Solar Cable Size Calculator PRO
Use this professional solar cable calculator to size both the panel to controller cable and the controller to battery cable in campervan, off-grid and low-voltage solar systems. It estimates current, cable size, voltage drop, power loss and a practical fuse recommendation for each section.
Enter your solar system details
Results
Panel → Controller
Controller → Battery
How this PRO solar cable calculator works
This calculator sizes the two most important cable sections in a campervan or off-grid solar system: the solar panel to controller side and the controller to battery side. That matters because these sections often behave very differently in real installations.
- Panel side: current depends strongly on panel voltage and controller type.
- Battery side: charging current is often higher, especially in 12V systems.
- Voltage drop: longer cable runs and lower voltages increase the cable size needed.
- Fuse suggestion: gives a practical starting point, but should always be checked against the real installation.
Why the battery-side cable is often larger
In many MPPT systems, the solar array runs at a higher voltage than the battery bank. That means the panel-side current can stay modest, while the controller output into a 12V battery can be much higher. As a result, the controller to battery cable often ends up thicker than the roof solar cable.
Calculation method used
| Step | Method | Comment |
|---|---|---|
| Panel-side current | Power ÷ panel voltage for MPPT, or closer to battery voltage for PWM | Reflects how controller type changes panel-side current. |
| Battery-side current | (Power × efficiency) ÷ battery voltage | Approximates charge current into the battery bank. |
| Voltage drop | 2 × length × current × 0.0175 ÷ cable area | Uses a practical copper DC formula with round-trip length. |
| Cable recommendation | Rounded up to the next practical cable size | Keeps the recommendation realistic for buying and installation. |
| Fuse suggestion | Calculated current × selected fuse margin | Useful starting point only, not a substitute for design checks. |
Typical installation patterns
A small single-panel weekend van may work well with modest panel cable and a relatively short battery-side run. Larger systems, especially 12V MPPT installs, often need much more attention on the controller-to-battery side.
Related tools
Recommended MKGT products
FAQ
The solar panel side and the controller-to-battery side often run at different voltages and currents. In a real MPPT setup, these sections rarely behave the same.
Very often, yes. This is especially common in 12V systems where charging current from the controller into the battery can be relatively high.
Usually yes. A small step up in cable size can reduce voltage drop, improve charging performance and leave room for future upgrades.
No. It is a practical sizing tool. Final choices should always be checked against the solar controller, panel specifications, fuse ratings, terminals and installation method used.