⚠️How long to charge the battery by idling the engine?!

[Sunshine&Snow]

Hi! Our battery died while camping and we have no hook-up. We switched on the engine to idling. Has anyone charged like this? We just need enough battery to get the fridge through to the morning. It's not ideal. Hopefully it's quick!

 

[Steve1]

Hi! Our battery died while camping and we have no hook-up. We switched on the engine to idling. Has anyone charged like this? We just need enough battery to get the fridge through to the morning. It's not ideal. Hopefully it's quick!

To get a fast charge you might need to turn on a seat heater on lowest setting, that will give a higher voltage charge and go faster (latter vans might have a max charge button for that). If the battery is quite low but in good health then around 45mins should give roughly a day of usage I found.

 

[egena]

Yes, about an hour of running the engine on Idle
HOWEVER - DIESEL EU6 WARNING
If you have an EU6 diesel engine, this has a Diesel Particulate Filter (DPF) which collects the soot from the exhaust in a special compartment. The management system then senses its getting a bit full and burns it off, whilst you're driving, by super heating the container to 680°c.
This is a fully automated system that activates a burn-off cycle when it reaches 100% (30mg soot) yet it has no real indicators on the dash apart from a DPF light that appears when the container is measuring 130% of maximum holding tolerance. Shortly afterwards, at 150%, it will permanently put your engine in "Limp" mode and illuminate the engine light to force you to a garage.
I use an OBD device

and connect an android app called "VAG DPF" to the OBD device via Bluetooth and it gives me a readout of the current percentage so I know when it's safe to run air-conditioning or battery charging where needed.

The top left "Soot Mass Calc" reads 30mg when the bar above reaches 100%.
The percentage bar is the only thing you need to peek at - super easy.

NOTE
The engine management system WILL NOT EMPTY the container using a burn cycle if;

- Fuel gauge is in the RED area
- Speed is below 30mph

It avoids performing a burn cycle when the fuel gauge is low because it uses diesel to do the process so could shorten your range considerably.
It also avoids the burn cycle if your speed is below 30mph because it needs the engine to be running above 12000 rpm (just over the number 1 of the engine indicator) so that exhaust gas flows through the container and assists in the burning process.

 

[egena]

TLDR: running engine on Idle for long periods can risk your DPF exceeding its maximum capacity and causing a forced trip to a garage