DC Charger using 3 pin Anderson
 

Will be installing a 40W DC charger in my caravan, to bypass the GC smart alternator. Power to be sourced from the GC jumpstart terminals using 8 gauge wire and 60W fuses.

My vision is rather than the traditional 2-pin Anderson Plug change to a 3-pin Anderson on both the GC and caravan. The third pin/wire being the isolator so that the DC charger stops functioning when the engine is off so as the GC battery wont be drained if remaining hitched up overnight.

A well intended person suggested wiring the isolator cable into the cig socket near the tail gate. Not too sure about this. Interested in hearing from anyone undertaken something similar, particularly locating/attaching the isolator wire.

You can get a simple relay that you place between your starting battery & your other battery etc. It is simply turned on when you turn on your ignition. You could also have a switch on the dash if you were concerned about having a flat caravan battery turned on while you are starting.
Supercheap even have a suitable box of tricks called a Dual Battery Isolator. It is rated at 140amps & cuts off the start battery when it drops to 12.8v & cuts in at 13.3v. They were under $50 when I purchased the 1 I have. Part number RR98404 PLU573993 Look it up on their site.

If you have solar on your van its not really needed, mine is 12 yrs old and the batteries are charged from solar all the time, power from the JGC is just for the fridge while running down the road, my 15 doesn't have a smart alternator so the run is from the jumper terminals to an anderson at the back with a fridge switch at back of fridge where it can shut off power to the fridge when stopped, its fitted there where the cable drops to a smaller gauge....

I looked at the fact that if my solar can't keep things going for a few hours driving down the road what chance do I have spending weeks by a creek, its never needed charging from the tug, in fact even in caravan parks the 240v is just for HWS, kettle and toaster, nowadays since I went lithium it doesn't even have a mains charger in van at all, my solar does it all ... running the Grand idling to charge shoudl never be an option though.

But if you need to then just tap into a clearance light circuit and drive with your parkers on, then if you stop the bells will start and remind you to turn the lights off hence the charging unit but really in a modern van set up for off grid its shouldn't be needed ... Im not sure that the 20 has a smart alternator actually.

Similar here, I leave the solar panel on the van to charge the batteries while driving...never had an issue.
I have a 2nd 135 amp Lithium battery in the Jeep continually charged through a 30 amp Redarc DCDC charger which runs the fridge, (and an inverter if I need some 240v to recharge the cordless drill.)
I do plug in to the mains at a CP if available and charge the battery off the charger in the van though just to top it up.
That said, traveling continually last year from free camp to free camp days on end I never had an issue with low caravan battery. I do have additional panels I put out to supplement the roof panel if on an extended stay somewhere...works well.

Why ? , install a Victron Dc-Dc and turns off when the engine stops automatically

https://www.victronenergy.com/dc-dc-...attery-charger

Thanks Drover and Jeeper6 for your responses that champion solar. Perhaps I should have covered-off that our van is fully solar enabled; and that specific personal (and private) requirements necessitate the DC charger.

There are a few Forums around that have threads on these types of mods. From what I read quite a number of "Caravanners" run power from their vehicle alternator back to a charger in their van to top up batteries as they drive.
Usually the DCDC Charger itself should have internal switching to prevent power from feeding back when the vehicle is not running. The Recarc in mine does...