Alternator does it charge your Battery or only maintain charge.

Submitted: Sunday, Aug 19, 2012 at 03:02
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Hi Guy's I'm a bit confused here I would have thought an Alternator will charge your battery from dead flat to fully charged after a jump start given time of course.

But some experts don't agree they believe a battery charger is the only way to top up a battery to 100% or the best the battery with age is capable of. And only then will the Alternator maintain that charge.

So what I'm getting at if I park for a while! leave my lights on with Caravan in tow and deplete my battery by 50% what is the go then! have I just reduced my batterys storage capacity cause the Alternator will not top up to more than 50% or what.

It just seems strange to me that an Alternator pushing some 14.4 volts max and reducing as charge is being absorbed! and some really big Amps getting pumped in the battery is not as effective as some piddly little 8 Amp charger I have at home.

Surely an Alternator will do the same job to the best of the battery condition as well....... won't it????

Or should I be sticking me battery on me 8 Amp charger after a lights left on for a while, radio going episode! to restore my battery to a higher capacity than the Alternator can do.

Cheers.
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Reply By: Life Member - Doug T (NT) - Sunday, Aug 19, 2012 at 05:32

Sunday, Aug 19, 2012 at 05:32
I would say it does both , re-charge the battery and also keep it fully charged.
Reason being if the battery were reduced to 50% the first time, the next time you use interior lights the rate would be 25% and so on until the time came you wouldn't be going anywhere and you'd eating your bacon and eggs in the dark.

.
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Reply By: Robin Miller - Sunday, Aug 19, 2012 at 07:13

Sunday, Aug 19, 2012 at 07:13
It depends on your batteries state of charge Roughas.

The alternator tries to put out approx a constant volts.

For sake of this post lets say 14.2 volts.

Now if your battery is at 12v the the alternator will pour in maybe 50 amps and far exceed your little 8 amp charger.

However if your battery was at 14 volts then the alternator has only a difference of (14.2-14v) to push current through the connecting cables and it may only be able to put in a few amps.

This is where your little charger can win because it is designed to raise its voltage so that in can put out a constant 8amps.

For these reasons a normal car alternator will quickly partly charge a battery and replace the starting current but will take a long time to fully charge the same battery.
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Reply By: Tonyfish#58 - Sunday, Aug 19, 2012 at 07:34

Sunday, Aug 19, 2012 at 07:34
As robin said above it will take some time but it will recharge the battery. You would have to go on a long drive.

I have been told that if you do not drive for at least 1/2 an hour, you are not replacing any charge.

Be interesting to know how good that advice was :-)

Regards Tony
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Reply By: Member - MUZBRY(Vic) - Sunday, Aug 19, 2012 at 09:10

Sunday, Aug 19, 2012 at 09:10
Good morning Roughas
Looks like you might have to resort to the old Bosch generator from an early Holden ,or some old English car , but steer clear of Lucas generators .





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Follow Up By: Allan B (Member, SunCoast) - Sunday, Aug 19, 2012 at 12:55

Sunday, Aug 19, 2012 at 12:55
LUCAS.......The Prince of Darkness!!


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Follow Up By: Member - MUZBRY(Vic) - Sunday, Aug 19, 2012 at 13:01

Sunday, Aug 19, 2012 at 13:01
Gday Allan
Long time no hear... Lucas What a great product ...
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Follow Up By: Allan B (Member, SunCoast) - Sunday, Aug 19, 2012 at 16:16

Sunday, Aug 19, 2012 at 16:16
Hi Muzbry, For more on Joseph Lucas, look in next Friday Funnies.

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Follow Up By: Member - MUZBRY(Vic) - Sunday, Aug 19, 2012 at 17:22

Sunday, Aug 19, 2012 at 17:22
Allan. i thought i had heard it all as an apprentice many years ago , but i can wate till friday .
Thanks and have a good day.


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Follow Up By: Allan B (Member, SunCoast) - Sunday, Aug 19, 2012 at 17:33

Sunday, Aug 19, 2012 at 17:33
You probably have heard them all and more Muz. But some of the newer fellas may find them amusing. But then perhaps not if they never knew Joseph L.

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Reply By: Member - Phil G (SA) - Sunday, Aug 19, 2012 at 09:46

Sunday, Aug 19, 2012 at 09:46
It depends n how flat the battery is.

If you leave the lights on for a couple of weeks, your battery will be dead flat - zero volts. In this state, the internal resistance of the battery is very high and it will accept very little charge. Alternator will be useless for the short period of time you'll run the car. The only way to resurrect a battery in this state is to put it on a charger for a week and see if its still alive. My daughter recently did exactly this and cut her losses and bought a new battery. I've resurrected a couple of batteries like this in the past, but its a long process, and they usually are not as good as they used to be.

If you leave your lights on for a few hours and drop the battery voltage to say 11V (which usually prevents you from starting the car), then the internal resistance of the battery is still reasonable - if it is in good condition, it will take a heap of amps from the alternator and will recharge to a cranking state fairly quickly. But it still takes a long, long time to get back to fully charged, so in this instance, I'd speed up this process by putting the battery on a charger overnight.

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Reply By: Member - Captain (WA) - Sunday, Aug 19, 2012 at 10:49

Sunday, Aug 19, 2012 at 10:49
Some "interesting" comments here about charging! To answer completely would take an essay, but the quick anser to your original question is yes, an alternator "can" fully charge a battery. The caveat is that it will take some time. Typically an alternator will charge a relatively flat battery to ~80% relatively quickly, but then it takes a considerable time to get to 100%.

For a vehicle starter battery this is rarley an issue as it actually only takes a very small amount of battery power to start a vehicle. The alternator can replace this power within a few minutes of driving, all things be equal. (another caveat!)

As a battery is discharged, its internal resistance gets lower, a flat battery can draw a higher amperage than a fully charged battery during recharge. As the battery is being recharged, the internal resistance increases and down goes the amp draw. If the voltage is now raised (like a multi-stage charger does) you can now head towards 100% recharge, but raise the voltage too high and you start to boil the electrolyte. Or keep the voltage relatively low, but for a long time, and you will also eventually achieve 100% recharge.

Also, a battery sholud be recharged as soon as possible otherwise you can begin to lose capacity. The lead sulphate that is formed during discharge is originally amorphous (jelly like) but turns crystaline over time. Recharging the battery converts the lead sulphate to lead oxide (+ plate) and lead (- plate).

But if the lead sulphate has turned crystaline, this reaction takes some time, if at all, to occur. Its why pulsing charging with a varying voltage can help break down the crystaline lead sulphate and "recover" otherwise dead batteries.

A battery is basically just a chemical reaction and its getting this chemistry right that is critical. There are so many types of batteries (AGM, wet cell, deep cycle etc...) all with their own differences that require supple differences to discharge and recharge regimes to get the best out of them. As they say, "oils ain't oils" applies just as much to batteries!

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Follow Up By: Member - Broodie H3 - Sunday, Aug 19, 2012 at 12:21

Sunday, Aug 19, 2012 at 12:21
Hi Captain, this is a very useful bit of info that I didn't know before so maybe you can answer this one, When we had the agm battery put in the van I was told to put it on the charger every time we came back from a trip as it would keep the battery healthy. The charger had to be one with a trickle feed, suitable for this type of battery, It also had to be one that could cut out and recharge automatically, and to leave it connected to the battery all the time the van is parked up and not being used, as you do lose some power from the battery when not being towed, now my question is this, Is what I have been told correct or should I just disconnect the battery like I normally do
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Follow Up By: Member - Phil G (SA) - Sunday, Aug 19, 2012 at 13:32

Sunday, Aug 19, 2012 at 13:32
Gday Captain,
Nothing like a good battery thread on a Sunday!!

What do you think of this graph taken from HERE which is the opposite of what you have said?



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Follow Up By: Member - Captain (WA) - Sunday, Aug 19, 2012 at 15:25

Sunday, Aug 19, 2012 at 15:25
Hi Phil,

The chemistry behind a lead acid battery is pretty straighfoward, but as anyone who has ever posted in electrical threads knows, there is always controversy!

I did preface my answers by stating it would take an essay to explain and so have tried to simplify my answers. Most people are familair with low reistance equals high current flow. So, simplisiticallly, as a flat battery draws a high current, its resistance would appear to be low. Conversely, a fully charged battery draws very little current hence it appears to have a high internal resistance.

The reality is that in a flat battery, virtually all the sulfuric acid has been converted to water, the chemical reaction (simplistically!) is that the sulfate has reacted with the lead to form lead sulphate. Now water has a much higher resistance than sulfuric acid so the actual electrolyte resistance of a flat battery is high!

However, if one applies a fixed voltage source to a battery, the flat battery will draw more current than a fully charged battery. The difference is the state of charge and its effect due chemical reaction that is occuring (the lead sulphate is changing back to lead oxide and lead). A battery has ohmic, inductive and capacitive resistance and to look at the ohmic reistance only takes away from the point I was trying to make.

One can discuss all day techincal detail about a battery, but the point I was trying to make is that a flat battery can accept more current than a charged battery for a given voltage.



Hi Brodie,

I too have AGM batteries in my Camper and I fully recharge them when I get home and once charged, I only put them back on charge periodically.

While my Ctec 25A charger is a multistage one, I have seen its float voltage creep too high for my liking (gets above 14V, should be closer to 13V) so once fully charged I turn it off. About every 2 weeks I put the charger back on to top up the batteries, as all batteries have some level of self-discharge.

Some people will leave the charger on all the time and that is fine, provided the float voltage is OK. But fully charging the battery but then leaving the charger off for extended time is not what I would do.

Cheers

Captain
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Follow Up By: Allan B (Member, SunCoast) - Sunday, Aug 19, 2012 at 16:53

Sunday, Aug 19, 2012 at 16:53
Captain, in regard to lead-acid batteries:

1. The battery impedance becomes greater as the SOC becomes lower.
However, with a constant voltage, the current increases with a lower SOC because of the voltage differential between the charge source and the battery. It is this voltage which drives the charge. With a higher differential voltage there will be a higher current.... simply Ohms Law. Introducing chemistry is merely confusing in the context.

2. A battery certainly has ohmic resistance but any capacitive or inductive impedance (not "resistance") is insignificant. Particularly in the context.
To introduce such expressions and concepts is confabulation which can only confuse both the OP and others without appropriate electrical training. It does not answer the question asked.

3. It doesn't really need an essay to explain unless you are trying to overcomplicate it.

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Follow Up By: Dennis Ellery - Sunday, Aug 19, 2012 at 17:59

Sunday, Aug 19, 2012 at 17:59
Hi Captain,
Your Ctek battery charger has a float voltage of 14 volts?
I'd ask for my money back.
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Follow Up By: Member - Phil G (SA) - Sunday, Aug 19, 2012 at 19:16

Sunday, Aug 19, 2012 at 19:16
Dennis,
Captain's 25A Ctek is temperature compensated - so when the ambient temp is less than 25 degrees it raises the voltages. This is good! Also it has a pulse mode which follows float - voltage might pulse up to 14.4V.

My CTek DC-DC charger is also temp compensated - on mornings below freezing, I've seen voltages of almost 15V.
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Follow Up By: Member - Captain (WA) - Sunday, Aug 19, 2012 at 19:54

Sunday, Aug 19, 2012 at 19:54
Hi Allan B,

Every electrical thread ends in an overcompilcation, you should know that :)

Just look at this simple question - Olclone says no while others say yes. Point being all are right, just depends on what one uses as their basis.!!!

All the regular contibutors all know their batteries and what the issues/problems/causes/solutions are, but in their explanantions they make unstated assumptions and then another knowledgable contributor takes them to task. Happens here and every other forum with electrical threads and then the bunfight starts.... :)

The reality is they are usually all right and good to the see the OP has actually worked out the right answer for him.

While we all expect eletrical threads to have a single correct answer, the answer depends on so many variables that thead drift is inevitable. I respect all the regular contributors, yet we so rarely agree on what really should be "easy". I am sure we would all agree 100% when sitting around a campfire and clarify our simplified explanations.

............
As for my Ctek, if I leave a lamp on (~0.2A draw) the float voltage works fine. But have zero power draw and it drifts over 14V after a few days, nothng to do with the pulse mode or temperature compensation. When i enquired about it, was told the charger should be indirectly connected to the battery to stop the drift. Didn't make technical sense but the small load certainly fixes the issue.

Cheers

Captain
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Follow Up By: Dennis Ellery - Sunday, Aug 19, 2012 at 21:23

Sunday, Aug 19, 2012 at 21:23
Phil,
Captain was talking about a float voltage.
For a float voltage of 14 Volt you need to be living in a fridge.
At 25 deg Centigrade the float needs to be around 13.2 volts.
At 0 deg it needs to be 14 volt
For a 15 volt float, that you quote, your battery needs to be at -10 deg C
If you are talking about pulse voltages then this is something different
This sort of information is readily available from battery manufacturers on the web.
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Reply By: olcoolone - Sunday, Aug 19, 2012 at 12:41

Sunday, Aug 19, 2012 at 12:41
An alternator will not charge your battery fully.......It pays to look at the original engineering criteria of what the vehicle manufacture wanted to achieve.

FYI... A starting battery has only one goal in life and that's to supply enough energy to start the engine with in a given time frame of around 5 to 15 seconds.... after that it has very little more to do.

When they design a charging system for a vehicle there are many aspects to consider.... what climate is the vehicle going to be operating in.... what conditions is the vehicle going to be operating in.... how long is the vehicle going to be run.... how long is it going to be to start the vehicle.... what load is going to be placed on the battery when the vehicle is not running.... when will the vehicle be run again.... what type or manufacture of the battery is going to be used in the future.... what quality of battery is going to be used in the future.... is the battery going to be maintained correctly.... and what effect on fuel usage and emissions is it going to have.

As you can see there are many criteria the engineers have to deal with, and there are many different charge conditions that have to be addressed.

A vehicle charging system has two goals.... firstly it must supply amply current and voltage to run the vehicle and everything factory fitted under all conditions.... the second thing is to charge the battery enough to enable the vehicle to start the next time.

The second one is the hardest criteria to design with so many unknown variables to consider, there has to be a big variable in charging the battery to not undercharge it or to over charge it, this is where this "a vehicle battery will only charge to 70-80% SOC".... 70-80SOC is reconsigned as a safe limit for charging battery's under most conditions, it enables the vehicle to start quickly, gives OK battery life, has ample reserve and places less load on the charging system.

Hence "lets dump big current and volts into a battery for the shortest period so the battery can start the vehicle next time"

Most charging systems fitted to vehicles prior to 2001 are very dumb in what they can do and how the function.... think " I'm not very smart but I can lift big weights".

Around 2001 more and more vehicles started to appear with a smart charging systems where by an ECU with it's own map would process the information and only charge when really needed, modern day charging systems can control voltage, current and frequency..... the down side of this; seeing it was really designed for better fuel consumption, better emissions, more engine power and making the NVH of the vehicle better is they have lowered the SOC of the battery down to 60-70%.... most new vehicle have smart start technology making them start with in 5 seconds of cranking.

Most new vehicle have time driven auto disconnect of factory fitted electrical gear just in case something was left on like interior lights..... they don't have to headroom anymore to get away with it.

As for secondary battery's....... the engineers who designed the charging system had no interest in even thinking someone may add an aux battery..... with some manufactures you can spec an upgraded charging system designed to charge the starting battery more and also charge a secondary battery fully, GM do it in the USA and some of the commercial vehicle manufactures in Europe (ambulance and rescue vehicles) but to my knowledge this is not available to the general public.

As for your 8 amp charger charging it to 100% SOC..... yes they do because the battery charger manufacture know the fixed non variable conditions the battery will be charged under.




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Follow Up By: Dennis Ellery - Sunday, Aug 19, 2012 at 15:11

Sunday, Aug 19, 2012 at 15:11
“Around 2001 more and more vehicles started to appear with a smart charging systems where by an ECU with it's own map would process the information and only charge when really needed, modern day charging systems can control voltage, current and frequency”
This doesn’t apply to the Toyota 70 series 2008 V8 Diesel’s alternator. It’s voltage starts at 13.9 volts and after the motor has warmed up drops back to around 13.5 volts.
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Follow Up By: olcoolone - Sunday, Aug 19, 2012 at 19:51

Sunday, Aug 19, 2012 at 19:51
No not all run ECU controlled alternators and as said more and more a starting to, especially in the passenger market with idle speeds as low as 400RPM and where fuel consumption is so critical.

A manufactures view regarding ECU controlled alternators offer them heaps of advantages over conventional charging systems.

An alternator can zap the engine of 6Kw's of power whilst charging.

You will find the Toyota V8 Landcruiser 70 series will only charge to that 60-70 SOC rate..... it won't be long till it gets one.

They have even been known to drop down to 12.9v, our 200 series will, years ago with the good old RE55 regulators you would see 14.2v and up to 14.6v constant with the HD version.

It's surprising how much .5v makes to the SOC of a battery and also fuel use and emissions.

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Follow Up By: Dennis Ellery - Sunday, Aug 19, 2012 at 21:37

Sunday, Aug 19, 2012 at 21:37
Hi olcoolone,
The 2nd battery of my 70 series V8 Diesel gets up to just on 70 deg C when towing a load on long trips etc. That’s why they have a low voltage alternator and thats temperature controlled.
Its a matter of opinion whether there is an advantage going to a smart charger.

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Reply By: Allan B (Member, SunCoast) - Sunday, Aug 19, 2012 at 17:27

Sunday, Aug 19, 2012 at 17:27
Hi Roughasguts, if you started out "a bit confused" I bet you are totally bewildered by now. Ask a simple question and you get a host of convoluted responses of technical expression which provide no assistance to you.

Doug T provided the simple answer and Phil G qualified it. Then there was a heap of pseudo-science!

When you say "dead flat" I would assume you meant such a low State of Charge that you were unable to start the engine. And when you say "fully charged" I assume you mean to the level that the car manufacturer designed. ( Because there can be other meanings of "dead" and "fully".

The simple answer then is yes, the car alternator can recharge from a discharged condition to a fully charged condition and maintain that charge. An illustration of this is where a car is jump-started from a second battery then proceeds to recharge the original battery to a fully-charged state in due time. A pretty common occurrence.

Using the cranking battery for your caravan lights or radio and discharging it to "50%" may well be below the level needed to crank the engine to restart. Furthermore, repeated discharges to a low level will eventually harm a cranking battery. If you need to run lights from a battery then it should be a suitable type installed in the caravan.

The car alternator is quite suitable to maintain the charge in your battery when that battery is being used as the manufacturer intended, i.e. cranking the engine to start. All the other loads, headlights, fan, radio, etc. are then being supplied directly by the alternator, not by the battery. If this were not so then there would be a lot of cars at the side of the road with their bonnet up!

Cheers
Allan

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Reply By: Roughasguts - Sunday, Aug 19, 2012 at 18:07

Sunday, Aug 19, 2012 at 18:07
Thanks Guy's actually that has cleared it up for me!
Don't mind the simple explanation or the technical answer it's all good.

Anyway what I have determined is that my Pajero that only does 20km per week ! and has the new truck battery in it! power everything! and tow vehicle, could do with a battery charge every month along with me Boat battery.

But the Toyota that does some 220 Km a day freeway trip! will not ever need a top up with a charger to keep in good condition.

Why the question is that my lovely 4 year old Son loves to hit interior light switches and has done it to both vehicles the Toyota a 0ne day old battery needed a jump start very next morning! and the Pajero which was left for over a week with the map light on needed a long stint on the charger to get it back to what I hope is a good condition.

Cheers
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