Is there any way of logging the charging current to battery from the alternator?

I mean using VCDS or an alternative way.

Using a current clamp ammeter?

Must be in a VCDS measuring block within whichever module is responsible?

 

For the VW? Ross-tech forums may be worth searching. Alternatively a guy on here called @fabdavrav is clued up on this stuff, I believe. 

37 minutes ago, PetrolDave said:

Using a current clamp ammeter?

 

That would measure it, but not directly log it. You could connect it up to a data acquisition system, but that would be overkill. There is probably a Raspberry Pi solution. if you have one of those.

 

Of course, you have to ask what you are intending to do as a consequence of making these measurements? There may be an easier way, after all, the automotive world has existed for many years without needing anything other that voltage measurements. You can argue that it is not ideal in some circumstances, but they've made it work. 

1 hour ago, Wino said:

Must be in a VCDS measuring block within whichever module is responsible?

I have searched for clues (including in RossTech forum) but no luck so far. The classic measurement needs a very big shunt in series with the alternator/battery which there isn't to my knowledge.

1 hour ago, Wino said:

For the VW?

Yes. The technology is common on all VAG cars. My hopes are related to that smart charging system that knows when to tell the alternator to charge without putting a load on the engine all the time. How does it know what is the instantaneous amperage of all loads?

1 minute ago, RicardoM said:

I have searched for clues (including in RossTech forum) but no luck so far. The classic measurement needs a very big shunt in series with the alternator/battery which there isn't to my knowledge.

Yes. The technology is common on all VAG cars. My hopes are related to that smart charging system that knows when to tell the alternator to charge without putting a load on the engine all the time. How does it know what is the instantaneous amperage of all loads?

The battery management / smart charging system uses the cable between the battery negative and the chassis as the current shunt (yes, it's very low resistance, but it's designed for that).

 

If you could find the measuring block (which depending on the car will be either in the 61 module or the battery management subsystem of the 19 module) that shows live current drain I'm pretty sure that you can log it using VCDS, see VCDS Data Logging

If you have to do a DIY messurement, you could use the alternator fuse as a shunt. Might be slightly non-linear but that could be calibrated out.

 

For any sort of accuracy you'd probably also need to measure and calibrate for local area temperature also.

Edited 25 October, 20205 yr by Wino

As others have said it should be in the measuring blocks section of VCDS for the CANgateway module or the engine or central electronics modules...I haven't looked there myself...(busy with other things)

 

The stop start & regen systems uses masses of data from numerous sources...here is the VW self study guide on it that I have:-

00028122020-Nr__426__Start_Stop_System_2009.pdf

Could you clarify your question a bit please Ricardo?

Do you want to know the output current of the alternator at any given moment, or the actual net charging current into the battery (alternator output minus connected loads consumption)? 

Or do you mainly want to understand how the alternator is controlled to achieve the required outputs?

5 hours ago, Wino said:

Could you clarify your question a bit please Ricardo?

I just need to log the charging current of the battery to make sure the battery management does a good job. Right now my impression is that the battery does never get fully charged, even on long trips on the highway.

OK, well that's the current that the battery management module shunt is telling the car/VCDS about. If there's a current flowing from the battery negative post through the shunt to chassis, then that is the battery charging current (generator current minus consumers current >0). If there's a current in the other direction through the shunt, from chassis to battery negative, then power usage exceeds generation by the alternator.

 

When the two currents balance perfectly - alternator matching demand -  there will be zero volts across shunt, no flow into or out of the battery.

 

Unless I'm going mad...

 

 

 

 

On 25/10/2020 at 11:22, RicardoM said:

Yes. The technology is common on all VAG cars. My hopes are related to that smart charging system that knows when to tell the alternator to charge without putting a load on the engine all the time. How does it know what is the instantaneous amperage of all loads?

 

The inference of fabdavrav's document (essentially, what new stuff is in the systems of Bluemotion cars) is that it can't be common across all VW cars, or there would be no new stuff to document. And, obviously, there wouldn't be commonality with pre-smartcharge cars, and there may be other steps in between.

 

Generally, it doesn't need to know the current accurately. It knows the voltage and you can make rough-and-tough-but-good-enough implications from the voltage.

 

The latest cars do more, in an attempt to chase increasingly small fractions of fuel economy, do more, but you don't have one of those. So, I will ask again, what do you hope to do with this information, because if there isn't another way of doing it, it looks as if you aren't going to do it.

 

On 25/10/2020 at 11:30, PetrolDave said:

The battery management / smart charging system uses the cable between the battery negative and the chassis as the current shunt (yes, it's very low resistance, but it's designed for that).

 

It is designed to pass the current, but I doubt that it is used for measurement. Firstly, there are many other paths to ground, which go the opposite way through this connection. These are mostly designed to be low current, but can be high current fault conditions, and there are a few exceptions - lights, HRW, heater, air con, gearbox, engine (ok, that's probably more exceptions than non-exceptions).

 

The other thing is that this connection would have to be a predictable and consistent connection. The tempco of copper wire is relatively high and a little corrosion at one of the connections would really mess it up. Additionally, it isn't uncommon for stranded wire to loose a strand or two over age, and that will also mess it up.

 

It is possible to get around these factors, but generally it isn't considered worthwhile to do it.

The "Energy Management" chapter within the document here is useful https://www.scribd.com/document/410157436/SSP-477-Audi-A1-pdf

Snapshot of key diagram: 

 

As an example, here’s an 8 hour data logged session from a 2014 2.0TDi VW Caddy with a 096 AGM. It shows fluctuating voltage based on current demands from the vehicle. The ‘A’s in the graph are engine starts where current draw is at its maximum. Depending on the system current requirements, the voltage is changed to allow charging, maintaining or battery only power supply. There is no S/S feature on this vehicle but the energy management principle is the same.

 

Neg current shows when drawing off the battery and voltage is low, Pos charging current when the alternator is operational and voltage is high. 

 

There is a significant current draw midpoint from an external device spliced into the harness that didn’t switch off with the ignition. The charge profile immediately called for high current next engine start to recover the battery charge state and tapers off back to normal once the battery is good.

 

its constantly monitored and adjusted. 

2 hours ago, RicardoM said:

I just need to log the charging current of the battery to make sure the battery management does a good job. Right now my impression is that the battery does never get fully charged, even on long trips on the highway.

It’s working just fine if you disconnect the battery for an hour or so and measure it’s voltage at around 12.7v, above 12.3 ish connected as the vehicle wakes up as soon as it’s unlocked skewing the voltage due to increased current draw. 

 

These says batteries don’t get fully charged, they don’t need to be. Charging targets about 80% and that keeps batteries happy enough to maintain performance and the vehicle needs.  

 

You will soon find out if something’s amiss. S/S not working when you expect it to is the first flag!

2 hours ago, RicardoM said:

Right now my impression is that the battery does never get fully charged, even on long trips on the highway.

That impression is correct, the battery is not charged above around 80%, supposedly to leave some headroom for regenerative braking by using the alternator to further charge the battery.

Probably also because the assessment of state of charge is approximate rather than exact, and if it were set to 100% it could result in overcharge/damage, and waste of energy.

 

Edit: Possibly also because when put in for emissions test cycle analysis during EU type testing the cars are allowed to start the tests with battery fully charged (I seem to remember). This would result in the possibility that during test cycle the battery management could operate its normal software whilst also never or barely having to load the alternator, as it could decline to 80% charge before any charging was invoked...

Jus' wondrin'...

Edited 26 October, 20205 yr by Wino

It’s always an approximation, the battery is an analogue energy store in a digital world and needs to be kept in an operational window above 12v open circuit. Energy can be borrowed off it frequently but it has to be put back soon after. 

5 hours ago, Camlobe said:

So, I will ask again, what do you hope to do with this information, because if there isn't another way of doing it, it looks as if you aren't going to do it.

Putting it simple, I am reluctant that the battery management (BM) is doing the best job of keeping the battery fully charged. It looks like there is a charge % threshold (say 80%). Over it, the BM doesn't bother kicking in. In other words, the battery will never be 100% charged.

5 hours ago, Camlobe said:

Generally, it doesn't need to know the current accurately. It knows the voltage and you can make rough-and-tough-but-good-enough implications from the voltage.

Well, I have a USB charger plugged in all the time. It shows the battery voltage. I tested its precision and it is better than 1%. When I start the engine in the morning, the voltage goes up to 14.5-15V for some 5 minutes then it drops gradually to 13.5V. On a long trip on the highway by day, the voltage drops to about 13.1V. To me instantaneous battery voltage doesn't mean something useful in terms of battery status. I would rather be happy with a SOC (state of charge %) displayed on the MFD exactly like oil temperature, average consumption, etc. I have installed a brand new 60Ah VARTA N60 EFB battery (640A EN = 700 CCA) and I am interested in having it in best shape.

 

Now, I have the luxury of having access to the latest PicoScope 4425A Master Kit. Yesterday I went to the car and did three specific battery/charging diagnose tests at 5 minutes intervals. I wasn't happy finding the battery voltage was 12.2V overnight. See for yourself. Comments appreciated.

 

4 hours ago, BigEjit said:

It’s working just fine if you disconnect the battery for an hour or so and measure it’s voltage at around 12.7v, above 12.3 ish connected as the vehicle wakes up as soon as it’s unlocked skewing the voltage due to increased current draw. 

That is pi$$ing me off, as I am not a big fan of modern cars, although for comfort and safety I own one. As soon as the computer modules wake up, they start chewing the battery big time. I have no possibility to know for sure what is the battery voltage first thing in the morning,as to open the bonnet means waking up all the guards of the car that draw an insane power from the battery. Where are the good old times when the only electrical load was the interior light dome when you opened the door... Furthermore, when switching the ignition key to ON, there is a big 50A spike for half a second or so...

4 hours ago, BigEjit said:

You will soon find out if something’s amiss. S/S not working when you expect it to is the first flag!

I always deactivate it, as it is a stupid technology.

The starting voltage there looks OK. It’s roughly where it should be. If you key off after a charge cycle it will be higher. The flare you see on the voltage after key start is also normal. 
 

The thing with measuring the battery voltage on the move is that it’s the entire system voltage being shown, not just the battery. You can’t isolate the battery when connected so there is background noise interference on the measurement. from the vehicle. Ideally battery voltage should be done at room temp in a stabilised open circuit condition. 

 

SOC is a theoretical value that cannot be accurately measured outside a lab. CCA for example varies with ambient temp as does voltage. A cold battery has slower chemical reactions suppressing output both V and A. Opposite at higher temps, hence the need for a week long lab test to grade a battery. 

 

Some EFB’s have slightly different acid gravity for performance and life expectancy targets which also affects voltage output. Without spec sheets, you can’t tell what it’s supposed to be. 
 

Switching S/S off only inhibits the signal to cut the engine. All other operational charging characteristics remain in place. 

8 hours ago, RicardoM said:

That is pi$$ing me off, as I am not a big fan of modern cars, although for comfort and safety I own one. As soon as the computer modules wake up, they start chewing the battery big time. I have no possibility to know for sure what is the battery voltage first thing in the morning,as to open the bonnet means waking up all the guards of the car that draw an insane power from the battery. Where are the good old times when the only electrical load was the interior light dome when you opened the door... Furthermore, when switching the ignition key to ON, there is a big 50A spike for half a second or so...

I always deactivate it, as it is a stupid technology.

Consider fitting an LCD voltmeter module somewhere where you will be able to see it from outside the car. I found an 'unwanted' one at work that has an operating current of only 350uA. It needed a 5V regulated supply for which I added an efficient regulator. The total addition to the car's quiescent current is just 0.5mA. 

Obviously at that power level it isn't backlit, but phone (or other) torch can help if you want to read it in the dark before opening the car.

 

10 hours ago, RicardoM said:

Putting it simple, I am reluctant that the battery management (BM) is doing the best job of keeping the battery fully charged. It looks like there is a charge % threshold (say 80%). Over it, the BM doesn't bother kicking in. In other words, the battery will never be 100% charged.

 

 

No, as commented earlier, the target will be something above 70% charge - and some other manufacturers are worse, targeting more like 50% charge.

 

The point of this is to allow 'room' for the regenerative braking of the 'micro-hybrid' system without overcharging the battery This is considered normal operation, these days. Now, I will admit that while I see the point, I would prefer a slightly higher percentage, particularly as the battery ages and loses capacity, but it is what it is.

Another avenue you could explore @RicardoM is to disconnect the LIN connection to the alternator. That will surely log a fault code, but I'm not sure if it will put any warning lights on.

According to that energy management document referred to earlier, 

 

"The alternator on a model with an energy management system
comes fitted with a LIN regulator. These alternators have two
terminals: the bolted B+ terminal, as well as a double connector in
which only pin 1 is assigned to the LIN line, and pin 2 remains
unassigned. The data bus diagnostic interface J533 sends LIN
messages to the LIN regulator. Depending on the status of the
onboard power supply, these LIN messages specify voltage values
of between 12.2 volts and 15 volts, which the regulator then sets.
If these voltage values are not set, e.g. because of a broken LIN
line, the regulator detects this and sets a constant alternator
voltage of 14.3 volts on expiration of a pre-defined interval."

 

That sounds like it defaulting to 'traditional' alternator behaviour which may suit you better. 

Experiment.

 

Lots of people report disconnecting the LIN wire at the battery management shunt module and getting the same result, which seems reasonable.  

 

Scaremongers will possibly tell you that this will over or undercharge your battery, and all sorts of disasters will happen, but I suspect that it will just work more like you want it to. It would be interesting to get some good data on this from a man of your scientific, methodical nature. 

@Wino

The battery monitor control unit J367 looks the most promising for experimenting indeed.

I would be very interested to know more about its inner parts. I am tempted to go the hard way by developing an independent current monitor based on Arduino/Pi, unless I find a better, ready made logger to connect it to J367. Only when I fully understand from the logs what has the battery management under the bonnet based on recording various trips, I will choose what tweaks deserve attention.

The strategy that keeps the battery undercharged to make room for recuperative braking contribution seems (for the moment) of little interest in terms of energy level recovery. My instinct is telling me the system is not contributing with more than 5% (to be generous) from total battery charge on an average driving trip.