# Aaargh! Battery Mystery



## perfrej (Dec 24, 2009)

Folks, 

I decided that I had a bad LH battery and got myself a brand new AGM 12V/95Ah 870CCA which I charged properly over two days with a large Ctek charger. 

Spendt the mandatory 45 minutes trying to figure out how the darn fuse thinge was fastened and finally got it off. The new battery went in with no problems apart from muscular catastrophy. Heater then fired up again nicely and all was well. 

Now I find that the heater is once again failing on me and this morning I decided to check on the current state of affairs in the battery department. Hear this: mild morning (-6°C). LH battery 11.7V, RH 13.42V. What? That is truly top charged! 

So, I get my extremeley expensive amp meter out and attatch it to the LH battery's positive thing, zero it out and open the driver's door. -4.6A. Fine. 

Next, push the start button without having the foot on the brake pedal, Xenon goes on, ding-dong etc. -52A. That too sounds OK for a W12 with tons of nice equipment. 

Start her up - need I tell you the cranking speed with that RH battery state?  

Now, LH is getting som +30A to begin with and this levels out and creeps down to +8A as the voltage climbs up to a little over 12.5V. Just to check... What's the RH battery doing? Yikes(!) 15.4V. 

Apparently, the alternator is doing its thing properly, but the distribution of produced goods appear somewhat uneven to say the least. 

Anyone had a similar problem? Am I looking at replacing the battery controller? 

HELP! 

Best, 

Per


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## PanEuropean (Nov 3, 2001)

Hi Per: 

You have a 2008 vehicle, so, you are well past the difficulties that we had with early versions of the battery controller on the 2003/2004 vehicles. 

I'm not sure what would cause your battery controller to send such a high voltage to the right-hand battery - I think this is one of those unusual electrical questions that we need Willem to help us figure out. 

Michael


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## Paximus (Aug 26, 2011)

Hi Per, 

In TPI 2008818/18, VW quote this voltage at the battery - they are talking about how to test the alternator. (I simplified the text a little) : 



"[After 5 minutes running] on vehicles with multiple screwed connection (e.g. Touareg, Phaeton) the voltage on the battery [when the alternator is charging properly at idle with all consumers on] must be at least 13.9 V. If the battery is discharged after a long motorway journey, check the alternator additionally for 20 minutes at 3000 rpm. 

Charge the battery according to the repair manual for 23 hours and check the battery after at least one hour waiting time. If necessary, replace the battery according to the repair manual. 

If a second battery is fitted, check it also with an open-circuit measurement. If necessary, charge and check it as well. An incorrect second battery can prevent the charging of the main battery."
 
I highlighted the red, because it implies that if the starter battery has raised internal resistance (high than normal voltage under charge) it can affect the charging of the main battery. 

But it is complex to consider battery charging effects, so that simple statement may not be relevant to you. 

Chris


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## perfrej (Dec 24, 2009)

Ah!, thankks Chris! I actually bought a starter AGM as well while I was at it. It proves to be more difficult than the left to replace, actually, because of the rear seat entertainment system that sits above it. It looks real difficult to get at, but I will attempt it today.

Michael, it is the 2006  and I have noted that it indeed is a late version of the battery controller.

/per


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## WillemBal (Nov 20, 2010)

Paximus said:


> [After 5 minutes running] on vehicles with multiple screwed connection (e.g. Touareg, Phaeton) the voltage on the battery [when the alternator is charging properly at idle with all consumers on] must be at least 13.9 V.


Chris, 
This must either be very optimistic or I have to replace my alternator then. Ghee, with all consumers on my LH battery voltage barely comes above 13 Volts! In addition, it seems a bit strange then that the SSG about the onboard power system states that the RPM is raised when the voltage drops below 12.2 Volts or near that value, until the voltage is again above a certain safe limit  I guess it must be a kind of "safety" feature, i.e. when that when the charging system is not operating as expected, the RPM is raised. 



perfrej said:


> Just to check... What's the RH battery doing? Yikes(!) 15.4V. Apparently, the alternator is doing its thing properly, but the distribution of produced goods appear somewhat uneven to say the least.


Hi Per, I have made many measurements using calibrated DMM's, oscilloscopes and by means of VCDS logging, and all of them indicate that the normal RH voltage is near 15 Volts.
I reported some measurements HERE, using an oscilloscope, so you can see the change in voltage of the 2 batteries before and after starting the engine.
I in fact DO have some notorious problems with the charge status of the LH battery, as the result of short trips and frequent use of the stand heater, but starting the engine was never an issue.
When you never had any starting problems, then it should be all right. FYI, I have the smaller, standard starter battery, which is a normal SLA battery with a capacity of round 60 Ah, if I'm not mistaking. Engine starts in 1.5 seconds after pressing the start button.

But did you experience any starting problems at all?


Willem


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## perfrej (Dec 24, 2009)

OK, I have moved some batteries around and checked the self study guide. It turned out that I had bought an AGM that was slightly larger than the starter battery so I had to revert to using the "old" (2011/w10) LH battery. So I now have a really good starter battery as well 

It appears that the new LH takes charge a bit better with the old starter battery gone. I am going to run it for a few days and monitor the state of affairs closely.

Getting the Rear Seat Entertainment system out of the way in order to replace the starter battery proved to be a bit of a challange as well. While I have that out of the way I am replacing the DVD player with a Pocorn Hour media computer with a TB of storage - just for the heck of it...

/per


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## Paximus (Aug 26, 2011)

> This must either be very optimistic or I have to replace my alternator then.
> WillemBal


I agree with you!

VW say that a car without screwed cable joints between the alternator and the battery should have a voltage of 14.1 at the battery. A car with joints, such as the Phaeton, should have 13.9V, both measured at engine idle speed.

VW also say that during the same test both should have an alternator current >30A. But I though the P drew >40A. So the battery must be discharging at least 10A. So surely it can't have a voltage of 13.9?

Chris


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## WillemBal (Nov 20, 2010)

Paximus said:


> VW say that a car without screwed cable joints between the alternator and the battery should have a voltage of 14.1 at the battery. A car with joints, such as the Phaeton, should have 13.9V, both measured at engine idle speed.


That's right, some voltage drop is unavoidable and acceptable and indeed should be less than 0.2 Volts. I measured 0.1 Volts between the battery post and the junction post of the LH battery under the hood, which is as close as you can get to the battery.


> VW also say that during the same test both should have an alternator current >30A. But I though the P drew >40A. So the battery must be discharging at least 10A. So surely it can't have a voltage of 13.9?


Hey Chris, this seems to be some information and math calculation that seems a bit puzzling to me. 
For instance, what do you mean by "Both should have an alternator current >30A". There is only one alternator, so there can only be one current. And the RH battery is fed by the controller. And the controller is fed by the alternator AND the LH battery. So what is VW trying to say here? 

It's also a bit strange that the system test requires an alternator current of >30A, given the fact that the specification of the alternator is 190 Amps. I can imagine that supplying 190A at 500 RPM (alternator RPM=1500 then) the supply is a little less, but surely a lot more than the stated 30 Amps.
Can you perhaps post the document where you found this text or copy/paste the text here on the forum? It sounds like interesting information...

Willem


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## Gabs08PHTN (Jan 6, 2011)

Hi all,
I have just checked the batteries voltage after returning from work with the engine iddling and I got 14.4V for the convenience battery and 14.6V for the starter battery. 
I made the measurements at the posts in the engine compartment.
Cheers.

Gabriel


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## Paximus (Aug 26, 2011)

> what do you mean by "Both"...


Hi Willem,

Sorry, my English was not clear (Netherlands people always speak better English than those from GB - true).

I only meant 'both' of these:

-- cars with no cable joints which should be 14.1V
-- cars with cable joints (Phaeton/Touareg) which should be 13.9V.

I'll post the doc when I get back to base.

Cheers,
Chris


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## Itzmann (Jan 16, 2006)

Fellows, I admit to much ignorance on battery matters but having owned a sailboat for a few months, I have learned:

1. AGM batteries require charging voltages that are different from other lead/acid batteries.

2. In the marine world you are advised to "never mix battery chemistries", i.e., banks of different batteries must be isolated from each other in their charge states and in their consumption states.

3. In the marine world, where battery chargers can be quite sophisticated, one is supposed to tell the battery charger what type of chemistry the battery bank being charged has, so that the charger uses the correct parameters (voltage / amps / bulk charge / float / maintenance cycles)

They say a little knowledge is dangerous. When I knew nothing about batteries, I did not worry about the left battery and the right battery. Now I wonder how that works.

For the record, our Phaeton is *currently in the shop with a dead left battery* being replaced (technician advised it holds no charge anymore). The new one will be the third battery. 52,000 miles.

Cheers,


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## Paximus (Aug 26, 2011)

> They say a little knowledge is dangerous. When I knew nothing about batteries, I did not worry about the left battery and the right battery. Now I wonder how that works.


Hi,

That marine experience is very relevant.

Clearly the VW engineers firewalled the right battery from the left battery/alternator charging system by inserting the battery control charger module between the former system and the right battery.

If the module decides it's OK to take normal alternator charge voltage across to the right battery it does that, but if it decides that is inappropriate it inserts the DC-DC voltage converter to take separate control of the right battery voltage/charge. This allows the system to have the choice of a lead-acid or AGM battery in the right position.

VW have stated that a poor right battery can corrupt the correct charging (and therefore life expectancy) of the left battery. I wonder if your right battery is causing the relatively frequent need to change your left battery?

Chris


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## perfrej (Dec 24, 2009)

Charging my left again...

I'm starting to think that maybe the cables are bad somewhere or the alternator isn't supplying enough juice.

On idle, after an hour-long drive, I have 12.7V LH and 2-3A going into the battery - nowhere near a proper charging current! I know the car uses around 50A with engine off. The RH battery is the previous LH battery re-conditioned for five days with a Cetek 100 (the larger one) charger. Said charger is now (at -10°C ambient) supplying around 8A to the LH in high voltage mode (15.7V) just to pump it full. I will then refrain from using the heater for a few days and see if it maintains charge or loses it.

/p


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## Gabs08PHTN (Jan 6, 2011)

Hi Per,
I know it may seem too obvious but every little helps....
I suggest that you clean the battery terminal posts with a scotchbrite and the battery connectors as well, just in case there is some dirt in there.
Cheers.

Gabriel


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## Paximus (Aug 26, 2011)

> On idle, after an hour-long drive, I have 12.7V LH and 2-3A going into the battery


Hi Per,

If that 2-3 amps is the current into the battery at idle after 1 hour of running then it doesn't sound too bad. The alternator should be producing sufficient current to run the car (as you say, 30 or 40 amps is feasible, depending on the consumers) so the battery will only need a stabilising charge of a couple of amps at a nominal 13.6V.

If an ammeter is in series with the battery then that will be dropping perhaps one or two tenths of a volt, itself causing a reduction in the current pushed into the battery.

The bulk of the car's current demand will be running along the alternator cable direct to the consumers, not through the battery terminal.

That VW figure of 13.9V at the battery was after only 5 minutes of running, not 1 hour, so the voltage would be higher than 13.6 to push a stronger recharge than 3A into the battery.

Chris


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## perfrej (Dec 24, 2009)

Well, I'm not comfortable with it. Somebody else is stealing all the current, given that the alternator is OK. I measure the amps with a Kyoritsu clamp meter that does DC (it was expensive ) so it doesn't steal anything and the measurements should be OK.

If the battery has a voltage of just 12.3 or something after a long ride and only 2A is going in, then something is amiss. An AGM battery will suck up twice the current of a normal L/A battery, which in numbers is 50% of rating for AGM and 25-30 for wet L/A. 95Ah means it should simply suck up at least 20-30 from a source that can deliver 190A, right? Probably even 45A or so.

I have AGM batteries in my boat and the alternators there crank out a mere 70A a piece. Still, the AGM battery with 11.9V in it will draw a good 30A off the alternator, slightly less when passing 12.84V.

Hmmmmm... Engine coming out? 

/per


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## PowerDubs (Jul 22, 2001)

Try unplugging the fridge?


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## WillemBal (Nov 20, 2010)

perfrej said:


> Well, I'm not comfortable with it. Somebody else is stealing all the current, given that the alternator is OK. I measure the amps with a Kyoritsu clamp meter that does DC (it was expensive ) so it doesn't steal anything and the measurements should be OK.


Hi Per,
Where you also able to measure the current directly from the alternator and how much amps did you measure? I think it should be possible to make some current logistics inventory by measuring the current going into junction TV22 (from alternator) as well as the two branches at the other side, one of which is feeding the central electronics controller and drive train controllers, the other of the two feeds to the electronics in the rear and the battery.
My estimate is that you should be measuring at least 80 Amps coming from the alternator and 2 x 40 Amps for the two going out.

Willem


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## spitfire1 (Apr 28, 2008)

dont forget that you might have a bad voltage regulator. check the voltage when the car is warmed up or after a half hour drive. if it is within spec it doesnt mean that its good, i have seen many bad regulators that work fine on day and fail the other. just did one last week. one other thing to remember is that resistance isnt as important as voltage drop. check the drop from the positive post in the engine bay to the main battery in the trunk. cant recall the spec but think anything over 1.5 volts is bad. good luck, remember its a phaeton and nothing makes sense in that car. btw does it set any fault for over/under voltage


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## perfrej (Dec 24, 2009)

New thoughts...

1. The LH battery is connected directly to the alternator
This means that if the cables are OK and the alternator is OK nothing can prevent the LH battery from getting adequate charge.

2. The RH battery is not connected to the alternator
It is connected to the alternator eaither via a direct relay path or via a DC/DC converter that lives in the battery management controller. So, even with a solid 11V (for example) out of the alternator, the RH battery will reach 15V by means of the DC/DC converter.

3. If I charge the LH battery to 13.2 volts and the alternator and the cables are OK..
Then I start the car, which takes about 50A. The generator can supply up to 190A continously. The voltage on the LH battery should stay at alternator output, which should be around 14V minimum

So, I disconnected the RH battery. LH is still getting a mere 12.4-12.8V. The instrument cluster meter shows just under 14V. Terminal 30 under the hood shows 0.1-0.2V less than the LH battery.

All I can think of now is either or two or three of the following:

A. Alternator bad
B. Cable from alternator via T30 to LH battery is bad
C. Sense wire to alternator is bad

There are no fault codes in the battery monitor and it doesn't do anything that has to do with LH battery charging...

/per


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## perfrej (Dec 24, 2009)

I have not had a chance to measure the alternator output current or voltage. I can hardly find the thing! Lots of stuff in there... 

/per


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## invisiblewave (Sep 22, 2008)

You can check the alternator by measuring the battery terminals with the engine running.


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## Gabs08PHTN (Jan 6, 2011)

Hi Per,
Have you checked the fuses of the main fuse box located on the left hand side of the luggage compartment. It is depicted on SSP 272 page 10. There is a fuse half way through the alternator and the on board power supply batery.
I guess it is worth checking! 
Best of luck!

Gabriel


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## WillemBal (Nov 20, 2010)

perfrej said:


> > 1. The LH battery is connected directly to the alternator
> > This means that if the cables are OK and the alternator is OK nothing can prevent the LH battery from getting adequate charge.
> 
> 
> ...


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## perfrej (Dec 24, 2009)

You guys are great!

I was just coming to the big fuse which I found disturbing. I'll measure it tomorrow!

And yes, the voltage was slightly higher under the hood, not slightly lower. Typo...

Off to bed and then some fusion!

/per


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## WillemBal (Nov 20, 2010)

Enjoy your fusion


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## Gabs08PHTN (Jan 6, 2011)

Per, if you produce enough energy during the fusion process, it might be a good time to charge up the left hand battery...


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## WillemBal (Nov 20, 2010)

This just HAS to end in a happy ending with both centre batteries discharged


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## perfrej (Dec 24, 2009)

OK, quick one: exactly where does the instrument cluster volt meter pick up its signal?

Reason I ask is that I do have 14 indicated there but it never gets to the battery. Also, it drops some when I turn on the heated rear window...

/per


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## n968412L (Apr 23, 2009)

perfrej said:


> OK, quick one: exactly where does the instrument cluster volt meter pick up its signal?
> 
> Reason I ask is that I do have 14 indicated there but it never gets to the battery. Also, it drops some when I turn on the heated rear window...
> 
> /per


Hi Per - we had a master class on this some time ago from Willem. The voltmeter is a trick, a con, a low down wheeze. It is not an analogue of the battery volts - it is a synthetic reading from one of the controllers... so you cannot really rely on it for diagnosis. It's not much more than an expensive and complex alternator warning light. If you can't find the thread, just shout and I'll have a root about for it.

Regards

M


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## WillemBal (Nov 20, 2010)

n968412L said:


> Hi Per - we had a master class on this some time ago from Willem. The voltmeter is a trick, a con, a low down wheeze. It is not an analogue of the battery volts - it is a synthetic reading from one of the controllers... so you cannot really rely on it for diagnosis. It's not much more than an expensive and complex alternator warning light. If you can't find the thread, just shout and I'll have a root about for it.


Hi Michael,
Hahaha...I'm still not sure though what exactly the dash panel meter is measuring. In my P, it apparently reads the same as the voltage as measured under the hood and directly on the RH battery. But perhaps that is true because the wiring is OK.



perfrej said:


> OK, quick one: exactly where does the instrument cluster volt meter pick up its signal? Reason I ask is that I do have 14 indicated there but it never gets to the battery. Also, it drops some when I turn on the heated rear window...


Hi Per,
If you have the Electrical Wiring Diagram of the 6.0 Engine - Motronic Fuel Injection etc.... then go to page 2 and there you will see the generator, marked C. It has B+, DFM and Terminal 61. The latter is an international designation for the *charge indicator (charge control light)* according to DIN-72552

This charge control wire (terminal 61) goes through connector T3, pin 2. Then a blue wire goes from that connector to another connector T17g, pin 9. That connector is probably located somewhere under the steering wheel.
In the end, it connects to connector T32 pin 12. This one is one of the Instrument Cluster Control Module connectors. It might be very difficult to find these connectors...at least I could not find them in the repair manual.

On the other hand, if we can trust that the dash panel voltmeter at least indicates the voltage at terminal 61 (what you refer to as sense wire), while you are measuring a different voltage at the battery, then this might indicate a malfunction of the generator or a bad wire junction (TV22 under the hood, just 4 mm next to the jump start post) or at the generator itself. It should be easier to measure those voltages than to trace that stupid charge control wire...which is working anyway.

Willem


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## n968412L (Apr 23, 2009)

WillemBal said:


> Hi Michael,
> Hahaha...I'm still not sure though what exactly the dash panel meter is measuring. In my P, it apparently reads the same as the voltage as measured under the hood and directly on the RH battery. But perhaps that is true because the wiring is OK.


Heavens Willem - don't confuse me with Michael... I'm not that erudite!

Not my memory... but as you made the tests I defer to your memory. Couldn't find the post where we did all that work - I think we logged all sorts of controller voltages - and you had an actual oscilloscope!

Mike


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## Paximus (Aug 26, 2011)

There is an opinion that the dashboard computer sets the dial to 14V whenever the real voltage is between 13.6V and perhaps 14.4V. This is so as not to cause the driver to worry about small fluctuations which happen in normal use.

If putting on your rear window heater drops the voltage to 13.5 the voltmeter will probably drop.

At least, that hypothesis seems to agree with the evidence presented so far.

Chris


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## WillemBal (Nov 20, 2010)

n968412L said:


> Heavens Willem - don't confuse me with Michael... I'm not that erudite!
> 
> Not my memory... but as you made the tests I defer to your memory. Couldn't find the post where we did all that work - I think we logged all sorts of controller voltages - and you had an actual oscilloscope!
> Mike


Sorry Mike, perhaps I considered you to be an erudite person as well. 
It is good you mention that. The full thread became pretty lengthy after a while.
It is over here: 
Help-Needed-for-Alternator-Problems-amp-Measurements-Using-VCDS
Perhaps you were referring to this oscilloscope screen shot, which was made with two sensing probes directly on the two junctions under the hood:

I hooked up two voltage probes on the TV2 and TV22 junction. The TV2 junction is tied to B+ of the starter motor though a very high diameter conductor, while the other end of that junction goes to the starter battery.
So when the car starts, it sees the voltage of the unloaded starter battery.

The other sensing probe was connected to the TV22 junction, better known as the jump start post. This guy is just one meter away from the generator, while the other end of that junction connects to the LH battery via a 5 meter long cable and the big 300 Amp fuse in the trunk.

Below picture was made while I started the car.










The horizontal scale represents the time scale. Each division represents 5 seconds; therefore the left most division represents a moment which is about 12.5 seconds prior to starting the engine.
The vertical scale represents the voltage value. Each division above the base line is 2 Volts.

The yellow trace represents the voltage at the TV22 junction, so that is basically the voltage of the LH battery when the load is low. You can see that it drops sharply during perhaps 1.5 seconds. That is about the time that the starter motor needs for starting the engine. Why that LH voltage drops during starting the engine, I'll explain later.
The blue trace represents the voltage at the TV2 junction, i.e. the jump post value and therefore is the starter battery voltage. Prior to starting, it sits at a little more than 7.5 divisions height. So the voltage then is a bit more than 7.5 div x 2 Volts/div = 15 Volts. Let's say it is 15.2 Volts.
That voltage drops more when the starter motor is engaged. The minimum of that first peak sits at 5.4 divisions, so the voltage shoots to 10.8 volts for a very short time. That is normal, since there is running a current of a few 100 Amps then.

When you look carefully, you can see that the orange trace (LH battery voltage) only drops AFTER the engine has started. That moment occurs about 1.5 seconds later, so just 0.3 divisions after the first negative going peak. I believe that at that particular moment, the battery charge controller starts demanding power from the LH battery to recharge the starter battery. About 5 seconds later, the LH battery voltage (orange trace) goes to 7 divisions, which is the equivalent of 14 Volts.

As you can see, the blue trace (starter battery voltage) needs a bit more time to recover. That is due to large power consumption during the starting procedure. Still, it recovers relatively quickly to 15.2 Volts, because barely 0.1 Ah of charge was used during starting.

Below shows how the oscilloscope probes were connected:









Connection C1 leads to the fuse box. (25 mm2 wire)
Connection B1 leads to the battery in the trunk (via a 5 meter long, 50 mm2 wire and a 300A fuse)
Connection A1 leads to the starter battery (95 mm2 wire)
Connection E1 goes to the generator. It connects to B1 and C1.
Connection D1 goes to the starter motor. It connects to A1

You may want to use a DMM and connect it to E1. Or when you lift the debris screen that covers the air intake plenum chamber, you can lift a small black panel that covers A1, B1 and C1.

Willem


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## WillemBal (Nov 20, 2010)

Paximus said:


> There is an opinion that the dashboard computer sets the dial to 14V whenever the real voltage is between 13.6V and perhaps 14.4V. This is so as not to cause the driver to worry about small fluctuations which happen in normal use.
> 
> If putting on your rear window heater drops the voltage to 13.5 the voltmeter will probably drop.
> 
> ...


Hi Chris,
You put it well: it is an opinion.  I've seen nothing else than that my dash panel meter follows the voltage as reported by the Central Electronics Controller. (which happens to be the closest to the generator of all controllers).
Btw... what do you observe when you did not yet start the engine, but turned on the ignition. Does it really indicate 14 Volts? And what happens during starting the engine? And shortly thereafter. Could it be that it first indicates a bit more than 12 Volts, then 11 or lower during starting, then kind of hesitates and then climbs to 14 Volts?

In Per's case, it could be that the B+ connection is corroded. The dash panel meter may be looking at terminal 61 of the generator, which is an unloaded voltage. So when the generator supplies current, the corroded B+ terminal causes a voltage drop. Or the generator is simply in bad shape.

Willem


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## Paximus (Aug 26, 2011)

Hi Willem,

My voltmeter agrees approximately with your scope measurements at startup, apart from the dip which is not shown on the meter. The voltmeter rises from its steady 11.8 to 14.0 between the 4th and 6th second from ignition.

Both batteries were only a few months old when I recorded this.

[Edit - on carefully listening, I can hear a change in the engine idle load between the 4th and 6th seconds as the voltmeter starts to climb. I wonder if the alternator current (and its physical load on the engine) is held off between 0 and 4 seconds while the systems stabilise?]

Chris


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## Nick900 (Nov 13, 2007)

Hi Per,

Have you managed to solve the problem yet?

Regards

Nick


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## Voodtje (Oct 23, 2009)

Dag Willem, Hi guys,

After reading this thread, i would like your opinion on the following:

I had a dead LH battery. After using another battery as help, the car started and I drove 100 km.
After the ride and one hour waiting: dead again. I changed the battery for an AGM type. After the change, all worked good, EXEPT the voltage meter on the dash: 0 volt.
After driving for an hour, the voltage on the battery raised to 17,8 Volt. Two hours later it was 13,6 and 15,4 Volt after starting the car and let it run at 3000 rpm.

Now I’m afraid to drive the car, as this high voltage might demolish electronical components. 

Why is this voltmeter not working? Could it have something to do with something disconnected while changing the battery? Could the voltage regulator have accidentally been disconnected or has broke up?

Could anyone give me some solutions as I’m not quite sure where to go from here.

Jean-Pierre


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## Tiger0002 (Apr 23, 2013)

Voodtje said:


> Dag Willem, Hi guys,
> 
> After reading this thread, i would like your opinion on the following:
> 
> ...



I would clean and inspect all external connections... alternator to battery connection... engine ground strap... add another ground strap to solid point of connection... It does not hurt to have more engine ground strap.

If you have loose or corroded ground strap, it will play a havoc on electrical system.


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## perfrej (Dec 24, 2009)

Nik,

I'm scheduled for a possible engine out operation May 27th (insurance claim  )

We'll see what comes out of it, be it corroded cable between alternator and T30 in engine compartment or bad alternator...

/per


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## Tiger0002 (Apr 23, 2013)

perfrej said:


> Nik,
> 
> I'm scheduled for a possible engine out operation May 27th (insurance claim  )
> 
> ...


Engine out! Wow... even if the connection is not corroded, Tell them to remove, clean, deoxidize and treat all available common ground connections.


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## perfrej (Dec 24, 2009)

*News...*

Today my mechanic started on the investigation. The cable from B+ on the alternator to T30 up by the jumper connection is broken. There is a crack in the insulation of the cable and it looks very corroded. He measured the voltage at idle on the B+ itself and it is in the neighborhodd of 13.6V.

So, it is a cable issue, something that may take it of the insurance's reach 

Has anyone had a W12 out and looked at how that cable is routed? We think we may be able to get another cable in there and leave the old in place - without engine-out...

/per


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## Jxander (Aug 5, 2008)

perfrej said:


> Today my mechanic started on the investigation. The cable from B+ on the alternator to T30 up by the jumper connection is broken. There is a crack in the insulation of the cable and it looks very corroded. He measured the voltage at idle on the B+ itself and it is in the neighborhodd of 13.6V.
> 
> So, it is a cable issue, something that may take it of the insurance's reach
> 
> ...


Per:

We're all hoping it is not an engine out task. It sounds like you think you can access both connecting points of the old cable. If so and assuming the old cable is not fastened somewhere else along its route, you may be able to attach the new cable to one end of the old and use the old to pull the new cable into position. Once the old is free at the two ends you will probably be able to tell if it's free along its length. Just a thought since it sounds great in theory. However, it sounds like you and the tech are on top of it and trying all options that seem practical. 

I don't mind seeing engine removal to perform significant repair or maintenance tasks, but I hate to see it done for the "little things." I think the V8 is around around 20 hours for in and out of engine. I assume the W12 is even more. 

Good luck.

Jim X


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## perfrej (Dec 24, 2009)

Thanks, Jim.

The cable runs in sleeve with the starter cable and is fastened, so the good old "pull the old one out and the new one in" trick is not an option. I have e-mailed the factory a routing plan for the cable in question...

/p


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## perfrej (Dec 24, 2009)

Insurance company said yes!

Engine's on its way out tomorrow morning.

/per


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## perfrej (Dec 24, 2009)

Ok, he managed to change the cable without taking the engine out. Lots of stuff was removed and in the end he got it all back together. The LH battery now sucks 45A out of the alternator, which is just about what an AGM battery should be able to accept (50% of the rating).

Drove through most of Germany today and wow, is this an autobahn eater or what? Too much traffic to get her up to top speed but I managed 280 km/h. No cigar today.



/p


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## Paximus (Aug 26, 2011)

Hi Per, 

That is really good news! (Both about the cable and the nice run through Germany!)  

Can you now confirm that the cable was corroded? Is the exact position of the corrosion known? This may be something for other folks to bear in mind if they suspect a problem. 

Chris


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## Gabs08PHTN (Jan 6, 2011)

Congratulations Per !!! :thumbup:
Please, post some pics. Would you?
Cheers.

Gabriel


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## WillemBal (Nov 20, 2010)

perfrej said:


> Ok, he managed to change the cable without taking the engine out. Lots of stuff was removed and in the end he got it all back together. The LH battery now sucks 45A out of the alternator, which is just about what an AGM battery should be able to accept (50% of the rating).


Djeez, that's a lot! I didn't know that and AGM battery could handle such a high charge rate. Did you measure the charge current near the battery (where it is net charge current to the battery) or near the alternator (which is the total current to the electrical system). Near the battery, I measure 20 Amps at best.



> Drove through most of Germany today and wow, is this an autobahn eater or what? Too much traffic to get her up to top speed but I managed 280 km/h.


280 km/h is the very highest speed I could reach on an empty road.




> No cigar today.


Well, that is ashame!

Regards, Willem


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## perfrej (Dec 24, 2009)

The only image I have is of the cable itself. I wasn't present during disassembly.










A normal lead-acid battery will consume up to about 25% of the rated capacity while charging. AGM effectively doubles that and adds a lot more deep discharge tolerance. A Phaeton with normal battery would thus be able to "suck" only 23A out of the system, while the AGM battery manages 45-50A. I saw above 60A directly after start.

I measured at the battery with a Kyocera clamp meter, a very good one. There is simply no way to measure near the alternator, but maybe up by T30 by the engine. That would show the real output of the alternator.

If you only see 20A, what is the drain with ignition on and engine off? Mine is 56-65A.

285 km/h is my current top rating and that was on wet asphalt with a head wind and the car was still accelerating  I think it will do 300-310 easily.

/p


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## Juhani (Sep 15, 2012)

*T61*

Exelent thread, it wuold interesting to know is T61 in alternator really good old lamp terminal controlling charge lamp in dashboard or something else, if it is "sense" in style of US-alts. then you could manipulate charging voltage with it. In cold weather voltage should be more than 13.9v I am having, and it drops to 13,6v when rear PTC are on, so I use Willems trick to put rear hvac off usually. in -10...-20 14.6V would be fine to get battery full.


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## Gabs08PHTN (Jan 6, 2011)

Hi Juhani,
I agree with you in that the starter battery charging voltage is slightly above that of the on board power supply battery. 
However, most of the times when I have measured the charging voltage of both batteries I have always had readings above 14.5V. 
E.g. left battery: 14.74-14.67V. Right battery: 15.18-15.03V.
In any case, the charging voltage readings that you can observe, change depending on the condition of the batteries in that particular moment. I mean that the readings that you get when the engine has just been started will be different of those that you would observe after a long journey and so on.

Gabriel


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## cbh123 (Aug 25, 2013)

WillemBal said:


> Sorry Mike, perhaps I considered you to be an erudite person as well.
> It is good you mention that. The full thread became pretty lengthy after a while.
> It is over here:
> Help-Needed-for-Alternator-Problems-amp-Measurements-Using-VCDS
> ...



I have a slight difference of opinion here, and I think it is worth sorting out. 

the Jump starting post TV2 is part of TV22 and it does not go to the LHS (AGM) battery. This is why it is always important to hook up a charger to the LHS battery in the trunk while performing service on the car. I am 100% sure the jump starting post goes directly to the RHS starter battery. I think we all agree on this. 

The problem is with TV22 and whether it can be a test point for the LHS battery - for sure TV22 has several connections. they are Identified on this part of the wiring diagram TV2 is a part of the overall TV22 connection point - they are labeled the same in the photo above.










a - from AGM LHS battery goes directly to fuse 2 (S205) 
b - From Starter RHS battery goes directly to A1

A1 directly to starter battery 
TV2 is connected to A1 and D1 
B1 goes to fuse 1 and fuse 3 (S204 and S206) 
C1- goes to starter 
D1 - Goes to fuses (not clear where) 
E1 goes directly to Generator (alternator)

the fuse S330 says fuse in wire connector (fusible link?) is drawn INSIDE V22 

in any case there is no connection to the LHS battery shown - I don't think that the statement above that TV22 represents the LHS battery is true. 

the LHS battery is only charged through the charging control module and then connects to the vehicle power. 

I don't think it changes the problems that a corroded wire ( as discussed and replaced ) will cause. and it does not change the solution either. 

It seems the wire in question that can corrode (E1) will lower the voltage to TV22 from the alternator... and this will ultimately lower the voltage to the LHS battery down the line. 

let me know if I a mixed up lol it is not simple to understand


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## jyoung8607 (Feb 14, 2006)

cbh123 said:


> I have a slight difference of opinion here, and I think it is worth sorting out.


Sure.



cbh123 said:


> a - from AGM LHS battery goes directly to fuse 2 (S205)


Here's the misunderstanding. That whole shaded area represents a bus-bar with several very large fused connections. It's in a plastic box in the upper-right of the LHS battery compartment, the one with several thick cables running into it. Follow the line inside that box carefully; you'll see the LHS battery and the alternator connect via 300A fuse S206. Refer to SSP 272 page 10 for a decent illustration, although I think its listed fuse sizes are incorrect or outdated.

Jason


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## cbh123 (Aug 25, 2013)

If "a" is is connected via S206 to B1, which in turn connects to A1 via S330, and then to "b" then how can the charge controller give different voltages to each battery? Let alone keep them separated so that the parallel relay has any point at all...

I see what is being said but I'm pretty sure "a" and "b" are not connected by fuses... 

Something is not adding up.


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## Beastmode6.0 (Jan 8, 2013)

*Electrical gremlins ?*

Fighting all of the above, new alt., new starter, new stock batteries on second LH-Battery,new battery controller. Question has anyone tried an electric battery (Kinetik 2000)? I ask because I want to upgrade the radio display, however I want to lock the closet on the electrical gremlins first.:banghead:


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## perfrej (Dec 24, 2009)

That battery is AGM, and as such should pose no problem for the Phaeton electrical system... 

It is very important to stick to AGM technology on the left side. Remember that a W12 with the ignition on sucks a good 50-65A, and the ability to "suck charge" from the alternator is twice as good for AGM compared to standard lead-acid.

/per


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## jyoung8607 (Feb 14, 2006)

cbh123 said:


> If "a" is is connected via S206 to B1, which in turn connects to A1 via S330, and then to "b" ...
> 
> Something is not adding up.


Yeah, on further inspection of your diagram, that threw me for a curve as well. I'm not aware of that fuse or fusible link S330 existing on our cars as part of the TV2/TV22 assembly. So, I researched a bit more and figured it out. It's the bridge between the two sides for the rare (if ever even produced) single-battery design. Fuse S330 would be bolted across the holes in C1 and A1 in WillemBal's picture, bridging the two sides together at that point, with only one battery cable routed to the back rather than two. It shouldn't be present for dual-battery design.

I'd say you're looking at the wrong diagram, but my copy of Bentley has the single-battery diagram with a different ID and style, and its dual battery diagram is the same as yours except for that change. So I'm hazarding a guess that you're looking at the right diagram, but your source has an uncorrected error.

Jason

*Bentley Publishers dual-battery version of TV2 and TV22:*










*Bentley Publishers single-battery version of TV2 and TV22:*


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## Juhani (Sep 15, 2012)

Yes, fusible S330 is not there, batterys are not connected together exept when relay does it. I dont see how battery controller could influence charging of left battery, as it is directly connected to alternator, if you wuold like to adjust charging voltage on left battery it wuold viable to do it by manipulating alternator regulator where field current is just few amps, not by using DC-DC conversion for whole load of the car up to 200A. I have looked inside battery controller and for sure there is no such parts inside, there are transistors, coil, bla..bla good for maybe ten amps, so it can make 15V charge voltage to keep start battery full out of left battery even if voltage there wuold be 10V. Also it is not recomended ever that you have something else than solid wiring between bat. and alt, opening that connection can destroy alt and fry anything connected to it. My car has Delphi alt,
it only has DFM, Lamp, B+ output terminals, so there is no connection from battery controller could adjust output, 99% sure that alt uses ST L9409F microchip for control. This controller has "sense" input but its not used probably and if there is no connection on that pin voltage reference is taken from post B+ controller +V input. L9409 has temperature compensation so it makes about 0,5V more -10C that on +90C which is normal temp in V of the V10, this is about the way my car performs, cold bit over 14V hot 13,6-7V, this wuold be OK if battery wuold not be in cold trunk, and if you dont care that it is newer fully charged. I think you can get to the alt controller and also to brushes without taking alt out, just oilfilter assembly must be removed. Going to look this on weekend, if possible wiring sense pin out from alt, to connect that to left battery it wuold need new wire to + post of it. You cant renew bearings in alt this way, but its gear driven in dry place, and never sees radial load from belt tension.
I think that I use TV22 and diode in "sense" wire to raise voltage 0,5-6V. This is normal trick in US made Delphis and most alts used in marine, there you always use sense from bat+ and overcome loses in dividing diodes and resistance of wiring.
Juhani


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## cbh123 (Aug 25, 2013)

Does this mean I am crazy....?
Or not crazy?


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## Juhani (Sep 15, 2012)

cbh123 said:


> Does this mean I am crazy....?
> Or not crazy?


Yes and no, we are all crazy having this car probably. Seriously I think that engineers have been worried about starting car in all situations, and forgotten left battery in process, newer cars have controller looking over how many amps in - out from bat. where you need to give battery type etc. Charging system for left battery could be from -80tees or even -70tees, typically in german cars, low alt voltage as batterys in hot engine bay, losing water and dying for heat on autobahn driving. GM Delco had allready at the time alt regulators with temperature compensation and sense from bat+ post, and alternators were aircooled sensing from incoming cooling air. From alternators point of view battery is just an other load which consumes amps depending it charge state, type, condition, just like other loads. Leadacid battery works on chemistry its also a small condensator and sucks spikes making system more stable, it likes to be charged on fixed voltage, it needs also high currents to prevent plate sufitation, small currents only will render parts of plate surface unused useless. To get battery full you need higher voltage colder it is, chemistry is less efficient, and effiency is not 100% more like 60-70% if you take out 10Ah you need to put 15Ah back.
Willem has done exelent measurements, so no need to duplicate those, even if engine+systems consume 60-70A alternator is rated 190A continious and something like 300A short time, so it should have no problem to keep batteries topped up, if voltage is right, unless you only drive wery short drives.


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## jyoung8607 (Feb 14, 2006)

cbh123 said:


> Does this mean I am crazy....?
> Or not crazy?











You're not crazy. Bad wiring diagram ****ed you. 

Jason


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## PowerDubs (Jul 22, 2001)

cbh123 said:


> Does this mean I am crazy....?
> Or not crazy?




Am I allowed a vote? :wave:


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## cbh123 (Aug 25, 2013)

I dare ya


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## Juhani (Sep 15, 2012)

*V10 Alternator*

Well you can see altenator from top, there it sits in V under fuelfilters and stuff, Filters Inlet manifolds, few hoses, pipes, wiring has to cleared out before you can get alt out. There is not really enough room to get to regulator either or maybe if oilfiller tube would come out someway first. have an other look next saturday.


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## Juhani (Sep 15, 2012)

*Charging system*

Facts about system: 

Alternator lamp works like any car, regulator controlled as from seventies, reg knows to charge when it gets + through lamp.
Voltage meter shows exactly same voltage as VCDS from kombinstruments klemme 15, I didn't find any "normalisation feature" it shows 13,6 or 15V when you have it.
It is possible to get to regulator and brushes when you remove oilfilter and cooling lines of alternator, oil filler tube is next to impossible to remove before inletmanifold.

My car has Delphi alt. Regulator regulates with + brush, other is grounded. Alt has 12 diodes and douple delta windings. Regulator 8 pin IC says: "Delphi 0759 R88200314 Singapore" with what you find nothing. By measuring what pin goes where, it's an ST L9466 not ST L9409 which has sense, older one does not, they look the same but pin layout different so no easy swap.

This 9466 takes regulation "istwert" from + feed connected to main +B output, alt does not have separate diodes for regulation power as usual in Delco alts, there is also one phase AC connection from it starts to work even without charge lamp. Brushes were wery good dispite of 220tkm proofing the clean placement. 

I modified + VCC feed to come, not from output directly but from underhood connection point shown in Willem's picture, that alone raised output to steady 14V on +90deg, this is because voltage near loads is with less ripple than on output of alt, with 50A diode in line you get 14,7V, IC uses 6W and max current to field is 9A usually around 4-6A, so diode heats up about 10W max, needs cooling, with sense pin current in that is usually 10mA so any diode could do it.

Now I can use 14,7V for winter sub zero temps and just short diode over to have 14V for summer and left battery is happy and full. To make it real clever you could wire + in brush out from alt and use any controller which can take battery temp, ambient, battery amps out/in in count, and keep battery super happy like in my sailboat has.

Some P. have Hitachi alts, Hitachi claims to have NB-magnets in rotor so it uses less magnetising current, I dont know does Delphi use them nor that is there Hitachi with V10 mounting system, thast wery special.


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## Juhani (Sep 15, 2012)

*V10 Alternator*

Here are datasheets of controllers:

I am 99% sure that this is used in Delphi in 2003/2004, my alt is orginal late 2003.

http://www.st.com/web/en/resource/technical/document/datasheet/CD00055101.pdf

This I wuold prefer but its newer.

http://www.st.com/web/en/resource/technical/document/datasheet/DM00046326.pdf

Taking VCC from TV22 made alternator work more it wuold have PID controller or PI, orginally it works more like only P, voltage drops with load increase.
It now sees load better and resistance of feed wiring dont matter, but when more field current is needed then resistance of controller feed kinda of raises output 
voltge a bit,and does away lazy P conroller characteristic.
Best wuold be take feed from left battery but lot of work to do that.

I also removed fuses from rear PTC heaters and now I can have rear HVAC on, works well this still, and backseat is empty 90% of the time anyway.

I have some pics but dont know how to put them here.

PS. Thanks Paximus


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## Juhani (Sep 15, 2012)

*V10 Alternator*

I learned how to put pics in here.....

Here what you can see from top oilfilter, cooling hoses, wiring removed











it is impossible to take dustcover out in one piece so its more or less destroyed, but its not really important.











this is how regulator and brushes look like, reg with new feed wire soldered on.


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## Juhani (Sep 15, 2012)

*V10 Alternator*

Refined system with Schotty 20A diode in regulator feed, those diodes have low and constant voltage drop in forvard voltage, this case 0,5V. Left battery voltage is 14,5V on 10deg+ and 14,2V with 90deg. With VCDS, Controller 1 shows 40-45% load on 600rpm idle, dropping to 30% on 2000rpm on engine.meaning something like 60-90A load on alternator, seems to to be right. It also shows voltage of 13.7V, this can only come trought either lamp or DF terminal, as they are behind diode, real voltage is 14.2V in system at the same time. After about 2000km driving, using aux. heat in mornings, when connected left battery to automatic charger it only charged half hour and then hit 14,7V and reported battery full. Right battery is alweys 14.7V and also full with controller "D" it was the same with "B" Now this works like it should


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## 53PL-50AAA-VW611BAN (Feb 10, 2015)

What automatic charger do you use? 

My NAPA charger stops at 12V 100 %.

-Eric


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## perfrej (Dec 24, 2009)

Eric,

12V is 45% full for a lead-acid battery (AGM or normal)...










maybe buy a "proper" one? 

/per


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## 53PL-50AAA-VW611BAN (Feb 10, 2015)

Maybe you're right, Per.  

My NAPA charger usually says my batteries are 12.7 V when I hook them up, but charged from 41% to 72% or so.

I have started rotating the cars and keeping one on the charger when it's not being driven (P1 from Fri-Mon and P2 from Mon-Fri). Right now P2 is charged to 12V @ 100%.

I know my NAPA charger can read higher than 12V, but it seems to stop charging and goes into maintenance mode at 12V.

-Eric


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## PowerDubs (Jul 22, 2001)

I've got so many chargers it isn't funny. Everything from tiny wall warts, to small boxes, mid size from a boat that can charge 4 batteries at a time up to a large Schumacher unit on wheels.. all with different capabilities. In fact, I just received a new charger capable of charging a lithium battery I bought for one of my bikes.



A coupe months ago, I even picked up a charger from a Veyron. Awesome.. you can never have enough chargers.


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## Juhani (Sep 15, 2012)

*Charger*

Dont remember the make, but its 6A , has program for AGM, normal acid, recovery, and maintain.
It goes to 14,7V comes down to 14,4 wet, 14 AGM for few hours and then goes to float 13,3V
so you can leave it connected for long time.
If charger wuold only give 12V battery will never be full.
Lead acid battery works on chemistry, its an idiot, on 20deg it needs 14,7V to get full,
14 or 14,4 is used to make sure all cells are equal, then 13,3 keeps it full forever without
making gas. To keep battery happy it needs also high currents time to time otherwise plates
will sulfate. Usually alternator is capable to keep steady voltage, battery will suck high current first
and gradually lower when it gets over 70% capacity, AGMs, especially Optima can utilize
high current, 60Ah empty Optima will take 90A for 40 minutes on 14,4V, it will be nearly full in
1 hour with 14,4V, it has spiral cell, straight cell plate AGMs are maybe 30% slower.
AGMs have low internal resistance, they dont heat up as much as normal wet ones.


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## perfrej (Dec 24, 2009)

Rule of thumb:

A standard lead-acid battery can take about 25% of the rating in charge current. A 95Ah battery will hence be able to draw 24A of charge current from a source.

An AGM battery has about twice the charge capability, so the Phaeton 95Ah left side AGM will charge 48A from the alternator.

Approximate figures; varies with manufacture and technology details, but gives an idea.

/per


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## phaetonjohn (Oct 24, 2014)

PowerDubs said:


> A coupe months ago, I even picked up a charger from a Veyron. Awesome..


Lucky.


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## _Taz_ (Jan 8, 2016)

just to add to this post...

I've been observing my 3.0tdi & have come to a VERY odd conclusion, during winter months, I was suffering the odd totally flat battery, no reason or rhyme...

Usually the LH battery was about 12.5v, so all cool ( and it was a 1yr old new higher ah one )....

Then I remembered reading a post somewhere about the HVAC...

On some mornings when I was DAMN cold ( about -5 in the uk lol  )....

I'd set the HVAC to about 28 deg C, never really got there as I do short journeys....

From reading something a while back this forces the car to do a max drain on this battery & for some reason continues to use juice when you park up & walk off !

Ever since, this & having to recover the LH battery from almost 9.5V shutdown... I did the same, HVAC, BUT before parking up, return the HVAC to below 23deg...

Guess what, It's never played up ever since..

Even left it parked up for over 2 weeks alarm on... measure LH battery, a solid 12.2V 

another Phaetonism ??! :facepalm:


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## 53PL-50AAA-VW611BAN (Feb 10, 2015)

Do you think the residual heater is kicking on when you set the HVAC to 28C?


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## _Taz_ (Jan 8, 2016)

Hi bud, I'm pretty certain I read it somewhere.... but just can't remember...

The load intervention is not so clever, as it does work, but only kind of cuts in when the LH battery is killed !

rubbish really ! 

I ended up disconnecting & CTEKing the battery back to life as it was a new one.

However, it has NEVER happened again, and only on the few occasions when I tried to warm up the car quickly... which is no good on a diesel anyway, they run too cold in the winter !

I'm still at a loss at to what the residual heater is doing, because I never got any more warmer air.....

Next time, i just use the heated seats


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## n968412L (Apr 23, 2009)

Sounds to me like the electrical heaters in the warm air feed to the back passenger compartment.... They're a big big drain. Shouldn't be the auxiliary heater - it would knock itself off when the ignition is off (after it's purged itself).


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## ravenflies (Oct 31, 2013)

Residual heat works only with ignition off and engine warm.
Auxillary heater runs only when manually started.
Electrical heaters could drain, don't really know how much. In a normal system without electrical heaters you really don't gain anything by turning it up to 28 degrees when started with cold engine, it usually works quicker and better to have it on the recommended 22 degrees. When you try to drain heat from a cold system it just slows the warm up period down. The electrical heaters primary task is to get one zone warmer if the other zones are set to a lower temerature.
The load intervention have never allowed me to drain the battery, it has disconnected some consumers on several occations without any other signs than codes telling that the load management has been active and every time I could make a fair guess when the code has been generated, so I have only seen it work as intended. The most common cause has been generous use of the auxillary heater and on some occations it has blocked the possibility to activate the heater and I have not even been close to fail any start attempt.
No direct answer on what could have happend here, just som answers on what didn't cause the drain.

Lennart


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## cbh123 (Aug 25, 2013)

Not that this has much to do with battery drain, but I feel it needs to be said . 

Turning the temp set point up is absolutely a useless move. 
( Same as for home thermostat.)

The set point of a thermostat is when the heating SHUTS OFF it has nothing to do with how fast the car (or house) warms up. 

Please trust the car enginers that it did in fact cross their minds that phaeton owners might like their car to get comfortable as quickly as possible. 
The auto program has control of the hot water flow, the air flow and more (direction of flow, and recirculating flap) it knows how many occupants are in the car too. 

To warm quickly there are two very basic things to consider, (and a lot of other things like humidity, sunlight etc..) 
First you need to ADD heat to the passenger compartment (there is zero point having the fan blow hard on a cold heater core) 
Second you need to limit the amount of cold air you are introducing inside the car. (And therefore the amount of already warmed air you are exhausting) turning Fan higher will actually slow down the warm up. 

it is a delicate balance of monitoring the heater core actual temperature, the incoming air temperature, the temp after the heater core and the cabin temp. The fan speed is controlled automatically in response to these things. 

It is frustrating for the people that spend countless hours optimizing the auto program, and then someone thinks they can outsmart the laws of physics.


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## n968412L (Apr 23, 2009)

cbh123 said:


> Not that this has much to do with battery drain, but I feel it needs to be said .
> 
> Turning the temp set point up is absolutely a useless move.
> ( Same as for home thermostat.)
> ...


All absolutely correct. I never touch the AC controls on my cars - the only thing I do on an unexpectedly cold day is start the parking heater 30 minutes before driving... if I have the time.

I must show this post to my wife to emphasize again to her that a thermostat is a set point, and not a volume control.....

I can't quite remember the details - but there are two, I think, electrical heaters supplementing the warm air blown into the cabin - rating a few hundred watts. I could imagine that a large difference between set point and actual might bring these on... but I don't think I've ever seen fully the modus operandi. 

Regards
M


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## n968412L (Apr 23, 2009)

ravenflies said:


> Residual heat works only with ignition off and engine warm.
> Auxillary heater runs only when manually started.
> Electrical heaters could drain, don't really know how much. In a normal system without electrical heaters you really don't gain anything by turning it up to 28 degrees when started with cold engine, it usually works quicker and better to have it on the recommended 22 degrees. When you try to drain heat from a cold system it just slows the warm up period down. The electrical heaters primary task is to get one zone warmer if the other zones are set to a lower temerature.
> The load intervention have never allowed me to drain the battery, it has disconnected some consumers on several occations without any other signs than codes telling that the load management has been active and every time I could make a fair guess when the code has been generated, so I have only seen it work as intended. The most common cause has been generous use of the auxillary heater and on some occations it has blocked the possibility to activate the heater and I have not even been close to fail any start attempt.
> ...


Hi Lennart - your experience is exactly the same as mine.
Regards
Mike


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## _Taz_ (Jan 8, 2016)

Lol, as you have all mentioned chaps, my setpoint now sits happily at about 22 - 23 !

Never had a problem since...

Interestingly on my E class estate, this has a very simple Warm air heater in the circuit which comes on when the engine is stone cold, but ONLY works when the engine runs to avoid a static drain on a non-running engine...

Weird that the load intervention didn't stop the battery going properly flat ( even though VCDS did show the fault code ).

And,. yes the HVAC is too clever ! 

Now that the summer is on the way, don't forget to have the A/C checked if it needs a gassing !


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## phaetonjohn (Oct 24, 2014)

I set mine at 20.5 C, and the only time that I have EVER cranked up the fan was when the car had about 1.5" of ice on it. Once the car and cabin got warmed up, I turned everything into high and directed the air up. I did that to help get the ice off. But boy, it sure was hot in there!


Sent from my iPad using Tapatalk


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