I'll state right up front that I do not believe a 12 VDC electric system is advisable in any but the most basic situations. Basic = a few lights and that's about all. But that is me and I wanted more than a few basic lights. I recognize this is my personal bias.

Note that when designing low voltage circuits it is desirable to keep the voltage drop to 3% or less over the run of the wire when under load.

Also note that standard home 120 VAC switches will fail after a very short time when used on DC circuits.

12 VDC RV microwave. Wow! The smallest microwaves are usually around 600 watts or so. That's cooking power. Most back of the case nameplates on a 600-650 watt m-wave will indicate a draw of about 800 watts at full cooking power. 800 watts / 12 VDC = 88 amps!

That's what the math says, unless there's some kind of magic they've discovered or I don't know about. I am amazed. I must be missing something. But if there was a draw of 66 amps, 12 VDC a person would need #4 AWG wire ti run just under 9 feet and keep the voltage drop at or less than 3%.

If it's the item I saw on a Walmart ad it draws up to 20 amps at 12 volts and the reviews I read are mostly by customers disappointed with the speed; 8 minutes to make 10 oz of cold milk hot. Anyhow, 12 VDC, 20 amps, 3% max drop, #10 AWG wire, maximum length of wire = 7.44 feet. #10 is heavy wire. Solid Romex type is hard to work with.

A 15 watt LED light would be drawing a theoretical 15 / 12 = 1.25 amps. For a 3% max drop that would mean...

2 lights total on circuit, #12 wire, 2.5 amps, a run of 37 feet is okay

3 lights, total on circuit, #12 wire, 3.75 amps, a run of 25 feet is okay

4 lights, total on circuit, #12 wire, 5 amps, a run of 19 feet is okay.

7 amps, like the max on the Shurflo Classic pump:

#12 3% drop 14 feet 5% drop 22 feet

#10 3% drop 22 feet 5% drop 35 feet

#8 3% drop 34 feet 5% drop 56 feet

How many lumens does the 15 watt LED put out? The 26 watt CFL's I have and like as they make it easy for me to read a book are rated about 1600.

Links for those 12 VDC items would be nice. Maybe some of them would sway my personal bias.