After much research, here is the system we decided upon.
- Summer operation - no heat required
- No generator or propane on board
- Run high-wattage cooking equipment regularly -- griddle, household refrigerator,
full-size microwave, coffee maker, etc
- Run and recharge laptops, cell phones, etc
- Run all user scenarios without access to shore power for 24 hours
- Recharge battery bank from shore power when available, or from engine alternator when underway
- All devices in the bus work identically on / off shore power.
- Magnum Energy MagnaSine 2812 Inverter/Charger.
MS Series Inverters
This inverter/charger has a lot of great features, and if you are doing a low-power-consumption RV, this is
about all you need. Plug your batteries into it, plug your shore power connection into it, and run a big
line to your AC distribution panel. It does the rest. If you want to run a generator, it will start/stop
the generator to top off your batteries.
- Trojan T-105 6v Golf Cart Batteries
- Blue Sea Systems Add-A-Battery". This provides intelligent
battery combining between the house battery bank and the vehicle electrical system. This lets us recharge
the starting batteries while on shore power, and more importantly, it lets us recharge the battery bank
while we're cruising down the highway. Our bus already had a 140A alternator installed, so in a normal day of
driving we'd completely top the battery back off.
- Blue Sea Class-T fuse block. There is more
current and bigger cabling involved here than what you need for welding. RV fires are ugly, so high quality
fusing components are warranted.
- Blue Sea 5026 Fuse Block. For DC distribution
inside the bus, this thing is really slick. I actually bought two, one for the drivers compartment and one for
the house DC wiring.
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.
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
McMaster Carr, which got a ton of my business while doing the bus
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
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.