Topping Up Optima Batteries

The headlights arent connected as these are aux batts via a Redarc solenoid charger.
According to Redarc, fully charged Optimas should be about 14v. If this is true then I do need to put them on a mains charger.

Hi Stan,

Robin already explained it pretty well.
Your battery seems to be fully charged at the moment.
And the alternator will keep them charged fully, unless you're going to discharge them deeply.
Then, they greatly benefit from an absorption charging stage @ 14.8~15V (at 25 degrees).

Don't listen to this Redarc recommendation. They aren't in the battery business hence don't know much about them.

cheers, Peter

Gooday Peter. That is something I have often thought about but never bothered to ask about. I regularly check hundreds of batteries every year on radio and telecommunication sites. Very rare for a battery to show more than 12.8 volts.
Is 14 volts a common site on a battery that is just sitting there and not receiving a charge? Seen plenty at 13.8 whilst charging.
cheers

Hi Bigfish,

you're speaking from experience - and I can confirm this from my own observations: neither flat plate nor spiral wound AGM (lead/tin/calcium versus lead/tin) show a resting voltage of higher than 13.00~13.2V when fully charged.

cheers, Peter

Hi Peter,
It was yourself amongst others who told me that the alternator would not charge more than about 80%.
"Note that you don't have to use solar on a daily basis to bring your batteries to 100% state of charge. The alternator does this for your up to around 85% SOC, use solar once per week to top up, or whenever the sun shines." BatteryValue July 2nd 2011

"And for those overcast days, plan your drive for early morning, so that the panels have time to harvest some solar energy in an attempt to get the batteries up to their daily absorption dose of 14.4V. If you'd drive in the evening, the little bit of solar during the day won't do much in terms of absorption voltage, and the alternator isn't capable of doing this either because it's limited to around 13.8~14V. The key for understanding this is that the battery voltage rises only reluctantly while the SOC is low, but begins to rise faster as the SOC increases. So once bulk charging (high current, alternator) has pushed up the SOC to around 80%, a lower current (but higher voltage) source like solar can be utilised to reach absorption voltage fairly easily.
So the order of charging is bulk, absorption, float.
For bulk the alternator is ideal, for absorption and float you want solar (with a good regulator). " BatteryValue July 3rd 2011


I dont understand why everyone told me this. I had 25sqmm cable put in, but other than that it was a standard install. Yet my alternator seems to charge the Optimas up to around 100%. Am I missing something here?

Hi Stan,

it's good to see you have an open eye for these things, and yes, I can understand battery charging can get confusing:

The key to understanding battery charging is that you ought to give it some over-charge to bring the SOC up to 100%. This is achieved by putting about 105% back, of what you took out of it. So the over-charge is ~5%.
So far so good.
But it gets a bit more involved because the exact amount of over-charge depends on the depth of discharge.
So if the DOD is only shallow, the battery will be happy with next to no over-charge, but if it gets discharged by 30% or more on a regular basis, then over-charging is the only way to prevent sulphation (gradual loss of capacity), and cell imbalance (which is a runaway effect leading to a dead cell).

Ok, and how do you go about applying just the right amount of over-charge?

Your email read like you're not deeply discharging your battery on a regular basis, hence alternator charging seems to be sufficient.
What's more, your battery shows a healthy resting voltage meaning the alternator voltage is set high enough.

Ok, so how does charging voltage come into play?

And this is the second key to understanding how the battery is being charged:
The charge inside the battery isn't only stored on a two dimensional surface area, but also inside the porous electrodes.
The deeper you discharge the battery, the more the small channels through which the electrolyte can reach into the deeper regions gets clogged up with lead sulphate.
Because there needs to be enough thrust behind the movement of the charge carriers (ions), it's easy to understand that you have to increase the charging voltage.
If that's neglected, the lead suphate inside the (negative) electrode will gradually transition from an amorphous state into harder/larger crystals which is largely a one way process in which the battery gradually loses its capacity to store charge.

How important this over-charging is can be seen when looking at the recommended charging routine for deep cycle-able yellow top O.tima batteries:

Cyclic Applications:
14.7 volts, no current limit as long as battery temperature remains below 125°F (51.7°C). When current falls below 1 amp, finish with 2 amp constant current for 1 hour.

You can see that in a cyclic situation, the over-charge is applied in two separate stages:
1) constant voltage charging at 14.7V until current tapers off to 1A
2) constant current charging with 2A for 1hr

I estimate that the total amount of over-charge recommended by this manufacturer for this type of battery in cyclic applications is 5~8%.
It's also interesting to note that in our lab we've measured the terminal voltage reaching a peak of almost 17V during the final stages of constant-current-over-charging a spiral wound AGM battery.
There's quite some gassing going on during this, but this is the lesser evil compared to early cell death due to chronic under-charging.

It can be said that spiral wound AGM batteries aren't really meant to be used in cyclic apps due to their thin electrode structure which makes them prone to negative electrode de-polarisation through the gas recombination. If that happens to a cell, the negative electrode of this cell actually discharges during charging (with a lowish alternator voltage) and the days of the battery will be numbered soon.

There's no way a single stage alternator set at 13.8v can achieve the recommended amount of over-charge (to recover from frequent substantial depth of discharges), hence the battery will suffer from chronic under-charging in the medium term, and quite possibly will lose a cell within a couple of hundred cycles.

To one of your other questions:
..or O.timas are capable of being fully charged by an alternator..etc

From this it seems you're confident that the battery is fully charged, but looking only at the resting voltage is actually not a sure fire way to tell the battery SOC.
The ONLY way, and I mean it, is to apply a constant current of 2~5A with unlimited voltage, and observe how quickly the battery reaches its deltaV.
That's the point in time when the terminal voltage reaches its peak and starts dropping off again. If this peak is reached within a minute or less, then you know the battery was fully charged at the beginning of the test.

cheers, Peter

Hi Stan,

Good to see you have a successful battery install.

As I said in post 88872, "... your alternator will be able to recharge the batteries to ~85% SoC, but will struggle to get higher for many reasons. 100% recharge is possible from alternator charging, but you will need BIG cables and a long driving time...."

Your choice to install 25mm2 cable has paid dividends, you have installed BIG cables and have spent a long time on the road, so you seem to have achieved 100% recharge from the alternator alone :)

Without starting WW3 again, there are so many caveats and techincal detail on why alternator charging will/won't get to 100% SoC, but it is possible as you have shown.

There is no "one size fits all" solution and so much depends on the individual use. What works for one may not work for another. But you have fitted something that DOES work for you, thats more than most with all things electrical, well done :)

Cheers

Captain

"To one of your other questions:
..or O.timas are capable of being fully charged by an alternator..etc

From this it seems you're confident that the battery is fully charged, but looking only at the resting voltage is actually not a sure fire way to tell the battery SOC.
The ONLY way, and I mean it, is to apply a constant current of 2~5A with unlimited voltage, and observe how quickly the battery reaches its deltaV.
That's the point in time when the terminal voltage reaches its peak and starts dropping off again. If this peak is reached within a minute or less, then you know the battery was fully charged at the beginning of the test."

But Peter, for heavens sake it was YOU who wrote earlier today that:

"Your battery seems to be fully charged at the moment".

I was confident that the battery was fully charged only because that is what YOU told me was the case, now you are telling me it might not be.

You also clearly told me previously without the caveat of depth of discharge that an alternator cannot charge an AGM battery more than 85%, now you say that it can dependent on the depth of discharge.

Frankly Peter, I am no longer confident in the veracity of your posts.
Could it perhaps be the case that when you were writing your posts advising me to get solar for top up charging, that at the time you were also trying to sell me your flat plate AGM's and maybe the fact is that you know for sure that your own AGM's cannot be fully recharged by an alternator?

Stan,

just to clear this up again: your original post read like you're not deeply discharging your batt - thus alternator charging will keep it near full SOC.
Only if you started to discharge it deeper, then alternator charging just won't cut it.

Right now you have us guessing.
But if you expect a concise answer please answer these questions first:

What is the load pattern like, depth of discharge on a daily basis, and how many hours driven per day.
Or, what are the loads like, while stationary, any Ah figures?

Then we need to know the alternator voltage measured right at the battery terminals when it is nearing full SOC.

The answer to these questions holds the key to the correct way of charging your battery, i.e. if alternator charging on its own will be sufficient for good battery health, or if you need to apply the recommended charging routine recommended by the manufacturer of your battery.
Or, of course you could just install a good MPPT solar regulator which applies the correct amount of over-charge for a majority of deep cycle batteries - regardless of your alternator voltage setting.

cheers, Peter

Nothing in any of my posts today has referred to the extent of my depth of discharging: you have decided to assume this on your own presumably as a cop out for the dead ends and contradictions of your posts.

I refuse to answer any more of your questions due to the fact that you keep changing your answers depending apparently, on the way the prevailing wind is blowing.

In short your persistent contradictions are misleading, your verbose but clearly designed to impress responses are as my mother used to say: 'All fur coat and no knickers".

huh Stan??

..that's ok we all have our ups and downs..

cheers, Peter

You would like to write off your contradictions by patronsingly putting it down to my apparently having "ups and downs". As a seasoned salesman, should you really be seen publicly to be trying to deflect your contradictions by blaming it on the customer? Bit of a PR mistake there Peter, but its not the first you have made today, now is it.
Nor does this explain how you seem to make it up as you go along.

Hi Stan,

While I don't agree 100% with all Peter writes, he does have a lot of good points.

I think though perhaps the biggest difference is the theoretical advantages of "perfect" battery charging in a laboratory versus the real world practicality of alternator charging. Ulitmately, multi-stage charging will give a "better" result, but the difference can be so infinitesimal when you have a decent alternator setup that the difference will take many, many years to become apparent.

Diagnosing over the internet is fraught with error as assumptions are made due to a lack of detailed info. You have a decent setup for your circumstances and it works well. But that exact same setup may not work as well for someone who has a different style of camping ie. long stays with infrequent, short driving.

Be happy you have made your setup work well for you and shown the "experts" that there is no "one size fits all" answer.

Cheers

Captain

Hi Captain,
This is about Peter firstly telling me that the alternator CANNOT charge more than 85%, then telling me that despite that, my batteries were in fact 100% charged by the alternator, then implying that I had wrongly convinced myself that the batteries were 100% charged when only his recommended test could let me know despite him telling me they were 100% charged HIMSELF. And when I finally have enough of and object to all of this salesman's nonsense this man then patronisingly puts all of his B.S down to my supposedly having ups and downs.
Enough.

Yes as captain said.... in a laboratory versus the real world there is a Hugh difference and some engineers forget this very important aspect.

A 4x4's engine bay is not the idea environment for batteries BUT there is not much you can do except make the battery as comfortable as you can LOL..

So the big question is will an alternator charge a battery to 100SOC or not?

One thing to remember an alternator in an automotive application was never designed to charge a battery to 100% SOC.... some newer vehicles will only charge to 65% SOC.

Batts are in a bed box in rear of van not in engine bay. An engine bay is no place for AGM batts I understand.

Stan re: battery in engine bay.

Your 100% correct in theory about AGM's not liking heat but theory is a great thing.... we have vehicles running around with AGM's under the bonnet that have been there for over 5 years with no issues and we have had batteries installed out of the engine bay last 3 years..... guess they call it luck of the draw.

In an ideal world if you can keep batteries out of the engine bay then that's a good thing for the battery.

Under bonnet temps are not as high as you may think.... try 40 to 60 deg on a 38 deg day.

Battery charge specs are calculated under ideal environments and if you fall outside these charge specs you might see a decrease in battery efficiency of 5 to 10%.

Sure if you fall outside the charging specs by a lot then the battery will suffer and have a short life.

You have to remember in an automotive environment it is nearly impossible to get the ideal environment... but every bit helps.

Think of a battery as a chemistry set because that's basically what it is..... applying different voltage, current and heat makes the chemicals react differently.

Stan best thing to do is jump on your specific batteries wed site and down load the spec sheet that should have the charging rates.

Redarc technical support.

Do you know who you spoke to, and yes they gave the wrong information.

Its those big 25mm2 cables you installed that does the trick :)

Think of your battery as a swimming pool - you have been filling it with a fire hose (25mm2 wire) while others try with a garden tap (say 6mm2 wire) and expect to fill it up just as fast - will never happen in a few hours of filing (driving).

You have a good install and it works great for your type of camping style.

Cheers

Captain

Stan you were able to nearly fully charge your batteries for 2 reasons..1. You had etremely large size cable compared to most others and 2. You did so on a long run.
Never seen a battery show 14 volts whilst at rest. We have huge banks of batteries for remote area communications and as stated 14 volts is a yowie. All of ours are solar charged and get 100% capacity. When we have had to charge batteris by a generator/charger we never get a thorough charge.

Try driving around town or going short distances only for a while and you will not fully charge the battery. Seems like your getting knickers in a twist over nothing. Teach em all a lesson and dont ask any more questions. That way you dont have to get an answer.
cheers

I have been consistently getting these readings without having to do particularly long runs but I put the readings down to the battery not having rested long enough. From that point the fridge etc was bringing down the SOC, so it wasnt until I got home, disconnected the aux batts from any power draw and went back after they had rested overnight, to see that 12.97v was still the resting voltage.

The installer uses 25sqmm cable as standard for all of his installations, and it was from this that I knew he knew what he was doing. But I only knew to ask the question 'cos of Captain!

Someone who uses logic...... at last... good call.