Battery charging through regenerative braking.

[Teesix]

I'm led to understand that the battery doesn't charge from ticking over on the drive because the van uses regenerative braking energy to charge it. That's right yes?

I haven't used my van much over the past 18 months and predictably, the battery tends to be quite down on its SOC. (I base this on the speed the starter motor turns the engine rather than through a meter). I can also tell when the battery is sufficiently charged because my stop/start starts working!

Anyway, I decided to top the battery up by giving it a run down the motorway. Despite a couple of hundred miles the stop/start still wasn't working but the battery turned the van over quickly enough so I was happy enough.

The second time I decided to top the battery up I drove around my area which is quite hilly and requires much more braking than on a motorway. After a relatively short period of time the stop/start began to work and the battery was therefore charged. Total distance around 30 miles.

Is it correct to assume that, in order to charge the battery the quickest way, I should find a steep hill and to ride the brakes down it as much as possible rather than say chugging along a motorway/dual carriageway?

 

[Pauly]

The term regenerative braking is very misleading because it has nothing to do with the actual brakes, they are just the trigger

To achieve maximum efficiency the alternator puts out smaller current during normal driving and takes the van braking as a signal to ramp up the smart alternator and put out maximum voltage, whilst braking you are effectively turning the engine into a generator and recouping free electrical energy

 

[Pete C]

To be honest the easiest way is to buy a decent battery charger and use that with the van on your drive.
If the battery needs charging then the alternator will give it charge, whatever your driving mode.
I suspect what you observed was a coincidence.

Pete

 

[VanDamMan]

Alternatively just use a battery charger ( unless totally impractical) ..save fuel …save any additional regens. Your battery ( assuming smart type ) will top up to 80% which allows for regenerative charging


ps What the boss said. Above

 

[mmi]

To disable the "smart" charging you can set your cabin heater blower to speed 2 (or higher) (with Climatic 4-speed blower). That forces the alternator to charge at (minimum) 13.4 Volts whenever the engine is running.

 

[Teesix]

Thank you all.

So, if I were to put a brick on the brake pedal and leave the van ticking over would it charge at its maximum? (Thinking about camping scenarios)

A battery charger sounds the most efficient route but I like to know these things!

 

[Teesix]

To disable the "smart" charging you can set your cabin heater blower to speed 2 (or higher) (with Climatic 4-speed blower). That forces the alternator to charge at (minimum) 13.4 Volts whenever the engine is running.

Brilliant. Thank you.

 

[t0mb0]

If the battery is below 80% then I believe the alternator will kick in to deliver charge to get it to 80%. After that, it uses regenerative braking only to spike current into the battery as and when you brake.

In summary, if you're having trouble with the battery during normal usage (i.e. not left for months) then there may be something wrong. This is usually either a duff battery (often a moll, which are known to have issues), or some kind of undue drain on the battery whilst parked up from a dash cam or the like. You really shouldn't have to manage the battery in a modern van yourself with hills and heaters....!

 

[mmi]

So, if I were to put a brick on the brake pedal and leave the van ticking over would it charge at its maximum?

Actually no, the regenerative braking takes place only when engine braking takes place - so foot off the throttle when moving - manual gearbox gear engaged or DSG coasting function off.
Just the heater blower at 2 or higher - you'll get the minimum 13.4 Volts, or depending on battery's state of charge even up to 14.8 Volts (the same as at regenerative braking).

 

[Pete C]

As @mmi says, it isn't the act of pressing the brake pedal that triggers it. Just going into overrun whilst in gear triggers the alternator to increase the voltage and thus charge the battery.

Pete

 

[DXX]

To disable the "smart" charging you can set your cabin heater blower to speed 2 (or higher) (with Climatic 4-speed blower). That forces the alternator to charge at (minimum) 13.4 Volts whenever the engine is running.

So if VW are stating in the Vehicle Handbook to leave the AC running at all times that would tend to mean that the blower is on 2 or more as well. In which case the 80% economic battery charge is void?

 

[Dellmassive]

Running the AC disables stop/start....

 

[oldiebut goodie]

Are you sure about coasting having to be off with dsg for regenerative braking? It is just that I have coasting on yet my blower fan speeds up on braking which to me indicates that the regenerative charging is taking place. Or is that happening due to some other reason, known or unknown?

 

[mmi]

So if VW are stating in the Vehicle Handbook to leave the AC running at all times that would tend to mean that the blower is on 2 or more as well. In which case the 80% economic battery charge is void?

Yes, based on my observations & measurements the "2"-rule has never failed. And indeed, then T6 charger works very traditoinal way. Also the statement of "80%" charge indeed is void. And as a side effect the Stop/Start works without fail, too - as the battery is more or less full always.

Actually I have tried to derail the "2" by charging the battery by a separate battery charger - still always at minimum 13.4 Volts.

Again, the behaviour this far verified on T6 Climatic system.. Still work in progress how/if it's different on T6 Climatronic.

Running the AC disables stop/start....

Disagreed here - just keep the blower at "2" - engine will shut off even at +28C - certainly AC has to have reached "stable" state, which takes a while (15 mins) at those temperatures.

 

[mmi]

Are you sure about coasting having to be off with dsg for regenerative braking? It is just that I have coasting on yet my blower fan speeds up on braking which to me indicates that the regenerative charging is taking place. Or is that happening due to some other reason, known or unknown?

Actually it's only engine braking. Thus having coasting ON and touching brakes engages a gear which then initiates engine braking. Would this make sense?

 

[oldiebut goodie]

That would make sense as you wouldn't really notice the engine braking coming into play as you use the footbrake normally, so the coasting must be overridden at some juncture - maybe dependant upon force of braking? I shall have to experiment at a place where I regularly notice the voltage rise and see if differing brake pressure has an effect at all.

 

[t0mb0]

It makes sense for only engine braking to trigger actual regenerative braking. Energy lost as the brakes are applied is lost as heat (somewhat hard to recover!), energy lost through engine braking can be (partially) recovered through the alternator. However, unless you’re actually coasting in neutral, or crawling forward without pressing the accelerator, presumably as soon as you take your foot off the accelerator to apply the brake then you do also naturally incur some engine braking so you are also likely to trigger regenerative braking at that point.

 

[oldiebut goodie]

Travelling at 70 with coasting turned on then taking the foot off the gas does not initiate any regeneration - it then takes a very long distance for the van to slow so there is no braking effect whatsoever so there must be some factor in the footbrake operation that switches the coasting function off. It isn't a normal function when the coasting is selected otherwise there would be no point in having coasting enabled!
Have you got coasting enabled? - if so try it.

 

[rover220]

Running the AC disables stop/start....

It doesn't

 

[mmi]

there must be some factor in the footbrake operation that switches the coasting function off.

I'm fairly confident it's simply brake light switch.