Im happy to explain pastermil. So first off let’s talk power. Most off-grid electrical systems have a few major components. A device that generates electrical energy, a battery that stores excess electrical energy for later, and a power distribution interface which allows for connecting appliances to the batteries in a safe standardized way.

My particular electric system has a 200w solar panel for power generation, two 20ah lifepo4 batteries for capacitance, and the charge controller acts as a very basic interface with two usba slots and a car cigarette port.

Now let’s talk about AC and DC appliances. Theres essentially two kinds of electrical power people deal with. The one most people are familiar with is AC power it comes to your home from power plants through power lines and transformer boxes. Its very high voltage so only high power devices like kitchen appliances and washing machines and AC compressors use it directly. It’s why american homes have a special circuit for 240v.

Besides that, most consumer devices dont actually use AC power, it uses DC power. Desktop computer power supplies, Laptops, monitors, vaporizers, led lights, DVD players, audio speakers, everything that can powered by usb and batteries. Everything that has barrel plug inputs and power bricks.

If you look closely on the power bricks that plug into your wall, you’ll see that it has an input and output voltage rating. The input tends to be 120vac here in america 240v over the pond, and the output tends to be either 5v, 9v, 12v, 15v or 20v DC usually up to 5 amps.

Laptops and computer monitors tend to be 20v, fast charging smart phones and the Nintendo switch docked are 15v, very bright home LED lights can be bought that are powered at 12v directly, the ps2 could be powered with 9v, and most usb devices charge at standard 5v. Would you like to guess which voltage profiles the USBC-PD protocol is capable of? Its all of them.

Now let’s discuss energy efficiency. Converting from AC to DC eats up some of your power. So does converting from DC to AC. And its not small losses either, each time you convert its about a 10-15% loss in efficency.

This loss through conversion doesn’t matter when you pay cents on a kilowatt and have unlimited power at the tap. It adds up very quickly when you have a limited power supply.

Let’s say I want to power a laptop on my offgrid DC system, and I only know how to power it with the AC cable that it came with. I would need to

Add these up and you get 30-40% of your power eaten up needlessly double converting the power. Wouldnt it be really nice if we could convert the battery DC voltage directly to the appliance DC voltage without those power hungry inverters and transformers?

Thats where dc to dc converters come in. They still introduce efficency loss but way way less only 10% total. A USBC-pd 100w car charger that plugs into a cigarette port can convert a batteries 12vDC into 5v, 9v, 12v 15v, and 20v dynamically depending on the device.

Do you know how magical that is? How much trouble that saves when it comes to mcguyvering a DC appliance that only came with AC cable to supply proper power directly? All I need is a 10$ cable to manually select the voltage needed and some barrel plug adapter bits to fit into the appliance.