Overland Electrical System desgin

1, Introduction

There are many ways to design a vehicle’s power system, a lot depends on how you intend to use your vehicle and how much money you decide you have budgeted to invest.

In this brief overview we will discuss a few critical aspects of system design, some suggested products and a few pitfalls that you may encounter.

This is by no means meant to be an exhaustive design guide. Motorcraft offer a system design service and are a Victron dealer, so for more technical details or services please contact us.

The main two functions of a power system can be broken down into Four main aspects; Generation, Storage, Usage and Monitoring.

2, Generation

The first part of any system design needs to be where are you getting your electricity from. There are five main ways to generate electricity.

Solar

By far the most popular means of generating electricity is through the use of solar panels mounted on the roof of the vehicle. It is alway worth fitting as much solar on the vehicle as you can possibly fit. While you will end up having too much in the summer months I can almost guarantee you will not have enough on the short winter days. Particularly in the far Northern or Southern hemispheres where there can be clear sky and bright sunshine but the shallow angle of the low sun will generate very little power.

Tilting solar panels can produce 30-40% more power and is the only way you will ever get close to the rating of a panel. At the time of writing, Motorcraft does not offering a tilting panel option, however this may change in the future. The reason we don’t is because you have two options to tilt the panels either automatically or manually. With the manual option, this introduces a significant fall risk for whoever is tilting the panels. Particularly when the weather is not favourable. With an automatic tilting method you are adding significant weight to the solar set up at the highest point of the vehicle, potentially, you are affecting the centre of gravity of the vehicle.

When connecting solar panels up you have two options; Parallel or Series.

When connecting in series, the panel output voltage will increase. This means you will start producing power sooner in the day and this will remain producing much later in the day. HOWEVER, you're at much greater risk of solar shading. If you shade one PV cell on a thirty-six cell panel you can reduce its output by over 75%. If you have panels wired in series this loss will ripple through your whole system.

When connecting in parallel the output voltage will remain the same, so you don’t get the early voltage gains and will produce for a shorter period in any given day. However, if you shade one panel in the array then the production of the other panels will NOT reduce.

At Motorcraft, our experienced installations take into consideration the roof layout and will wire in an array that best suits. This could be a combination of Series and Parallel.

Solar panels should not be wired directly to the batteries. For this you will require a solar charge controller, for regulating the output voltage. Although most chargers are now a ‘maximum peak power tracking’ (MPPT) it is recommended that you make sure that you buy this style because they are around 30% more efficient than the older ‘pulse width modulation’ (PWM) chargers. Victron energy has a very good calculator to work out what size MPPT charger you need based on your panel size.

https://www.victronenergy.com/mppt-calculator

An aspect that is often overlooked in many non professional solar installations is the use of solar isolators. It's very hard to stop a solar panel from producing electricity, while this may not seem like an issue, in bright sunlight a panel could produce 60v which is potentially very dangerous. But by using a DC double pole isolator, as close to the panel as possible, means in an emergency or during maintenance you can isolate the power coming in without having to go onto the roof of the vehicle and try to cover up the panels.

Wind

Alternator

Most modern overland vehicles have a battery to battery charger. This means the alternator charges the vehicle battery and then once this is fully charged the power is redirected to charge the vehicles leisure batteries.

With AGM/Gel/Lead acid batteries this is relatively straight forward.

With lithium Ion batteries, this battery to battery charging is possible but requires some careful installation and design. Due to the low internal resistance of the lithium iron batteries they can draw a very high current. Due to how a vehicle’s alternator cools itself, at low revs or Idle if you draw its peak output you run the risk of overheating the alternator and damaging it irreparably.

There are two ways to stop this from happening. The most common is to put a current limiting device in to limit the current draw from the alternator. So a typical 100ah truck alternator will only charge 60ah to the lithium battery bank. While this is slightly limiting it is safe and affordable. The second option is to replace the original alternator with a temperature controlled alternator that will adjust the output to suit the alternator’s internal temperature. This is an expensive solution but in optimal conditions it would allow you to take the full output from the alternator.

Generator Petrol/ Diesel

A generator is a commonly carried piece of equipment that is very useful for supplying a charge current to your vehicle. They come in many different varieties and we shall explore the most common.

Portable v Permanent Mounting

Permanent mounted generators like the Whisper power or the Fisher panda range are normally significantly more expensive than a portable petrol generator. However the advantages are as follows:

Normally diesel powered, requiring extra fuel
Much quieter, due to its size, sound insulation and water cooling
Auto start/stop functionality meaning you do not have to worry about state of charge
Better integration into the power system

Output

Generators come in a huge range of outputs from 700w portable to 12,000w permanent mounted diesel generators. The output required would depend on your battery capacity. The limitation is the peak charge current for the battery bank. The power required for the typical 200ah Lithium battery would be 1200w. This can be multiplied by the number of 200ah batteries in your system.

So why have a 12,000w generator? I hear you ask. Remember the rating on a generator is the peak power out and the sound pressure level (Noise) is often at 50% load at a 7m distance. So charging 2x200ah batteries at 2400w will form a 2400w generator running at 100%, which is much noisier than changing the same at 20% off a 12000w generator.

AC or DC voltage

Permanent mounted generators can come in both AC or DC outputs. AC voltage at 240v (or 110v) can be consumed directly or inputted into a charger and converted to 12v/24v to charge the house battery bank. A DC generator is more efficient as you're not converting the voltage twice and the output can be higher to charge a battery bank; however they offer no redundancy should you suffer an inverter failure. It is for this reason motorcraft predominately fit AC generators.

Petrol or Diesel

There are benefits to both diesel and petrol generators. Here are the main points:

Diesel generators are generally much larger than petrol generators so they only come in permanent mounted options and not a portable option.
Diesel generators are nosier so you end up spending more money to achieve the same sound pressure level (db)
Diesel generators do not require a second fuel source and can draw fuel directly from the main tank.
Unlike Petrol, Diesel generators can suffer from poor operation in temperatures under -16c

Shore line/Hook Up

We would always recommend installing a mains hook up point and suitable battery charger on a vehicle. While you may not often use it, should you ever need to put the vehicle into storage it could ensure your batteries maintain a healthy charge. If installing a shoreline connection to your vehicle for mains charging alway consider the countries where you are likely to use it and ensure you have a charge that’s able to suit that country’s energy supply. This may be a simple 110v /240v charger or something that’s able to cope with fluctuating voltages of developing countries.

PTO Generators

A lot of vehicle's have PTO’s (power take off) allowing you to hydraulically power equipment. These are very prevalent in former military vehicles.

One option is to use this hydraulic power from the engine to power a generator either 240v or 24v. However the initial installation cost and the cost of running a large diesel engine to make power, often makes these financially not viable.

There is also an argument of redundancy. If you break down due to engine failure, you really do not want to be in the situation where you also don’t have a means to charge your batteries. Particularly if this is due to fuel theft (we have experienced this first hand) and you are relying on electrical energy for your secondary heating system, For this reason this is not something we currently offer as a service.

3, Storage

Great, you have decided on how you are going to generate your electrical energy now you need to work out where and how to locate it. There are lots of types of energy storage solutions but the two most viable solutions at the time of writing are; Batteries, either Lithium Ion or AGM. There are other emerging technologies but these won’t be covered due to costs, reliability and serviceability.

Lithium

Lithium batteries have got a lot of bad press over the years because of the fires in portable devices. When talking about lithium batteries its important to understand that there are several lithium battery chemistries

Lithium Iron Phosphate (LiFePO4)
Lithium Cobalt Oxide (LiCoO22)
Lithium Nickel Manganese Cobalt Oxide (LiNiMnCoO2)
Lithium Titanate (LTO)
Lithium Manganese Oxide (LiMn2O4)
Lithium Nickel Cobalt Aluminium Oxide (LiNiCoAlO2)

In this article we will be talking about Lithium Iron Phosphate (LiFePO4) batteries. These are not the same as the batteries in portable technology products because they actually have a very low energy density compared to other lithium battery chemistries. Why do we use them in our overland adventure vehicles? Lithium Iron Phosphate (LiFePO4) have better thermal and structural stability, making them the safest battery type available. Providing they are used within the manufacture’s specifications, these batteries pose no more hazards than a traditional chemistry battery.

In order to make sure that your battery operates safely within a preset set of parameters, a battery management system (BMS) is used with all lithium chemistries.

External VS Internal BMS

Some batteries have their own BMS built in while others need an external BMS connecting. While an external BMS requires more wiring, it gives a greater degree of flexibility for system design and generally they are ok to use in systems with a higher current draw. If using internal BMS you should make sure the voltage and current limitations are taken into account in the system design.

A good BMS should offer protection against:

Over and under-voltage
Over and undercurrent
Cell Imbalance
Over and under temperature

LiFePO4 vs AGM

Weight

Lithium batteries are about 70% lighter than lead acid ones. While payload may not be a major concern on an expedition build weight, distribution should be at the front of your design criteria. Having 70% less weight to be concerned about is a real benefit.

Space

Lithium batteries are around 70% smaller than the equivalent lead acid battery meaning you can fit twice the capacity in the same footprint.

Charging

A typical lithium battery can charge at a rate between 0.5c and 2c meaning a 200ah battery can charge at a rate between 100ah and 400ah resulting in a charge time of between 4 hours and 30 minutes. However the more aggressive charge times are not recommended as the battery will struggle to maintain cell balance. This is far faster than a AGM battery

Discharge

One of the major advantages of lithium chemistry is there is no damage caused by deep discharges. Unlike AGM which can be severely damaged if discharged below 50%. A lithium battery has a discharge floor of 95%, meaning that on a 200ah AGM battery you have a usable capacity of 100ah and on a lithium battery you have a whopping 190ah. Coupling this with the space saving it makes a huge difference to your build.

The second advantage when it comes to discharging a lithium battery, is it can be discharged at much higher currents than AGM batteries with no long term damage. This makes it more suitable for higher power inverters that run cooking equipment for example.

One negative point for the lithium is that it will be irreparably damaged if charged at temperatures under 0c. Considering a functioning battery is normally 10c-15c above ambient it is only the coldest of climates this may be an issue. However with consideration to the placement of the battery this can be avoided.

Motorcraft can provide an ‘extreme use’ lithium battery that has a heated internal core. This battery will heat internally, prior to charge. Once it is up to temperature it will automatically start charging and no damage can be caused.

Costs

There are no two ways about it, the initial financial outlay for lithium batteries is significant but the benefits make it worthwhile.

A typical lithium battery is currently 3-4 times the price of a same size AGM. However, considering the increased usable capacity of a lithium battery, you will need less batteries to start out with. It is also worth considering the battery life.

Battery Life / Cycles

When discharged to 50% most AGM batteries have a 500-750 cycle life. That means it can go from 100% to 50% then back to 100% approximately 50-700 times in its life.

A lithium battery at 50% is rated to 5000 cycles . If discharged to 80% it is still 2500 cycles. So £’s per cycle, a lithium battery can work out to be the same cost as an AGM battery but with all the benefits of the lithium battery.

Note

Batteries can be installed in either 12v, 24v or 48v systems depending on how they are configured.

Without giving a full electrical lesson, the general rule is the lower the voltage - the higher the current draw. The higher the current draw - the larger the cables, buss bars, switches etc etc required. This in turn increases the cost of the installation and the space required.

For Systems with very low current draws, 12v systems are normally sufficient. If you're going to start drawing more current the 24v systems are normally the way to go, This is the most common system used. The 48v systems are rarely used because any voltage above 30v is considered to be dangerous in terms of electric shock risk.

4, Usage

Now you need a means to charge and a means to store your electrical energy for when you need to use it.

There are two ways that you could consume your stored electrical energy. In low voltage direct current (DC) systems and high Voltage (AC) systems.

There is often a misconception that you should try to run as much as possible on low voltage. Whilst this was true in the early days, when inverters were not very efficient, modern high quality inverters like the Victron Energy MultiPlus have an efficiency of 95%. Using the fridge as an example, the 95% efficiency of the inverter coupled with an A+++ fridge (this rating system has now been updated and a product previously rated A+++ will, in the new system, be rated B) will often use less power than a 12v fridge. This is because domestic appliances are constantly developed to meet environmental standards where there is no requirement for this in low voltage applications.

DC System -

When using a DC system you should match the voltage of the appliance to the voltage of your battery bank and you can connect them directly to the battery with a fused feed or with a low voltage distribution board. Always ensure that the negative feed off the DC is connected to the right side of any shunt that’s used. Failure to do this would mean your energy meter would display incorrectly.

If you are using a battery bank at a voltage that is different to your appliance rating, you should use a DC-DC converter to either step the voltage up or down to suit your requirements.

Note - With a DC system the lower voltage results in higher current draw. This means that cables and fuses must be of the correct rating or you run the risk of an electrical fire.

Victron energy has a phone app called the Victron Toolkit. There is a good cable calculator in the toolkit. For an online calculator we would recommend this website

https://www.solar-wind.co.uk/info/dc-cable-wire-sizing-tool-low-voltage-drop-calculator

AC System -

AC or Alternating current is the same form as you use at home. This will either be 240v or 110v depending on where you live. In order to get an AC voltage from your batteries you will need to install an inverter. Inverters come in different power ratings. You will need to match the power of your inverter to your estimated peak power usage.

AC installations should be installed in accordance with your local wiring regulations.

5, Monitoring

The final part of the puzzle is how you are going to monitor your energy use. This is normally done via a shunt. Motorcraft use Victron Energy shunts and they come in two types; standard and Smart.

A standard shunt connects to an onboard digital display and will show you a host of information about your current battery status.

The newer smart shunt does not use a screen but allows connectivity via bluetooth to a smart portable device like a phone or tablet. Motorcraft coupled this with the Cerbo GX to give both an onward 7in touch screen and connectivity Theo the very powerful Victron VRM portal for global monitoring of all our vehicles.

6, DISCLAIMER Last updated September 06, 2022

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