Many of our electronic gizmos plug into a common 120 VAC outlet. Most of the time, you don’t need to know anything else: things just work. But, living in a van is not “most of the time.”
The typical electrical system in a van, RV, or boat is nominally 12 VDC (often closer to 13.8 VDC). To get 120 VAC, you need an inverter. This conversion process is anywhere from 50% – 95% efficient, depending on the quality of the inverter, input voltage, and load. Take a look at the manual for an inverter to learn about efficiency. You should find a curve showing efficiency vs. load. Lazy manufacturers will just give you a single best-case efficiency number. Cheap inverters often don’t list efficiency, and, in these cases, I assume the worst. In any case, using an inverter wastes 5% – 50% of your precious, limited power.
To rub salt in this wound, consider that most small electronics, including computers, LCD monitors, and phones, internally operate off low voltage DC, often between 3.3 VDC – 24 VDC. So, these gizmos contain an internal AC-DC converter or an external AC-DC “brick”, which are between 20% – 90% efficient. You waste power converting from low-voltage DC to 120 VAC. Then, you waste more power converting from 120 VAC to low-voltage DC. And, you waste space for both the inverter and possibly one power brick for every gizmo.
What can you do? How do you eliminate this waste? In some cases, you can connect a gizmo directly to the 12 VDC system bypassing the inverter and power brick. In other cases, you can connect your gizmo via a DC-DC converter, which regulates the voltage to whatever the gizmo requires.
- Make sure your gizmo has an external power brick. If the 120 VAC power cord connects directly to the device, then you’re out of luck, short of hacking up the internals of the device. Shop around for devices with external power bricks.
- Figure out the power requirements. Typically, there’s a label on the device listing input voltage or voltage range, peak current, and AC or DC. You might also see peak power instead of current. Divide power by voltage to get current. If you can’t find the power requirements printed on the device, look on the power brick or in the manual. If your device requires AC rather than DC, it’s probably not worth the effort to eliminate the inverter and power brick. I’ll assume the device requires DC power, which is the case for most small electronics.
- Understand that your vehicle’s 12 VDC system may range from 11 VDC – 15 VDC, depending on temperature and battery charging. If you gizmo accepts this voltage range, your life is easy. Along with a suitably sized fuse and wire, you may connect directly to your vehicle’s electrical system.
- If your device needs a voltage within this range but does not specify that the entire voltage range is acceptable or if your device needs a voltage outside this range, you cannot connect directly. You need a DC-DC converter. The Internet is your friend. Jameco Electronics and Digikey sell a huge selection of DC-DC converters. Shop for a converter that accepts 11 VDC – 15 VDC input (or greater range), an output voltage within the range printed on your gizmo, and an output current at least as large as that printed on your gizmo.
Here are a few tips to help with wiring:
- Always use wire rated for at least the maximum current. Better still, make sure the gizmo’s maximum current is no more than 80% of the wire’s rated current, just as a safety margin. There’s no harm in using larger wire than necessary, except for higher cost and more difficult routing.
- Always use a fuse or circuit breaker to match the wire’s current rating.
- Swipe the connector from the device’s original power brick. Most gizmos have a small round power connector of various diameters. Cut off and reuse the original plug. Make sure you get the polarity correct when you rewire the connector.
- Use heat shrink tube and electrical tape to protect connections and bare wire.
- If you need part of your wiring harness to be removable, consider using Anderson PowerPole connectors. They’re easy to assemble and durable.
Living in a small DC house, I find these changes to reduce wasted power and to reduce piles of power bricks worthwhile and relatively easy. So far, I’ve converted a monitor and modem, and I’ve specifically chosen other items that run directly off 11-15 VDC input.