charged.
I know this, because I've watched the float charge current decrease over the following days or even weeks (in the case of a motorbike battery in winter!). I've never recorded the figures properly to know how many more Ah are going in. Over and above the permanent float current of course!