You’ve calculated your solar. Planned your build. Bought some components and made sure it’ll all fit. Now, how does it all go together?
A tip before you begin: If you are new to electricity, then there’s a good chance you’ll make mistakes. It’s much safer and cheaper if those mistakes are on paper (or screen). We find it helpful to draw out what you plan on doing and asking experts on an electrical forum if your plan is correct. Even if you’re experienced it’s not a bad idea to have some more eyes on things. Solarpaneltalk.com and Northern Arizona Wind and Sun forums are full of helpful folks. And now, the warning:
Start With Wire Size
Electricity has to be able to fit in the metal wires you install. Trying to pull too much current through them can reduce their efficiency and even make them burn up.
Wire thickness is determined by
- Wire length
- The amount of Amps passing through it
Wire diameter is commonly measured in AWG, or American Wire Gauge, increments. The smaller the gauge, the larger the diameter of the wire. A 16 AWG wire is tiny compared to a 4 AWG wire.
Below is a chart for picking your minimum wire size. To use the chart:
- Figure out how many amps will pass through the wire.
- Figure out about how far away the component will be from the battery. The length of your circuit is the total length, meaning double the distance between component and battery.
- Choose a wire that can handle the amps with a little buffer (25% or so).
Example: if you have a set of lights that draws 4 Amps and is 7 feet away from your battery: 4A x 1.25 buffer factor= 5A. Go to the 5A column. 7ft x 2 positive and negative circuit= 14ft. Go to the 15ft row. You find that 16AWG is the minimum wire size.
Buy multi stranded wire as it is easier to route and better able to handle the vibrations of a car. Don’t use solid copper household wiring (known as Romex).
A fuse’s primary purpose is to protect the wiring. Most of the rules for fuses derive from this.
- Never install a fuse that is larger than the current rating for the wire. Smaller is fine. Use the same wire chart above above for your maximum fuse size.
- Install the fuse as close to the battery (or “hot” end) as possible. This way if the fuse operates, there will be less wire that can still carry power.
- Fuse all circuits that can have power running through them. A circuit is the full (+) to component to (-) loop. No fuse is needed on the (-) return wire for this type of system.
Fuses come in all shapes and sizes, but functionally they all work the same way. They have a small element in them that will break at as calculated number of amps passes through:
Fuse Blocks and Bus Bars:
To organize power running from your batteries to all of your small electronic accessories you use a fuse block. This way you don’t have to manage a bunch of dangling wires.
A bus bar is essentially a piece of metal to attach all of your return (-) wires to. Many fuse blocks have them built in. This is cleaner for circuits as the power is all passing to the battery at the same point.
Using the vehicle chassis (or not!)
Almost all vehicles on the road have a chassis ground. What this means is that the (-) post on the vehicle battery is connected to metal on the frame, motor, etc. as part of the electrical system. This also means that in vehicle wiring you can feasibly just attach the (-) wire on your components to the metal frame instead of running a long wire back to the bus bar. In theory, you can do this with your van electrical system as well.
This practice is tempting but discouraged for several reasons, especially on newer vehicles:
- Galvanic corrosion. When two different types of metal are touching with electricity passing through them they can corrode. Older vehicles were build using all steel parts bolted together, but newer ones mix in aluminum and other metals and you don’t want electricity passing through.
- Vehicle construction. Many newer vehicles use rubber and plastic pieces to reduce vibration. Because of this, there are less metal surfaces touching between the cab of a van and the battery. Not great for electrical current to pass through.
- Feedback loops. If you have several different lengths of routes of electricity with different resistances they can create feedback loops that can mess with some electronics in your vehicle (and audio equipment).
- It’s easy to avoid. Just running a pair of wires instead of one isn’t much more effort or money as long as you plan for it.
Caveat: you should still ground your battery as well as any metal ground terminals on your electrical parts! You don’t want a full floating system as that gets more complicated. Most big items such as inverters and refrigerators have a (+), and (-) and a ground terminal. The ground terminal is usually just a metal thread with a nut on it and should be attached with a wire to metal on your frame. “Grounding” your metal components to the chassis is important and we rarely see it properly done in DIY van builds.
Planning your wire routes:
For all of your 12V systems you want as short of a wire as possible. This is even more true for your high current parts to stay efficient. You want your batteries close to your charge controller, which should be close to your inverter, etc.
We like putting in wiring on top of insulation and flooring so that you don’t have to dig up too many things if it goes wrong. For the ceiling you might run wires above paneling for the lights. For the major planners out there, we’ve seen people run PVC pipes through the walls to be able to add or troubleshoot wires!
Any wiring coming from your inverter can be quite long without any efficiency loss, so put it close to your battery with extensions coming from it.
Terminals and Crimping
For any wire thicker than 8 AWG it’s recommended to buy wire with terminals pre-installed or have them installed at a battery store. It takes an additional special crimper tool to apply enough pressure to attach larger terminals.
Make sure to use a connector that is appropriate for the wire size. They are usually labeled.
When attaching cables to your battery or frame, you want the electricity to flow through as few of surfaces as possible. This means that you don’t want to sandwich any washers between the connecting surfaces (but above them is fine).
Wire connecting order:
- When wiring solar panels, always connect the panels to the system at the very end and disconnect them first. You don’t want that voltage connected to a charge controller with nowhere to go.
- After the above tip, it’s a good habit to disconnect the negative (black) battery terminal before working on electrical systems. The order of assembly should be: 1) Connect all system wires 2) Connect negative battery terminal. 3) Connect solar panels to charge controller. Disassembly is in reverse of this.
- Get a Digital Multi Meter (DMM). This is critical for anyone doing electrical work as well as troubleshooting many electrical issues. For basic wiring you don’t to spend more than $20 like this Craftsman DMM to get the job done.
- Use dielectric grease on your connections. This is used to keep bare metal connections from corroding. Vaseline works for this as well if you already have some.
- Get a variety of fuse sizes here
- Wiring is the cheapest if you buy directly from a hardware store so that is what we recommend