This is going to be long and isn't directly going to help, but may assist your auto electrician when you get it fixed. I am afraid your pictures bring back bad memories for me: I also purchased a Camper King 2017 T28 that had an identical electrical installation to yours (minus the MPPT solar controller, that looks like an after Camper King addition). Same components, same locations, same fuses, etc. It had passed a full electrical installation check with the dealer who sold it me, but I immediately noticed that aux battery was not charging very well, and the fridge not working as expected - so the investigation begun.
I also had a melted fuse box (but not as bad as yours, I caught it before it got quite so bad) plus a load of other melted crimps, wires and components damaged and melted when I took it all apart. (To be fair, the motor home dealer agreed to replace the meted fuse box and replace the crimps, but nothing else; and I had already seen enough to recognise this problem was far bigger than a few melted fuses and crimps, so I did it myself).
(Caveat: I can't be 100% sure that my installation hadn't been altered after leaving Camper King, but it all looked unaltered, no signs of being changed, original parts etc and with no signs of modification or additions).
It was out of warranty with Camper King and they were not at all interested in helping to sort it out - not even providing copies of wiring diagrams or permitting their electrical guy to talk to me. Luckily, I am competent enough to completely re-wire it - and that's what I did. I ripped it out completely and started from scratch. Mine was a complete catalog of horrors - hopefully yours is not the same, but below are a few pointers/notes you might want to discuss with your auto-electrician when you arrange to get it fixed. They will be able to quickly home in on these points in your installation and determine if yours is similar and if it should be rectified at the same time they sort the fuse box. Fuse boxes don't melt for no reason, so there is probably an underlying fault that also needs to be sorted when the fuse box is replaced. (Although it could also be as simple as loose crimps).
Issues with my installation that may be relevant to you:
- Standard rigid conduit cable (2.5mm^2) had been used for the feed from the front to the rear of the van - for the 30 amp DC-DC charger! plus 1.5mm^2 conduit for several other rear circuits (eg fridge and diesel heater)! There was no outer conduit protection anywhere and it is not (in my opinion) the correct type or size of cable. The cable showed signs of chaffing where it was passing sharp metal edges with no protection.
- They had picked up the feed for the rear from the center lower fuse box in the front and used a 40amp fuse with this 2.5mm cable!
- They had used the same blue conduit cable for both positive and 0v cable runs.
- You will/may find a Sterling DC-DC battery charger behind the board that has all the parts in your pictures mounted on it. This has three fuses in it that are not accessible without dismantling the whole rear cupboard (which you will have to do anyway). Check those fuses - one is 40amp,. On this DC-DC charger, the 0v connection on mine was a tiny 1mm^2 cable (thin wall stranded this time though)- this needs replacing if yours is the same. (With such inadequate cable runs from front to rear and from DC-DC to rear battery and 40 amp fuses on each end, (in my opinion) the weakest part is the cable and the awful crimps that had been used.
- Consider relocating this DC-DC unit if you have it to make it easier to set-up/program and check/change fuses. (Mine was also set to the wrong battery type, wrong charging parameters and incorrect simulated ignition-on/engine running settings).
- All crimps looked like they had been squashed with pliers rather than using the correct crimping tool.
- Many of the crimps had exposed loose strands of wire hanging out of the rear of the crimps (further reducing the current carrying capacity of the already undersized cable).
- Many of the crimp's insulation had started to melt and blacken/burn. There was a combination of reasons for this - poor crimping, and poor fitting onto the terminal (see fuse box comment later) and too much current passing through them.
- There was no single, main fuse in the feed from the rear aux battery and no isolator to enable a quick shut off of the rear battery. Consider fitting a single main fuse. (Especially if you don't re-locate the DC-DC charger as there is no quick way to isolate that item as you cant get to it's 40 amp fuse (and the fuse is too far from the aux battery anyway). (They appeared to rely on the internal fuses of items that had one, but this leaves a reasonably long length of (undersized) cable from the aux battery positive terminal that is not protected).
- There was no cable restraint at all in any of the installation (except one large 'p' clip around the bunch of cables coming out of the CBE control box that didn't really do anything). Cables were just all hanging and chucked on top of the battery (you wont see this until you take the rear cupboard apart). Consider adding cable restraint (p clips and sticky pads with zip ties to prevent cables vibrating lose and putting strain in the crimp terminals.
- That type of 4 way fuse box (in your picture that has melted) is really difficult to get the crimps onto the terminals correctly due to the way they have mounted it - a small cut out in the wood to feed the wires and crimps though so you cant get a good grip to ensure the terminals go on correctly. Several of mine were pushed down the side of the crimp rather than in to the crimp. This could lead to the problem you have seen with the melted fuse box, but I suspect something else has 'happened' to trigger the situation if you have had the installation for a while.
- I had a very small (1mm^2 wire on the "B1" terminal in the CBE DS300 control box that was then connected to the DC-DC charger positive stud- I think I can just see it in your picture of the DS300 wiring in your picture - furthest right red wire looks like it is in the correct place to go to the B1 stud). This fed the front battery (via the same 2.5mm^2 conduit cable that fed the sterling DC-DC - they just joined them at the DC-DC charger stud) with a small current (<2 amps) from the 12v CBE battery charger/PSU when on mains hook up. This is fine (but far from ideal) when the Sterling DC-DC charger is operating correctly. However, if any of the Sterling DC-DC internal fuses blow (on mine an internal 10 amp fuse had blown), the sterling does not start up when you start the engine and the CBE/DS300 unit has a very primative split charge relay built in. Now you have a situation where the CBE unit is trying to supply the whole rear battery charging current through the tiny "B1" wire. This was the root cause of my most severe burned crimps and melted wire insulation.
- If you do have the Sterling DC-DC charger fitted, you should not have the CBE internal split charge relay operational (you shouldn't have it operating anyway with a smart alternator). On mine it was still operating. Sterling Power have provided guidance to disable the internal split charge relay which I have now done and can confirm it works. You have to just snip one leg of one resistor on the PCB to deactivate it in certain older (red banner branding) units.
-These last two points are quite important and I believe they were the root cause of my installation having major issues. (although I consider the whole installation (who ever did it) to have been extremely poor).
I appreciate this may not make complete sense to you, and it is certainly not meant to frighten you - your auto electrician may find it helpful in sorting your installation (if we both did indeed have a similarly poor Camper King electrical installation).
I'm not close enough to help you directly, but happy to expand or clarify anything if you / your electrician needs it.
Kind regards,
something has produced some serious heat.
