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12V electrics and wiring for my campervan conversion


Yet another major part of the build that can probably be as simple or as complicated as one likes. I think I went for somewhere in between. For solar panel installation please see installing the solar panels

Update: In my book I go through and explain everything needed, in clear detail, for the vans electrical system (and a solar panel setup). I start with basic electronics so no one is left out. Get the ebook as an instant download here

Here’s a list of the materials I used

Item Description Cost Quantity Supplier
midi strip fuse holder  used for fusing each battery




12 way blade fuse box (RIPCA) for main 12V power distribution £20 1

Ebay (2nd hand)

Battery isolator cut off switch  100A switch often seen in marine and automotive applications £5 2

Amazon (radio world)

2.5mm2 cable  I got 10m of red and 10m of black for general low power stuff such as lights and general hook up

£6.99 for 10m


Ebay (CCS-UK)

10mm2 cable  5m of red and 5m of black for utility terminals

£2.10 per metre


Auto electric supplies (AES)

20mm2 cable  4m red 4m black for wiring the solar controller up.

£3.60 per metre


Auto electric supplies (AES)

Analog panel meter ammmeter  0 to 20A reading £3.97 1

Amazon (sourcingmap)

LCD digital volt panel Voltmeter


£4.39 1

Amazon (lgking supply)

Smartcom split charge relay 30A voltage sensing relay with inline fuses and terminals (kit) £17.00 1

Ebay (Brocotts)

heatshrink sleeving 4.8mm before heat Used for cable terminals £0.77 1

Auto electric supplies (AES)

Assorted cable crimps I already had most of these

After I had a decent collection of wire and bits I started by scribbling a few sketches for how I thought the batteries should be connected, fused, isolated etc and then just made it up as I went along.

Assembling the 12V power distribution panel

I’ve been gradually collecting parts. Now I’m ready to have power in the van
I took the parts and put them on a piece of wood that Matt took out of a skip
I wired something pretty much something like this. One thing worth mentioning here is that the 0v terminals on the solar regulator are not common which caught me out! so I only grounded the battery negative – the load negatives are ‘floating’ otherwise the solar charger would not work
I like to fix wires down to minimise flexing or a fault occurring from disturbance.
I didn’t want to buy a £50 hydraulic tube crimp tool and I think I got away with it. First I tried soldering the cable into the crimp but a 60w iron is not powerful enough so that was a fail. The next thing I tried was crimping with mole grips which worked but looked quite messy. The best method I found was hitting hard just once with a hammer against a stone paving slab
I installed the power distribution stuff under the smaller part of the bed. It seemed to be a convenient place right near the batteries and out of the way but easily accessed
Some more stuff to go under here like the CTEK charger and mains hookup incomer
I used a 16mm2 wire to ground the battery negative common rail to the van chassis. Shakeproof washers – important
I wire brushed the grounding point to get a nice electrical contact
Here is the latest picture of the electronics. 1. mains consumer unit with RCD and breakers. 2. 12v distribution. 3. midi fuse inline with battery. 4. CTEK MXS25. 5. audio amp. 6. 1000W inverter
Since I have ridiculous batteries, I’m not gonna bother building boxes for them. I just made sure they wouldn’t slide around. This is only a temporary solution for now until decide whether these batteries suit me
The blue LCD and battery monitor can be turned on/off with the small rocker switch to the right of the display.

Mains hookup

The mains hookup will be used for when there is mains available – campsites, lamp posts etc. It will be used to power the CTEK charger which will charge the batteries and supply the normal 12V power.

The mains hook up stuff consists off an RCD, two breaker, two sockets and a 240V mains indication light. The RCD and breakers are housed in the garage consumer unit (left). Each breaker feeds one socket which gives the option of a 6A feed and a 16A feed.
The mains indication light is wired after the RCD and before the breakers. Ideally, I’d have a double pole isolator before the RCD.
Keeping wires neat and tied down. I’ll cover this all up later

So thats about it for the electric stuff, although it may be adapted, improved or even simplified as I start living in the van but its a start. Also I’m still yet to wire and test out this smartcom voltage sensing relay for split charging of the leisure batteries. I’ll report back on that one….

Split charging relay (Smartcom Voltage sensing)

The traditional method for split charging is to take a wire from the ignition to energise a relay when the engine is running. The relay will then switch in the alternator feed to the leisure battery to let it charge just like the vehicle starter battery.

The other (and much easier) method is to use a Volt sensing circuit which detects a rise in voltage (when engine running) and energises the coil of a split charge relay to charge the leisure battery. There are many products that do this all in one package but by far the cheapest is the smartcom relay and it works very well!

For basic split charging, only 3 terminals are needed; 12V in, aux battery output and GND/0V
The smartcom turn on Voltage can be adjusted via this potentiometer. The turn off voltage is a bit less than the turn on Voltage to give it some deadband and prevent oscillation. I set it to about 14.4V. I also noticed the part number has been scratched off the chip U1. Cheeky! my guess is a 555 timer
I used some more terminals to let me quickly wire in my leisure battery just incase the start battery becomes flat.
I referred the LDV electronic schematics to find the best place to take the feed for the split charge relay
This ‘fuse post’ is deceptive – I thought it was a ground post until I saw the schematics. I took the + feed for the split charge relay from here

Observations (regarding split charge relay)

It can take a few seconds for the smartcom to de-engergise after the engine has turned off because the start battery Voltage takes a while to settle back down to its quiescent Voltage. Before adjusting mine it took about 2 minutes to turn off.

It would probably be best to set this up on an adjustable power supply to get a better idea of the exact switch on/off Voltage.

The components do not look very heavy duty but it should be OK for me since this is only my backup charging setup. For a permanent charging circuit I’d go for a much more heavy duty option such as the Durite Voltage sensing relay

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