22 hours ago, RicardoM said:

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.

 

There is a simple solution to that Ricardo unless you live in a high crime area.

 

With the bonnet open engage the locking mechanism latch using a screwdriver or similar, the car should then think the bonnet is closed & the maxidot display should confirm this (no bonnet open icon). You can then put the bonnet down unlocked but with the secondary catch holding it open a couple of inches and lock the car for the night.

 

The next morning you can open the bonnet and take your battery voltage reading without the car knowing and waking up.

 

I understand exactly what you suspect and are trying to achieve, I think you are correct in your suspicion & ultimately when you remove the shunt link & go to a standard charging profile you will probably extend the life of your new battery.

 

I think you can do this by simply watching the charging, standby and resting voltages without having to measure the current, I have a simple LED voltage readout on my centre console which I can see from outside the car while it is locked & when I am driving, it would do all that you want at present and warn you if ever you need to start the car to charge the battery if it has been standing too long, there are ones that plug into the cigar lighter socket but I prefer the fixed ones:

 

https://www.ebay.co.uk/itm/12V-24V-4-2A-Dual-USB-Car-Motorcycle-Charger-Socket-Adapter-Outlet-LED-Voltmeter/264627199821?ssPageName=STRK%3AMEBIDX%3AIT&var=564417022622&_trksid=p2060353.m2749.l2649

Doesn't that take quite a lot of current @J.R.? Have you measured how much?

Just now, Wino said:

Doesn't that take quite a lot of current @J.R.? Have you measured how much?

 

Mine have switches on them to switch off the display although only the one on the standby battery in the shed is switched off, I dont know how much current, you have me concerned now, I will measure it!

 

10.6 milliamperes Wino.

 

Significant, 3 times what I thought and enough to reduce the standby autonomy of my vehicle by 1/3. Of course it can be switched off.

 

Not a problem while I am using the vehicle even infrequently and on balance I would rather be able to see that its getting towards 12v (lowest I have seen is 12.3) so I can start and drive it or charge it.

 

What I dont want to do is leave it switched on if its left at an airport during a holiday (I wish!) and also accidentally switch on the towing relay while removing the cases!

 

And I forgot to confirm that it drew no current when switched off, you cant assume anything!

Edited 27 October, 20205 yr by J.R.

Update

 

The BMC J367 has a microcontroller inside acting as a LIN slave. It gets data from the current shunt, the thermistor, and the voltage on battery then packs it according to serial LIN protocol.

 

I took the battery out, recharged it overnight using an intelligent battery charger with a 7-step charging current. The battery showed 61% charged at the beginning, 100% at the end.

Installed the battery on the car. The voltage on battery while driving in the city couldn't be bothered to go over 13.1V, sometimes so low as 12.7V.

Now I have two options:

1. Rest assured that VW knows what is doing in terms of charging % and charging strategy to minimize the load on the engine and prolong the life of the battery. Note: original battery lasted 5 years but gave up without warning in a mall parking lot after staying 15 minutes inside the mall.
2. Dig in by decoding the LIN bus and monitor the 3 input parameters, correlate them with the driving phase and go on from there.

Your call please?

If you have the knowledge/skills to decode the data stream, I for one would be very interested in what it revealed. I suspect you won't be able to resist the challenge?

 

VW's charging strategy will include many factors, but making the battery last as long as possible probably isn't one of them.

 

This looks promising.

 

I wonder IF and HOW the BCM knows the SOC (State of Charge) of the battery. Anyone?

You could use a split-core hall-effect current transducer to measure current.  Then you just need a data-logger or multimeter with logging abilities.

 

https://www.ebay.co.uk/i/283216689221

 

There are many cheaper if you go for a lower current capacity.

UPDATE

So far I'm monitoring the voltage on battery first thing in the morning. I have installed a cable from the battery poles that ends with a 2-pin black socket with a black protective cap and a fuse for extra safety. I tucked the socket near the front grill. You can't see it unless you know it is there. So I can use a multimeter to check the voltage without "waking up" anything.

 

Observations so far:

The first worst thing that can happen to a battery on a VAG car is driving around in a city for short trips (less than 10 km) using low electrical loads. The BCM will charge the battery only for about a minute. The rest of the time the alternator will deliver 13.1-13.5 V to the battery. Basically will stay in the so called Fuel Economy Mode. This strategy will result in discharging the battery to about 12.0 - 12.2 V in the morning thus lowering the SOC of the battery to less than 50% every day.

 

The second worst thing that can happen to a battery on a VAG car is not using the car for more than 3 days. Depending on type of computer modules and sensors installed on a VAG car (anti-theft, proximity sensors, keyless doors, remote engine start, various convenience sensors, etc.) the battery will end up discharged.

 

By comparison I have attached an article that describes the BCM on General Motors cars. Their strategy is far better. For instance, anything under 80% SOC will trip the alternator to start charging and reach back 80% leaving room for brake regenerative charging. VAG strategy is to lower the fuel consumption at the expense of a low SOC and short battery life.

Charging System Description and Operation.pdf

Edited 3 November, 20205 yr by RicardoM

I dont think that you need to measure the current, the charging voltage will give you everything that you need.

 

13.1-13.5 after the initial replacement of the start up current drawn does not sound too bad to me, perhaps a little early but would not result in a discharged battery.

 

Let us know what the voltage is one hour after stopping from a journey like that and what it is the following morning before waking anything up.

 

I have a voltmeter but have to look down to the centre console to survey it, I dont have battery problems at present so am not constantly watching it, after a start it will be at 14.4v while driving and will then drop some, how much and fater how long I'm not sure but it will definitely drop to 13.1v after say a 15 mile journey, perhaps a long time before that.

 

It will be at 12.9v on shut off, dropping to say 12.7/12.6 an hour later, the next morning it could be at 12.4/12.3 (the battery has once been overdischarged so is not 100%) and that may drop to 12.2v after a few days of non use and then remains there for as long as I leave it which is never more than a week, it will of course continue to fall if I were not to drive it, IIRC when I tested the parasitic consumption was 22ma but now I have to add the current for the voltmeter or to switch it off.

 

Mine is non stop/start and standard alternator charging system.

Edited 3 November, 20205 yr by J.R.

1 hour ago, RicardoM said:

The first worst thing that can happen to a battery on a VAG car is driving around in a city for short trips (less than 10 km) using low electrical loads. The BCM will charge the battery only for about a minute. The rest of the time the alternator will deliver 13.1-13.5 V to the battery. Basically will stay in the so called Fuel Economy Mode. This strategy will result in discharging the battery to about 12.0 - 12.2 V in the morning thus lowering the SOC of the battery to less than 50% every day

 

Long term observations, MY2018 superb 1.4 SEL with Columbus fitted with OE 59Ah Exide EFB battery, most runs, short, long, with low loads the battery almost always ends ups parked in my garage at approx 80% SOC. (As determined below)

 

1 hour ago, RicardoM said:

The second worst thing that can happen to a battery on a VAG car is not using the car for more than 3 days. Depending on type of computer modules and sensors installed on a VAG car (anti-theft, proximity sensors, keyless doors, remote engine start, various convenience sensors, etc.) the battery will end up discharged.

 

For my car (no KESSY), at 13.5 volts, standby quiescent current drops to 10mA when everything has gone to sleep (which usually is no more than 3 mins). Every 10-20 mins, something wakes up for around 30 seconds or so and the current increases to around 50-60mA. I think its the phone subsystem.

 

I am confident the average is under 15mA which is 0.36Ah per 24hr.

 

Too complex to explain my methodology in any detail, briefly I use a variable Lab power supply with accurate voltage and current measurement and determine the total Ah charge to fetch the battery to a full 100% charge, which usually takes at least three or four days depending on the charge voltage I set. (Taper charge, this is all you can really do with a lead acid battery, they won't be rushed to 100%)

 

Older and partially discharged batteries of course may exhibit additional self discharge and lose capacity with age, cycling and elevated battery temperatures which are seen during even normal use.

 

This is all I have to say on the subject, I barely raised enough energy to post this (pun unintended) so don't ask me any questions.

 

 

 

Edited 3 November, 20205 yr by xman

1 hour ago, xman said:

Too complex to explain my methodology in any detail

If I understood it correctly, you don't have am instantaneous method of measuring/computing the SOC of the battery in the car.

UPDATE

The outside temperature dropped by some 5-10 degrees. The BCM started to command the alternator to charge harder (for the same electrical load I have used for the last 2 weeks). The voltage on battery stays at 14.7-15.1V 90% of the drive time. In the morning I have measured a higher and higher voltage. Today the voltage was 12.4V. We're getting there...

 

My conclusion so far is that the firmware in the BCM seems to know how to handle the SOC of the battery. Not having access to the firmware source is a drawback but given the proper free time I could deduct the charging strategy by studying relevant logs.

Edited 10 November, 20205 yr by RicardoM