Installing the DIY camper electrical system including a split charger & leisure battery.
The last major job to do on the conversion is the wire up the electrical system. Even though I did a lot of it a few months back, I wanted to wait until I’d completely finished before I wrote about it. So if you’re sitting comfortably, I’ll show you how I created my DIY camper electrical system.
The first stage was pretty straightforward. All I had to do was drill holes in the roof lining where the lights were going to be…
and then route the wires either across the roof and along the sides and down inside the window pillars, to finally end up at the seating unit by the sliding door. This is where the auxiliary battery and fuse boxes are going to be housed.
Wiring the cupboard and shelf lighting:
I have 240v and 12v lighting circuits in the campervan. I used multi-pin connectors which made the final connections very easy to do.
The picture above, shows me just about to fit the small cupboard by the sliding door. The picture below shows how the cupboard is wired up.
Wiring the lights for the shelving unit was slightly more complex. This is the left side…
the wires then run through some conduit to the right-hand side…
…ending at another multi-pin connector.
This picture shows the shelf connected to the campervan.
Finally, I made a couple of covers to protect the wiring.
The original build diary also covered the 240v side, but I’m not going to turn this bit into a wiring tutorial — mains electrics in a metal van are not the place for guesswork. Current caravan and motorhome installations are covered by BS 7671 Section 721, and whoever does the work needs to be competent to design, install and test it properly.
That was the mains side as it was fitted in the van at the time.
Wiring up the 12 volt system
Now for the 12v side, which consists of lights, water pump and fridge. At present, I’m not going to be using the fridge but I will make provisions for it, which will make connecting it up later on a lot more straightforward.
First things first, I need an auxiliary battery. Normally a leisure battery would be the battery of choice here as they can handle being discharged and recharged over and over much better than a normal car battery. I was just about to buy a 110ah leisure battery when a friend of mine asked me if I wanted his (huge) spare Taxi battery. Yes please! So, for now, that’s what I’ll be using.
One thing I would treat differently now is the battery installation itself. I don’t have a record of the exact chemistry of that Taxi battery, so I wouldn’t present the setup shown here as a template. Any battery inside the living space needs to be installed to the manufacturer’s instructions, securely restrained, with the terminals protected against accidental shorting, and ventilated where the battery type requires it.
Now to keep the battery from going flat it obviously needs to be charged. On this van I used a split charger so the alternator could charge the auxiliary battery as well as the starter battery. That was the system I chose at the time. If you’re doing this now, don’t assume the same arrangement suits every van or battery: smart or variable-voltage alternators, and some battery chemistries, can need a compatible DC-to-DC charger. I cover the current choices in my campervan electrics guide at the end. With my original split-charge setup, once the engine was off the two batteries were isolated from one another, so I wasn’t drawing power from the starter battery.
I know eBay can be a great place for finding bargains. So I did a search for split chargers and found an Antares 140 amp auto split charge unit which was finishing in a day or two. After a quick bit of research, I found that these were expensive pieces of kit at the time. I placed my bid and won it for just £5.00! What a bargain. That’s part of the original build story rather than a current recommendation; if you’re choosing a charging system now, I’ve linked to my current campervan electrics guide at the end.
Wiring the split charge system:
Although connecting the main battery and auxiliary battery to the split charger is very straightforward, wiring up the split charge system needed more thought and research. The size of cable used is very important and depends on stuff like the amperage of the alternator, the distance of the auxiliary battery from the starter battery and the total amount of amps being drawn through the circuit. The Antares website had a useful tool which helped with cable sizing at the time. That original tool is no longer available. For a current low-voltage reference, MKGT has a 12V, 24V and 60V cable size calculator. It is a planning aid, so final cable selection still needs to be checked against cable current rating, installation conditions, fusing and applicable standards.
The cable and fuse figures below are simply what I used on this build. I no longer have a verified mm² size for the charging cable, so for a new installation I would size the cable from its conductor cross-section, the length of the run, voltage drop, installation conditions and the actual load, then choose the fuse to protect the cable and circuit.
For this particular build, putting the auxiliary battery under the bonnet would have made the cable run much simpler, but the battery I was using ended up under the seating unit instead. That meant the cable had to run under the vehicle and up through the floor to the battery. For this original build I bought 8 metres of heavy red charging cable, 2 metres of matching black cable, 8 metres of conduit, two 40 amp fuses, 2 fuse holders and some tube terminals. I don’t have a verified mm² size for that old cable now, so those cable and fuse details are part of the historical build record, not values to copy for a new installation.
Installing the split charger
OK, now time to install the split charger. It’s important to fit one fuse close to the starter battery and one close to the auxiliary battery. In this picture you can see a short length of the heavy charging cable coming from the starter battery, then a fuse.
Another length of cable comes from the fuse, across the bulkhead to the “Main” terminal of the split charger.
From the auxiliary terminal on the split charger, the same charging cable then runs under the campervan, then up through the floor to another 40 amp fuse at the auxiliary battery.
The auxiliary battery is then earthed to the body of the campervan.
That’s the split charger wired up. Now I need to get the power from the auxiliary battery to the lights and water pump. This was a separate distribution feed from the split-charge circuit: I ran a cable with a 30 amp inline fuse from the positive side of the battery to a 6 way blade fuse box. That fuse box was simply what I used on this van, not a current product recommendation. Again, that’s simply what I used on this build; a new system needs its cable and fuse sized for the actual loads and cable used.
I’m only using only two of the feeds out of the fuse box. So I’ve got another 4 spare for any further additions, one of which will be the fridge.
So the lights and water pump can be isolated, I’ve fitted a couple of master switches. I bought two small 10 amp illuminated switches from Maplins and fitted them next to one of the double sockets.
And that’s my DIY camper electrical system taken care of. We now have power wherever we go!
If you don’t want to make up your own split charging system and want to simplify the process, ready-made systems are another option. I cover the current choices separately in my campervan electrics guide.
Cost so far £730.00
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