The core of the system is an inexpensive single-stage solar charge controller. No, solar is not required.

This kind of controller is used because:

• it is cheap
• it is very compact
• it can prevent overuse of the battery
• it has USB outlets
• it allow panels to be added if desired

Here is how they are wired:

• the SOLAR terminals will be left empty if one has no panels. If you have panels those wires plug in here. A 20A controller has been selected so one could run up to 200w of 12v panels with this setup.
• the BATTERY terminals connect to whatever your battery is: starter battery for single-battery systems, the aux battery for dual-battery systems
• the LOAD terminals are where you take your 12v power from. This is critical because the controller can be configured to turn that circuit off at a predetermined voltage like 12.7v; this is called a Low Voltage Disconnect (LVD). Your battery cannot be drained when used this way.
• the USB output is also controlled by the LVD.

One might use a $10 adapter like this one, cut off the single male plug and insert the wires into the LOAD terminals.¹⁾

Users with more complex power needs might wire a fuse panel to the LOAD terminals and from there to the various loads.

There are three setpoints that need to be configured. Terminology will vary but basically:

• LOAD OFF - the voltage below which the LOAD terminal should be disconnected. 12.7v for example.
• LOAD ON - the voltage at which LOAD terminal power is restored. The battery is assumed to have been charged again, so something like 13.4v is realistic.
• CHARGE OFF - the voltage you want the controller to hold when solar panels are present. When no solar is present this has no effect.

Insert the panel wires into the SOLAR terminals.

For portable panels where you will be plugging/unplugging a lot a quick-disconnect of some kind would be useful. A common solution is to use an MC4-to-SAE adapter on the panel side and a short SAE connector on the controller side. Those willing to drill can install a port to allow plugging in the panel into the body of the vehicle instead of running wires through a window.