The concept is simple: use 4-Way Round Trailer Connectors with 2/3/4 conductor cables. A standard-fare AC cable will have three conductors, which are typically used for hot, common & ground. We can use those same three wires for 24VDC nominal, 12VDC nominal & ground. Of course, the AC cable must have both stock connectors removed before use as a DC cable.

Note the use of the word nominal. A 12VDC system may exceed 14 volts while charging. A 24VDC system may exceed 28 volts while charging. Both may sink lower than their nominal voltage. Most 12VDC & 24VDC devices include circuitry to tolerate such fluctuations. This spec is designed to support those two systems without adding any additional circuitry. If a given device supports either 12 or 24VDC, it should be wired up to use the 24VDC nominal contact.

Why 4-Way Round Trailer Connectors? They're not really used for anything anymore, they're tough & they're designed for low-voltage power applications. Most older cars & trailers have had their 4-Way Round connectors replaced with 4-Way Flat or 7-Way Round connectors. You can still get them at most auto parts stores. 4-Way Round Sockets are almost always panel-mount & have a spring-loaded cover to help reduce risk of corrosion. 4-Way Round Connectors rarely require solder. There are many other great options, but for now this project will only focus on 4-Way Round Connectors.

In the coming months I'll be documenting installation examples. In-wall power outlets & bigger devices will feature panel-mount sockets. Smaller devices & extension cords will feature plugs.