Electrical System

Design Parameters

After much research, here is the system we decided upon.

House AC Power

A tip I got from the skoolie.net forums was to use outdoor extension cords for your AC wiring. Automotive applications are supposed to use stranded wire for vibration resistance reasons. Most standard house wiring is done with solid wire. Buying stranded wire is expensive, but buying extension cords and cutting off the ends is very affordable. In North Dakota you can get freeze-proof outdoor extension cords that are 14ga, 2+G conductor. This is perfect for interior AC bus wiring, so that's what I used.

I bought a small power distribution box with conventional circuit breakers, and fed that with an 8/4 SOOW cable that came directly off the inverter output. All A/C power always goes through the inverter.

Battery Bank

Our battery bank this year was 6 T-105s, configured in 3 parallel groups of 2-battery 12volt series strings. The battery wiring is 2/0 pre-made cabling from McMaster Carr, which got a ton of my business while doing the bus conversion. A 3x2 configuration gives us right around 675Ah at 12v. You don't want to discharge your batteries more than 50%, leaving around 330Ah of usable capacity between recharges. 330Ah @ 12v is 3960wh or 3.9kW-H of input battery power. An inverter with 3.9kW-h of batteries can supply about 3.9kW-h of AC power, less some inefficiency factor. Taking 3.9kW-H and thinking in terms of AC appliances, we could run our 1000 watt electric griddle, our 1000(ish) watt microwave, and about 1900 watts of other stuff, continuously, for 1 hour. Then the batteries would be half spent.

In actuality, we couldn't do that for a variety of reasons, one being that the inverter will only put out 2800 watts of AC power, and I've got a 225A fuse on the DC side because I couldn't get 4/0 cabling pre-made. It works great for cooking though -- a microwave uses perhaps 1500w but only for a few minutes. We had fresh eggs, bacon, sausage, pancakes, etc, prepared on the electric griddle, no problem. Running 1000w for 30 minutes of cooking was no trouble.

I think we could actually run air conditioning over-night strictly off of battery power, which is kind of the holy-grail of RV life. Alas, we have no A/C currently :)

Since I installed the batteries in such a way that I couldn't easily water them, I installed Water Miser battery vent caps. These are supposed to do a really good job of containing water that would otherwise be lost to evaporation.