How do I choose the right cable for connecting the solar system and solar charge controller? The solar panels are already supplied with some cable. However, these are usually only about one meter long and, therefore, much too short to reach the solar charge controller inside the camper. This raises the question of a suitable cable extension. Luckily, some cables have been developed specifically for use on the camper, which does justice to the changing conditions on the camper roof. Solar cables for mobile homes and campers are designed for outdoor use, i.e., they are waterproof, dust-resistant, aging and UV-resistant, and are made of tinned copper wires.
What cable thickness do I need?
The required cable thickness depends on your solar system and the voltage. Most of the time, however, 6mm2 cables are used. Ensure an MC4 plug connection is already mounted on the cable when buying. It would help if you had these to connect the cable to the solar system.
Solar charge controller
You need to know this for installing the solar system in the camper. The solar charge controller is the heart of your system because it regulates how much voltage is allowed from the solar modules to the battery. If the battery charge status is low, the full power from the solar modules is let through. However, if it is fully charged, less voltage is released to the battery to not destroy it.
Solar charge controller types • MPPT or PWM
There are different solar controller models on the market, which work differently and therefore offer different advantages and disadvantages. In the following, we explain which solar charge controller we chose and the reasons for this decision.
PWM solar charge controller for the camper
The PWM solar charge controller works on a simple principle. It allows current to flow to the battery until it is fully charged. It then separates the circuit between the bifacial solar panel and the battery and only switches it on again once the voltage in the battery has dropped a little. The PWM controllers are cheap but deliver less power than the MPPT controllers. Since the lower performance is greatest in cool to moderate climates, in particular, the PMW controllers are unsuitable for mobile homes and campers in Europe.
MPPT solar charge controller for the camper solar system
The MPPT (Maximum Power Point Tracking) solar charge controller is more complex. It acts as a “switch” between the battery and the solar module and analyzes the power curve of the solar module. The solar panels are thus able to provide their maximum output, which, depending on the weather, is around 10-30% higher than the output of a PMW controller. Since the MPPT solar charge controller can also handle higher input voltages, it is possible to use several solar modules connected in series. The 12 volt lithium battery can be connected on one side, while two 12V solar modules in series, i.e., 24V, can be connected to the other. Since we wanted to connect two solar panels, this property was particularly important.
Determine the correct size of the MPPT solar charge controller
The MPPT solar charge controllers are typically provided with two key figures. In our case, for example, “100 / 20”. What does that mean? The first number (in our case, 100) indicates the maximum input voltage, and the last (in our case, 20) is the nominal current. But you don’t have to worry too much about the right choice because you will find the right controller for almost all camper solar systems here:
Preparations for connection
Before connecting the cables to the solar charge controller, there are a few important precautions. When the first ray of sunshine falls on your solar panels, they produce electricity, which flows directly when connected. This can cause sparks or (if you are not careful) a short circuit. It would help if you covered the solar panels so they are impenetrable to light before connecting them. Alternatively, you can, of course, simply connect it in the dark. Since we expanded in the dark winter anyway, that was our most comfortable solution.
Since you are in the middle of your electrical expansion, you are probably also dealing with a wild tangle of cables. At least, that was the case during our electrical installation in the camper. Just make sure that the plus and minus cables never meet. This would lead to a short circuit.
The inputs of the solar charge controller
Depending on the solar charge controller type, it has four or six connections. Two connections, plus and minus, for the solar system (PV), the battery (BATT), and optionally the load (LAST), i.e., your consumers in the camper. For the solar charge controller to correctly identify the voltage of your battery, you should always connect the battery to the solar charge controller first. To do this, insert the plus and minus of the battery into the connection points marked BATT. Be careful not to reverse the poles when connecting. If the battery cables are firmly connected, you can attach the solar cables and the load output to the slots provided.
Our experience connecting the MPPT solar charge controller
Connecting the solar charge controller is very intuitive. However, the connection points of the controller are quite tight, so the 6mm2 cable and attached ferrules were difficult to push into the contact points. Next time we would therefore organize a good pair of square-type pliers beforehand. This would have significantly reduced the workload. It is also very important to purchase a dedicated power inverter for your camper.
Since most battery types should never be discharged below 50%, keeping a close eye on the battery charge level is important. Depending on which charge controller you have chosen, you can, for example, install a small onboard computer. But that was too much technology for us in our sweet camper. We decided on the 100/20 smart solar charge controller, which transmits all data to a smartphone app via Bluetooth.