How to Connect Your DC-DC Charger and Solar Panel at the Same Time

Many 12V setups use a DC-DC charger to power batteries while driving and also include a solar panel for off-grid charging. The good news is — most modern DC-DC chargers support both charging sources at once!

In this guide, we’ll explain how to wire both correctly, what to avoid.

? What You’ll Need

• A DC-DC charger with solar input (e.g., Renogy, Victron Orion-Tr, Enerdrive, Projecta, etc.)

• Solar panel (blanket or fixed)

• Battery (LiFePO4 or AGM)

• Properly rated fuses or circuit breakers

• Anderson plugs, ring terminals, wiring tools

• Optional: battery monitor or voltmeter

⚡ How It Works

A typical DC-DC charger has two separate input sources:

• Alternator (Vehicle Input): Charges the battery while the engine is running

• Solar Input (MPPT): Charges the battery when there’s sunlight, even with the engine off

The charger automatically switches between sources — often prioritising solar to reduce vehicle load.

? Wiring Instructions

Step 1: Connect the Vehicle Input

• Wire from the start battery (positive terminal) to the DC-DC charger vehicle input.

• Use correct gauge wire for the current draw.

• Add an inline fuse near the start battery (typically 40A–60A depending on charger size).

• Ground the charger input to vehicle chassis or battery negative.

Step 2: Connect the Solar Panel

• Connect the solar panel (positive and negative) to the solar input terminals on the DC-DC charger.

• Use MC4-to-bare-wire cables or an Anderson plug setup.

• Ensure polarity is correct.

• Add a fuse or circuit breaker on the positive solar wire if not already fused.

❗ Important: Do not connect the solar panel directly to the battery if you’re already using the solar input on a DC-DC charger — this can bypass the MPPT controller and overcharge your battery.

Step 3: Connect the Output to Your Battery

• Wire the DC-DC charger’s output to your auxiliary battery (positive and negative).

• Add another fuse close to the battery for safety.

• Use suitable cable size to prevent voltage drop.

✅ Tips for Best Results

• Use a DC-DC charger with built-in MPPT solar regulator

• Size your solar panel based on expected power usage (e.g., 200–400W for camping setups)

• Use Anderson plugs for portable solar panels — makes setup quick and safe

• Add a battery monitor to track input/output and battery health

• Keep cables as short as possible and use correct gauge wire

? Safety Reminders

• Always fuse both inputs and output circuits

• Avoid mixing different charge sources directly into the battery

• Do not exceed solar voltage or current ratings for your charger (check specs)