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I've finally concocted a way to create in-home outlets that provide direct 12 volt DC power to wall outlets. No inverter needed.

Solving the Mystery of Pure DC In-Home Power Jun 25, 2016 4:54am UTC
Over the past months, I've been thinking on and off about a potential way to get 12 volt DC power straight from a solar panel into a wall outlet without needing any inverters.

At it's face, this sounds like a simple problem. Just hook the outlet up to the solar panel, right? Easier said than done. Let me walk through the more detailed implementation and point out a few of the problems along the way.

The recurring theme throughout this write-up will be connectors. Let's start with the solar panel itself. Most off-the-shelf panels are equipped with special interconnects at the ends of their lead wires which are meant to be usable outdoors where they might get wet or dirty.

My cell phone has no such notion of those harsh, harsh conditions. So the solar panel connector (by itself) is not suitable for use with the target devices (cell phones, cameras, Chromecasts, portable speakers, etc...), many of which have a USB connector, but we'll come back to that.

Now let's get a little more involved than directly connecting a solar panel to a target device. After all, this is supposed to be power for a home, not just for a single device at a time.

We'll need batteries.

Big batteries.

We'll need something to control the charging of the batteries,

And we need more solar panels.

Great! So we get a large AGM 12V 250 Ah battery (maybe even a few), we get a charge controller, and we start hooking them together. Wait, this expensive hardware needs some protection. Let's throw in some fuses.

Wait, fuses? DC fuses?
Yes, they do exist. Think of the ones under the hood of a car. So called "blade style" fuses.

Okay so NOW we hook everything up. And now we have to start making some tough decisions. We've got raw wire coming out of the batteries supplying our 12 volts of power. We need a standard way to connect that to our multitude of devices.

If the end goal didn't stipulate the lack of any power inverters, we'd be pretty much done. Just wire the 12V DC to the inverter, wire the other end to a normal 3 prong outlet, and plug stuff in.

For some devices, this is bound to be the only way to do things. Those devices would be the ones without a "wall wart" as it's called. So simply stated: No wall wart? Use a DC/AC inverter.

But what about all of these devices that do have a wall wart? You know, the big chunky things that get really hot and convert AC to DC. Pretty much every cell phone... well... pretty much every modern electronic device includes one of these. Wouldn't we be effectively taking raw 12V DC power, converting it to 120V AC, and then converting it back to 12V DC?

Yep. Stupid, I know.

So then how do we eliminate the middle man? Well there's some challenges:
1) Some devices charge via USB
2) some charge via DC connector
3) And (worse yet) some use a proprietary connector

There's literally no consistency here. No single standard, like the 120V AC power outlet, that everyone agrees to use.

If we go with USB connectors, we lose out on the other two connector types unless we start splicing wires. Also, when's the last time you've seen a "ready-to-wire" usb "outlet" thingy that doesn't take AC as input? More wire splicing... more... wire... splicing...

If we go with DC connectors, then we have to pick a size (of which there are many), so we lose out on devices that way, and then we also lose out again on USB and proprietary connectors (without some wire splicing). And don't even get me started on differing plug polarity with the DC Connectors... ugh...

Plug option 3 is just dumb, so let's skip that one and move on.

Where do we go from here? What option gives us the most flexibility, doesn't cost a fortune, is reasonably future-proof, and is tried and true?

The epiphany I had was these:

The fact that almost everyone knows exactly what this is at first glance means we're off to a good start. And if you don't, this is a 12V DC socket outlet. Formerly known as a cigarette lighter outlet, but with the rise of portable electronic devices has become less often used for lighting cancer sticks.

As far as limitations, these things are rated for about 10 Amps of current, but that's okay, we can limit that with our blade fuses from before. An added bonus is that many of the plugs that fit into these include their own fuse. We're stuck at 12 volts only, but we can rely on what gets plugged in to manipulate that voltage as it sees fit.

This outlet is compelling because products like this one exist in vast diversity and for relatively cheap prices:

Furthermore, this is not the only type of device available that makes use of a 12V socket outlet. And for the ones that don't (DC connectors and proprietary connectors), you can go to basically and electronics store, like radio shack, and pick up a plug for one of these with lead wires that are ready for solder. The only extra thing you might need is a voltage regulator if your device requires something other than 12V for its input.

So there you have it. This is most likely the solution I'll be going with to build a proof-of-concept on the way towards a house with pure DC outlets direct from a solar panel. Green energy at its finest!
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