Engine running charge rate being minus?

[monster-mash]

Please forgive me if this has been mention before ( i have searched) and it may be in the wrong section??? never noticed before but on generator (engine running/charging) im displaying -0.2, 0.4 and occasionally which i always thought to be correct same figures but without the minus, on the mains plug in its normal starting at 0.4 and settling around 0.2. Voltage is about 13v to 14v. Could this be the start of a alternator issue or main vehicle battery fail?
Any thoughts appreciated and typically we are on hols at the moment in France i can minimize my journeys if needed

 

[Loz]

I get this when the Alternator is set to idle by the bcu and causes a drain on the leisure circuit. But if yours is a 2008 it is unlikely to have regenerative braking so for some reason the alternator is not charging when you see this,

 

[andyinluton]

Isn't that just showing that there is more going out of the battery than coming in ? for - 15.4A I would guess the parking heater is just starting up.

The alternator charges the vehicle battery first and that display is for the leisure battery, so if you just start the engine all the charge will be going to the starter battery for a while, but things like the fridge will still be drawing current therefore showing a minus figure on that display.

 

[monster-mash]

No regenerative braking here, im guessing the same andyinluton and the reason its not been apparent before is that the main battery is slowly getting worse. A planned replacement is in order i think.

 

[Loz]

Isn't that just showing that there is more going out of the battery than coming in ? for - 15.4A I would guess the parking heater is just starting up.

The alternator charges the vehicle battery first and that display is for the leisure battery, so if you just start the engine all the charge will be going to the starter battery for a while, but things like the fridge will still be drawing current therefore showing a minus figure on that display.

No air heater, that is parasitic drain because the alternator is idle and the leisure batteries are recharging the starter battery at that moment and the reason I'm going to swap the factory Split charge relay for a dc-dc intelligent charger.

 

[andyinluton]

the leisure batteries are recharging the starter battery at that moment

Hows that work then? unless you've rewired the charging circuits the leisure batteries are always completely independent of the starter battery.
The split charge relay just switches which set of batteries are being charged from the alternator.

 

[Loz]

Unfortunately not, have a look at the wiring diagram there is a 100a fuse from main battery to a 150A relay that goes to an 80A fuse straight onto the leisure battery.
As long as your not in start/stop stopped than the relay is closed and current can flow in either direction depending depending on which battery has the most charge.
Units with (bluemotion) regenerative braking idle the alternator to hold the starter battery at 80% to keep room for the regeneration under braking.

The result is the leisure batteries end up matching the starter battery at 80% so why I plan to swap out the relay for the dc-dc unit.