12v charging system - fuses

Nov 1, 2020
Hi, below is the plan for my caravan (in transit) power/charging system - we are a family of 4 with a moderate 12v demand who do a mix of touring and off grid for 2-3 weeks, we have 3x 110amp batteries - no solar yet as new to this but it's on the list. The boot charging facility will allow us to rotate and top up the batteries while out and about with the van sited. I believe the cables might be oversized, but they're what I have available for nothing so won't do any harm and the sterling charger was an eBay bargain.

What I'm particularly not too sure about is the fuses, I've included one on the positive at the battery (this mirrors the sterling but I'll be using my own cables not the ones supplied with it - their cables are to short.
After that I haven't a clue! The sterling has fuses on the + and - of its charging output so I guess I should keep these (and they'll protect the cables all the way to the leisure batteries) but what about the loop out to the fridge relay? Do they need fuses, on both + and - and where?

I will be connecting the new cables in the caravan direct to battery/fridge and there will be no 12S supply so will I need to disconnect anything in the caravan that might cause problems?

I know a lot of questions but any little help would be appreciated.

In case you haven't gathered, I consider the 12S power system a waste of space in a modern set-up, particularly as it's imperative (due to where we keep the caravan) that we have a fully charged battery to power the mover when we get home from any trips. We don't really do EHU. The big cables/DC charger and Anderson connectors set-up is apparently quite common in Australia and the US where they do this stuff "properly".
My caravan is a 2000 vintage Eriba.


Nov 6, 2005
I suggest you check some of the international forums dedicated to bigger SUVs as many contributors will tow in similar conditions - for instance ClubTouareg.com has contributors who take their Touaregs off-road in Australia with caravans in tow and have successfully modified their vehicles.

On a technical point, the 12N/12S connection system was never well regarded and has been replaced in Europe by a single 13-pin system - but your use of Anderson plugs for the high current circuits will be much better.

Your suggested circuit has one potential issue - the Boot Leisure battery and Caravan battery will be linked during towing so will equalise with no priority to either one.
Mar 14, 2005
Your quest about fusing is important.

From an electrical safety perspective I'm concerned about the cabling that links between the car and the caravan becasue each cable it has two points of support where it leaves the car and where it enters the caravan, and the articulation of the outfit will put additional stresses at both these points. Obviously I don't know what strain relief or support these points will have but they may prove to be weak points and for that reason I would definitely fuses in the +12ve lines both in the car and caravan just in case the insulation is breached and it shorts to metal work.

Providing its a reasonably modern caravan the caravans chassis and body work should not be carrying any significant currents so 0V fusing should not be necessary.
Nov 1, 2020
Thanks. I'll get onto the fuses! Regarding charging multiple batteries, I wouldn't do it - I'll manage it manually (quick release battery clamps for the boot and only used when caravan is not connected, I have two (non matching) leisure batteries in the caravan, I wasn't even going to connect them in parallel, just keep an eye on the voltages and rotate the three batteries as necessary. If I get an effective solar set up in future I hope the need to charge one in the boot while out and about will become largely unnecessary.