Cables, Fuses, and Switches
After selecting the appropriate batteries, the next and most critical step is their correct and safe connection. The proper cables, the right fuses, and the isolation switches are what will protect your van from short circuits and, above all, from the risk of fire.
1. Cables
- In electrical systems, the cable cross-section plays a massive role. The longer a cable is and the more Amperes an appliance draws, the thicker the cable needs to be. Always use flexible automotive/marine cables (multi-strand copper) that can withstand the vehicle's vibrations, and never stiff household cables.
2. Fuses
- It is the "weak link" intentionally placed in the circuit. If more current than normal passes through (e.g., due to a short circuit), the fuse blows and cuts the flow before the cable can melt.
- Every positive cable leaving the battery or going to an appliance must have a fuse. The main battery fuse must be placed as close as possible to the positive terminal (within 18-20 centimeters).
- Types: For the main high-Ampere lines, ANL or MEGA type fuses are used, while for small appliances (lights, USB), a central fuse block with classic blade-type fuses (ATC/ATO) is used.
3. Isolation Switches (Battery Isolator Switches)
- They allow you to completely cut off the power supply from the batteries with the turn of a lever.
4. Small Switches (Toggle / Rocker / Push Button Switches)
- They allow you to turn individual appliances or low-consumption circuits on and off, such as lights, the water pump, or USB chargers.
- Types: The most common are Rocker switches (which rock back and forth and often have an LED light) and Toggle switches (with a lever). They are usually all grouped together on a central control panel (switch panel) for convenience.
- What to watch out for: You must always check the Amperes that the switch can handle (usually 10A or 20A at 12V). If you want to control a very powerful appliance, the small switch should not be connected directly, but instead give a command to a relay.
5. USB Chargers and 12V Lighter Sockets (USB Chargers & 12V Sockets)
- 12V Lighter Sockets: These are the classic cylindrical car sockets. They are ideal for appliances that draw more current, such as a portable refrigerator, a small air compressor for tires, or a 12V laptop charger.
- USB Chargers: These are built-in ports (USB-A and the newer fast USB-C) that convert 12V to 5V or 9V. They are used continuously for charging phones, tablets, flashlights, and power banks.
- What to watch out for: Even when no device is connected, USB chargers (especially those with a built-in digital display for Volts) consume a minimal amount of power. For this reason, it is a good idea to connect them after a small switch so you can turn them off completely when not in use and prevent them from draining your battery.
Cable and Fuse Selection Guide per Appliance (for 12V Systems)
| Device | Typical Ampers | Suggested Fuse | Suggested cable size for max 2-3m |
|---|---|---|---|
| LED Lights | 2A – 5A | 7.5A | 1.5 mm² |
| 12v outlet / USB | 5A – 10A | 15A | 2.5 mm² |
| Watwr pump | 5A – 8A | 10A | 2.5 mm² |
| 12v Fridge | 4A – 7A | 10A – 15A | 2.5 mm² – 4 mm² |
| Diesel heater | 10A – 15A | 20A | 4 mm² |
| Inverter 12V σε 220V until 500w | 40A | 50A | 10 mm² – 16 mm² |
| Inverter 12V σε 220V 1500w | 125A | 150A | 35 mm² – 50 mm² |
| DC-DC charger 30A on small distance | 10A – 40A | 50A | 8-50 mm² depending on the distance from the starter battery. |
*Always, once we have selected our appliances, we do thorough research on what is required in terms of cable size and fuses. The above table is indicative and not a rule.