To make a van liveable, you need to have a fairly sophisticated electrical system. Without such a system, you run the risk of flattening your starting battery and being stuck where you camped. In this article we discuss what goes into a van electrical system and the system that was built into Tin Lizzy.

Choosing a battery

Central to any van electrical system is the house battery. There are several choices from a lead-acid starter battery through to a high end lithium iron phosphate (LFP or LiFePO4) battery that will probably last longer than the van.

Lead acid wet cell batteries in this space come in two broad categories: deep cycle and non deep cycle. Starter batteries are designed to give out a lot of current in a short period of time – ie when starting a car – and then charge quickly so that they are ready to start the car again. Deep cycle batteries are designed to be discharged slowly to a relatively low level and then to recharge. Deep cycle batteries are what you want and need for a house battery. A starter battery will tend to fail after a much shorter period of time because it is designed for a very different workload.

There is much chatter on the 4WD forums about using marine batteries for deep cycle. Marine batteries may well do a reasonable job – I have no experience of them. What they do bring to the equation are plates that are heavy duty and also tightly locked to the battery case. This is very good over rough roads and heavy duty plates give them some of the features of deep cycle.

Running wet cells for a house battery is not for the faint hearted, they will need to be installed upright and if they are not maintenance free, vented to the exterior of the van. A better, but albeit, more expensive option is to select an Absorbed Glass Matt (AGM) battery. As far as I am aware, these are all maintenance free. What really sets them apart though is that they can be installed in any orientation you choose.

The next price range up is the Lithium ion batteries, essentially the same kind of batteries that power mobile phones and notebooks. However, these tend to be a bit more finicky about their power sources and are also much more expensive.

The last tier is the LiFePO4 batteries that have a very long life but cost a lot. For Tin Lizzy I chose a 170Ah AGM deep cycle battery. It is in a slim form factor – about the size and shape of a large DVD player and I have installed it in that orientation under a seat. At this point, I believe that AGM is the best option for those on a budget.

A much deeper investigation of batteries is found in this article.

A key thing to consider when installing a battery is how you will fasten it down. These batteries are very heavy. My 170Ah is somewhere in the order of 50kg. For this reason and to encourage good ventilation around the battery, I built a steel cage that fastens down to the floor.

Charging

Generally you want to have your battery always charged - unless of course you have been using it. This means you need to consider how to charge the battery. There are going to be times when you will want to charge the battery from 240v mains. To do this you should purchase a multi-stage battery charger designed for your battery chemistry and which includes a float stage. Your battery will spend a lot of time charged and so a float stage is essential.

It is possible – depending on your battery chemistry – to charge the house battery while driving along. AGM is fairly rugged and charges well from an alternator. However there are issues you should be aware of. You need to be able to connect and disconnect your house battery from the charging system. A house battery that is always connected will drain your starting battery as it is drained by lights and fridges etc.

The three main options are a dumb relay that closes when the ignition is on, a smart relay (VSR) that watches the voltage and opens and closes based on whether the alternator is charging, and the top of the range is a DC to DC power supply that has lots of smarts to manage the relationship and the price tag to match.

In my case I chose a voltage sensitive relay (VSR) with an override switch. This cost in the order of $50. It means that if I have a flat starter battery, I can override the VSR and trickle some power into the starter battery and hopefully recover at the flick of a switch.

Currently Tin Lizzy is equipped with a dual battery kit consisting of a fuse, the VSR and some cable allowing charging from the van charging system and also an 8 stage smart charger. In the future we plan to add solar panels so we can spend extended time off the grid. 170Ah lasts us one to two nights without charging.

Output or Load

The load that Tin Lizzy supplies to the battery consists of a series of LED based low power lights, a 70L fridge freezer in fridge mode, a television, various phones and tablets and an inverter that runs a CPAP machine.

Just as it is important to avoid flattening the starter battery, it is also important to avoid over flattening the house battery. Our battery’s warranty is void if the voltage goes below 10.8v across the battery. The voltage across the battery when unloaded, varies from 12.8v+ at 100% to about 11v flat. Generally the more you flatten these batteries the shorter their lives. Some will tell you never to take the battery below 60% others 50% etc. The two ways to monitor this is a Low Voltage Disconnect (LVD) or a volt meter. Tin Lizzy has both. The LVD will start beeping when the voltage gets to 11v (under 10%) and then disconnects. It also flashes various coloured lights at various voltage levels. In my opinion 11v is too low and if I was purchasing again, would get an LVD that was, or I could, set to around 12v which is about 50%.

The other big mistake I made was that most of my lights are 24v. I didn’t realise that they were 24v when I bought them. However a $20 transformer, 12v to 24v DC, from Ebay will fix that by allowing me to run their circuit at 24v converted from 12v.

One important thing to include is a switch to completely isolate the load. This will ensure that your battery won’t go flat due to some appliance that is left on by mistake.

Cabling

There is lots of chatter about cabling on the forums. 6mm² is quoted by some as the minimum cross section. The reality is that it all depends on the load at the other end, the distance from the source and the relative resistance of the cable. After spending a lot of time reading contrary opinions I wired the van as follows. I had some nice heavy duty cable (probably 8 - 10mm²) that came with the dual battery kit. I ran this from just away from the battery to the fridge. It was the most sensitive, longest away and highest load. I purchased 6mm² house power cable from Bunnings at about $4 per metre. This had two cores of 6mm² cable and an earth cable at a much lower cross section. The biggest issue with all these cables is terminating them. The cores are huge, stiff and hard to work with. Also if you are crimping then you may need a heavy duty crimping mechanism. I used my 12 ton swaging press/pliers and also automotive crimping pliers. Using the swaging press resulted in very flat crimps but the connection was made.

There are an awful lot of connections that have to be made to the battery and on the load side. I made up a little distribution board. This consisted of four bolts coming through a piece of ply wood and the heads sandwiched to insulate them. The eyes terminating the various cables can then just be bolted down and together. I needed four terminals because I needed postive and negative for each of 12v and 24v.

I needed to add some light switches. Generally these can be difficult to source and sub optimal for 12 or 24v DC. 240V AC gear will handle and be vastly over spec for switching 12 or 24v DC loads. Because there are so many made though, those switches are as cheap as anything else, they also look like a light switch. So I used the cheapest light switches I could find from Bunnings.

I had a series of 12v power points I wanted to put in. There is no standard for 12v power points. The three preferred connectors are heavy duty cigarette lighter sockets – how do you know they are really heavy duty? Anderson plugs and T plugs. In line cabling I used anderson plugs – things like to the fridge. These were crimped with my swaging press. For the wall sockets I used T plugs which cost me around $10 per set of plug and socket. There isn’t a standard for wiring these either. I followed the recommendation from Clipsal the manufacturer which says the top of the T is positive and the stalk is negative.

One consideration is how to cable to the fridge. In Tin Lizzy – and many other vans – the fridge is on a slider and so moves. A cable will get tangled and eventually break. The standard solution is to use a drag chain which supports the cable and ensures that the cable moves in reasonable ways. The cable goes through the chain which is fastened to the bed frame and also the slider. The cable terminates in an anderson plug on the slider before attaching to the fridge.

Trunking

Once you have run a dedicated cable for the fridge, a cable for left and right side to power points and lights plus speaker cabling, you have lots of wire going down the van. Care needs to be taken to ensure that cables wont rub and so short onto the bed frame. Under the main bed, we have storage areas that are separated by MDF sheeting. Cables were attached to this and also the bed frame in square Aussie-duct style conduit that had a removable top. If you do this be sure to get conduit cross section that is big enough for the cables. This can be deceptive and I did buy some that was too small.

Monitoring

I wanted to be able to understand what was happening in the system – things like where the electricity was flowing (in or out) and the voltage of the two batteries. I purchased three analog ammeters I liked the look of – kind of retro steam punk – and a two way volt meter. This allows me to see the charge in either battery at a flick of a switch and separately monitor the load, the direction and flow between the house and starter batteries, and also the flow on the charging circuit. When I add solar panels I just need to plug them through a controller into the charging circuit and it will also be covered.

Voltage meters are wired directly across the battery – positive to positive and negative to negative. Ammeters are wired to a shunt resistor that is in-line with the positive cable. That is the positive cable is broken and wired to each end of the shunt resistor. These resistors have very little resistance but have the ability to handle high amperage. Each ammeter needs a specific rated resistor and so a purchase should include both the ammeter and also the resistor.