12 volt electrics

First off, I am not an expert on van conversions or electrics by any means.  If you’re not happy playing around with electricity, stripping cables, and so on, then it may be best to get someone else to do this lot.

However, I scraped through a GCSE in Modular Technology many years ago and I distinctly recall there being a module about electrics/electronics, so figured “how hard could it possibly be?”.  As it turns out, about as hard as you want to make it!  I certainly made some mistakes and made life difficult for myself with some of this, and where I think I went wrong I’ll point it out below.

The big picture

Before I bore you with the details, here is a high level overview of the electrics installation :

High level circuit diagram

12v vs 24v

I didn’t consider 24v simply because I’ve never dabbled with it, and almost all of the devices I’ve seen online such as fridges and lights are all designed to work with 12v.  I’m sure there are benefits to 24v but I can’t speak to them.  So I went down the 12v route.

Batteries

As I was expecting to be using 12v electrics most of the time with only occasional opportunities to plug into a mains supply, I opted for 2×110 Ah leisure batteries, connected to the main starter battery via a B2B charger.  More on that later.  The batteries were connected in parallel.

I installed a battery under each of the cab seat bases, seeing as that was ‘dead space’ really.  The remaining space was used to house the charging components (again, more on that later).

Charging

I had 3 ways of charging the batteries:

• Sterling B2B charger

This was installed under the passenger seat, and sat between the starter battery in the engine bay and the first of the two leisure batteries.

• CTek MXS 7.0 Mains Charger

This was installed under the driver seat, connected to the battery under that seat (which was itself connected to the other battery) and used to charge the battery whenever I was hooked up to the mains.  Surprisingly, this was most nights.

Under the driver’s side seat – battery 2, CTek charger and AC/DC transformer (silver box)

• Solar panel with charge controller

I kept the solar panel in a bag in the ‘garage’ section of the van and only used it a couple of times during the entire trip.  The charge controller I got along with the panel packed up after a couple of uses so I replaced it in Lusaka, Zambia.  In theory you’re supposed to route everything through the controller but I never bothered with that – it was just connected to the battery under the driver seat and hooked up to the panel as and when required.

AC/DC Transformer

In addition to the chargers I decided (in hindsight, perhaps unnecessarily) to install an AC/DC transformer, allowing me to run everything off 12v when plugged in without, my thought process being, touching the batteries.  I guess I was obsessed with trying to eek out as much life from them as possible so figured that if I had a transformer that was supplying 12v DC directly to the distribution panel etc, then the batteries would be less likely to be ‘hit’ whilst on mains.

However the batteries were permanently wired in to the mains charger, which was always ‘on’ when on mains (most of the campsites), so in reality the transformer was probably entirely unnecessary.  I remember thinking at the time that the charger only outputs 7A which was a concern to me with the fridge drawing 3-5A at any given time and the charging points in the living area all potentially drawing current at the same time.  I’m sure someone who knows about electrics will dismiss all these fears but not knowing any better, thats what I did.

Either way, had the batteries been totally drained, I would have still been able to run the van’s internal lights, charging points, and fridge with knackered batteries, when plugged in at any rate.  All of the lights are 12v DC.

DC/AC Inverter

Slightly more useful than the transformer, I suspect, was the 1200W pure sine wave inverter I installed behind the passenger seat.  Its the black box at the top of the photo above with the Sterling B2B charger in it.

This was permanently wired into the battery under the passenger seat with 25mm² cable and a whopping big 80A fuse (the first one wasn’t whopping enough, apparently, blowing as soon as I tried using the inverter – fortunately whilst in the UK so I had the time to get some replacements).

I only used this a few times, for charging my laptop or camera batteries whilst on the road when I knew that I was staying, or suspected I might end up staying, somewhere without electric / mains hookup (eg doing a game drive for a day and knowing the campsite I stayed at last night, and will do that night, didn’t have a hookup).   Overall it was useful enough to justify taking up the space, but maybe the 1200W output was a bit overkill.  I would never use it with the engine off as it would kill the batteries in no time.  In fact I think I tried that once (as an experiment) before leaving for Africa and vowed ‘never again’.

Isolation switches

I installed 2 isolation switch boxes, made from some random plastic/ABS electronics project boxes I picked up from Maplins or something.  The isolation switches themselves were fairly standard 12v/100A battery isolators.

One isolator sat under the passenger seat (the lower of the two seat bases in the picture above – isolator in bottom left corner), between the cables coming from the engine starter battery and going to the B2B charger, allowing me, not surprisingly, to completely isolate the engine electrics from my ‘leisure’ electrics.  This would also stop my leisure batteries from charging whilst the engine was running, and I think I only used this when shipping the van to/from Africa in the end.

The other isolator sat behind the drivers seat (top seat base in above picture, isolator behind handbrake), and could be used to shut off all power to the leisure ‘accessories’ and circuits, ie: breaking the link between the batteries/transformer and the distribution/fuse box.  This was used a bit more often to allow me to do maintenance on the accessories/lights etc in the living area without worrying about zapping myself.  Far more useful than the other one, which was really there to prevent any leakage or short circuit affecting the starter battery.

Cables, crimps, connectors and inline fuses

I had intended to use the 25mm² cables for everything up the distribution/fuse box if possible but I didn’t have a way of connecting it to the majority of the components.  I tried ‘welding lugs’ which worked ok on the connection to the B2B charger but I couldn’t find anything that would let me connect such a large lug to the starter battery without a daunting prospect of ripping out all cables that connect to essential engine bits and pieces.

In the end I gave up as I was spending far too long trying to find ways around this, and switched to using 4 lengths of 6mm² 50A cable, having read somewhere that its the overall cross section is all that matters so 4 x 6mm = 28mm (200A – way in excess of what I needed I believe) which is a greater cross section than the original plan of 25mm and hence collectively the cables would carry the load without problems (the B2B manual recommended 25mm² for the distance/alternator output).

Each cable had a fuse at some point.  Each of the 4 cables carrying the load from the starter battery to the B2B charger were fused with 20A fuses.  Each of the cables linking the two leisure batteries were fused  (10A fuses on each of 3 x 30A cables).  The cables from the B2B charger to battery 1 were each fused (20A fuses, 3 x 30A cables).  And so on.  My theory was that I didn’t want any of the individual cables to melt and potentially cause a fire.  Probably sensible.

As the potential amperage being carried dropped significantly once past the B2B charger, I started to reduce number of cables (hence the cross section).  Between batteries ‘1’ and ‘2’ I used 3 cables (capable of carrying a combined load of 150A, I believe, way in excess of anything I was expecting to carry and as such, massively over the top).  Between battery ‘2’ and the isolator I used 2 x 50A cables.  Once past the fuse box, one cable per circuit.

Overall, too many cables and too much paranoia about voltage drop, I think.  I still think you need a decent cross section between the battery and inverter, and definitely between the starter and the B2B charger but I would need to go back to the Sterling documentation to see what its maximum output amperage is.  I suspect that the overall draw from the leisure electrics, when everything was being used, was less than 30A, and as such maybe 1 or 2 cables from the B2B through to the distribution box would have been sufficient.

As a result, it all got a bit complicated and cluttered, particularly under the passenger seat where I had the B2B charger and the connections from the engine, the mains (AC) cabling coming in and the inverter cabling:

Either way, nothing fused, nothing melted, and despite the B2B shutting down due to overheating several times ^† in Zambia, nothing blew up.  Which I take to be a positive sign.

^† I believe this was due to a lack of ventilation under the seats.  I added plywood covers to prevent things dropping down into the electrics, which I removed while cleaning the bases out in Lusaka, and removed the inspection hatch in the side of the passenger seat base to improve airflow ; I didn’t have any overheating issues after this.

Distribution / Fuse box

Behind the driver’s seat sits the 12v fusebox.  Not much to say about this, every circuit needed a fuse, most of them small ones in the 3-5A range, but the circuit going to the Webasto heater and the circuit for the power points had 20A fuses, if memory serves.  The 3A fridge fuse blew several times so I replaced it with a 5A, after which it was fine.

Many conversions put a switch panel in but I couldn’t see the point – I could turn it all off at the isolator, so why bother?  Well it turns out that one or two circuits could have done with a switch.  In particular the water pump’s dedicated circuit, as the pump would cycle continuously if the water ran out, as it tried to prime the pressurised system.  It wasn’t the end of the world though as I could just pull the fuse.  For some reason I remember thinking that the fridge could have done with a switch, but can’t think why!

Monitor panel

I did fit the The B2B charger came with a remote display unit (I paid extra for it, I suspect) which I installed in another ABS project box alongside the water tank level  monitor.  The B2B monitor wasn’t as useful as I had hoped.  I guess I expected it to tell me things like expected life of the charge, current voltage drain and so on.  It didn’t – it just told me how much voltage it was receiving from the starter battery and the current voltage of the leisure batteries, and how long it had been on charge.  I’m not sure its worth the money frankly.

In hindsight, having the water level indicator in the cab area was a bit of a pain at times, as I couldn’t see what the level was without going into the cab, through the door, which usually meant removing a section of kitchen worktop.

Lights

In the living area I installed 7 lights which was probably overkill.  3 of these were spotlights, 2 of which were intended to provide ‘task lighting’ whilst sat on the sofa (for reading etc) and the other a similar function over the kitchen unit.

In the sleeping area I installed 2 spotlights on flexible stalks – again to allow for reading in bed and so on.

Finally I installed a light in the ‘garage’ section, just to make life a bit easier when ferreting around inside that part of the van.

All lights were 12v LED lights with varying output.  I can’t remember the output but they were very bright!  All of them had built-in switches so I had plenty of control over the lighting levels.

Charging points / 12v sockets

In the ‘cab’ area I installed a single 12v outlet to provide an alternative to the one built into the vehicle itself.  In hindsight I probably should have installed a 2nd.

In the living area I installed 6 outlets, 3 on each side of the sofa base.  This was probably overkill but I think I used up to 4 at any given time for charging phones and most importantly, camera batteries.  I could charge 1 x SLR battery along with 2 x compact digital and 1 x GoPro at any given time and still have space for a phone charger.

These sockets were all connected to the same circuit on a 6mm² 50A cable.

Fridge

I took a Waeco CDF-16 Coolfreeze fridge with me, mounted underneath the sink unit on a set of runners – its a top loading fridge so it had to be pulled out every time I wanted to access it.  I was concerned that this would be a bit tedious but actually it worked quite well.

What didn’t work too well was the temperature adjustment on the fridge.  The unit is capable of freezing, the temperature being governed by a rather exposed slider control on the top of the unit, positioned just about where your hand goes if you’re pushing it under a sink, for example.  Several times I found I’d managed to freeze the entire contents of the fridge, or knocked the gauge in the other direction and everything was a bit on the warm side.  It wouldn’t maintain an even temperature, it always seemed to be quite ‘relative’ rather than for example maintaining an even 5c or something.

If I were to do this again I would choose a different unit with a proper temperature controller/thermostat.  One guy I met in Zambia had 2 units, one which he used exclusively as a freezer, the other as a fridge.  At the time it seemed a bit excessive but he was often away from shops for several weeks so you can understand why.

Solar panel / charger

I took a 50W panel with me, but didn’t use it very often.  In fact I think the first time I really used it was while I was in Zambia in a campsite for a week or so without a hookup.

The thing about solar panels is that they need sunlight to work.  Now you would think that in Africa this wouldn’t be a problem.  And you’d be right, except most campsites have plenty of trees and you generally find yourself parking underneath them to create some shade and keep your ‘home’ cooler.

In that respect I’m glad I didn’t permanently mount the panel to the roof (as is common practise) and attached it to a long (5-10m) length of 6mm² cabling, allowing me to park the van in the shade and just move the panel out into the sunlight.

Once I tried leaving the panel in the cab, hoping that enough light would come through to top up the battery (I was away for a week on a safari trip in the Serengeti / Ngorongoro etc) but sadly this didn’t seem to work and I came back to 2 flat batteries.