# Can we fix our low voltage issues permanently?



## jyoung8607 (Feb 14, 2006)

I think everyone here has dealt with left battery issues more than once. For better or worse it's a design issue on this car. The right battery will be maintained in an excellent state of charge, but the left one will be kept partly charged at best, particularly during winter. My battery and alternator were struggling just to keep up with accessory load during this cold snap, and I don't even have the heated windshield and aux heater options some of our European friends do. We'll have this sometimes no matter how new our battery is, and this usage pattern is really detrimental to the battery itself, which ends up making the problem worse over time.

Can we permanently work around the design issue? I've had some ideas and I'm interested in feedback.

1) Disable the second stage rear defroster. This is quickly and easily done by pulling a relay or fuse. The lines are interleaved so defrost will still work, it'll just take a bit longer. Each stage is fused at 25A, so figure they really draw 15-20A. Intervention load management will do this for you eventually, but only after a prolonged sag that will have visible effects on cabin lighting and such. Freeing up 15-20A at idle during winter warm-up would be a really good thing. I have not tried this yet, so I can't yet say with certainty that half-power operation will produce acceptable results.

2) Modify the power supply sense lead into the Vehicle Electrical System Control Module J519 (known as Central Electronics in VCDS). There's a dedicated wire from the main terminal 30 bus bar in the trunk all the way up to J519 just for monitoring power supply voltage. J519 runs Intervention Load Management logic based on that input. If one were to splice in a small resistor to drop voltage on that line - call it 0.2 volts for sake of discussion - the ILM algorithm thresholds would move with that change. ILM would be quicker to raise idle speed to boost alternator output (might not work on W12s). If that's not enough, or if the engine isn't running, it would be much quicker to shed optional loads (all engines). We would have to experiment to find the right resistor value, but after that it would be a reasonably easy modification.

3) After each shutdown, use an intelligent DC-DC charger to top up the power supply battery using the starter battery. The starter battery is almost always 100% charged because it's charged with the factory intelligent DC-DC charger while the engine is running. If you upgrade your starter battery, you can safely borrow quite a bit of energy. It will be put back very quickly on next startup. I had originally thought it would be a difficult project because we'd need extra custom circuitry for triggering and to protect the starter battery from being overdrawn. However, I called and spoke with Lou at Chargetek Inc today. They can take something like this and customize it to our needs at a very fair price. 

Thoughts?

Jason


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## jyoung8607 (Feb 14, 2006)

Below is the email I sent to Lou at Chargetek as a followup to our phone call. Sharing for background and for extra eyes in case I forgot something critical.

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Lou,

Thanks for your time earlier today. This is to recap what we talked about over the phone.

Problem application: 2004 through 2006 Volkswagen Phaeton with a dual battery electrical system (common ground but they supply separate circuits). Simplified, one of the batteries is reserved for starting the engine, and the other battery handles all other power supply needs. The starting battery is recharged while the engine is running by a factory DC-DC intelligent charger, and is generally kept in an excellent state of charge. The vehicle power supply battery carries tremendous accessory loads, especially in winter, and it gets float-level voltage at the very best from the alternator, sometimes quite a bit less. Many people have chronic low-voltage issues.

Our plan: After the engine is shut down, use a DC-DC charger to top up the vehicle power supply battery from the starting battery, with some protection against excessively draining the starting battery. This isn't expected to charge it from zero, it's just meant to improve its average state of charge over time. The factory DC-DC intelligent charger will rapidly replenish the starting battery next time the car is used.

The two batteries in this application are identical: 12V AGM rated at 92Ah and 850 CCA.

Using your standard model CKV-1125 as a basis for discussion, we would like the following customizations:

1) Remain in the area of 5A output, but per our discussion I'm not married to that specific value if it makes things easier.

2) Temperature compensation definitely needed to tweak the charging algorithm according to the battery's temperature.

3) Stop charging when input voltage drops to 12.3 volts (about 60% SoC for the starting battery). This is to preserve enough power to start, avoid deep cycling and avoid freezing of the electrolyte in deep winter.

4) Stop charging when the absorption phase is complete. That is to say, don't bother with float. It's a waste of energy in this application.

5) Remote enable when the ignition is shut off. Ideally the charger would start when +12V is *NOT* present on the remote control line - I guess this would really be a remote disable line. If this cannot be provided, we could live with a conventional enable on +12V signal and use an external NC relay.

6) In terms of environment, it will be in a vehicle trunk protected from all but temperature extremes and mild vibration. The stock -20C to 50C range would be acceptable, but I would be interested in options to push the lower bound to -30C or better if reasonably possible and cost-effective. We have many owners in Canada.

7) Regulatory approvals, probably not needed. If it makes a difference in component selection and build quality, we might want to talk about it; we are definitely willing to invest in a solid reliable solution. If it's just a fee to put a stamp on it, I don't think that's of value for us.

Questions:

1) What would be input parasitic draw be after the charging algorithm is stopped? Your website lists an 0.5ma parasitic draw on the output when the charger is off, but there's no spec for input parasitic draw, most likely because there's no stock option to turn it off while powered.

2) Roughly what sort of transfer efficiency should we expect? We have been guesstimating about 80% total between the charger losses and the battery chemistry losses.


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## Tiger0002 (Apr 23, 2013)

The real issue is this... a battery takes about 5 hours of driving to be fully charge... from ordinary daily driver... not for those car that sits for long time before starting.

With that in mind, you can see why even daily driver cars don't get battery fully charged... especially if your commute is short... even 1 hour total... so the longer you commute, the better you battery state is in. This is silly... we don't want to waste our life driving that long just to keep the battery in better shape.


I can only imagine if you want both batteries to be used for convenience system yet keep the battery viable for starting. I'd imagine hooking up the batteries in parallel... just the positive to positive and have a device in the middle of that circuit for two purpose...

1. Disconnect the circuit when key is in ignition and about to start the car.

2. Disconnect the circuit when the starter battery is weaker than say 450CCA... electronic monitoring. or voltage based.

3. Optional... emergency override for emegerncy jumpstarting purpose.

In this case, it would take a thick battery cable... connecting positive of each battery and have a relay device by the starter battery... fused at both end of the circuit.


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## Paximus (Aug 26, 2011)

Hi Stan,

Your points are good from the engineering standpoint of a regular car design but I wonder if the Phaeton's software and power controllers are too deeply interactive with the vehicle power arrangements to allow cross-connection for charging purposes. I suspect that the controllers would cycle into a deadlock.

Forum posts report that the left battery only achieves recharge after much more than a few hours winter driving, perhaps even taking a week or two. Even then it only seems to reach 80% of capacity, apparently.

Jason's approach is sophisticated, but would quite possibly get the desired result without having to use a maintenance charger overnight.

Chris


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## n968412L (Apr 23, 2009)

Paximus said:


> Forum posts report that the left battery only achieves recharge after much more than a few hours winter driving, perhaps even taking a week or two. Even then it only seems to reach 80% of capacity, apparently.


Now I understand the battery arrangements on the car, I find it no trouble at all to hook up my cetek charger to the LH battery overnight about once every six weeks in the winter. The V6 battery is coming up 6 years old and still seems perfect. It generally I think only seems to need about 6 hours to charge to an indicated "full". I guess if I knew I'd been using it a lot more.... such as using the car as an office with the engine off a lot, or if it was very very cold (it hardly ever is here) then I'd charge it more deliberately. To me, with running conditions here (typically 40 minute commute) and typical weather, I'd not contemplate doing anything more than a top up charge occasionally. However my view would change if occasionally became weekly!

REgards

M


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## jyoung8607 (Feb 14, 2006)

Tiger0002 said:


> The real issue is this... a battery takes about 5 hours of driving to be fully charge... from ordinary daily driver... not for those car that sits for long time before starting.


For our VPS battery this is probably optimistic, and it never does get truly fully charged.



> I can only imagine if you want both batteries to be used for convenience system yet keep the battery viable for starting. I'd imagine hooking up the batteries in parallel... just the positive to positive and have a device in the middle of that circuit for two purpose...
> 
> 1. Disconnect the circuit when key is in ignition and about to start the car.
> 
> ...


Paralleling doesn't really help us in this case. We definitely can't be hooked up in parallel with the ignition on, or the battery monitoring controller can't charge the start battery and now we're doing a bad job charging both batteries. If we truly needed all 184Ah from both batteries while the car was shut down, we could think about paralleling then, but we don't really have a reserve capacity problem. We have a charging problem. In other words, the size of our electrical "tank" is fine, we just do a bad job keeping it full.

Jason


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## Tiger0002 (Apr 23, 2013)

Once the ignition is on... the batteries are disconnected from each other... so it act normal separate batteries...

Like you said... it is more of the voltage regulator system issue... it is not a simple voltage regulator on back of the alternator.

Even a larger alternator would not solve the issue either...


Reserve capacity is the best way to deal with this issue... the biggest and largest reserve capacity as possible... which is pretty much what we have now.


That is why I said in other post... you just have to hook up the electronic battery charger to any of the car batteries you own once in a while to keep the battery in better shape than your car/commute can possibly give. It is really not much of a hassle... you charge it when you are not using it... going to sleep... and in the morning, it is done.


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## jyoung8607 (Feb 14, 2006)

Paximus said:


> Forum posts report that the left battery only achieves recharge after much more than a few hours winter driving, perhaps even taking a week or two. Even then it only seems to reach 80% of capacity, apparently.
> 
> Jason's approach is sophisticated, but would quite possibly get the desired result without having to use a maintenance charger overnight.
> 
> Chris


That's my goal. I put my VPS battery on a smart charger about once a month but as you know, its average state of charge tends to drift down at the best of times. I'm trying to figure out a reliable set-and-forget design solution, something that will let the car take care of itself without manual help.

During our -17C cold snap I did some monitoring through the battery charger module and I could see power supply voltage crash down into the 11V range regularly with the engine running, particularly in stop-and-go driving while the car is trying to carry heavy defroster, rear PTC, mirror and wiper park position heat, HVAC blower and seat heater loads until everything is up to temperature. That can take 20 minutes or more if it's very cold. When that's happening, not only is the VPS battery not charging well, you're pulling dozens of amps OUT of the battery and doing a poor job putting it back later. ILM will try to help but it won't even begin turning stuff off until you dip below 12.2V for 30 seconds, which is deep into battery-draining territory.

All this deep cycling is damaging to the VPS battery and reduces its lifetime, which compounds and makes the problem worse, which is one reason why we always seem to be replacing VPS batteries.

This is a supply versus demand problem. My ideas #1 (disable second stage defrost) and #2 (modify J519 sense lead) are attempts to reduce demand. My idea #3 (customized DC-DC charger) is an attempt to increase supply AND reduce demand for VPS battery charging current. This doesn't all have to be done together, it's just brainstorming. Personally I'm going to try #1 right away because it's easy, and just see what kind of effect it has. I am negotiating with Chargetek for #3 but it will take a while.

Jason


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## jyoung8607 (Feb 14, 2006)

Tiger0002 said:


> Once the ignition is on... the batteries are disconnected from each other... so it act normal separate batteries...
> 
> Like you said... it is more of the voltage regulator system issue... it is not a simple voltage regulator on back of the alternator.
> 
> ...


We have enough reserve, if that reserve is actually charged up.



> That is why I said in other post... you just have to hook up the electronic battery charger to any of the car batteries you own once in a while to keep the battery in better shape than your car/commute can possibly give. It is really not much of a hassle... you charge it when you are not using it... going to sleep... and in the morning, it is done.


That's true for the Phaeton at present. It's usually not true for most other modern cars.

I'll give an example of my wife's Chevy Trailblazer. The battery is right next to the alternator. The voltage regulator is temperature-compensated between about 13.9 volts in summer and 14.3 volts in winter. That's enough to meaningfully charge the battery. It puts out enough at idle to maintain that voltage at idle no matter what's turned on. I do throw a battery charger on it every now and then for maintenance, but its battery is always in a reasonably good state of charge.

In comparison, the Phaeton gets about 13.6 to 13.8 volts to the battery at best after losing about 0.2 volts on the 6 meter cable run, often less. This is barely float-level voltage for a lead-acid battery. I'm not sure if it's temperature compensated. There is sometimes more accessory load than the alternator can handle at idle. This is why the VPS battery doesn't usually have a great state of charge.

Easily the #1 problem you hear about here is low-voltage problems or something that traces back to a low-voltage issue. There's a little competition from mechanical issues now that the cars have aged a bit, but that doesn't erase the original problem. When talking to Chargetek, the ballpark number for a turn-key, plug-and-play custom charger was in the low to mid $100s. That's less than a new battery. If that makes our problems go away forever, that's a bargain in my view.

Jason


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## Tiger0002 (Apr 23, 2013)

All automotive batteries are designed to handle the fluctuating voltage. There is a reason for using AGM battery on the left side... because it can handle a harder depletion and still have serviceable life.

All batteries suffer from extreme cold and sctreme heat degradation. This is why batteries in Arizona or other very hot areas don't live past 3 years at all... I would say same for the extreme cold area. You just buy new battery and get over it. There are places to buy batteries for much lower price and that would alleviate the cost issue.

Other than that, not much we can do other than to make sure our electrical charging system is working as dsesigned. That is it.

Charging battery with external battery charger will prolong the service lifespan... I believe it now because I got two batteries that are 9 years old and still have 80% of original CCA rating. Usually I would be on second set of battery by now but they are still alive.

Phaeton is the newest in the family so I am up to the challenge to keep it alive with the battery charger and see how long it will last. Right now the battery is about 1.5 years old average and still has 100% of CCA rating... according to my electronic battery tester. That's good enough for me.


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## PowerDubs (Jul 22, 2001)

I'll have to go back and reread our electrical system SSP, but the issue shouldn't be the charging capability of the alternator itself. It is capable of 300 amps if need be.

I may be mistaken, but I thought the car was designed to raise the idle speed if need be for charging reasons.


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## jyoung8607 (Feb 14, 2006)

PowerDubs said:


> I'll have to go back and reread our electrical system SSP, but the issue shouldn't be the charging capability of the alternator itself. It is capable of 300 amps if need be.


It's capable of 190A continuous, 300A short term. However, it can't do all that at idle.



> I may be mistaken, but I thought the car was designed to raise the idle speed if need be for charging reasons.


It is indeed. It's part of the intervention load management algorithm. I linked to a TSB above that Michael dug up; it's more current than the SSP. However, it doesn't do so aggressively enough for proper charging. It's just enough to keep things from outright malfunctioning. Raising the idle speed actually really does help voltage levels a lot but the ILM thresholds are pretty lax.

It might be worth looking at stepping up the idle speed 100RPM or so permanently. VCDS can do that on at least some ME7 platforms, and something like Unitronic's Unisettings can do it on many more. I'll have to look at see if I can make it happen on my W12 ECU.

Jason


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## PowerDubs (Jul 22, 2001)

If you can't, I have a buddy that can do *anything* to the Me7 ecus.


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## vwgeorge2 (Mar 24, 2008)

PowerDubs said:


> If you can't, I have a buddy that can do *anything* to the Me7 ecus.




Hey, get in line.... He is spending time on my car first.

I cant wait to drop that thing off to Jeff.


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## PowerDubs (Jul 22, 2001)

You drop off a V8, I'll drop off the W12.

Jeff has had the factory ECU files from my V8, as well as Dennis's and QBN's for quite some time. He also has existing files already made for the Audi chain 4.2

He just wants a belt V8 car in his hands to make sure everything is spot on.


:laugh:


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## PanEuropean (Nov 3, 2001)

Hi Jason:

I've read your analysis and proposals for mitigation, and as always, you have thought things out very carefully and presented some interesting ideas.

I kinda-sorta tend to agree with Chris that it might be easier in the long run (although perhaps not as technically elegant) to just hook the left battery up to a battery maintainer periodically - that being a solution that has been pretty thoroughly tested over the past 8 to 9 years and proven to work.

I don't feel entirely comfortable (from a 'potential consequences' point of view) with the proposals to either disconnect the second-stage rear window defrost, or install a resistor in the power supply monitoring line for the purpose of increasing the aggressiveness of the Intervention Load Management system. We, as drivers, have direct control over the current draw of the rear window defroster, in the sense that it will only draw current if we turn the thing on. Arguably, if we do turn it on, it is because visibility out the rear window is impaired, and for that reason, we want the rear window to clear in the shortest possible period of time. I guess what I am suggesting here is that disabling the second stage of that defroster system is a bit like throwing the baby out with the bath water.

I'm also wondering if it is necessary to increase the aggressiveness of the onset of intervention load management. The diagram below shows that the PTC heaters that warm the rear seat footwells comprise 3 of the first 5 functions that intervention load management shuts down. We can completely disable the PTC heaters ourselves using the controls on the big center screen - all we have to do is turn off the 'air conditioning' in the rear of the car. If the car is operated with a single occupant, or with only two occupants (both in the front), the instantly available electric heat provided by the PTC heaters to the rear footwells is of little or no benefit to us. It is unfortunate that if we disable rear cabin PTC heating using the controls on the front display panel, that selection does not persist across power cycles - it has to be re-selected every power cycle.

Maybe pulling the fuses that supply power to the PTC heaters (or, more precisely, interrupting the control voltage that triggers the PTC heaters - the fuses themselves are a nightmare to get access to) might be a better 'permanent' load-shedding fix than pulling the fuse for half the rear window defrosting capability? I say this because I could count on the fingers of one hand the number of times I have carried passengers in the back seat of my Phaeton over the past 10 years.

My own experience with the left battery issue (keeping the thing at peak charge) has been that if I am only using the car for short driving cycles (less than 1 hour per cycle average time), I need to periodically charge the left battery using a battery maintainer to keep the battery topped up. "Periodically" depends on the number of cycles, and in my case (very low utilization of the vehicle), that translates to one overnight spent on the battery maintainer every 6 to 8 weeks. I have easy access to a 110 volt outlet when I park the car, so it's no problem for me to charge the car up. It might be a problem for someone who does not have easy access to 110 volts when the car is parked.

For the benefit of readers who are not familiar with the battery maintainer concept, here's a link to that discussion: ....Purchasing and using a Battery Maintainer for your Phaeton (Includes TB 00-03-11)

Best regards,

Michael

*Intervention Load Management - Load Shedding Sequence*


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## perfrej (Dec 24, 2009)

Just a quick note, folks!

An AGM battery can utilize about 50% of the battery capacity as charge current. A standard lead-acid one 20-30%. This means that our dear left-side battery will eat no more than about 50A, regardless of what the alternator supplies. When I had my alternator problems on the W12 I measured currents carefully and the above holds true. The top figure I saw was just after the cable from the alternator to T30 had been replaced and the engine started for the first time: 63A for a short while, then about 45A steady.

Turning on the ignition in the W12 sucks a whopping 50A or more! In order to supply the car AND charge the battery we are looking at a need of around 100A.

I think the alternator is capably of supplying a decent charge current even on idle RPMs, but probably not 100A. Anyone have a figure for that (RPM vs current)?

/per


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## n968412L (Apr 23, 2009)

perfrej said:


> I think the alternator is capably of supplying a decent charge current even on idle RPMs, but probably not 100A. Anyone have a figure for that (RPM vs current)?


Don't know the figures, but it won't be RPM dependent. It's an alternator, so as the RPM goes up, for a fixed field, the voltage goes up in proportion to speed, but so does the synchronous reactance... ie the internal impedance of the alternator is propoortional to speed too, so I don't think increased RPM helps beyond minimum necessary to provide the 15V or so we need.... but happy to be corrected by any engineer who actually understands car electrics!

Regards

M


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## steveskinr (Oct 31, 2007)

I wonder if the shut down sequence is why some people have had trouble with slow acting rear window defog?

I haven't yet.


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## jyoung8607 (Feb 14, 2006)

PanEuropean said:


> Hi Jason:
> 
> I've read your analysis and proposals for mitigation, and as always, you have thought things out very carefully and presented some interesting ideas.
> 
> I kinda-sorta tend to agree with Chris that it might be easier in the long run (although perhaps not as technically elegant) to just hook the left battery up to a battery maintainer periodically - that being a solution that has been pretty thoroughly tested over the past 8 to 9 years and proven to work.


I fully agree that hooking it up to a charger periodically does help. I just view it as something akin to adding a quart of oil every time I stop for gas. Does it effectively work around the problem? Sure, at least somewhat. But every time I have to do it, it reminds me there's still an underlying chronic problem that will get worse if it's neglected. If there's a reasonable and cost-effective way to fix the problem closer to the source, I'd like to do that. It also has the side benefit of being "wife compatible", a.k.a. set and forget.



> I don't feel entirely comfortable (from a 'potential consequences' point of view) with the proposals to either disconnect the second-stage rear window defrost, or install a resistor in the power supply monitoring line for the purpose of increasing the aggressiveness of the Intervention Load Management system. We, as drivers, have direct control over the current draw of the rear window defroster, in the sense that it will only draw current if we turn the thing on. Arguably, if we do turn it on, it is because visibility out the rear window is impaired, and for that reason, we want the rear window to clear in the shortest possible period of time. I guess what I am suggesting here is that disabling the second stage of that defroster system is a bit like throwing the baby out with the bath water.


This is a reasonable concern. It's not without trade-offs.



> I'm also wondering if it is necessary to increase the aggressiveness of the onset of intervention load management. The diagram below shows that the PTC heaters that warm the rear seat footwells comprise 3 of the first 5 functions that intervention load management shuts down. We can completely disable the PTC heaters ourselves using the controls on the big center screen - all we have to do is turn off the 'air conditioning' in the rear of the car. If the car is operated with a single occupant, or with only two occupants (both in the front), the instantly available electric heat provided by the PTC heaters to the rear footwells is of little or no benefit to us. It is unfortunate that if we disable rear cabin PTC heating using the controls on the front display panel, that selection does not persist across power cycles - it has to be re-selected every power cycle.


ILM seems quite reluctant to start turning stuff off on my W12. I can sit and watch MVB 043(?) in the Auto HVAC module with VCDS to get an idea of what it's doing. Testing around -10C, with cold PTCs and rear defrost and other miscellaneous heating, my PS voltage at idle will wallow around in the high 11V range with visible dimming and flickering of the instrument cluster back-lighting. After several seconds ILM it will increase idle a bit and maybe eventually get to the first or second stage shutdowns but it doesn't shut off enough stuff to get me above the low-to-mid 12V range. If I'm doing stop-and-go driving, ILM closes down when I'm moving fast enough to generate a bit more power and then has to start over again when I'm back to idle. IMO it's not nearly aggressive enough. Even at 1500-2000RPM while driving, it still struggles to maintain 13.1-13.2V until the cabin has fully warmed up and heater loads trail off. That can take longer than many short trips. 



> Maybe pulling the fuses that supply power to the PTC heaters *(or, more precisely, interrupting the control voltage that triggers the PTC heaters - the fuses themselves are a nightmare to get access to)* might be a better 'permanent' load-shedding fix than pulling the fuse for half the rear window defrosting capability? I say this because I could count on the fingers of one hand the number of times I have carried passengers in the back seat of my Phaeton over the past 10 years.


I had initially written off disabling the PTC heaters because as you say, the two thermofuses are quite difficult to access and I was trying to think of a more accessible solution I could share. However, since you've brought it up and mentioned the control circuits I've done some more research and had a change of heart.

It turns out the PTC transistor control input from the Climatronic module connects to the PTC heaters with just one wire on its very own two-pin (one pin empty) harness. That means it's easy to disconnect without modification. It's also not that hard to access. If you move the front seats all the way forward and up, you'll see where the front and back carpet meet and overlap. If you pop the plastic HVAC duct grille out, you have enough room to lift up the front carpet and reach underneath. The two-pin connector can be identified and disconnected by feel.

In terms of load reduction, I like this solution better than the defrost solution now. Disconnecting the control input took me five minutes total for both sides and no tools were necessary. It sheds 60 amps of load whereas the defrost solution would only shed 25 amps. The trade-off set is different but probably more acceptable to most owners. It creates no trouble codes in the Climatronic module; it actually doesn't seem to notice they're missing. It doesn't increase HVAC noise in the cabin like disabling rear air conditioning does. It might have some impact on cabin warm-up and/or rear side-window defrost, particularly with diesels that don't create as much waste heat, but I can't imagine it would be that much. They are rated at 12V * 30A fuse * 2 units = 720 watts maximum which is less than half of your average hair-dryer.

I am travelling for the next couple of days. When I get home I'll post some snapshots from the service manual and from my car that show how it's done. I do still plan to look at the self-recharging solution but this is a very good first step.

Jason


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## seawind3000 (Sep 17, 2010)

For the past few weeks, I have been turning off the rear A/C to save amps on short trips, the volt meter rises from 13.6 to 14.2 when I do this. Today I went under the front seats and disconnected the trigger wire in the electric foot-well heaters so I don't need to turn off the rear A/C  not as hard as I thought it would be.

Mike


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## vwgeorge2 (Mar 24, 2008)

seawind3000 said:


> For the past few weeks, I have been turning off the rear A/C to save amps on short trips, the volt meter rises from 13.6 to 14.2 when I do this. Today I went under the front seats and disconnected the trigger wire in the electric foot-well heaters so I don't need to turn off the rear A/C  not as hard as I thought it would be.
> 
> Mike





I think my car must be broken? It stays at 14 volts all day long, every day....

Is it wrong to do this?


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## Gabs08PHTN (Jan 6, 2011)

seawind3000 said:


> the volt meter rises from 13.6 to 14.2 when I do this.
> 
> Today I went under the front seats and disconnected the trigger wire in the electric foot-well heaters


Hi Mike,
Are those voltage readings taken with the engine at iddle or off? I think that most of us have reported (without disabling the rear heaters) that when the engine is off we tend to see figures around 12V and when the engine is running, of steady 14V. In case that you spotted 13.6V when your engine is running I would say that perhaps you have a fault in the electric system, namely alternator that is not able to cope with the required current demands, weak batteries or even wiring.
With regards to disconnecting the rear heaters, first bear in mind that when you do that the HVAC blower runs at higher speed, therefore I would say that the energy savings are not that large. And second, your rear windows might fog up, since the rear heaters are also in charge of warming up the air that defogs them.

Gabriel


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## Paximus (Aug 26, 2011)

> I think my car must be broken? It stays at 14 volts all day long, every day....
> 
> Is it wrong to do this?


My car's in-dash voltmeter reads 14.2V and always has, at all times, except with the engine stopped or during cranking.

Of course, here in the UK we do not get the extremes of ambient temperature that other world locations have, so perhaps the PTC heaters rarely switch on.

Chris


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## jyoung8607 (Feb 14, 2006)

I've been running with mine disconnected since late January and it hasn't created any problems. I only ran into major voltage issues when it was very, very cold outside and the engine was at idle before the cabin temperature had been completely stabilized.

I don't necessarily advocate disconnecting the PTCs as a permanent solution. For me, it was mainly an experiment. I've now got some operational history without the PTCs and I have a better feeling for how that affected the car during winter. I plan to hook them back up soon, and explore other ways to support system voltage next.

Jason


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## Cantrellc123 (Aug 5, 2012)

My W12 stays at approx 13.6-13.7. I think that's less than ideal but it hasn't caused any issues as far as I know.

Cantrell


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## seawind3000 (Sep 17, 2010)

Just to clarify, my idle voltage will slowly move from 13.6ish to 14.2ish depending on many different electric consumables. When I turn the rear A/C off, there is a noticeable gain in available voltage. With this years extreme cold (-25c) there is little to no humidity so defrosting is not a problem. With the electric floor heating disabled, the volt meter remains very steady with little movement at just over 14v. With all my short trips I like the extra voltage for left battery recharge, every little bit helps.

My left battery voltage dropped to 11.9 a few weeks ago after I locked it in a local drug store lot, when I returned a few minuets later, the un-lock button on the fob would not work and the key cylinder in the door was seized before I bought the car in 2010 , I had to open the trunk and open a door by the inside handle. A new door cylinder is now at my dealer, ready to be installed. The left battery is 1 year old.

Mike


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## invisiblewave (Sep 22, 2008)

I checked my brand new LH battery yesterday. It was already down to 12.4, and after a full charge only manages 12.6.


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## Gabs08PHTN (Jan 6, 2011)

Hi,
I have just made some measurements with VCDS and the engine iddling. Ambient temperature 7.5ºC (45.5ºF). The readings are as follows:

1) Rear AC on:
- Dash voltmeter reading: 14V.
- VCDS starter battery: 15.1V.
- VCDS OPS battery: 14.3-14.5V.

2) Rear AC off:
- Dash voltmeter reading: 14V.
- VCDS starter battery: 15.03-15.18V.
- VCDS OPS battery: 14.67-14.74V.

Gabriel


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## jyoung8607 (Feb 14, 2006)

Gabs08PHTN said:


> Hi,
> I have just made some measurements with VCDS and the engine iddling. Ambient temperature 7.5ºC (45.5ºF). The readings are as follows:
> 
> 1) Rear AC on:
> ...


WillemBal did a bunch of testing a while back with several members. I think we established all the TDI alternators put out higher voltage. Don't know why.

Jason


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## seawind3000 (Sep 17, 2010)

How often do you drive your car and for how long. My battery is living in -20c to -35c lately. I would love to see 14.3v on my left battery, I would have no problems, but these brutal low temps and short drives (2km or less) are killing my stand-by voltage. 

Your A/C on and off did show a difference in the retained voltage in your convenience battery.

Mike


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## Gabs08PHTN (Jan 6, 2011)

Hi Mike,
I fully agree with you. Short trips and very low ambient temperature are no good for batteries. 
I am lately driving my Phaeton every other day, for about an hour and a half. However when I do not drive it too often I hook up a battery charger from time to time. The one I have has a "winter" setting that is meant to be used when the ambient temperature is low. Perhaps you could try to find a similar one. I am also aware that you can purchase heating mats, that you can connect to a socket to warm the batteries up.

Gabriel


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## seawind3000 (Sep 17, 2010)

Hi Gabriel, 

I would like the car to be self sufficient with "no wires attached" . Going to fires at 3am would have me towing half of an extension cord all the way to the fire hall  

Mike


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## Gabs08PHTN (Jan 6, 2011)

I have got the ideal solution for you Mike! Buy yourself a horse!!! And park your phaeton in a heated garage. 
Other than that, if you do not want to have any attached wires, we can always envisage some sort of induction device to keep your batteries charged up and warm.  However I do not know how the miriads of control units in the Phaeton are going to get on with the magnetic fields.

Gabriel


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## seawind3000 (Sep 17, 2010)

Hummmm read this. http://www.cnn.com/2014/03/14/tech/innovation/wireless-electricity/index.html?hpt=hp_t5


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## Juhani (Sep 15, 2012)

seawind3000 said:


> For the past few weeks, I have been turning off the rear A/C to save amps on short trips, the volt meter rises from 13.6 to 14.2 when I do this. Today I went under the front seats and disconnected the trigger wire in the electric foot-well heaters so I don't need to turn off the rear A/C  not as hard as I thought it would be.
> 
> Mike


Hmm. I did this, but it did no make any change? Voltage still drops from 13.9V to 13,7V when I put rear HVAC on, I have digital accurate voltage meter wired from left battery to handrest opening so I can see voltages when driving also. Any other ways to delete PTCs than taking fuses out?


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## noname123 (Aug 23, 2016)

Sorry to resurrect such an old thread, but I have a solution for those without access to mains voltage (or the inclination to do so). For the past 5-6 years I've been using an Accucel-6 battery charger (used for RC toys) to top off my batteries. The advantage is that it can take anything above 10.6V and step it up to 15V (or more, but not the case here). The only thing to watch out for is to not charge lead batteries too often at that voltage, 15V is a bit over the limit but is quite useful to prevent sulfating or restore a bit of CCA. So about once a year, for seldom-used cars, a top-up is good for a battery.

The other thing about Accucel-6 is that it doesn't fully shut down once the input voltage reaches 10.6V. It still draws 200mA, which is significant for a small battery, possibly killing it. So either charge at a low current (1-2A) if left unattended for the night or use a 'disposable' battery. I have a 40Ah one that I use for stuff around the garage. Or just use a beefy charge current (3-5A) and tend to it. This way, you can use the right battery to charge the left battery, with the engine off, with minimum hassle.

The gadget is pretty light fits in a jacket pocket. Might have to build your own cables, it only comes with a single pair of alligator clips. I've charged batteries hundreds of times with my unit (NiMh, LiPo, lead, Ni-Cad), no negative side-effects that I can observe so far, if the charged battery is in decent condition.

Still unrelated, but if a battery is <50%, just change it, there is no way to revive one. I've tried every method. And don't cheap out, a good quality indication is the weight of the battery. On my old 5-series I had an 80Ah battery which weighed >50 pounds, original, lasted for almost 10 years. A 'cheap' replacement, at ~20 lbs, lasted only 2 years. This quality issue was especially visible on my bike batteries, cheap ones required almost yearly replacement.

Sorry for the long and perhaps unrelated post, but this device (plenty of similar things on the market) has literally changed my life.


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## richmondvatdi (May 17, 2003)

Resurrecting this old thread to see if I can get to the bottom of this week's episode of "It's Never Boring in Phaeton Land". Halfway through my 30-mile commute home Thurs evening, the voltage gauge, which normally sits steady on 14V, started bouncing around between 10V and 12V for a few min. Then dropped to 0V and ILM started turning stuff off.

Got home and checked batteries. 12.5V Left and 13.1V Right. Hooked up maint charger and left it til Sat. Two short drives Sat and no issues. Two more short drives Sun and the ILM kicked in as voltage dropped to 0V.

It's winter but not terribly cold in Virginia. We use power hogs like heated seats liberally as do our back seat passengers. I assume this is part of the problem, and I'm willing to cut down on the use of the power suckers and keep it on a maint charger (no big deal as I have a warm garage in which to park). However, I am somewhat concerned about the sudden drops to 0V. I would think I'd see a drop, but not to 0V. Autoscan doesn't reveal any issues with the charging system and both batteries tested good at NAPA. Ideas?


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## Paximus (Aug 26, 2011)

Hi Paul,

So, the Intervention Load Management sees a drop in voltage and the in-dash voltmeter sees it too. But presumably the engine controllers and the KESSY can't see a drop to zero or the engine would stop.

A drop to zero volts on the voltmeter implies it's a bad connection in a power wire common to the in-dash voltmeter and the ILM, rather than a whole-car battery problem.

The trouble with the wiring diagrams is that they are a little old-fashioned, being mechanical-centric. They show the connections from the periphery of the vehicle back to isolated parts of the controllers, rather than centering on an entire controller and working their way out, so it's a complete rat's nest to trace. That means that finding out about all the 12V feeds into the in-dash display (ie the voltmeter) is awkward, spread over dozens of diagrams. There is no in-dash display diagram that I can find, to trace where the voltmeter gets its voltage from.

I can't remember where the heart of the ILM lives, it is so long since I looked at the system. Probably in the central comfort controller, but I wouldn't be absolutely sure, that might just obey commands from somewhere else.

Chris


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## Phaetonlvr (Feb 26, 2013)

Not too familiar with the whole battery management system but I think the thin brown wire on the negative battery terminal on each battery is going to the battery controller. Since the dash is only measuring the VPS battery circuit as far as I know, maybe the nut that secures it to the VPS battery is loose or the wire is broken and has intermittent contact?! This is just a guess as I haven't looked at the wiring diagram.


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## robbie-rocket-pants (Mar 25, 2012)

Perhaps VW updated the battery charging system or logic at some point since I have not once had a battery problem with my 2009 or 2011 Phaetons.
I did, however, wire up a small solar PV charger to the left battery during the first lockdown so this may have helped as the car has had very little use for a year.

Or maybe it's just the V6 diesels that don't suffer as much as the larger engined cars ?

Of course, I'll now go out to drive the car and get a battery problem......


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## richmondvatdi (May 17, 2003)

Phaetonlvr said:


> Not too familiar with the whole battery management system but I think the* thin brown wire* on the negative battery terminal on each battery is going to the battery controller. Since the dash is only measuring the VPS battery circuit as far as I know, *maybe the nut that secures it to the VPS battery is loose* or the wire is broken and has intermittent contact?! This is just a guess as I haven't looked at the wiring diagram.


Ding! Ding! Ding! I think we have a winner! After several hours of reading and flipping from page to page on the Pheoton wiring diagrams, I took a break and decided to go out to the garage and check that wire. Sure enough it was loose. Very loose. Tightened it up and all was fine on the drive in this morning. 

My philosophy is try the simple solution only after all other, more complex solutions have been eliminated.  Thanks, Stephan.


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## Phaetonlvr (Feb 26, 2013)

Glad it was a simple fix! I figured that because you didn't have drive-ability issues, the battery control system erroneously thought the battery voltage is low when in fact it wasn't.


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

Wow, good call Stephan. It's always best to check the simple stuff first.

I just got done pouring over the wiring diagrams myself. 

I am posting the portion pertaining to J285 which contains the voltage gauge for future reference. 

Saving it as a .pdf makes it blurry so I typed out the following notes:

On page 9 is the start of J285. It's connected to the OBD connector 1 (B444). It's grounded via 371 ground connection 6 in main wiring harness.

On page 10 are fuses SB23 and SB54.

On page 11, the Voltmeter is Y11 (Voltage Supply Display). It's in J285, the Control Module with Indicator Unit in instrument panel insert. K106, the Battery Emergency Operation Indicator Lamp is also in J285 as is the left and right turn indicators.

J285 is connected to B449 Emergency operation connection (in main harness), J518 Access/Start Control Module pin k/30 and J367 battery Monitoring Control Module pin A/15.

J285 is also protected by fuse SB27 and powered by B317 Plus Connector 3 in main wiring harness.

J533 The Data Bus Onboard Diagnostic Interface is on the right side of the page. It's connected to the CAN Bus.


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

robbie-rocket-pants said:


> Perhaps VW updated the battery charging system or logic at some point since I have not once had a battery problem with my 2009 or 2011 Phaetons.


That may be the case. I picked up some F revision battery controllers from a seller on eBay but haven't had the guts to swap them out yet. 

My battery controllers are both 3D0915181D. 

I wasn't sure if the Fs were good to use on GP0 Phaetons (with the Bus changes) but they are listed on the VWOA website as being correct for the 2004.


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## hanzy88 (Jan 2, 2018)

Hi guys!

Reading through this thread with great interest! I'm daily driving a V10 TDI (2004) - dual battery and this is my second Phaeton. I have a constant problem with the VPS battery being low and the starter battery being at perfect charge. I've replaced both, but not with AGM, I put in identical basic lead acid Bosch 95Ah batteries, since having an expensive AGM didn't seem to do much improvement for the system.

One mechanic even pointed out that the AGM batteries were not used in cars when my car was made and thus isn't smart to put the AGM battery in the car with sophisticated electronics and might cause problems because the AGM batteries have a little lower charge - a 0,6V lower across all six cells, so the 14,7V from the system would overcharge the AGM, causing overheating and eventual early failure of the car system or the battery.

I daily drive it to work and back for about 5km (10min), even in very cold. I regularly use Webasto to preheat the car, here I'm sad that Webasto is not heating up the engine as well (at least not directly, after 10-15 min of Webasto preheat I notice engine coolant temperature at about 20-30C, with the outside temperature being well bellow 0C), but the cabin is nice and toasty. But this usage is depleting the VPS battery so much the car won't turn on the welcome lights or even interior flood lights after 3rd or 4th day (after being charged from mains or driven for more than 1h). 

So my solution was buying a Ctek batery charger/maintainer, installing a wire from the VPS (left) battery to the bumper tow hook hole (screw-in recovery hook) and used that hole to install Magcode magnetic connector on the right bottom side of the rear bumper. The connector is water safe and without it's proper male-partner won't be energized (it needs a magnetic field from the male connector to couple the wires to the pins). I than made a wire with the male magnetic connector from the charger (in the garage, the Phaeton is parked in front of the garage), to the Phaeton bumper. I connect it regularly during the night, it's magnetic, so even if I forget to disconnect it or someone not knowing is there tries to move the car, the connector will uncouple without any damage. I can post some photos if you're interested, the build was simple and fast, took me and a friend about an hour to wire and install.

Now, I have no problems using Webasto even for longer periods (up to 40 mins total, 10-15min preheat before starting the engine), every morning and every time I need to drive it in the cold, I have no problems with welcome lights not coming on and so on. I noticed the car doesn't increase the idle RPM anymore, which was a regular thing before and I even noticed quite much lower fuel consumption. I'm not kidding but on the short drives in cold, I average about 14L/100km, using a mains charger it dropped to 12,5L, solely because of lower alternator demand. I also don't have any electrical gremlins and stuff refusing to turn on or pausing and thinking if it should turn on (stuff like seat heating, massage function, or trunk lid opening....).

But the question I have for you guys one here! 
*Will the dual battery Phaeton start with only one battery present?* The backstory; I know from SSP that it should work with either battery depleted or low charge. But it doesn't say if the battery needs to be connected or not. As I wrote at the beginning, this is my second Phaeton, the first one is parked for parts (also V10, 5 steater... so don't hesitate to hit me up if you need any spare parts from it). The one I have parked for parts is currently still complete enough to start the engine, and I can do that by only hooking up one good battery on the right side of the car (haven't yet tried hooking it up only to the left side). All I have to do is to flick the key around twice to engage emergency start procedure, where the computers get powered up from the starter battery (RH side) as well and it starts right up. The VPS battery is not even connected. The problem I have with my daily driver... if I get the VPS battery empty to the point I have to unlock the doors manually with the key, I'm unable to start the car with the starter battery only. My mechanically inclined friends don't believe me it should be working with only one battery, saying it's something wierdly wrong with the parked Phaeton that does start on one battery only. But I think the sole purpose of the second-starter battery is to not to leave you stranded if either battery gets empty. As I said my daily driver doesn't want to start if the VPS battery is low, I than have to take the jumper cables, and connect the starter battery with the VPS battery in the trunk, and voila it starts. 

Does anyone have any idea where to look for the problem? Is it the switch over relay or control unit for battery monitoring? Did anyone have a similar problem? Is anyone willing to try do disconnect either of the batteries and start the engine with only one battery connected? (maybe when replacing them or servicing something that needs a battery disconnecting).

Thanks for help, ideas and all previous posts, after driving Phaetons for about 5 years I'm still learning about their quirks and perks. And a photo of my nearly mint Phaeton, trying to get it back to it's original glory, planning quite a big restoration maintenance on cooling system and undercarriage in a month or so, wish me luck.


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## Juhani (Sep 15, 2012)

Hi, check this, there are also other ones.








My Phaeton's electrical problems are now long gone...


My belt seems to be in good shape. I have a W12. Thanks for the info and please post if you do find a resistance spec for the cables.




www.vwvortex.com


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## hanzy88 (Jan 2, 2018)

Juhani said:


> Hi, check this, there are also other ones.
> 
> 
> 
> ...



Nothing really for my case...

UPDATE: Yesterday I intentionally emptied the LH side battery (VPS), left the parking lights on for a few hours. And than after the car won't unlock itself with the remote, I used a physical key and entered, tried to start it. The car came alive, despite very depleted battery, but didn't want even to try to start. The parallel connection for the batteries is apparently not working correctly in my car. I can hear the relay clicking, but besides that, no actual power comes from the RH battery to the system and it doesn't run all the computers and the car refuses to even try starting. Until I cross connected the RH side battery positive terminal with the positive terminal of the LH side battery with the jumper cable. Then it started right up, as if there was no problem, no hesitation, no problem cranking.

This leads me to believe the parallel connection relay is not working properly, but I'm not sure where to start my fixing? Is it just the big heavy duty relay that's not letting the power through or is there something wrong with battery control unit?

Thanks for the help!


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## rangsudh (Mar 20, 2013)

It is unlikely to be anything wrong with the "battery control unit". I would first check the parallel connection relay. If you can hear the relay clicking, measure the voltage at and across the switched terminals of the relay to ensure that it has close to zero voltage across it when it clicks on. (And check if it is remaining on, or clicks multiple times and switched off because of insufficient energizing current to the relay coil.) Also check that with the relay on, the RHS battery voltage is appearing at the LHS battery terminal through the relay.

This may also help you: http://www.volkspage.net/technik/ssp/ssp/SSP_272_d1.pdf


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## rangsudh (Mar 20, 2013)

Also note that the mechanic who told you about AGM batteries is somewhat mistaken.

While AGMs were new to the automotive scene back in 2004, the Phaeton LHS battery was designed from day one to be AGM and only AGM. Indeed, it would be suboptimal, possibly wrong, to put a non-AGM flooded battery in there. The reasons have been covered elsewhere in this forum.

Secondly, AGM batteries exhibit a slightly higher OCV than regular flooded lead-acid batteries, not less. It is usually about 0.2V higher, not 0.6V. e.g. 12.8V instead of 12.6V. AGMs are designed to accept higher charge currents than non-AGM batteries, and can usually do so at the _same or lower_ voltages than regular batteries. This is due to the lower internal resistance of the AGM construction.

However, it should be noted that Phaeton TDI alternators almost uniformly provide 14.7V instead of the 14V -- 14.4V they are designed for (14V is printed on the alternator itself, but alas not clear if that is a 25 degC or 90 degC spec.) 14.7V is a tad high for some AGM batteries -- older AGM batteries preferred lower voltages like 14.4V, newer ones are accepting of 14.6V but few 14.7V. But even this should not be a problem for most Phaetons, given the alternator voltage drops a little before reaching the LHS battery. So as long as you have a good battery, overcharging an AGM will not be a problem even at 14.7V or lower. (Phaeton TDI alternators are almost all Hitachi units, which have a different voltage regulator and probably temperature compensation curve than the Delphi units found in W12 cars.) Moral of the story, measure the actual charging voltage at the battery terminal and if you're <14.7V, you should be fine, indeed that is preferable.

The idea of using a magnetic disconnect for charging has come up on this forum before, but you may be the first to actually implement. That's amazing, kudos -- please share pictures when you get a chance.


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