A useful RV solar diagram identifies panels, controller, battery, protection and isolation, with each cable's design values attached.
Understanding how a solar system wires together prevents mistakes and makes troubleshooting easier. Here's the complete picture.
System components
A standard van solar setup has these components in order:
- Solar panels → PV cable → MPPT controller PV input
- MPPT controller battery output → battery cable (fused) → battery bank
- Battery bank → bus bar → loads (fridge, inverter, lights, etc.)
The wiring diagram (text version)
[Solar Panels]
|
| (MC4 cable, 10 AWG, fused at PV input if MPPT doesn't have one)
|
[MPPT Charge Controller]
|
| (battery cable, 8–10 AWG, fused within 12" of battery positive)
|
[Positive Bus Bar] ←→ [Battery Bank] ←→ [Negative Bus Bar]
| |
| (fused per circuit) |
| |
[12V Loads: fridge, fan, lights] [Shunt if installed]
| |
+------------------------------------------+
Component connections in detail
Panels to MPPT
Cable type: MC4 (pre-terminated on most panels) for the panel-to-gland run. Standard 10 AWG stranded copper from the cable gland to the MPPT controller inside the van.
Fusing: Most quality MPPT controllers (Victron, Renogy Rover) don't require a fuse on the PV input side — if the wire shorts, the panels can only push short-circuit current (Isc), which the controller handles. However, some builders add a 30A inline fuse on the PV positive cable for belt-and-suspenders protection.
Polarity: Red = positive, black = negative. MC4 connectors are keyed, but verify with a multimeter before connecting.
What the MPPT sees: PV input voltage (e.g., 40V for two 20V panels in series) and PV current.
MPPT to battery
Cable type: Stranded copper, 8–10 AWG depending on controller rating.
Fusing: CRITICAL. A fuse on the positive cable from MPPT to battery, placed within 12 inches of the battery's positive terminal. Size the fuse at 125% of the controller's maximum charge current:
- 30A MPPT → 40A fuse
- 50A MPPT → 60A fuse
This protects the wire if a short develops between the battery and controller.
Connection point: Connect to the positive bus bar (not directly to a battery terminal, unless you have only one battery and no bus bar). Connect to the negative bus bar or battery negative.
Battery connections
The battery connects to a positive bus bar and through a shunt (if installed) to the negative bus bar. All charging sources (MPPT, DC-DC charger, shore power charger) connect to the bus bars. All loads connect through the positive bus bar and back through the negative bus bar.
The SmartShunt or BMV-712 battery monitor shunt installs in the negative cable between the battery negative terminal and the negative bus bar — all current to/from the battery passes through it.
Wire size reference
| Connection | AWG (30A system) | AWG (50A system) |
|---|---|---|
| Panel to MPPT (PV) | 10 AWG | 10 AWG |
| MPPT to battery | 10 AWG | 8 AWG |
| Fuse to bus bar | Same as above | Same as above |
For longer runs (over 10 feet), increase one gauge size to keep voltage drop under 3%.
Common wiring mistakes
No fuse on MPPT-to-battery cable: This is a fire risk. The battery can supply thousands of amps into a short circuit — a fuse prevents this from burning the van down.
Connecting loads directly to the battery terminal: All loads should go through the bus bar, not directly to the battery. Direct connections bypass the shunt (killing your battery monitor accuracy) and make the wiring harder to manage.
PV cable too small for the run: Panels on the roof may be 15–25 feet of cable from the MPPT controller. At 15A of PV current, 25 feet of 12 AWG wire has ~3% voltage drop — acceptable but borderline. 10 AWG keeps drop under 2% for most van roof runs.
Wrong polarity on MC4 connectors: Double-check before connecting. A reversed PV connection won't damage most modern MPPT controllers (they have reverse-polarity protection) but some cheaper controllers will fail.
Worked planning check
Annotate one example panel-to-controller circuit with Voc, Isc, cold correction, cable length and conductor size. Then annotate the controller-to-battery circuit separately: its current can differ because the controller converts voltage. One current label for both sides is insufficient.
The figures or dimensions in this example are explicit planning assumptions, not a product test or an installation specification. Replace them with your equipment data and actual measurements.
Planning questions
Should campervan solar panels be in series or parallel?
Compare the resulting voltage and current with the controller limits and evaluate the actual shading pattern. Series adds voltage; parallel adds current. Neither is universally best.
Why does a solar panel produce less than its rated watts?
Nameplate power uses specified test conditions. Sun angle, temperature, shade, dirt and charging-system limits change actual output. Size from seasonal daily energy, not maximum watts alone.
Can I add another panel later?
Recalculate cold open-circuit voltage, short-circuit current, controller output, mounting, cable and protection first. Matching wattage does not prove panels are electrically compatible.
Related
- Solar setup guide
- How to install solar panels on an RV
- AWG wire gauge guide
- Van electrical system diagram
Use the free electrical planner to organise your daily loads and charging assumptions.
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Jack Kennedy is a self-builder who has built two vans. He created Roam Wired to simplify conversion planning and share free tools, supported by affiliate links.
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