hi folks
installing a second battery in my 2014 Ford transit connect to turn it into a micro camper.
Bought a battery isolator (this one: https://www.amazon.ca/NOCO-IGD140HP...9224149&sr=1-1&keywords=noco+battery+isolator) to separate the batteries but apparently this version of Ford has a 'smart charge' alternator which is foiling me.

When wired as suggested (a1.png) I get a battery warning light, and no output from the alternator (abusing motor symbol in my schematic). I'm guessing since it detects no voltage at the junction of the diodes the 'smart charge' turns off the alternator.

I've wired it as in a2.png, with the 'house battery' wired directly to the alternator to outsmart the smart charger - now the alternator outputs a charging voltage. I've chosen to isolate the ignition battery in case I leave something running off the house battery, I can still start the van.

I'm a bit worried about starting current draw from the house battery - I've used 4Ga to connect the house battery, and the run is about 10 feet. I'm hoping the resistance of this connection to the starter motor will be higher than the connection from the starter battery so most of the cranking current will still come from the starter??

Aside from having paid $70 for a high current diode, does anybody see a problem with this set up?

 

The problem here is you put a diode in the circuit of the Vehicle battery, creating a half a volt drop in the circuit in a system with a smart generator that's not realy suitable for dual battery systems. The only way to do this is return the wiring on your van to how it was originaly. To charge a second battery use a Relay type battery charging system that's made by Red Arc. Its automatic sensing the vehicle battery voltage & connects the second battery as the charge voltage rises & disconnects it when the vehicle is switched off & the voltage starts to drop. That's how its done here in Australia on RVs.

 

This is what I am refering to.

 

You can also use a 30A or larger automotive relay activated from the accessory output on the ignition switch to isolate the batteries.
The relay is connected between the two batteries and only is on when the ignition switch accessory voltage is available, indicating the motor is running to charge both batteries.
The relay will be off when the starter is engaged or the ignition is off to keep starter current draw from the camper battery or discharging the motor battery by the camper load when the motor is off.