Designing a reliable, high-output mobile electrical system for an RV, camper van, or boat requires balancing seamless shore power management, heavy AC appliance support, and efficient solar harvesting.
By combining the rugged AC inverter/charger capabilities of Mastervolt with the ultra-efficient solar harvesting of Victron Energy, this electrical architecture delivers dependable 120V power and smart 12V DC distribution wherever the road takes you.
Here is a complete breakdown of how this hybrid electrical system is wired, how power flows through it, and the design decisions behind its layout.
The Distribution/Breaker Panel Board
Located under the fridge in the E-Pro 20FBS model, this is where you find the breakers and fuses for both the 120V and 12V systems. Each breaker is numbered – these correspond with the numbers shown in the diagram below.
System Architecture Overview
This diagram is explained below.
1. AC Shore Power and Dual-Stage Distribution (120V)
Incoming AC power from a standard 30A shore hookup or onboard generator enters through a dedicated 30A Main Breaker #3.
Smart Load Splitting
Instead of routing all AC loads through the inverter, the system splits incoming power into two distinct paths:
- Non-Inverted Dedicated Load (Water Heater): Controlled by a 15A breaker #1, the electric water heater runs strictly when connected to shore power or a generator. This prevents a high-draw heating element from accidentally draining the battery bank when dry camping.
- Inverter Pass-Through Line: A dedicated 30A breaker #2 (Inverter IN) routes power directly into the Mastervolt Combimaster. When shore power is present, the Combimaster automatically passes current through to your outlets while simultaneously using surplus power to charge the battery bank.
Inverter Sub-Panel and Appliance Feeds
Exiting the Combimaster through a 30A Inverter OUT breaker #5, power feeds the main interior AC distribution panel:
- Air Conditioner (20A Breaker #6): Dedicated circuit sized for startup surges and continuous compressor loads.
- Microwave (15A Breaker #7): Independent circuit for high-wattage cooking.
- GFCI Outlets (15A Breaker #4): Protected standard branch circuit powering wall plugs throughout the living space. This is used by the Roku TV, Starlink, Coffee Maker, etc.
2. Solar Harvesting: Dual Victron SmartSolar MPPTs
To maximize solar harvest across different panel orientations and ratings, the solar array is split into two independent charging circuits powered by Victron MPPT charge controllers.
There are two fuses (not shown in the diagram) – 20A for Array 1, located next to the Combimaster. and a resettable breaker under the frame (near the front hitch) for Array 2:
Why Split Arrays?
Running separate charge controllers prevents shade on smaller or differently angled panels from degrading the output of the primary 600W array. Each MPPT tracks its own optimal voltage curve independently.
3. DC Backbone and Battery Storage
At the center of the DC side sits a high-capacity lithium battery bank (Mastervolt MLI Ultra 12/6000, 460Ah) engineered for deep discharges and rapid recharging.
- Mastervolt Combimaster Inverter/Charger: Connects directly to the main battery terminals via heavy-gauge DC cabling to support heavy AC surge demands.
- Master Safety Switch and DC Fuse Block: A high-amp rotary master disconnect switch isolates the auxiliary 12V DC fuse block, which supplies power to all native 12V loads (LED lighting, water pumps, ventilation fans, and USB ports).
- Negative Bus and Shunt: All DC return paths (solar, inverter, and 12V loads) tie back through a central ground/shunt block for complete system monitoring.
4. Monitoring and System Control
Real-time visibility is vital for managing energy off-grid:
- Dual Digital Displays: Dedicated digital monitors provide clear, at-a-glance status updates for:
- Inverter Display: AC input voltage, pass-through status, inverter load wattage, and fault codes.
- Battery Display: State of Charge (SOC %), remaining runtime, voltage, and net current flow.
- Remote Inverter Control: A Battery Switch (located in the front bay of the 20FBS) controls the power flow from the battery to the 12V system. It has two settings ON/OFF. The Combimaster is wired to this Switch – meaning it will switch off when the Switch is in the OFF position.
Key Takeaways
- Intelligent Power Separation: Isolating heavy heating loads (water heater) upstream of the inverter preserves battery capacity for critical essentials like refrigeration, cooking, and air conditioning.
- Independent Solar Tracks: Dual Victron MPPT controllers ensure optimal solar production in variable lighting and partial shading conditions.
- Seamless Hybrid Operation: The Mastervolt Combimaster bridges AC and DC smoothly, providing automatic shore-charging and reliable off-grid inversion.
