Problem with Gel Battery Banks in C/Van

Submitted: Sunday, Jul 16, 2017 at 21:00
ThreadID: 135267 Views:1132 Replies:4 FollowUps:43
Until just recently I have had 2 x 6v -200ah SunGel Batteries (made year 2000) as one bank and 6 x 2v -250ah Sungel Batteries (made year 2002) as a second bank in my caravan. (15 years for the 2 volt is not a bad run, the 6 volt are 17 years old and still going well)
A master switch allows 1st bank only or 2nd bank only or both banks to be on or for both banks to be off.
Solar panels on the roof supply to which ever way I have the main switched.
There is also a 40 amp Xantrex on-board charger for when 240 v is available.
And a 50 amp dc-dc charger in the vehicle can be connected via Anderson plug to the c/van.

Now to the question. One of the 2 volt batteries has died of old age leaving only 5 siblings.
Buying one replacement 2 v the same size is not an option considering the age of the other five and the price.
What are the options for replacing that quantity of Amp/Hours?.
Is it ok to replace the whole 2 volt bank with a 250 a/h AGM deep cycle or 2 x 120 a/h thus making a mixture of AGM and Gel?
Would I then need to run the AGM independently and also charge it independently to the SunGels ?
Any info is appreciated

Scrubby.

I don`t know where i`m going but i`m enjoying the journey.

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Reply By: Battery Value - Monday, Jul 17, 2017 at 08:18

Monday, Jul 17, 2017 at 08:18
G'day Scrubby,

I don't know what the absorption/float settings are for your gels, but probably lower than that recommended for modern AGMs (14.4V to 14.8V, 13.8 to 13.9V).
Therefore I wouldn't charge them in parallel.
But there's a solution.
Solar charge one bank after another by utilising your battery selector switch.
Every time you switch from one bank to another you need to change the two charging set points Vabs/Vfloat.
There are solar regulators which come with an app and bluetooth connectivity to your smartphone which makes this a breeze.

You can discharge the two dissimilar banks in parallel (switch selection both) if you like but because of the higher voltage of the new AGM bank the gels won't do a lot of work in this position.

Cheers, Peter
AnswerID: 612556

Reply By: The Bantam - Monday, Jul 17, 2017 at 10:41

Monday, Jul 17, 2017 at 10:41
No matter what you replace the defunct bank with you should be charging them ( and probably discharging ) separately.

No matter what, you will have one bank of brand new batteries and one bank of flogged old batteries.

for any multi-stage charger to work effectivly it needs a direct relationship with one battery ( or bank of batteries). They will tolerate two very similar batteries or banks, but much of the advantage is lost.

The internal resistance, charge acceptance and pretty much every behaviour will be wildly different even if you replaced with exact same batteries but new.

In both charging, discharging and static the older battery, regardless of type will act like a millstone around the new battery's neck.

In a static state the old battery's self discharge and leakage which have got much worse with age will slowly suck the life out of the new battery ( sometimes not so slowly)

In charging the old battery will slow the charge rate of the new battery, the much increased charging losses of the old battery will predominate.

In discharge, the new battery will supply more of the load, possibly quite a lot more.
IF you connect two fully charge batteries, one having a higher voltage than the other ..... current will shunt from higher to lower ..... there can be large currents flow upon connection.

In some of the charging systems I have seen, there are series diodes in the discharge path to prevent current shunting and one battery discharging the other ..... but these diodes need to be big and I have never seen this in 12 volt systems.

This is probably because in a 50 volt system 0.6 of a volt is neither here not there, but in a 12 volt system 0.6 of a volt is significant.



I would not be pissing about changing charging profiles when you change banks, as long as the charge voltages and maximum charge currents are not above limits the batteries no matter what type will charge .... maybe not as fast as they might but they will charge.

As far as AGM ... "needing" any particular voltage ....... I am yet to see a manufacturer document that tells me that AGM won't charge from single stage 13.8 volt chargers.

AGM and other batteries may benefit from higher voltage charging profiles, but that does not make any particular charging profile necessary.

Many multistage chargers do not have seperate profiles for AGM and gell ..... some simply have two profiles, low and high ...... the low profile is for batteries that need something similar to screw top wet cell batteries and another, more aggressive profile with higher end points for AGM, sealed maintenence free and the like and charging batteries in cold conditions.

AND THEN we get into generalisations ...... this idea of a preset charging profile for AGM and another for gell ...... realy does not account for the wide variety of manufacturer specs ..... we need to be looking at actual manufacturer specs and not some sweeeping generalisation.

The difference between AGM and gell is not as clear as it once was ..... some gell charge and perform very similar to AGM and some AGM have gelled or partly gelled electrolite.
Some specific types of what is sold as AGM, will tolerate very high charge voltages, others won't.

when looking at batteries we need to look at the specifics of the battery and what the actual differences are in the charging profiles .... and if that matters at all.

cheers
AnswerID: 612561

Follow Up By: Battery Value - Monday, Jul 17, 2017 at 11:52

Monday, Jul 17, 2017 at 11:52
Bantam,

...As far as AGM ... "needing" any particular voltage ....... I am yet to see a manufacturer document that tells me that AGM won't charge from single stage 13.8 volt chargers....

Some charging 101 for you:
Charging a medium or high SG AGM battery (particularly Chinese sourced brands) and to a lesser extent gel to only 13.8V is a recipe for short battery life.
The gas recombination will leave no over-potential for the negative electrode which sulphates up as they're being starved of charge @ 13.8V.
13.8V should only be applied after the battery has received a full charge.

It's best to follow the manufacturer's advice which is charging to absorption setpoint of 14.4V to 14.8V until the rate decreases to about 0.015C.
Only at this elevated level, both pos/neg half cells can absorb their maximum individual charge.
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Follow Up By: The Bantam - Monday, Jul 17, 2017 at 12:07

Monday, Jul 17, 2017 at 12:07
On thematter of what to replace with ..... individual 2 volt cells will be easier to handle, your housing will be set up for them and individual 2olt cells with get you into a better class of battery.

As for exactly what ... well that depenmds on whay you can access and what deal you can get

cheers
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Follow Up By: The Bantam - Monday, Jul 17, 2017 at 16:18

Monday, Jul 17, 2017 at 16:18
Battery value

how about a bit of comprehension 101.

did I not post

"AGM and other batteries may benefit from higher voltage charging profiles, but that does not make any particular charging profile necessary.





Most sealed batteries with be happy at a constant voltage charge of 14.4 volts indefinitely as long as temperature and charge current do not rise above spec.

That said, to this day most alarm panels and other simple stationary battery back up systems run a 13.8 volts (voltage regulated current limited) 24/7/365 & I don't see any shortening of life.

Most sealed batteries and sealed battery specs I see call 13.8 volts ish for batteries in standby use and 14.4 ish for cyclic use.

When I get into a servicing cycle I can see between 8 and 12 of these batteries each day ...... these are cheap batteries not high class overpriced AGM. .... though in truth they could be rightly called AGM.

Those that don't get changed annually get load tested every service, they will get 3 to 5 years out of them, I see one over 4 years old I change it even if it load tests OK and often the temperature is less than ideal.

We mostly know exactly how old batteries are because we date them on install.


The bottom line is there is no necessity to have different charging profiles for gel and AGM unless the charging profile is over agressive.

Most sealed batteries will be perfectly happy with the same charging profile ....... other things will be a greater cause of shortened life.


BUT regardless we must look at the spec on the individual battery ...... mostly the important stuff is printed on the side.

cheers
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Follow Up By: Battery Value - Monday, Jul 17, 2017 at 17:33

Monday, Jul 17, 2017 at 17:33
Bantam,
"...As far as AGM ... "needing" any particular voltage ....... I am yet to see a manufacturer document that tells me that AGM won't charge from single stage 13.8 volt chargers...."
"AGM and other batteries may benefit from higher voltage charging profiles, but that does not make any particular charging profile necessary."
My comprehension skills are fine.
In your first statement you imply that it's probably ok to charge an AGM to 13.8V (without any ill effect).
After I pointed out the necessity for absorption charging, you try to prove your point by coming up with charging profiles which pertain to backup/standby applications which have zero relevance to caravan/RV use.
What you've got to understand is the type of application determines the charging algorithm.
And since the caravan/RV world is concerned with cycling the batteries frequently, absorption charging isn't optional. It's absolutely crucial for good battery life.
Ask Allan B why he thinks his AGMs have lasted 6 years and still going.
Every time he turns the key, his DC/DC charger gets the batteries to 14.4V for some time before switching back to float.
His AGMs would be dead as a doornail by now if his charger was set to output a constant 13.8V in his type of application.
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Follow Up By: The Bantam - Monday, Jul 17, 2017 at 22:21

Monday, Jul 17, 2017 at 22:21
You lack of comprehension is as obvious as your one eyed view of caravan and RV use and battery charging.

Worse is your insistence that battery failure will rapidly result if people don't follow what you insist.

The majority of caravans spend month after month parked up ...... float charging at 13.8 volts with an analogue charger would be ideal for most batteries and arguably more reliable than the long term use of an easily confused multi-stage charger.

Not everybody is hammering their batteries every night and slamming the charge into them every day.

NO Allan's DC to DC charger WON'T get his batteries up to 14.4 volts every time he turns the key ........ If he heavily discharges overnight and drives only a short distance the battery voltage may not reach 14.4 volts

And NO his batteries may not be dead if they where charged at 13.8 volts, because you simply do not know the specifications of, history of his batteries or how he uses them.

Higher charging voltages and multi stage chargers most certainly will charge sealed batteries faster, and most definitely have other benifits, for most sealed batteries, But the notion that you are somehow signing a death warrant for you batteries if you don't use a DC to DC charger is utterly false.

The battery charger industry has tried to tell us that the whole battery charging thing needs to be far more complicated than necessary ....
7 stage battery charger, Oh please.
Endless charging algorithms . give me a break

The point is only the rediculously pedantic are going to change charging algorithms when changing battery banks.

So you are telling me that your battery charger has a different algorithm for each and every battery type and for different applications too.

That is the whole point of multistage chargers ... the algorithm is supposed to account for different and changing uses of the battery

BTW exactly what is the difference between the the multiple different algorithms .... betya it's little more than charging end point voltage

I know pretty much the story on my 5 or 6 different multistage chargers.

cheers


cheers
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 09:04

Tuesday, Jul 18, 2017 at 09:04
.
I think that my "AGMs have lasted 6 years and still going." is for a number of reasons........

1) They are a quality battery..... Exide Stowaway ST27DC105
2) They are positioned away from heat.
3) They are sized to not excessively discharge on a daily basis.
4) They mostly get the opportunity to fully recharge each time.
5) They are charged in a controlled 3 stages by the BCDC's.
6) They receive a good maintenance charge from a mains charger regularly.
7) I talk to them nicely from time to time.

Actually, my Redarc BCDC chargers get them to 15.4v -- then when the Absorption current falls to 4A for 30 seconds they switch to Float of 13.3v -- At least that is Redarc's specs, and it seems to be the case.
My Ctek XS15000 mains charger runs Absorption at 14.4v until Float at 13.6v.

Whatever the numbers, I seem to be doing something right. That's a change. lol

Frankly, I am surprised that they have lasted 6 years. I must do a controlled discharge soon to see how they are faring.





Cheers
Allan

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Follow Up By: Battery Value - Tuesday, Jul 18, 2017 at 11:23

Tuesday, Jul 18, 2017 at 11:23
Allan, apart from talking nicely to your batteries, it seems your 'controlled 3 stages' of charging is key.
IIRC your DC/DC charger is left alone with the batteries when it's charging, by switching the loads from the output to the input of the unit via a relay.

That trick enables the DC/DC to correctly terminate absorption stage charging, based on its tail amps setting of 4A.

And at this dizzying 15.4V that's crucial for good battery life. Any extra time spent at this level unnecessarily, would just gobble up electrolyte and corrode the grids.

If you don't mind me asking what's the reason for choosing 15.4V over the other two available settings of 14.5V and 14.9V?
Cheers, Peter
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 12:00

Tuesday, Jul 18, 2017 at 12:00
.
Yes Peter, that charging regime is important. Much better than my old 'direct from alternator' setup.
And yes again, I do transfer the loads past the chargers via a 60A relay. Pretty simple but it leaves the chargers to correctly interrogate the battery state and at the same time allows their full output to be devoted to charging, not supporting loads. I'm rather surprised that Redarc do not propose that method.

The choice of the "15.4v setting" came from Redarc's installation recommendation..... "Battery type selection" of 14.6v for "Standard Lead-acid, 15.0v for "Calcium" and 15.4v for "Gel & AGM".
I obediently adopted the setting for my AGM's.
Although those settings are nominated by Redarc as "maximum", the actual output voltage must
by-need be regulated to not exceed the 20A rating of the charger so the voltage may well be less than that --- never bothered to measure it. And it would not necessarily be the stage termination voltage as that is determined by the "less than 4A" algorithm to switch it to the Float of 13.3v.
Are you perhaps suggesting that I may do better with another setting?

If all this is important with a simple constant voltage alternator, how much more important must it be for recent vehicles with "controlled" alternators?
Vehicle manufacturer's are devoting much to engine management and stability & braking automation yet stuffing up the battery charging for the sake of a couple of emission points.

Cheers
Allan

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Follow Up By: Battery Value - Tuesday, Jul 18, 2017 at 13:07

Tuesday, Jul 18, 2017 at 13:07
They constant current charge to the absorption voltage level, until the current drops to 4A for 30 secs, which is when they switch to 13.4V float.
They also have an overriding absorption timer which limits outgassing if there are concurrent loads.

...The choice of the "15.4v setting" came from Redarc's installation recommendation..... "Battery type selection" of 14.6v for "Standard Lead-acid, 15.0v for "Calcium" and 15.4v for "Gel & AGM".
I obediently adopted the setting for my AGM's....

Their BCDC 1225 manual has this the other way around:
gel/AGM 14.5V
lead acid 14.9V
calcium 15.3V
https://www.redarc.com.au/images/uploads/files/bcdc1225_instruction_manual.pdf

Cheers, Peter
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 15:39

Tuesday, Jul 18, 2017 at 15:39
.
Peter, my understanding of the Redarc BCDC1220 algorithm in the Absorption stage is that the charger outputs whatever voltage is necessary, up to its set limit (of say 15.4v) in order to achieve the 20A charge rate. As the battery voltage rises the current will decrease with falling voltage differential until at 4 Amps (for 30 seconds) it switches to Float Mode. This behaviour seems to be revealed on my charging meters, although there is some limit to observation whilst driving!
Yes, there are timing over-rides in both Absorption and Float which I elected to not describe.

The "1225 Manual" that you offered sure does have it the other way around.
Yet if you approach the two Manuals from their "Product Pages" links they are both as I described so Redarc has some inconsistency in their documents. Not the first time, I have advised them previously of an error and they agreed and replied politely but never changed it.
I would have expected the AGM voltage to be higher than the "Standard" (flooded?) Lead-acid voltage would you not? What is your opinion of appropriate AGM voltage. Bear in mind that Redarc express there as "Maximums" not terminating voltages.




Cheers
Allan

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Follow Up By: Battery Value - Tuesday, Jul 18, 2017 at 16:37

Tuesday, Jul 18, 2017 at 16:37
Allan,
.....As the battery voltage rises the current will decrease with falling voltage differential until at 4 Amps (for 30 seconds) it switches to Float Mode. This behaviour seems to be revealed on my charging meters, although there is some limit to observation whilst driving!...

In the first (bulk) stage, the charger acts as a constant current source.
During this stage the charging rate remains constant as the battery voltage rises towards the first setpoint Vabsorb.
Vabsorb is the tightly controlled voltage ceiling. As the battery's SOC rises, its appetite for charge fades, which forces the rate down exponentially (current taper), similar to charging a cap through a resistor.

I briefly googled your batteries but couldn't find charging instructions for them.
To be honest I've never seen AGM charging recommendations as high as 15.4V.
I'd drop this by one/two notch/es in winter/summer.
Cheers, Peter
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Follow Up By: Allan B (Sunshine Coast) - Tuesday, Jul 18, 2017 at 18:01

Tuesday, Jul 18, 2017 at 18:01
.
Peter,
Are we not saying the same thing regarding operation in the Absorption Stage?.....
Me: "falling voltage differential".
You: "appetite for charge fading".

Nah, Exide don't seem to publish much technical detail.
I am reluctant to change anything as it is all working so well.
I may take a close look at exactly what voltages the Redarc charger is delivering and could change their selector connection to the "Calcium" setting at their nominal 15.0v if need be. Redarc are good, but not perfect in my opinion.

Anyway, the way things are performing, I probably won't need to consider new batteries for a while yet. I'll see what the stored capacity/discharge tests show. That is the easiest test to perform.
Cheers
Allan

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Follow Up By: Banjo (WA) - Wednesday, Jul 19, 2017 at 08:56

Wednesday, Jul 19, 2017 at 08:56
I have been following this discussion as I am going to get new equipment soon that will require a dc-dc charger.

I currently have a Ctek mains charger and have been tossing up what dc-dc to get. I thought the Ctek D250S, but was open to Redarc or Projecta.

If Redarc can't be accurate in their manuals (visible to me) how could I have confidence in their product (invisible to me)?

Paul
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 09:19

Wednesday, Jul 19, 2017 at 09:19
.
Hi Paul,

Ctek, Projecta, and Redarc are all products with good reputations.

I use a Ctek mains charger but Redarc for the vehicle chargers. My preference for Redarc was because of ease of access to their technical information and the practical designs of their products. Plus their Australian manufacturing.

I have encountered a couple of errors or omissions in their information which disturbed me even more because everything else was so good. Access to their technical staff is open and responsive so I will contact them about the apparent anomaly Peter and I discussed above and see what they say.

Cheers
Allan

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Follow Up By: Battery Value - Wednesday, Jul 19, 2017 at 09:40

Wednesday, Jul 19, 2017 at 09:40
.....If Redarc can't be accurate in their manuals (visible to me) how could I have confidence in their product (invisible to me)?...

At least on paper, the Projecta and ctek do a better job.
Their float voltage is closer to the mark, and both come with battery temperature sensor for precision charging, extending battery life.
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 10:04

Wednesday, Jul 19, 2017 at 10:04
.
Paul,

I have been delving into this Redarc specification anomaly and it may seem that Peter (Battery Value) has chucked me a 'curved ball'. Without malice of course.

When accessing the specifications online via the "Manuals" link, I view essentially the same data for the BCDC1220 as the 1225 models. The voltages are consistent. However when using the link to the 1225 that Peter posted I arrive at a pdf page that reverses the specification.

Peter, if you are still watching, where did you obtain that pdf reference? It is not the one that I access through the "Manual" product link. I don't want to get a "Redface" from Redarc if I raise it with them!!!

As it stands, the data currently published for the public seems to be correct, although you can argue the finer points of precise voltages until the 'cows come home'. I could easily spend most of my waking hours perusing the specifications of battery chemistry, voltages et al, and still be non-the-wiser! I really have better things to do. I tend to elect sources of information and products that look good to me and leave it at that. DISCLAIMER: That comment is not aimed to offend anyone. I am not wishing to get flamed again for an innocent remark.
Cheers
Allan

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Follow Up By: Battery Value - Wednesday, Jul 19, 2017 at 10:44

Wednesday, Jul 19, 2017 at 10:44
....Peter, if you are still watching, where did you obtain that pdf reference?...

Allan, I used the Google search engine, then selected a link which points to their URL:
https://www.redarc.com.au/images/uploads/files/bcdc1225_instruction_manual.pdf

In another version they refer to battery types as A,B,C.
https://www.redarc.com.au/Content/Images/uploaded/Manuals/BCDC%20Instruction%20Manual.pdf
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Follow Up By: The Bantam - Wednesday, Jul 19, 2017 at 12:37

Wednesday, Jul 19, 2017 at 12:37
A couple of comments and observations.

Prior the the battery nearing the end of it's bulk charging phase and beginning to "gas freely" ..yes sealed batteries gas but we don't want them to gas freely or excessivly. ... because excessive gassing causes damage to the plates and outpaces the recombination process ..... causing excessive pressure resulting in the battery venting. .... ( if the vents don't work the battery blows up like a balloon or the joints split, yeh seen it, changed it cleaned up the mess)

Anyway prior to that point .... voltage matters little, the limiting factors are current and temperature.

Most battery chargers are current limited by some means or another.

Calling it a constant current source realy is not correct ....... it is a current limited, voltage regulated source ... there are significant differences.

15 to 16 volts is nothing new for charging batteries ......

many old school tranny and rectifier chargers had open circuit terminal voltages in that range

One of my multistage chargers has a manually activated 16 volt cycle ... it is time limited and used for breaking down charge resistance and boost charging.

Now back to current limited chargers ........ this is something that is all to often overlooked.

Pretty much ALL of our well engineered charging systems have some sort of current limiting factor. ... it is just that the advertising department does not go round blowing a trumpet about it.

It is very important that the charging system and the battery are sized with their limits in mind.

you may not think that current limiting is a factor in many systems but it is there

Even if you have a 100 amp alternator, there will be some sort of current limiting to prevent excessive current in the battery.

If you have a 100 amp alternator and a standard N70 battery ...... the ability of the charging system to deliver is limited by design to be within what the battery will tolerate.
Some vehicles with larger alternators and perhaps smaller batteries are effectivly current limited by use of small wiring in the charging path providing a series resistance ....... that wire might look reasonably beefy .... but do the maths and that fraction of an ohm is your current limiting factor.

My eyes where opened to this when I hooked up a 7Ah SLA to the charging system of my old Corrona which charged at 13.8 volts.

That reasonably healthy battery got quite hot quite quickly and greatly exceeded its maximum charge rate. ... like a matter of seconds as I held it.
I connected an older less healthy battery of the same size, the charge acceptance had suffered with age and the charge current was far less excessive.

I keep coming back to the issue, that within reason voltage matters very little, it is current and heat that are the parameters to be controlled.

It is current that will charge your battery
It is current that will break down sulphation
It is current that will cause excessive heat and it is current that will cause gassing and excessive gassing
It is current that will overload the sometimes inadequate internal connections in the battery.

Voltage only serves to cause the required amount of current to flow.

NOW many of the smaller and cheaper multistage chargers, change stages based on voltage alone, they have no current sensing capacity.

All but the upper end of the market multistage chargers lack on battery temperature sensors.

So much of the time charge voltages and stage changes are voltage based ..... because there is no means to do otherwise.

As long as the charger is not very large in comparison to the battery ( by that I mean will not produce more than the battery will safely accept) the maximum charge voltage of that initial stage is not particularly important ..... PARTICULARLY if the change from the first bulk charge stage to the second is current bassed. ... even more particularly if there is an on battery temperature sensor.

BECAUSE most of that charging step will be spent sitting on the current limit and the terminal voltage will be lower than its regulated point.

Now to the float charge stage. ...or in truth the "non boost charge stage"
Pretty much every lead acid family battery I have seen to date calls a long term stand by voltage of around 13.5 to 13.8 volts.

YES you can fully charge pretty much any healthy lead acid family battery from anything a little over 13.2 ish volts.

that voltage has be chosen as I have mentioned because it does not cause excessive gassing and heating.

exactly what voltage is selected is a compromise, the lower the voltage the less gassing, heating and lost energy, the higher the voltage the more electrolite loss and so forth ......... designers will argue about this all day, many times i will come down to voltage steps and component values available.
13.8 volts is convienient because it is 23 (0.6V)silicon semiconductor junctions in series 14.4 is 24, 15 is 25 ..... they may seem to be wisely contrived voltages ... but it realy is near enough is good enough

These battery charger manufacturers try and baffle us with science, but much of what they offer simply is not borne out by battery manufacturer recommendations.

as for recommending a string of different voltages for different generic classes of batteries ........ here we are back at unreliable generalizations.

That maximum voltage limit on the initial charge stage is a compromise no matter the battery.

You could pretty much effectivly charge any lead acid family battery long term at an initial charge voltage limit of 14.4Volts ...... or push it at 15 volts or higher if you are in a hurry ....... as long as the stage is current or time limited and the charger is not too big for the battery.

Anybody who thinks this is a finely divided science is dreaming.

Cheers
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Follow Up By: Allan B (Sunshine Coast) - Wednesday, Jul 19, 2017 at 13:21

Wednesday, Jul 19, 2017 at 13:21
.

That's DAMN GOOD Bantam. Agree with every word. Especially the last sentence!



Cheers
Allan

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Follow Up By: Battery Value - Wednesday, Jul 19, 2017 at 13:46

Wednesday, Jul 19, 2017 at 13:46
Bantam,
....YES you can fully charge pretty much any healthy lead acid family battery from anything a little over 13.2 ish volts.
that voltage has be chosen as I have mentioned because it does not cause excessive gassing and heating....

Again.
If you don't allow the charging voltage to increase to at least 14V in an attempt to charge an AGM battery, you cut its life short considerably.
I gave you the hints earlier - please google them and try to absorb the knowledge.

VRLA cell over-potential (or over-voltage, or polarisation) favours the positive half cell due to the gas recombination. This leaves barely anything for the negative half cell which sulphates up if charging continues at low voltage.
As can be seen in the diagram below, a slightly aged AGM cell receives zero over-potential at its negative electrode @ 2.3V (13.8V) with the positive half cell receiving 100% of the available 150mV.

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Follow Up By: The Bantam - Thursday, Jul 20, 2017 at 11:36

Thursday, Jul 20, 2017 at 11:36
Battery Value your continued lack of comprehension stuns me .... not only your lack of comprehension of what I post but the documents you reference.

Further you show that you are not keeping up with the discussion ..... my most recent post was addressing the issues of voltages and voltage thresholds chosen in multi-stage chargers and some of the reasons why.

In pretty much every decent multistage charger the battery has already been slammed with a voltage way above 13.8 volts and a high charge current (assuming the charger has been sized appropriately for the battery).

Thus a fallback voltage of the next stage of anything above 13.2 volts will finish off, the charging cycle and maintain the battery at a high state of charge ...... how much above 13.2 volts is something engineers could argue about for days .... the voltage actually chosen probably has more to do with engineering convienience than hard technical reason. ...... but I doubt that the charger manufacturers will admit that.

Relatively high charge voltages and currents have been well understood to be advantageous and benificial to all types of lead acid batteies for a very long time .... PROVIDING, it is within specification and the duration is limited .........certainly long before some marketing guru came up with the term AGM to describe starved electrolite batteries, which is what we called them in the 70's and early 80s.

HELL people who manage batteries have been doing multistage charging since the 50's ......it's nothing new ..... it's just that we did it manually ..... even fairly modest crude old chargers had high and low charge switches ....... get into the serious stuff we had in big battery rooms, we had milti-tapped transformers and charging control panels with huge voltage a current meters that where constantly supervised

The graph you reference shows clearly that a healthy lead acid battery of pretty much any family will fully charge without ill effect from 13.8 Volts.

I don't see the word " slightly" in the documentation you reference.

You consistently fail to acknowledge that I clearly state that voltages higher than 13.8 volts are advantageous for most sealed batteries.

And yeh the graph you show does not deal in specifics.

Tell me what is the difference between an AGM battery and any other battery that has calcium and other metals in the plates, modified electrolite, plates packed in glass mat and a sealed valve regulated package?

cheers
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FollowupID: 882959

Follow Up By: Battery Value - Thursday, Jul 20, 2017 at 13:09

Thursday, Jul 20, 2017 at 13:09
Bantam,
....YES you can fully charge pretty much any healthy lead acid family battery from anything a little over 13.2 ish volts...

...The graph you reference shows clearly that a healthy lead acid battery of pretty much any family will fully charge without ill effect from 13.8 Volts...

So now we're up from 13.2V to 13.8V.
I like the trend, but the target voltage is still not good enough to cover all the bases for AGM.

Here's what the diagram tells you:
@ 13.8V (2.3Vpc) there's a total polarisation of 150mV (blue line on the left).
For flooded, positive pol is 80mV with the balance of 70mV going to the negative.
New gel: 90mV pos, 50mV neg
Aged gel: 125mV pos, 25mV neg
New AGM: 127mV pos, 23mV neg
Aged AGM: 150mV pos, ZERO neg

Therefore, aged AGM cannot be fully charged @ 13.8V, as it takes about 2.33Vpc (~14V) for a tiny neg pol of 10mV.
For new AGM, the bare minimum is 2.27Vpc (13.6V), leaving 10mV of neg pol.

Also note, the above pertains to batteries with a SG of 1.3.
Many deep cycle AGMs coming out of China these days run a very high acid concentration of >1.32 which requires an even higher charging voltage to overcome the hurdle of uneven polarisation.
Consequently I would not recommend anything lower than 13.8V for new AGM, 14V for slightly aged, 14.2V for aged.
Cheers, Peter



0
FollowupID: 882963

Follow Up By: The Bantam - Thursday, Jul 20, 2017 at 16:44

Thursday, Jul 20, 2017 at 16:44
You continue to over think and over argue and fail to comprehend.

The graph tells us absolutely nothing with certainty, because we have no idea where it comes from or any specifics about the batteries it references.

While the term AGM does make some specific references it is still a very wide term ..... there are a lot of differing batteries that can claim to be AGM, with a range of behaviours.

Gel has changed a great deal, since Sonnenschein lodged their patents over 50 years ago .... the more advanced gel types these days no longer exhibit some of the behaviours and limitations they previously did.

HELL some of the batteries claimed to be AGM (and rightly) have a foot in both camps because their electrolite is partly gelled .... where is the curve for that.

As for flooded ..... HELL .... what do they mean by flooded ...... cheap nastly old school screw top flooded without modified plate metalurgy or electrolite chemistry, or the various forms, with various levels of modification right up to flooded batteries that are identical to AGM but have not had the excess acid tipped out.

You keep arguing fine and obtuse points, without knowing any specifics.

Both Allan & I have been pointing out two things ( speaking from trade training and experience) and you fail to grasp them.

1/ In this day and age the vast majority of generalizations about batteries are unreliable, because there has been such a range of small changes that change behaviours of batteries. ... we can only rely on specific information about specific batteries.

2/ Nothing about batteries is precise or 100% predictable .... any attempt to make finely measured insistences is nothing more than shouting into the wind.

however a couple of things are pretty certain

13.8 volts WILL fully charge pretty well all lead acid families in good condition and result in a reasonable service life. ... given time.

pretty well all sealed batteries will benefit from being charged with somewhere around 14.4 volts possibly higher as long as currents and temperatures remain within spec.

BUT both these figures are rubbery ...... some charging circuits as found will actually operate at non stereotypical voltage figures ... simply because they are conveinient ..... 13.5V is common, 14 volts is not uncommon ... hell some chargers bang it in at 15 and 16 volts.

A lot of the charger circuits can't reliably produce realy accurate voltages ....so if it reads anywhere between 13.5 and 14 volts we call the job a good un and move on.

cheers
0
FollowupID: 882973

Reply By: Member - Scrubby (VIC) - Monday, Jul 17, 2017 at 16:10

Monday, Jul 17, 2017 at 16:10
Thanks Peter and Bantam.
So please tell me if this is ok?
At this stage the bank of 6 x 2 volt has been removed and I reckon on replacing it with a 12 volt AGM. 200 a/h maybe larger.
If I use this battery for General full time use i.e. running the van fridge, water pump,lights etc. and use the solar to recharge and the generator ( I will be out bush away from anti generator campers) supplying 240 v when available for the 40 amp xantrex, and the 50 amp dc - dc while mobile.
Then only use the 2 x 6 volt gels separately when circumstances require.

Thanks again Scrubby.
I don`t know where i`m going but i`m enjoying the journey.

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AnswerID: 612565

Follow Up By: Battery Value - Monday, Jul 17, 2017 at 16:57

Monday, Jul 17, 2017 at 16:57
Hi again Scrubby,
yes you could replace it with a 200Ah AGM or larger.
It'll probably be cheaper to use two smaller AGMs in parallel though, plus you get failure redundancy which could come handy down the track.
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FollowupID: 882837

Follow Up By: The Bantam - Monday, Jul 17, 2017 at 23:00

Monday, Jul 17, 2017 at 23:00
two 6 volts in series will always be a better option than two 12 volts in paralell.
0
FollowupID: 882851

Follow Up By: The Bantam - Monday, Jul 17, 2017 at 23:03

Monday, Jul 17, 2017 at 23:03
200 AH 12 vot batteries are very heavy and difficult to handle and yes you will get better leverage on two smaller packages. ... or even go to 6 x individual 2 volt 200Ah cells.

cheers
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FollowupID: 882852

Follow Up By: qldcamper - Thursday, Jul 20, 2017 at 09:53

Thursday, Jul 20, 2017 at 09:53
two 6 volts in series will always be a better option than two 12 volts in paralell.


Could you please explain why?
0
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Follow Up By: The Bantam - Thursday, Jul 20, 2017 at 10:49

Thursday, Jul 20, 2017 at 10:49
two 6 volt batteries in series will always be better than two 12 volts in paralelle because
all cell in a series connected battery will recieve the same charge and discharge current, and bear pretty much equal wear and tear.

When connecting lead acid ( and most other battereies) in paralell you simply can not guarantee that charge and discharge currents will be equal in both batteries.

There are small differences between batteries even if they are the same age, same brand, same size and same batch
There are also small irreglarities due to the wiring.

These small differences result in one bank getting more charge and or more load and one bank will get more wear and tear ...... as the batteries age this becomes cumulative making the problem worse and worse, till one battery fails and drags the other down.

This is why all factory built lead acid battery packages are a group of series connected cells.

Yes you can do things to manage batteries in paralell .... but series connected is always the technical preference.

cheers
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Follow Up By: Battery Value - Thursday, Jul 20, 2017 at 11:10

Thursday, Jul 20, 2017 at 11:10
qldcamper,
charge inside a battery is stored in the electrodes.
The amount of charge the battery can store depends on the mass/volume of its electrodes.
Mass being equal for this comparison, a greater number of thin electrodes have larger surface area than a smaller number of thick ones.

What are the pros/cons?
Thick: smaller surface area, less instantaneous power, slower charging, but longer cycle life because of better active mass retention. Thin plate batteries are just the opposite.

6V batteries usually consist of thicker plates than 12V ones.

There's one more thing to consider: failure redundancy.
If there's only one pair of 6V in series, a single cell defect brings the whole 12V system down.
If a cell failure happens in a 2x12V parallel configuration, the faulty 12V battery can be isolated and the system continues to work albeit at half of its original capacity.

Cheers, Peter
0
FollowupID: 882957

Follow Up By: qldcamper - Thursday, Jul 20, 2017 at 13:32

Thursday, Jul 20, 2017 at 13:32
"two 6 volt batteries in series will always be better than two 12 volts in paralelle because
all cell in a series connected battery will recieve the same charge and discharge current, and bear pretty much equal wear and tear."

Possibly so in a technical sense but not so practical in our situation as Peter pointed out that a faulty cell can be removed from a parallel system and leave you with an operational system albeit a lesser capacity.

Peter, i might be splitting hairs here, but.

It has always been my understanding(since my tafe days at least) that it is the migration of the hydrogen ions from the electrolyte into the plate material that created the flow of electrons in the circuit, hence the specific gravity of the electrolyte returning to water when the battery is discharged and becoming more acid when the ions are forced back into the solution by charging.

I have always looked at it as the charge is stored in the electrolyte, but it could be said that the lack of hydrogen ions in the plate material is the stored energy.

Bit like people generally accept current flows from positive to negative, but the electrons are in fact flowing the other way, it is the void left by the electron moving that is flowing from pos to neg.

hmmm, im putting lots of words here but saying little, i better stop before people start confusing me with someone else. (said in gest)
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Follow Up By: Allan B (Sunshine Coast) - Thursday, Jul 20, 2017 at 13:55

Thursday, Jul 20, 2017 at 13:55
.
Bantam, shoot me an empty email to allanb.qld@gmail.com
There is something I would like to tell you privately.
Cheers
Allan

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Follow Up By: The Bantam - Thursday, Jul 20, 2017 at 16:53

Thursday, Jul 20, 2017 at 16:53
In a practical situation paralell connected systems more frequently fail, because people fail to do the maintenance required to keep them running AND regardless a series connected system will produce a longer service life and more measured capacity than a paralell connected system.

YES redundancy is frequently achieved in battery systems ...... nearly every mission critical battery system has either a paralell or independently charged second bank. ........ but they require more management than a single series bank.

ADM ... the original poster already has a two bank system, so already has redundancy ...... a single series connected bank is what is needed for replacement ..... I would recommend a bank of 6 single 2 volt cells .. as originally fitted.

cheers
0
FollowupID: 882975

Follow Up By: Battery Value - Thursday, Jul 20, 2017 at 21:05

Thursday, Jul 20, 2017 at 21:05
qldcamper,
...I have always looked at it as the charge is stored in the electrolyte, but it could be said that the lack of hydrogen ions in the plate material is the stored energy.
...

You're right, strictly speaking there's no charge stored in the electrodes.
There's no big lump of ions or electrons to be found anywhere inside the battery, which is meant to carry a total charge of say 100Ah.
What the electrodes contain is the active mass, lead and lead dioxide, fuel for the charge producing main reaction so to speak.

Sulphate and H ions are present in the electrolyte though which were produced when the sulphuric acid got mixed with water.
In open circuit there's no electrons flowing in the external wire and therefore no ionic flow in the electrolyte, but there's voltage between the electrodes.

When an external electrical circuit is formed, the ions in the electrolyte start to react with the active mass on/in the electrodes.
This causes a flow of ions from one electrode to the other which is balanced by a flow of electrons in the external wire connection between them.

And that's the current we're interested in as it produces usable power outside the battery.
0
FollowupID: 882982

Follow Up By: Allan B (Sunshine Coast) - Thursday, Jul 20, 2017 at 22:19

Thursday, Jul 20, 2017 at 22:19
.
What the hell are you two blokes on about?

"Polarisation of Flooded Batteries"
"Charge is stored in the electrodes"
No, "Charge is stored in the electrolyte"
No -- wait -- "Lack of hydrogen ions in the plate material is the stored energy"

What on earth does it matter here on this forum?
Is is hardly of value to earthly mortals who simply have an interest in a reliable auxiliary battery system. Stop confusing them.
This is the stuff of pseudo-academics debating on a physics forum and endeavouring to prove others know less than they do.

The following is a cut-and-paste from the Forum Rules ....
"This Forum is for discussing issues relevant to self-drive camping/caravanning adventures in Australia."
Is what is being debated here relevant?
Poor Scrubby who sought practical advice in the opening post must be wondering which planet he landed on!


Cheers
Allan

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FollowupID: 882983

Follow Up By: Battery Value - Friday, Jul 21, 2017 at 07:06

Friday, Jul 21, 2017 at 07:06
Allan,
I agree with you which is why I kept my reply to qldcamper as short as possible because I knew there'd be forumites who are easily offended when they see others talking about nature's little miracles on the side line.
See we're discussing these things at the tail end of a long thread well down - not exactly in the limelight on top of the main index. Nobody is being forced to read any of this.

Please show some lenience towards us curious critters who don't mind a little look behind the scenes.
As someone with your background would agree - no curiosity, no knowledge.
1
FollowupID: 882985

Follow Up By: qldcamper - Friday, Jul 21, 2017 at 09:50

Friday, Jul 21, 2017 at 09:50
Didnt know anything was being debated, just two guys discussing their take on how something works, one, other or neither of us might be 100% correct but it is how we as a race learns, drives us to research more and progress.

Sorry you are too tired to want to learn but please dont condem those that do.

Anyway i am going back to work so wont have time to get bored enough to visit this site much for a while.

Just a refresher of some advice to members that i have stated before.....

Beware of who give advice on forums, check their credentials or you might be taking advice from people that only know how to google subjects and parrot it without understanding it, big words do not always = knowledge.

Experience beats google every time.
0
FollowupID: 882986

Follow Up By: Allan B (Sunshine Coast) - Friday, Jul 21, 2017 at 10:39

Friday, Jul 21, 2017 at 10:39
.
Qldcamper,

You really know how to get up my nose, don't you?

Of course there was a debate and pissing contest going on, but choose the right forum for "discussing your take".
This was Scrubby's thread to resolve a simple problem. You are just muddying the waters.

But I will agree with you regarding "Beware of who gives advice on forums, check their credentials". Mine have been on view for some time.




Cheers
Allan

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Follow Up By: qldcamper - Friday, Jul 21, 2017 at 12:05

Friday, Jul 21, 2017 at 12:05
It seems so Allan, but believe me it is unintentional.

I consider both giving good advice, and pointing out bad advice both to be helpful to an OP. I will never offer advice if i am not 100% sure(or at lease think i am) that the advice is correct so most times i opt out, but some things are suggested that are just so wrong i can not resist.

This along with other forums amaze me that nobody has been sued for wrong advice, without professional indemnity insurance any advice given in writing needs to be spot on, otherwise the poster can be held responsible for any damages it may cause if people take it, or even misunderstand it if the judge deems it that you did not explain yourself well enough.

I have never seen anything you have posted as bad advice and have never hinted towards it, you just seem to want to blindly support someone that i have had differing opinions with and now seem to target me for some reason.

By the way thanks for the advice you gave me with the op amp, i have come up with a circuit but have not had time to try it out, work interferes with my lesure time too much.

Where have you displayed your credentials? Maybe there should be a section on all forums for such details.
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FollowupID: 882988

Follow Up By: Allan B (Sunshine Coast) - Friday, Jul 21, 2017 at 13:55

Friday, Jul 21, 2017 at 13:55
.
Hi Qldcamper,

Yes Ok, and fair enough. I'm not looking for a stouch.

If you are referring to Bantam as "bad advice" I would implore you to reconsider. I too, earlier, had issues there but looked deeper. Bantam has a lot of experience and is no fool and his advice is based on realistic considerations of practical application.

Credentials? I did have some info posted under "My Profile -- About Me" until recently when my EO data was hacked (yep!) so, on restoration, I have abridged it there.
I am a retired Instrument/Electrical Engineer. If you want more detail, email me on 'allanb.qld@gmail.com' and I'll be happy to indulge my ego!!!!

Thanks for your FollowUp. The air is a bit better now. lol
Cheers
Allan

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Reply By: Allan B (Sunshine Coast) - Saturday, Jul 22, 2017 at 21:14

Saturday, Jul 22, 2017 at 21:14
.
Well I have completed the load test on my two 6 year old AGM's and the position is not as bright (literally) as I had been bragging and really, I should not have been surprised.
They each returned only about 15% of the new-condition capacity, assuming that the new capacity was 100Ah as manufacturer specified.
The test being done at 5.0A discharge rate from full charge 12.5v down to 10.5v yielded little more than 15Ah from each battery.

It would appear that the ongoing acceptable performance supplying my auxiliary loads was due mainly to being well-charged and having low load.


Cheers
Allan

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AnswerID: 612670

Follow Up By: qldcamper - Sunday, Jul 23, 2017 at 09:36

Sunday, Jul 23, 2017 at 09:36
What brand are they Allan?

The fact that they were so close after 6 years indicates uniformity on the production line at least.
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FollowupID: 883022

Follow Up By: Allan B (Sunshine Coast) - Sunday, Jul 23, 2017 at 11:10

Sunday, Jul 23, 2017 at 11:10
.
They are Exide Stowaway ST27DC105 AGM's.
They were bought several months apart.
One is in the engine bay, but reasonably insulated from heat, the other in the cabin.

I intend to refit new with a single battery in the cabin. Less cost, less weight, simpler system.
Cheers
Allan

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Follow Up By: qldcamper - Sunday, Jul 23, 2017 at 11:40

Sunday, Jul 23, 2017 at 11:40
and apparently you dont really need 200 Ah, wonder how long you have been getting by with less than 100, can always add more later if you find you need it.

It would seem it busts a couple of the other myths about battery placement etc. if the one under the bonnet lasted the same there abouts as one in an air conditioned cabin.
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FollowupID: 883026

Follow Up By: Allan B (Sunshine Coast) - Sunday, Jul 23, 2017 at 13:09

Sunday, Jul 23, 2017 at 13:09
.
Yep, I didn't really need 200Ah.
But no, the "myths" re battery placement are true alright!

The first AGM in engine bay had short life. I measured engine bay temperature at 70c plus on a mild day after 15 minutes.
Accordingly I arranged a heat barrier with cool air channelled (see pic below).
It brought the temp at the battery down close to entry air, but perhaps not to cabin temp.


Cheers
Allan

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