Overland vehicle electrical installations guide

by | Car Talk | 2 comments

From the day we saw our Landcruiser the first time in Gouda, we knew that we would have to rebuild all the electrical installations. On one hand, we knew that the living room battery was dead. On the other hand, a look under the engine hood revealed a jumble of wires. Therefore, we built all the installations from the scratch to match our needs. In this blog post we will share our considerations with you.

Old electrical installations

This is how the living compartment electrical installations used to look like.

From occasional camping trips, you may be used to plug your fridge or lamps directly into one of your vehicle’s outlets. If you are going on an overland trip, your car becomes your home. A fridge, for instance, will be running 24/7. Several weeks in a row. At the same time, you will not necessarily be driving every day. Your vehicle battery’s critical task, however, is starting your engine. Especially in remote places you do not want to risk its ability to do so. Therefore, it is wise to install a second battery in an independent circuit. This is the best way to supply electrical energy to all the devices that did not come with your vehicle.

Determine and reduce your power demand

Your demand for electrical power determines the size of all the components in the electrical circuit. Keeping your demand low allows you to rely on smaller components and, therefore, saves money and weight. Here are some power saving tips.

Fridge

To make a long story short: get a compressor fridge! Absorption fridges will drain your battery in no-time and are not really an option. The extra money a compressor fridge costs, is a good investment. To keep your food and beers cold at all times, the fridge will be running around the clock. Hence, even a compressor fridge will most likely be the biggest load in your circuitry. Our fridge, a National Luna Weekender 50 Twin, has an average running current of 2.5 A according to the manufacturer. Generously assuming that the compressor is running 40% of the time, this corresponds to a charge use of 1 Ah per hour or 24 Ah per day.

Lighting

An ordinary light bulb converts around 5% of the electrical energy it uses into light. The other 95% are transformed into heat. Does not sound very efficient, huh? Despite, the often cited energy conversion efficiencies of 80% and more for LED lighting are only met under lab conditions, compared to light bulbs, LEDs are still pretty good. Realistic energy conversion efficiencies are in the 25% range, which is still five times better than a light bulb. This means 80% energy savings!
Although the absolute amount of energy for lighting – and potential savings – are relatively low, we still recommend changing all the lighting to LEDs. These days, they are easily and inexpensively available. And there is another advantage to LED lighting: Their lifetime is around 20 times higher than the lifetime of a light bulb. With lifetimes of 20,000 hours and more, you can leave your spare bulbs at home. In fact, you will probably never change a bulb of your interior lighting again.

Voltage levels

The voltage level in your vehicle is 12 V, or 24 V if you have an older all terrain vehicle or a truck. Your home appliances, however, run on 110 V or 230 V AC. To make these devices work in your overland vehicle, you need an inverter that generates the high AC voltage from 12 V DC. We decided not to follow this path. Inverters cost around 100 €, add up to your weight and only have a 90% efficiency. Plus, you can get a 12 V version of most devices – except maybe a hair dryer or a rock drill. We only carry chargers for our camera, notebook and phones. They work with output voltages in the range of 3 to 20 V. There is absolutely no point in transforming 12 V DC to 230 V AC and down to 20 V DC again.
Other than if you carry a device that requires high voltage alternating currents and there is no 12 V version of this device available, we recommend you to not spend any money on an inverter. A list of those devices includes: toasters, hair dryers, coffee makers, water boilers. Actually anything that is made to generate a large amount of heat. 12 V versions of these devices are mainly junk. However, 12 V are completely fine for all your electronic gadgets. And it is much more efficient than using an inverter.

Demand calculation

If you have sorted out, which devices to put into your circuitry, you are only one step away from laying down your daily energy demand. To do so, we have put together an Excel workbook for you. We wanted to put up a web form on this page, but we failed. If you know a simple solution, leave us a message or comment.
Just fill in the data of your devices in the white fields. Note that you can choose to give your power rating in watts or amps. Always use an amp rating for 12 V devices if there is a value given in the technical data sheet. Use the watts rating for high voltage devices or if no amp value for 12 V is given. The table then calculates a charge consumption by simply dividing by 12 V. Although it is a good one, this is only an approximation. Here is the calculation for our devices:
Electrical load calculation for overland vehicles.
Note that we have not considered the auxiliary heating in this calculation. Due to the fan’s high energy consumption, our charge consumption will be quite a bit larger during cold winter days. But we are not planning to see too many of those. Therefore, a daily charge consumption of roughly 30 Ah should be a realistic value for most days.

Overland vehicle electrics circuitry design and components

Wires we ripped out of our overland vehicle

These wires were connected to one of the batteries. We took them all out.

For about two hours, we tried to trace all those wires that were connected to the batteries and understand the circuitry. Then we decided to rip the whole mess out instead. Our Landcruiser came with three 50-ish Ah batteries. Two starter batteries and one living compartment battery. Confusingly wired, generously neglecting the first rule of overland vehicle electrics: Keep your circuits separated! This way you are sure that you do not drain your starter battery with your living compartment appliances. In fact, you could build a living compartment circuitry, that is separated from your vehicle circuitry at any time. But it makes more sense to connect your circuitries when the engine is running. This way, the alternator charges both batteries. After a couple of kilometers down the road, you are left with plenty of electrical energy.
Here is what our wiring diagram looks like (we have not used wiring diagram notation to make it easier for all non-electricians of you):
Wiring diagram for overland vehicle electrics

Electricity generating components

We rely on three sources of electrical energy. When the engine is running, the alternator charges both batteries. After a one hour – or so – drive, they should be fully charged. When camping on a campground, we make use of a 230 V battery charger that is built into our vehicle. If we do backcountry camping, a solar panel provides a fair share of our daily demand and extends our time in self-sufficiency.

Alternator wiring

The alternator produces enough energy to charge both batteries. When it is running, the D+ signal closes a 75 A cutoff relay. Starter and living compartment batteries get connected. There are more sophisticated systems available, that only connect the living compartment battery if the starter battery is fully charged. This is very reasonable if you have long periods of time, where your vehicle is not running and your batteries get drained a lot. Our vehicle, however, will be running several times per week. Therefore, we did not spend that extra buck on an intelligent system and settled for a simple relay.
Both connections to the two batteries are 16 mm² wire cross section, fused with 70 A AGU fuses.
Additionally, we have installed a battery master switch to manually connect both batteries if necessary. This way, we can start the vehicle from the living compartment battery or charge both batteries using the 230 V battery charger.

Battery charger

Our vehicle came with a built-in battery charger. It is mounted into a bodywork cavity in the back of our car. A 230 V Schuko plug in the engine compartment can be connected to the AC 230 V grid.

Solar panel

We have a 100 W solar panel on our roof. A Steca PR2020 solar charge controller charges the living compartment battery and functions as a battery computer, simultaneously. It observes the battery’s voltage and counts the charges coming in from the solar panel and going out to the loads. At a battery voltage of 11.1 V it disconnects the loads and protects the battery from deep discharge. It is mounted in the back of our vehicle, next to the battery charger.
Solar panels for mobile use are widely available. For loads comparable to ours, we recommend sizes in the range of 80 to 200 Wp. They are in the 100 to 200 € price range and should be powerful enough to cope most use cases. Plus, they have good a good size for most overland vehicle rooftops. Get a monocrystalline panel for a higher efficiency at a slightly higher price compared to a polycrystalline one. Note that the given power rating is a lab value. It is only achieved at a pretty high illumination in a perfect 90° angle at 25° C. Not exactly real life conditions.. In our Excel tool, we assumed an 70% achievement of this power rating. This is a good assumption for sunny conditions in Europe. Our tool is capable to do a more precise calculation based on your real life measured currents.
On sunny days, our system gives us output currents of around 6 amps. On cloudy days, we are left with 1 A or less. Find a solar panel that is able to compensate a large portion of your daily demand under average usage conditions. You can still run your engine when the crunch comes! Here are our values taken from the Excel.
Solar panel charge calculations for overland vehicle electrics.

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Electrical energy storage: the living compartment battery

The vast majority of options for a living compartment battery makes this one a hard decision. There are four different technologies and a large number of available sizes to be considered. But let us go through this step by step.

Battery types

Battery types in question are based on two different battery technologies. Lead acid and lithium iron phosphate (LiFePO4) batteries. Lead acid batteries are the classical ones; widely used as starter batteries. LiFePO4 batteries are a newer, more powerful technology. Its energy density is way higher. This results in a lower battery weight. Moreover, this technology allows way higher depth-of-discharges. Hence, you get the same usable energy at a lower battery capacity. Here is a comprehensive overview over available technologies:

Recommended depth-of-discharge (DOD): < 30 %
Cycle life (@ < 30 % DOD): up to 1000 cycles for deep cycle designs.
Sensitivity to heat: Good. Can be stored in the engine compartment.
Possibility to start the engine: Yes, high currents are not a problem.
Weight: ~20 kg (100 Ah battery)
Price: 100 € and up (100 Ah battery)
Bottom line: Low acquisition cost, comparably short life times. Engine compartment installation is possible.

Recommended depth-of-discharge (DOD): < 30 %
Cycle life (@ < 30 % DOD): 1500 and more.
Sensitivity to heat: Bad. Best stored outside of engine compartment.
Possibility to start the engine: Yes, high currents are not a problem.
Weight: ~20 kg (100 Ah battery)
Price: 150 € and up (100 Ah battery)
Bottom line: Slightly higher acquisition cost, comparably short life times.

Recommended depth-of-discharge (DOD): < 30 %
Cycle life (@ < 30 % DOD): 3000 and more.
Sensitivity to heat: Bad. Best stored outside of engine compartment.
Possibility to start the engine: No, high currents reduce battery life.
Weight: ~20 kg (100 Ah battery)
Price: 170 € and up (100 Ah battery)
Bottom line: Medium cycle life. Sensitive to high currents and temperatures.

Recommended depth-of-discharge (DOD): < 80 %
Cycle life (@ < 80 % DOD): 10,000 and more.
Sensitivity to heat: So-so. Best stored outside of engine compartment.
Possibility to start the engine: No, high currents reduce battery life.
Weight: ~12 kg (60 Ah battery)
Price: 900 € and up (60 Ah battery)
Bottom line: High initial costs, otherwise superior. High life time, low weight.

We decided to go for a flooded lead acid battery for two technical and one financial reason. We wanted to keep the installation location in the engine compartment and be able to start our engine from the living compartment battery, if necessary. LiFePO4 options at the time of our search were well above 1000 €. This was more than we wanted to spend, although we think it is the most sustainable long term investment.
After a little tweaking to our battery mounting plate, we were able to fit both batteries – starter and living compartment battery – into the engine compartment.

Battery mounting plate for a Landcruiser HZJ78

Battery mounting plate that required a little tweaking to house a 120 Ah and a 100 Ah battery.

Battery size

The battery size you need is determined by the number of self-sufficient days, your solar panel and the battery technology you chose. Although AGM and gel lead acid batteries are not as sensitive to high DODs as flooded lead acid batteries, we recommend you to not discharge your lead acid battery by more than 30 %. This is the best way to guarantee a long service life. So here is the rest of our calculation from the Excel file. We bought this 120 Ah lead acid living compartment battery.
Battery size calculation for overland vehicles.

Wires, connectors and fuses

We used 16 mm² wires for all direct battery connections. Based on the statement of a friendly electrician, these are good for currents of 40 amps and above. Larger wire cross-sections result in smaller resistances and, therefore, voltage drops. That’s why we also used a 16 mm² wire to connect the living room battery with the battery charger and the solar charge controller in the back of our vehicle. This wire is approximately two meters long and although we are not expecting any currents larger than 20 amps, the 16 mm² wire should keep the losses at a minimum.
1.5 mm² wires connect most of our loads with the positive and negative pole distributors. The positive pole distributor acts as a fuse holder, as well. The loads are individually fused with blade-type fuses, according to their current rating. If not too long, 1.5 mm² wires can be used for currents up to 10 A, easily. We only used some 2.5 mm² wires for far away, high power loads.
We are using crimped ring terminals on the 16 mm² wires and blade terminals on all other wires. Crimped connections are the only ones to withstand the constant vibrations, when used in (overland) vehicle electrics.

After completion of assembly, it is a good idea to perform some testing. First, you should measure the leakage currents in your system. Switch of all your loads and measure the current from your living compartment battery. It should be smaller than 0.5 A. 100 to 200 mA would be a good result.
Another test would be to switch on several high power loads at the same time to see if your system is robust enough. You should not see any melting fuses or devices refusing to work because of low voltages. If everything is working fine, you are almost ready to go on an overland trip!

If you have any questions or additions to this post on overland vehicle electrics, just write us a message or leave a comment. We are happy to discuss this topic with you and further improve this summary.

This is the fourth step of our Overland Vehicle Preparation Series. You can read all steps here.

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