Planning the motorhome electrical system is a complex subject; unless you are an expert, it is better to have your body checked by a qualified person. But how do you go about planning the electrical system in the campervan?
It is essential to estimate how high the power consumption will be reasonably and, therefore, choose and install the right equipment. Everyone needs a different amount of electricity for their individual needs. For example, some don’t need a fridge at all and want to charge their cell phone, while others have a compressor fridge and regularly charge laptops and camera batteries. So first, you should ask yourself the following questions:
What do you want to do in the van, and what is important to you? How long do you want to stand up? Which electrical devices do you want to operate in your van? Do you regularly go to a campsite and want to connect your camper to the electricity there?
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Since this van conversion is now our sixth campervan, we have already tested a lot. Our first van in Australia had neither a second battery nor a solar panel and only charged our mobile phones while driving. We had to go to a library to charge our laptops or camera batteries – quite expensive. We didn’t have a fridge, just a tiny cool box that you had to fill with ice. After a day, there was always water in the cool box. That not only sounded cumbersome, but it was also totally impractical and complicated, and after a week, we decided to do without the cool box.
In our next van in New Zealand, we had a second battery and a small solar panels system, enabling us to run a small compressor fridge. We could also charge our laptops with the voltage converter – a real luxury.
During our five-year trip around the world, we had a total of five different campervans, and with our current van conversion, we knew precisely which electrical system we wanted to install in our Sprinter.
To answer this question, the performance of the devices is summed up and determines how often they are used on average.
So we determined our daily electricity requirement by looking at the power consumption of all consumers. This includes the compressor refrigerator, the lights, the water pump*, or our diesel parking heater. The usage time in hours per day must also be taken into account.
One of our LED ceiling lights has a power (P) of 3W. In our case, the voltage (U) is 12V. The searched current (I) is searched for.
P = U x I -> I = P / U
So our ceiling light has a current consumption of 0.25A per piece. We installed six of these lights, which adds up to 1.5A. If you let all the lights run together for a whole hour, we use 1.5 Ah. Accordingly, we could operate the sunshine with a 100Ah 12-volt battery, which we can use 50Ah (AGM) for around 33 hours.
With this scheme, you can now calculate your total power requirement. Consider the actual usage of your consumers. The water pump probably only runs 15 minutes daily, i.e., 0.25 hours. A compressor refrigerator only actively cools a quarter of the time, i.e., arithmetically, 6 hours a day.
Once you have calculated your electricity requirement, you can think about how many days you want to be self-sufficient. That means without having to recharge your batteries. If your total power requirement is around 30Ah a day, you will get two days with a 100Ah battery.
You should, of course, select the required components and set a budget. Because there are rarely any upper limits, a lithium battery can easily cost around €1000. The sum can quickly triple if you add high-quality solar cells and a compressor refrigerator.
It has always been essential for us to work with our laptops in the van, we also want to charge our mobile phones regularly, and a fridge is now a must. There is nothing better than drinking a cold cola or eating a delicious ice cream. Of course, you would also like to have lights in the van and an electric water pump to operate a water tap.
We spent 1508€ on the pure electrics in our mobile home. The essential components were:
During our van conversion, we recorded all costs in an extensive parts list. We entered EVERYTHING there, from the tank bracket to our diesel parking heater. Everything is included. You can download it here for free.
We used different types of lights for the lighting in our van. A total of two LED bars* and seven LED recessed ceiling lights were installed.
The LED bars brightly illuminate the van when you need a lot of light. The other seven LED spots are used for selective lighting and offer us a pleasant morning, which we mainly operate in the evening.
The LED bars are designed for 12V DC and can be connected immediately. They even have an integrated on/off switch. We ordered the LED recessed ceiling lights online from LEDKIA, which are intended for use at 230V AC in the house. A small transformer is supplied each morning, which is optional for use with 12V DC. If you leave out the transformer and connect the lamp directly to 12V, it will work the same way. However, the voltage in the van continuously varies between 11 – 13.5 V. This is why the light sometimes overheats quickly and breaks after a short time.
The solution to this is a small and cheap series resistor. Alternatively, an LED dimmer or a suitable LED driver can also be used, but these are a good deal more expensive than the small resistor.
In our case, we chose 6.8 Ohm / 3W power resistors. It should be noted that the resistor is connected in series with the lamp and can become hot during operation. It removes the excess voltage, and the lights work perfectly with it. We combined the lights themselves in parallel. Of course, the lines must be adequately secured, so we used a small fuse box to connect all our consumers. In addition, the entire line is appropriately covered with shrink tubing or insulating tape before it is laid under the ceiling paneling so that no short circuit can occur. The image below is for illustration only.
Addendum: The online shop now also offers pure 12V LED spots to save yourself the series resistor.
If you want to learn more about the lights used, we have published a video on YouTube. Incidentally, the lights were the cheapest we could find on the Internet for our van conversion at around €3 per piece (light incl. series resistor & toggle switch)!
Electrics in the mobile home: which battery is right for me?
As always, when choosing the correct utility battery, budget comes first. There are four types of batteries. Of course, each of them has individual advantages and disadvantages.
Gel batteries are usually maintenance-free and are well-suited for continuous power delivery over a long period. They also tolerate being deeply discharged. On the other hand, they can only deliver short-term high currents very poorly, which is why the gel battery could be better suited for operating a voltage converter.
AGM (Absorbent Glass Mat) contains a special glass mat that absorbs the acid and ensures high cycle stability. Therefore, these batteries are often called deep-cycle batteries. An AGM RV battery should never be drained more than 50-60% in everyday use. So from a 100Ah battery, 50 – 60Ah can be used. AGM batteries score with long service life and are maintenance-free.
Lithium as supply batteries are relatively new and still have a very high price. According to some manufacturers, LiFePo4 batteries are cheaper than lead batteries because they have a very long service life and a high current output. They are also lighter compared to other batteries. Lithium batteries can be discharged up to almost 100% so that the total capacity can be used. The most significant disadvantage is the high price, so we decided against these batteries.
Once you have selected and coordinated all the components, you should find the cables and connectors required to interconnect all the features.
A power line can be thought of as something like a water hose. The more water you want to transport, the thicker the hose diameter should be. A power line behaves similarly, but the voltage drop must also be considered. If you send too much current through a too-thin cable, it heats up to an impermissible extent, and a cable fire can occur. Therefore, a minimum cross-section should always be maintained. In case of doubt, it is better to oversize.
The required cross-section can be calculated using this formula:
A = 2⋅ l⋅ I / γ ⋅ Ua
If you find these formulas too complicated, you can search the Internet for tables for the cable cross-section, which are easy to read. If in doubt, always choose one larger size to be safe.
In addition to the cross-section, the voltage drop must also be considered. Because electricity cannot simply be routed through a 100-meter-long cable, in the end, only a minimal amount will arrive. Twelve volts will quickly become 10 volts, and consumers like the refrigerator will no longer work. The conductor cross-section must, therefore, always be adapted to the voltage, current, and length.
A = ( I x 0.0175 x L x 2 ) / (fk x U)
I am the maximum current in amperes 0.0175 is the specific resistance of copper in ohms x mm2 / m L is the cable length FK is the loss factor, example: 1% is 0.01 U is the voltage
Image source: bigcommerce.com
Finally, you can still think about how you want to recharge your supply batteries. The most common options are shore power, camping solar panels, and when driving via the alternator. These are often used in combination with one another. We charge our batteries via the solar system and the alternator. Our batteries are charged while driving and also continuously from the sun.
If you often go to campsites, you can charge the batteries via an outside socket and a charger. The downside is, of course, that this is only possible in a camp, so there is a particular dependency. Since we will rarely be in paid places, we have decided against this option.
You need solar cells and a charge controller to obtain the energy from a solar system and thus charge the batteries. Excess energy can also be made available directly for consumers so that you can get a very long time with your batteries. Investing in a solar system makes sense, especially if continuously running devices are installed.
If a refrigerator runs all day, the batteries can be immediately recharged by the sun, and more capacity is left for other consumers. We opted for two 160W solar modules, giving us a total of 320W solar power. Our AGM batteries are charged using solar energy via the Active DSC 25 MPPT solar charge controller with a charging curve and speed that is perfect for them.
The supply batteries can also be recharged while driving using an isolating relay or charging booster. A charging booster is recommended for EURO 6 vehicles with an intelligent alternator, as this limits the charging current while driving, and the batteries need to be appropriately charged. In addition, a charging booster uses unique charging curves to charge an AGM or lithium battery optimally and as quickly as possible.
In older vehicles, if the starter battery is the same type as the supply batteries, these can be connected via a cut-off relay and charged directly by the alternator while driving.
Conclusion on the electrics in the mobile home
If you are unfamiliar with electronics, seek help from a good friend or professional because the choice of cable cross-sections alone can decide whether your van will survive. Cables that are too thin with high current or incorrectly dimensioned fuses can fail the entire electrical system or cause a cable fire.
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