RV solar not charging: how to troubleshoot panels, controller and wiring

How an RV solar system fits together

A typical RV solar setup has four parts:

1. Panels on the roof (or a portable suitcase panel).
2. Wiring with MC4 connectors, often through a roof entry plate.
3. A charge controller (PWM or MPPT) that regulates panel power into battery charging.
4. Fuses or breakers between panels, controller and battery.

When solar "stops working", start at the controller, because its display tells you most of what you need to know.

Safety: Solar panels produce voltage whenever light hits them, and you can't switch that off at the panel. Strings of panels can produce voltages high enough to be dangerous. Cover panels with a blanket or cardboard before disconnecting wiring, and never disconnect MC4 connectors under load because they can arc. Working on a roof is a fall hazard. Use a solid ladder, check that your roof is walkable, and avoid wet or frosty roofs. Follow the battery safety tips in RV battery not charging: how to troubleshoot the converter and 12V system.

Step 1: Read the controller

Check what it reports in good sun:

• Panel (PV) voltage present, charging current zero: The battery may be full (normal), the controller may be in an error state, or the battery side fuse may have blown.
• No PV voltage at all: The problem is between panels and controller, such as a breaker, fuse, connector or broken wire.
• Low charging current in good sun: shade, dirty panels, wrong settings, undersized wiring or a failing panel.

Many controllers show error codes. Look them up in the manual.

Step 2: Confirm the battery settings

A controller set to the wrong battery type can stop charging early, never reach full, or refuse to charge at all. This is especially common after a lithium upgrade. Make sure the controller is set to the correct battery chemistry and voltage. Lithium batteries may also refuse charge in the cold (see below).

Step 3: Check fuses and breakers

Look for:

• A fuse or breaker between the controller and the battery.
• A breaker or fuse between the panels and the controller (often near the controller or at a combiner box).
• A battery disconnect switch that isolates the controller.

Replace blown fuses with the same rating. A fuse that blows repeatedly indicates a fault. Find it before you replace the fuse again.

Step 4: Measure panel voltage

With a Digital multimeter (auto-ranging, with DC amps) on DC volts, measure at the controller's PV input terminals (or at the panel leads, if accessible) in full sun. Compare with the panel's open-circuit voltage (Voc) printed on its label. In series strings, the voltages add up. Readings well below expected suggest shade, a bad connection or a failed panel in the string.

Step 5: Inspect connectors and roof wiring

• MC4 connectors can pull apart, corrode or loosen. Make sure each clicks fully home. Use an MC4 spanner to disconnect them properly.
• Look for chafed cables where they cross the roof or enter the roof plate, and for cables pinched in slide-outs or cabinets.
• Check the roof entry plate sealant. It's a common leak point, too. See RV roof leak: how to find the source and fix it properly.
• Tighten controller terminal screws. They loosen with road vibration.

Step 6: Rule out shade and dirt

Partial shade has a large effect: even a vent cap's shadow or a tree branch across one cell can cut a panel's output dramatically, and in a series string it can drag down the whole string. Dust from Alberta gravel roads, pollen, bird droppings and snow all reduce output. Wash panels with water and a soft brush. Avoid abrasive cleaners and pressure washers.

Step 7: Account for season and location

Calgary sits at around 51° N, so the winter sun is low and days are short. Flat-mounted roof panels collect far less energy in December than in June, even on a clear day. A system that easily keeps up in July may barely trickle-charge in January. That's physics, not a fault. Tilting panels toward the sun and keeping them clear of snow helps.

Lithium batteries and cold charging

Most LiFePO4 batteries shouldn't be charged below about 0 °C unless they have internal heating or a protection system that blocks cold charging. If your solar "stopped working" on a cold morning, the battery may be blocking charge to protect itself. Check your battery's specifications and app or monitor, if it has one.

Step 8: Test the controller

If panels deliver voltage to the PV input, the battery is not full, settings are correct, fuses are good and still nothing comes out, the controller may have failed. Some can be reset by disconnecting both the panels (first) and the battery, then reconnecting in the manufacturer's specified order. The order matters for many controllers.

Good practices

• Install a shunt-based battery monitor so you can see true amps in and out.
• Use correctly sized wire. Long, thin runs waste power.
• Fuse everything near the battery, per the controller and battery manufacturers' guidance.
• In winter storage, keep a little solar on the battery to maintain it, if your controller and battery chemistry allow it.

When to call a pro

Call a qualified installer for high-voltage panel strings, roof penetrations you can't seal properly, inverter/charger integration, or any sign of heat damage, melted insulation or scorched terminals.