Question:

I’m planning to install a straightforward 12V dual battery system with an isolator, fuse block, and a couple of breakers for protection. I’d also like to include a simple voltage sensor to monitor the charge levels and ensure there’s enough voltage to prevent the Webasto heater from malfunctioning. I believe the Webasto has a built-in feature to stop it from running if the voltage drops too low. The entire system will be DC-only, with no need for an inverter. With a basic fuse block, I can easily add more circuits later, and we can include one with the proper amperage for the furnace.

Answer:

For your setup, a super simple 12V dual battery system with an isolator and fuse block is a solid approach. Here’s a quick breakdown of what you’ll need and how it can work:

  1. Dual Battery Isolator: This will ensure that your auxiliary battery charges when the engine is running but prevents it from draining your starter battery when the vehicle is off.
  2. Fuse Block: A basic fuse block will allow you to safely add and manage multiple circuits later on. Make sure the fuse ratings match the devices you’re adding, such as the furnace.
  3. Circuit Breakers: Install a breaker or two at key points in your system to protect against overcurrent situations. One near the battery will protect the entire system, while additional breakers can be used to protect specific high-demand devices.
  4. Voltage Sensor/Monitor: A simple 12V voltage monitor will let you keep an eye on your battery levels. The Webasto heater, as you mentioned, has its own low-voltage cutoff to prevent damage, but monitoring voltage is always a good idea to prevent any surprises.
  5. All-DC Setup: Since you’re going with a DC-only system, you won’t need an inverter. This simplifies the wiring, reduces power loss, and allows you to focus on efficient DC power distribution.

With this setup, you can easily expand and add more circuits when needed, with the right amperage for your furnace and any other future devices you want to power.

Here’s a breakdown of recommended components and wiring tips for your simple 12V dual battery system:

Components:

  1. Dual Battery Isolator (Voltage-Sensing Relay)
    • Example: Renogy 12V 140A Dual Battery Automatic Isolator. or similar
    • Why: This type of isolator automatically detects when the engine is running and allows the alternator to charge both the starter and auxiliary batteries. It also disconnects when the engine is off to prevent draining the starter battery.
  2. Auxiliary Battery
    • Example: 100Ah AGM or lithium battery (lithium preferred for its efficiency and lifespan)
    • Why: AGM is affordable and easy to maintain, while lithium is lighter and provides more cycles.
  3. Fuse Block
    • Example: Renogy ANL Fuse Holder with 4 Slots and a Negative Busbar.
    • Why: This will allow you to safely add circuits as needed for future components (like lights, fan, heater). Make sure to use fuses appropriate to the devices you’re connecting (e.g., 15A for MaxxFan, 25A-30A for Webasto).
  4. Circuit Breakers
    • Example: 50A breaker at the battery and smaller breakers (30A or as needed) for individual circuits.
    • Why: Protects your wiring and devices from potential overload. Place the breaker near the battery to protect the system from faults.
  5. Voltage Monitor
    • Example: Renogy 500A Battery Monitor with Shunt.
    • Why: It helps monitor battery health, voltage drops, and ensures your Webasto heater has sufficient voltage to operate. The Webasto will likely shut off below 10.5V to protect itself, but keeping an eye on your voltage helps prevent issues.
  6. 12V Distribution and Wiring
    • Wiring Gauge: Use 4 AWG for connections between the batteries and the isolator. Use 10-12 AWG wiring for smaller loads like the MaxxFan, heater, and lights, depending on the amperage needs of the individual devices.
    • Why: The right wire gauge minimizes voltage drop, ensuring efficient power delivery without overheating.
  7. Grounding
    • Ensure that both the starter and auxiliary battery are properly grounded to the chassis. This is critical for safety and proper electrical function.
  8. Connectors and Fittings
    • Use marine-grade connectors, heat shrink tubing, and quality terminal lugs for all your connections to ensure durability and protection from corrosion.

Wiring Tips:

  1. Main Battery to Isolator to Auxiliary Battery:
    • Connect your starter battery to the isolator, then the isolator to the auxiliary battery using 4 AWG wires. Ensure the isolator is placed as close to the batteries as possible.
  2. Fuse at the Battery:
    • Place a 50A breaker between the auxiliary battery and the fuse block. This breaker will protect the entire system.
  3. Fuse Block for Accessories:
    • Run a 10 AWG or 12 AWG wire from the auxiliary battery or fuse block to the devices like the MaxxFan and Webasto heater, ensuring the fuse ratings match the device’s amperage needs.
  4. Ground Wires:
    • Each component should be properly grounded back to the negative bus or directly to the van’s chassis using appropriately sized wire (10-12 AWG depending on the device).
  5. Future Expansion:
    • The fuse block gives you flexibility to add more 12V devices like lights, USB outlets, or other electronics in the future. Simply add new fuses and run wires to the new devices.