Car battery

Run-flat tyres? Or do VW think Passat owners are too posh to use plug-in 12V compressors to pump their own tyres?

They have supplied a jack and a spare wheel.

I didn't say there was in yours. There is a bloody great chunk of electronics and software to do with working out the varying amounts of charge needed to get the battery to 100 or 80% charge in my car. It monitors how much was needed over time and knows how old the battery it so it can charge the battery more as it ages. This info is reset when you swap the battery and re-code it. If you swap an old battery with a new one and don't re-code then it will be overcharged and reduce the life. And yes it's a pain to have to do this.

Of course you know better even though you don't work with major EU car manufacturers on their in-car computers and ECUS like I do. Anyway, you can't even find the 12V accessory socket in your car. The cabin one may be switched with the ignition though this can be changed on many VWs by moving the fuse to a different slot in the box. The accessory socket in the boot is normally unswitched.

Ok, I'm going to bite here. You were doing well up to now.

Please define overcharged. It's pretty much impossible to overcharge a lead acid battery. %age charge is dictated by voltage and time.

I'm not convinced you do. If you believe a car built with ESM will inherently overcharge a low capacity battery, then you're simply wrong.

Some Fords too.

That is what the place I normally get mine from does...

I was wondering how modern?

New to me are 68 plates. They just have faulty water pumps.

My car has a jack and a spare wheel, but it still has a "cigarette lighter" in the boot for a 12V compressor. People do use them for top-ups, not just for punctures.

Well I have consulted those with more knowledge, searched the VW forums and carefully read the relevant sections of the 20mm thick handbook. Nothing has pointed to re-coding being necessary although VW would clearly prefer their fitters do the job.

Umm. I won't annoy you further by offering an agricultural opinion of the bulk of the electronics found in my 10 year old car. As you rightly say there is a 12V outlet to be found in the luggage compartment. There may well be 230 and 115V available for passengers. I don't smoke so had no reason to look for sockets hidden in ash trays. If my simple code reader device is capable of inputting a new battery fitted, I will attempt the job.

connected a small 12v battery to the cig lighter

I'd have thought that the battery by pass method was good enough if you were not expecting it to be off for more than a few minutes. Car batteries are hardly sophisticated, are they. I still do not see why most modern things in a car should not store data in a simple flash memory chip. I'm sure that by this time most people who might be equipped to nick a sound system would know how to get around the code problem. Brian

Surely this is just for service time reasons Hardly something to worry about. Brian

Yes that sounds just like stupidity at the design stage then. Brian

My car can have AGM or wet but sealed batteries. You can specify which and the battery capacity through the battery recode procedure and the charging current is adjusted as AGMs charge faster but suffer more easily from overcharging. Overcharging heats them up and they can distort plates and they gas and loose electrolyte. If you keep the charge current controlled any gas is reabsorbed so the electrolyte level remains constant and the battery lasts longer. Mainly the smart charging is for the fuel saving.

With the smart charging system, the battery is normally not charged to

But it needs to know a lot about the battery state which it knows from you telling it the max capacity, the type etc. It can measure the terminal voltage and it knows how much charge it has applied to know more accurately the state of charge for the actual battery in your car not just generically. One of the things the recode does is when you say new battery it measures the voltage and as you are telling "fitted new battery that is fully charged" it knows the offload and onload voltage when charged for your battery and can calculate the 70-80% level. It is able to determine how old the battery is and further adjust when to charge or not. This means it knows when to stop charging using the engine driven alternator and how much charge capacity is left when using regenerative charging. This is so it doesn't overcharge and shorten the life of the battery.

It's not just to save fuel by recovering the final charge current from motion. It uses the knowledge to know how much stop/start charge is available. If the charge state is insufficient it wont stop/start. You could get some of that from the terminal voltage but if you are trying to save fuel, it knows whether it's worth stopping the engine for an unknown time and using the battery to restart or if it will likely use more energy to recharge the battery after the restart. If it's already in recovery charging it will be worth stopping the engine.

The odd thing is that you may achieve a higher state of charge when driving around town or country roads where you lift off or brake a lot that on a long journey on a motorway. This is counter intuitive to what older drivers have learnt.

You can see this working by measuring the battery voltage and starting the car. If the charge level was above the recovery level, the voltage on the battery wont jump to 14.4V. You can often start the car a few times before you see it start charging again. Again, a non-smart charging system will always try to get the battery fully charged which is often unnecessary. The amount of extra electronics and software needed to achieve a notional small 3% saving is considered worthwhile.

As for working on ECUs, car software etc. Recently, last 18months has been on a range of ECUs for GM. Before that 24months for Audi in-dash electronics. Also quite a bit of work on AUTOSAR implementations for inter ECU comms.

Your welcome.

Maybe they are the ones who posted a request on the uk.r.c.maintenance NG asking Mr Cheerful for a code for xxxxx radio.

Andrew

That was standard on Citroens and Peugeots at the time and introduces conflicting requirements for my 2008 Xsara Picasso. You're supposed to wait 3 minutes to ensure the electronics have gone completely to sleep before disconnecting the battery.

They also specify a weird procedure for reconnecting the battery: WAIT 1 minute Keeping the doors closed, lean in via the drivers window Switch on the 'ignition' (Don't start the engine) Switch on lights (Dipped, normal driving lights) WAIT 30 Seconds Start the car

My car often stands for several weeks without being used so I've taken to disconnecting the battery while not needed to avoid ending up with a flat battery next time I need it. Following the recommended procedure would mean leaving the car with the front electric only window wide open all the time after disconnecting the battery.

Fortunately the battery is inside the car under the passenger seat so the whole process is performed inside the car without needing to open the window and the front doors can be locked manually with the key afterwards. But there's no way of locking the rear doors manually so I have to lock the car with the remote before starting the 3 minute countdown. This means that the electronics never completely shut down because it's still listening for an unlock signal and blinking the marker light on the top of the dashboard.

So I have the choice of following the manufacturer's procedure to protect the electronics but leave the car with both rear doors unlocked or I can secure the care properly with some risk of upsetting the electronics. So far the secure option doesn't seem to have affected the electronics.

So in a nutshell, if you replace the battery with a like for like technology, you won't overcharge the new battery.

Glad we got that one sorted.

I'm sure you know better than the people who design this stuff.

In message <tn22me$1ll75$ snipped-for-privacy@dont-email.me, mm0fmf snipped-for-privacy@invalid.com writes

Surely you must have, on many occasions, said to yourself "Why on earth did they have to make this all so complicated? What is the real advantage? Even I could do a better job!"

In message <j00PPSGg$ snipped-for-privacy@brattleho.plus.com>, Ian Jackson snipped-for-privacy@g3ohx.co.uk> writes

We perhaps shouldn't mention the exhaust test avoidance software currently still operating on my VW. 105BHP out of a 1600cc diesel is pretty impressive no matter how it was achieved.