Lazy Daze Owners' Group

A few of us have installed (or have had installed) whole-house inverter systems. It's a major project.

First, as Jota pointed out, the factory standard (225 amp-hour) batteries are insufficient to power the microwave oven for a useful length of time, so batteries will need to be upgraded to at least 400 or more amp-hours. Also, lead-acid batteries, including AGMs, are poorly suited to massive current drains, so LiFePO4 batteries would be a much better way to go.

How massive? Your 1,000 watt rated microwave oven draws about 1,500 watts when operating, so a 2,000 W inverter would be needed. That's 12.5 amps of 120 VAC. Powering that microwave through an inverter with 90% efficiency, you'd be drawing about 140 amps at 12 V from your batteries. And in fact, that's what I saw when running my Lazy Daze's microwave from its whole-house inverter.

Bear in mind that you also need a way to replace the power you took out of your batteries. I had 600 watts of solar panels, but I had to watch my charge level closely... or run my generator to recharge.

If you were to do this kind of whole-house installation, you'd want to mount your batteries as close to the inverter as possible, to minimize voltage drop and hence wasted power. In my midbath, I put two AGM batteries in the regular outside battery compartment, and three more under the refrigerator, about a foot away. The inverter was mounted in the outside compartment that's below the battery compartment. All batteries were wired in parallel, and the total 12 V cable run (for each leg) was about six feet.

With that setup, 2/0 cable (AWG 00) would have been adequate, yielding a 1.4% voltage drop (as calculated with this voltage drop table). I went overboard and used 4/0, but I wouldn't do that again.

I had 500 amp-hours of AGM batteries, but even running my microwave oven for two minutes was a considerable strain on them. And at 75 pounds per battery, that's a lot of lead--hundreds of pounds that could otherwise be used for your possessions. (500 amp-hours of LiFePO4 batteries would have performed better and weighed less, but that would cost almost $5,000 for the batteries alone.) The total cost of my AGM-battery-plus-inverter installation was several thousand dollars.

So yes, it can be done, but it's a major and expensive undertaking. It's a lot more practical to learn to cook with the propane stove. In fact, after years of using my Lazy Daze's microwave oven (and often needing to run the generator to recharge the batteries), with my last two RVs I removed the factory-installed microwave oven in order to free up a large storage space. I just use the propane stove.

While it is convenient  to have 120 VAC available at all outlets when not plugged in and not running the generator, there aren't many things nowadays that can't be bought in 12 VDC versions, or adapted to run on 12 VDC with small (less than 200 watt) plug-in inverters such as this 75 W model or this 150 W model. I have 12 V power adapters for my MacBook laptop, my Ryobi power tool batteries, and most things I need to power.

"I can run the microwave from a Samlex 1500 watt inverter fed by 400 amp hours of lithium batteries with 4 gauge wire."

Assuming a 6' (one way) cable run, including the interconnects between the batteries, that works out to a 4.3% voltage drop. That doesn't sound like much, but it would bring 12.7 V (a full charge) down to 12.15 V at the inverter inputs, and that's cutting it pretty close.

Aside from that, the standard ABYC ampacity table rates #4 wire at a maximum of 125 amps, which is well below the 140 amps the inverter will need to power that microwave oven.

"I use it to run heated mattress pads overnight instead of the furnace."

I've been really happy with my 12V blanket. It draws only 4 amps at 12 V, and it shuts off automatically after either 30 or 45 minutes (settable), which makes it perfect for preheating the bed. (I find that I don't need it once I climb into a warm bed.) No need for 120 V, and no need to pay the price of an inverter's less than 100% efficiency.