A simple explanation for overland vehicle electrics

Electrical design can become very complex, especially if you’re not sure where to start. This article provides a thorough, yet simple explanation of the areas you ought to consider before modifying your overland vehicle electrics.

Do you want to modify your vehicle for overland adventures but don’t know where to start? Click here for the best advice you can get.

Why consider overland vehicle electrics?

As overland travellers, we live out of our vehicle. If you’re planning on staying in guest houses or hotels, you’re likely to use your vehicle only as a mode of transport. You may have a 12v socket or two fitted by the vehicle manufacturer which is enough to charge your phone or camera batteries while you drive. With the appropriate adaptors, you can charge your laptops and other electrical appliances in your hotel. Assuming of course, your hotel has electric!

For those wild camping or staying on campsites, or indeed have motorhomes, this isn’t enough power. With nowhere to recharge your battery operated devices, or with appliances needing continual electrical output to operate you need an electrical system to support them.

Overland vehicle electrics – what are your options?

Do nothing

You could do nothing. If all your appliances run off a 12v battery, you could in theory, simply plug your devices into your 12v sockets. However, this will result in your main battery draining to the point your engine won’t start. You could mitigate this by running your engine but this isn’t a viable living arrangement. If you have only one or two devices and you’re not planning on staying in one spot for more than a day or so, this maybe a viable option for you.

Extension lead

If this solution does not meet your output needs, you’ll need an alternative approach. The next simplest solution is to use an extension lead. When you are in a location with a hook up facility, simply plug your extension lead in and run all you appliances from this. Whilst this protects your main battery, it’s rather restrictive. You’re wholly dependent on an available hook up facility and all your devices need to use the same voltage as the supply.

Auxiliary battery

These options don’t meet the needs of most overland travellers. You need an auxiliary battery, separated from the main battery and at least one mechanism for charging it.

overland vehicle electrics

The main battery and the auxiliary battery are designed to work in different ways. Battery technology is continually developing but to put it simply:-

The main battery is designed to provide high doses of energy for short durations for cranking the engine i.e. switching on the starter motor. Once the engine fires, you switch off the starter motor through the ignition key.

The Auxiliary battery is known as a ‘deep cycle battery’ and it’s designed to allow energy usage over long periods and at a lower energy value. This is the type we use to power appliances like our fridges, lights and phone chargers in our overland vehicles.

Read more: 12v fridge choices and the energy they use

Charging the auxillary battery

There are several options for charging the auxiliary battery and this is where it can become complex. Here is a simple explanation of each:

Split relay on your main battery

By fitting a split relay to your alternator output, when you are running your vehicle, the power is prioritised between the 2 batteries. The main battery receives all the power until it’s fully charged. All power is then allocated to charging your auxiliary battery.

This is a simple, effective and cheap solution charging solely from your engine. In the event the auxiliary battery runs low, you could run your engine to top it up. The downside is in the event your relay fails, some emergency repairs are needed to charge any batteries.

Separate alternator

To protect your main battery, you can fit a separate alternator to your engine as a dedicated charge to the auxiliary battery. As your engine runs, both main and auxiliary batteries are charged, leveraging otherwise redundant power. An additional benefit is if the main battery alternator fails, you could rewire to the auxiliary alternator, if you know what you’re doing of course.

Shore power / hook up

In addition to charging your auxiliary battery from your engine, you can also use a hook up facility. As this power is 240v, you will need to fit a battery charger to the vehicle. This allows you to effectively plug the battery charger to the shore power and trickle charge your auxiliary battery from this.

overland vehicle electrics

Solar or wind power

One option increasing in popularity is solar power. Recent advancements in technology and reduction of price are fuelling its use. You will need to fit a controller to convert the solar panel output into a DC charge. This is not the complete answer just yet. You need some pretty big panels and a significant amount of daylight hours for them to completely replace all your energy consumption out of the auxiliary battery, depending on your usage. The same applies for wind power with the additional challenge of mounting and demounting your wind turbine to travel. These do give you 24/7 access to power though, assuming the wind is blowing.


There is also an option of packing a generator to act like a campsite hook up. I’m not a fan because it’s too noisy when it’s running. I’d also need to carry additional fuels types and lifting this heavy item in and out of the vehicle is a tad awkward.

Mowgli, our overland Unimog uses a combination of solar power, hook up and a separate alternator fitted in the engine.

Read more: Solar power, auxiliary battery usage and panel size calculations

My TV won’t work

Try to have all your equipment using a 12v supply; this will simplify your electrics. If you cannot avoid the need for 240v or 115v AC power, you will a 12v DC to AC inverter. This in itself is heavy on battery use so try to use it sparingly. You should also understand the supply needs of your 240v /115v appliances.

overland vehicle electrics

Some of cheaper versions of inverters provide a square wave as opposed to a nice, clean sine wave. Some delicate electronics such as TVs, do not work well on square waves. Ensure you invest in the product meeting your needs. If you’re planning on watching TV, investing in a sine wave inverter is a must.

Overland vehicle electrics – tips on wiring looms & circuits

The electrical systems can become complicated and have wiring looms with multiple switches, fuses and relays.

You should make sure they are high quality marine grade components. This specification is built to withstand tough environments.

Isolate every component through fuses or isolating switches, not to protect the appliance, but to protect the battery from voltage and current spikes.

If you are not confident in your own skills, this is an area where it pays to get professional assistance with the installation. After all, you don’t want an incorrectly fitted system to cause a fire!

Electrical support power from you battery has one very simple rule: you must put in more than you take out. My best advice  for any overland vehicle electrics is to keep it simple and your output needs to a minimum.

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