If you’re running a dual battery setup in your caravan or towing a camper with significant power needs, a DC to DC charger is one of the most reliable ways to keep your auxiliary batteries charged while on the move. Unlike basic isolators or standard alternator wiring, DC to DC chargers deliver a stable, regulated charge — especially important for lithium or AGM battery systems that require specific voltages.
These units are increasingly popular among caravanners looking to travel off-grid, power fridges and lights, or integrate with solar. Installation isn’t overly complex, but it does require a good understanding of your van’s electrical layout and some basic tools. If you’re still preparing your setup, many caravans in Heatherbrae offer layouts that make battery management and upgrades easier to install down the line.
What Does a DC to DC Charger Do?
A DC to DC charger sits between your vehicle’s start battery and your caravan’s house battery. It ensures that your secondary battery receives the correct voltage and charge profile, regardless of alternator fluctuations or cable length. This is especially important in newer vehicles with smart alternators that don’t consistently produce high charging voltage.
Unlike standard battery isolators, DC to DC chargers actively manage the charge process. Most units also accept solar input, which means you can combine alternator and solar charging without needing separate controllers. This makes them perfect for off-grid caravans where battery life and efficiency are critical.
Tools and Materials You’ll Need
Before starting, gather the following:
- DC to DC charger (sized for your battery type and amp requirements)
- Automotive-grade wiring (typically 6–8 B&S cable depending on run length and current)
- Fuse holders and appropriate fuses (usually 40A to 60A)
- Anderson plugs (for connection between vehicle and van)
- Heat shrink, cable lugs, and crimping tools
- Multimeter
- Cable conduit or split tubing for protection
- Drill, grommets, mounting screws
Some DC to DC chargers come with wiring harnesses, which can simplify the process. Always refer to the specific wiring diagram in your charger’s manual, as layouts can vary between brands.
Choosing the Right Mounting Location
The DC to DC charger should be mounted as close to the caravan’s battery as practical — usually inside a battery box, near a storage hatch, or under a seat. Choose a spot that’s dry, well-ventilated, and protected from vibration. The unit needs to stay cool during operation, so avoid tightly enclosed areas without airflow.
If your unit accepts solar input, make sure the panel wiring can also be routed cleanly to this location. It’s also smart to keep the charger easily accessible for future diagnostics or maintenance.
Wiring and Installation Steps
Start by disconnecting all power sources. Safety first — batteries can deliver serious current. Once safe:
- Mount the charger securely to your chosen location.
- Run cable from your vehicle’s start battery to the Anderson plug at the rear of the car. This cable will carry charge to the caravan while driving.
- Install fuses on both ends of the run — one near the vehicle battery and one near the DC to DC charger input.
- Wire the charger’s output to the caravan’s house battery, using correct cable gauge and secure terminations. Add a fuse on this line as well.
- If using solar, connect the panel’s positive and negative leads to the charger’s solar input terminals.
- Ground the unit according to the manual — either to the chassis or battery negative, depending on manufacturer specs.
- Double-check all wiring for tightness, polarity, and correct fuse sizes.
Once everything is connected, reconnect the batteries and start the vehicle. The charger should detect voltage and begin its charging cycle.
FAQs
Do I really need a DC to DC charger for my caravan?
If you’re relying on your vehicle to charge a secondary battery in your caravan, then yes — a DC to DC charger is highly recommended. Modern vehicles often have smart alternators that reduce voltage once the starter battery is full, which means your caravan battery won’t get a consistent charge. A DC to DC charger solves this by regulating input voltage and ensuring your battery gets the correct multi-stage charging profile. This is especially important for lithium and AGM batteries, which require specific charging voltages. Without proper regulation, you risk undercharging or damaging your battery over time. While basic isolators can work for older vehicles, they simply don’t match the performance or protection of a DC to DC system. It’s a small investment that pays off in longer battery life and better off-grid performance.
Can I install a DC to DC charger myself?
Yes, many caravan owners install DC to DC chargers themselves, but it’s important to follow wiring diagrams carefully and understand the basics of 12V systems. The job involves cutting and terminating heavy cable, selecting the right fuses, and securely mounting the unit. If you’re confident with electrical tools and safety, it’s very doable — but always double-check your work before reconnecting any batteries. Getting it wrong can damage your gear or create safety hazards. Some people choose to do the mounting and cable runs themselves, then have an auto electrician do the final wiring and testing. That’s a good option if you’re unsure about fuse sizing or charger settings. As with any 12V work, be methodical, label everything, and don’t rush.
Where should I mount a DC to DC charger in my caravan?
The best location is close to your caravan’s auxiliary battery to minimise voltage drop and keep cable runs short. Many people mount the unit inside a front storage compartment, battery box, or under a bench seat near the battery. Make sure the area is dry, protected from dust and vibration, and has some ventilation — chargers can get warm during operation. Avoid mounting it near gas appliances or in spots that might collect condensation. If your unit also handles solar input, consider panel cable routing when choosing a location. Always mount the unit on a solid surface using screws or bolts, and allow enough space around it for airflow and future maintenance.
What size wiring and fuses do I need?
This depends on the size of your charger (measured in amps) and the distance between your vehicle battery, the charger, and your caravan battery. For most 20A–40A chargers, 8 B&S cable is a common choice for runs under 5 metres. For longer distances or higher current, you may need 6 B&S. Fuses should match the manufacturer’s recommendation — typically a 40A fuse on both the input and output sides of a 25A charger. Make sure fuses are mounted close to the battery or power source, ideally within 150mm. Use automotive-rated fuse holders and quality crimp lugs for secure connections. Undersized cable can cause voltage drop, which reduces charging efficiency and risks overheating. Always follow your charger’s manual or speak to an auto electrician if unsure.
Is it safe to combine a DC to DC charger with solar?
Yes — and in fact, many DC to DC chargers are designed with built-in solar regulators so they can manage both vehicle and solar charging. These units automatically prioritise the best available input source. When the vehicle is running, they use alternator power; when stationary, they switch to solar. This makes them ideal for off-grid caravanning. Make sure your charger supports the type of solar panel you’re using — especially the voltage range. For example, many units handle up to 25V or 30V solar input, which is fine for 12V systems, but may not be compatible with higher-voltage panels. Wiring must be done correctly, with the panel’s positive and negative cables going into the designated solar terminals on the charger. If your charger doesn’t have solar support, you’ll need a separate MPPT or PWM controller to manage solar input.
Installing a DC to DC charger the right way
Adding a DC to DC charger to your caravan’s setup is one of the smartest upgrades you can make for reliable battery performance on the road. With the right planning and wiring, it’s a straightforward project that pays off every time you travel — especially when paired with solar for a fully self-sufficient system.
Start your journey with confidence — visit 7th Street Caravans or give our team a call on 02 4012 6009 for friendly, local advice.