Dash-mounted solar panel trickle charger van setup

The Problem

The owner wanted a solar trickle charger for the starter battery using a portable 100W panel that could live on the dash full-time or be moved outside for camping. The original plan used a Renogy Wanderer PWM controller and the owner was unsure about cable sizing, connector choices, and routing the cable into the engine bay.

Note: this writeup is based on one specific van layout. The bulkhead and engine-bay details in step 3 (the scuttle sleeve, the bolted plate behind the battery, and the grommet position) vary considerably between platforms. Confirm the routing for your own van model and year before starting — a Transit, Sprinter, or VW T6/T6.1 will each have a different bulkhead arrangement and the steps below will need adaptation.

Solution

1. Swap the planned PWM controller for a Victron MPPT 75/15 and mount it inside the cab near the glove box on a bracket so it stays in place permanently.
   • The Victron gives Bluetooth monitoring via its app and handles bulk, absorb, and float cycling automatically.
2. Use MC4 connectors throughout the solar side of the circuit and an Anderson connector only where the battery feed detaches.
   • Use 2.5mm² cable or larger for a 100W panel drawing up to 6A. This sizing assumes a short run — a dash-to-engine-bay feed of a metre or two. For longer runs, particularly to a rear/leisure battery, voltage drop increases with distance and you should uprate to 4mm² or 6mm² to avoid undersizing. If in doubt, check the cable against a voltage-drop table for your actual run length and current.
3. Route the battery cable through the existing bulkhead grommet: pull back the rubber scuttle sleeve, remove the two bolts on the plate behind the battery, push the cable through the grommet, then pull it up through the passenger footwell carpet. (This layout is specific to one van platform — confirm the equivalent route on your own model and year before drilling or removing trim.)
4. Connect the cable to the battery positive terminal with an inline fuse, and run a ground to chassis.
5. Prop the panel on the dashboard angled to face south — a broom handle works as a prop.
6. Open the Victron app to confirm bulk, absorb, and float cycling; optionally configure the LOAD terminal as a basic battery-protect relay for a fridge or dashcam.