Congratulations on avoiding van life. In addition to exchanging the ability to play house on dirt roads for actual off-road capability, you’ve also netted the ability to skip the extreme complication and cost associated with a van build out. And nowhere will that be more evident than in electrical systems. Let’s make this as easy as possible.
Dual Versus Auxiliary Batteries
A dual battery system adds a second battery under your hood, which charges from the alternator and powers 12V accessories like lights and fridges, and gives you the ability to charge gadgets. Over a stock vehicle, the advantage here is none of the above ever draw power from your starter battery, leaving that free to be as reliable as possible. If you venture into remote areas, the advantage there should be clear.
Auxiliary batteries—like those made by Goal Zero, Jackery, etc—can charge from your vehicle’s electrical outlets, solar panels, or both. They’re typically offer a lower upfront cost, and easy portability. They may not prove as reliable or convenient as a dual battery system, especially in extreme temperatures, and they take up space inside your vehicle.
Installing a dual battery also typically requires a DC to DC charger, a battery controller, a custom housing for all that and the battery, and an inverter. Auxiliary batteries typically include all of that inside a single housing.
Calculating Your Needs
How large a battery do you need? How many solar panels? How powerful an inverter?
The easy way to figure all that out is to add up your power needs, then work backwards. Devices intended to be used with mobile charging solutions like a 12V fridge-freezers should provide you with a robust spec sheet. Figuring out how much power your camper lights, or other less sophisticated devices need can prove more complicated.
If you already have, or can borrow a portable battery with a detailed power display, that can be one of the easiest ways to calculate the total draw is simply to plug all your stuff in, switch it on, and look at the numbers on the screen. Whether it lists watts, amps, or both, just multiply that number times the hours you want to run that stuff for, then go with a battery with adequate capacity. If you need to convert between watts and amps, there’s online calculators that make that incredibly simple.
You’re probably going to find those capacities a little disappointing. A 75-liter 12V fridge-freezer will draw about two amps each hour when set to normal temperatures, in warm weather. Plug that into a 40 amp-hour battery, and you’ve got less than a full day of battery capacity. You either need a larger battery, or the ability to charge it in the field.
Most of us aren’t going to want to run our trucks all day when parked, enter solar panels.
Solar panel output is listed in Watts. But, that output is calculated in ideal conditions, at the equator, where the sun in strongest. In the real world, factors like season, latitude, cloud cover, panel orientation, and shade created by terrain and trees, limit performance. Assuming 5 hours per-day of direct sunlight and 75 percent panel efficiency can get you into a safe ballpark of average output for most summer days in the contiguous United States. A 100 Watt panel can reasonably be relied on to produce 375 Watts per-day, with obvious caveats around.
Let’s go back to the power draw of 75-liter 12V fridge-freezer. Converting its 2 amp draw to Watts gives us 24 Watts per-hour. That 100 Watt panel will not produce enough power to offset the a single-day’s draw from the fridge. It will slow the rate at which the battery capacity is depleted, but not entirely offset it. Adding a second 100 Watt panel will be needed to keep the battery topped up, and the fridge running indefinitely.
Installation and Wiring
Solar panels can easily be added to the roof of your GFC using our solar panel trays mounted between Beef Racks. The trays bolt to the bottom of those racks and carry the panels lower than the top of the rack, so you can still use the racks to transport other stuff. Note that any shadow cast by cargo will limit the output of your panels, and that some cheaper panels are unable to generate power from entire rows of power cells if even one of those cells is occluded.
From there, you’ll need to run wires to the location of the battery you’re trying to charge, and fit them with an appropriate connector compatible with that battery or its charge controller. Consult the GFC owners forums for examples and ideas, or ask the shop where you had your GFC installed for help.
You can also buy portable solar panels. Those may prove convenient in camp, but you’ll have to make room to carry them, take time to set them up, then re-orient them throughout the day.
Product Considerations
One of the chief benefits of a dual battery system is that you’ll be able to run long-lasting, high quality, reliable batteries designed to withstand extreme temperatures. While incredibly convenient, most auxiliary batteries are produced in the far east, and tend to be of poor quality. Check any battery’s warranty and return policies before buying, and consider those the primary value proposition while achieving the necessary capacity for your power needs.
Solar panels are another class of products where quality varies widely, and may impact both their output and longevity. Cheaper solar panels don’t tend to perform as efficiently as their marketing might claim, and then lose that efficiency over time.
Put two products of low quality together, and your odds of failure are doubled. The shop where you had your GFC installed will be able to point you in the direction of quality batteries and panels, help determine the capacity and output levels appropriate for your needs, and will know the best practices for installing solar panels, dual battery systems, or both.