[meggsy]

As we all know the AGM battery is fitted to these vehicles. The recommended maximum charging rate for an AGM battery is 0.4 C which for a 100Ah battery equates to 25A -The maximum charging current depends on the battery size, for a rough estimate of the max current in amps [A], divide the battery amp-hours [Ah] by 4 .

So theoretically a 230 Amp alternator can want to pump a significantly higher current into a battery with a remaining "say"60% charge. And that is also dependent upon battery temperature.

Since many people are getting 7+ yeas from an OEM battery VW must have some smarts there to limit the charge and look after the battery.

So my question is how VW maximise the service life of a battery. As far as I know the ECU /smart alternator function controls the voltage output of the alternator based on monitoring certain parameters... but as far as I know don't limit current.

Just to get one and all scratching their heads on a public holiday AUSTRALIA DAY....

 

[Black Grouse]

Alternator output in linear through much of it's speed range so the maximum power is much less than 230A lower down the rpm range - in addition most of the alternator output is use to drive all the 12v equipment in the car - but how it manages that current I don't know.

 

[meggsy]

Alternator output in linear through much of it's speed range so the maximum power is much less than 230A lower down the rpm range - in addition most of the alternator output is use to drive all the 12v equipment in the car - but how it manages that current I don't know.

Black Grous -- Thanks and to a certain extent I agree however I doubt that the vehcle electrics will take up anywhere close to more than 100 amps at any one time. - its going to be an interesting discussion methinks.

 

[SaVAGeSoot]

Use VCDS to log MVBs and look for things that interest you.
If you check my battery post, you can also see the "electrical history" that you can extract from these gen models that gives you all sorts of parameters to review, etc.

 

[Dannyboy485]

Limiting the voltage limits the current in a nutshell. That's why after you start your vehicle voltage will increase to 14.5 volts and after the battery is nearly full voltage will drop to 13.x volts as current demand is reduced.

Voltage regulator is what controls the voltage and alternator field strength. That's why theres different profiles for the battery management system on these vehicles. They just adjust voltage curve for the specific type of battery size and chemistry. Basically fine tune the charging system.

 

[meggsy]

Limiting the voltage limits the current in a nutshell. That's why after you start your vehicle voltage will increase to 14.5 volts and after the battery is nearly full voltage will drop to 13.x volts as current demand is reduced.

Voltage regulator is what controls the voltage and alternator field strength. That's why theres different profiles for the battery management system on these vehicles. They just adjust voltage curve for the specific type of battery size and chemistry. Basically fine tune the charging system.

Thanks and Basically the theory is sound, - If that is the case then why does one need a DC to DC charger to ensure the correct voltage is applied to second AGM or van battery?? the additional AGM battery is still a load sensed by the vehicles charging system -- in otherwards if my vehicle battery is fully charged and then I attach a say 50% charged AGM battery of similar capacity (100 A/Hr) the vehicle system should recognise the need to provide the appropriate charge voltage charge which it does not. However, at the same time the vehicle battery will see the voltage difference between it and the other battery and actually try to provide a charge to it ..... with the additional under load current draw the vehicle battery will drop its voltage so the vehicle system would/should increase its voltage output and hence current (which from my measurements it does not). Our vehicles with AGM batteries (start/stop mode) also have a regenerative mode that increases the current and voltage briefly whence braking/overrunning which can spike up to 17 volts (I am led to believe). this again is a function of the ECU - long gone are the old-style conventional voltage regulators and transistorised semi modern ones.

.

 

[Dannyboy485]

You need a second DC to DC charger because the second battery can be at a different SOC (state of charge) so if the output is example 13.5v because of the primary battery, it won't charge the secondary battery correctly.

If you have both batteries in parallel and one is low, under ideal conditions the stronger battery will actually slowly discharge into weaker one as voltage is higher and will want voltages to balance out. The alternator will charge but definitely not at the optimum level or rate. AGM batteries are sensitive to charge level voltage and will shorten their life significantly if overcharged. They can take voltage spikes way better than flooded but there is limits

Solid state regulators with LIN bus are awesome compared to the dinosaurs of yesteryear.