Part 2 Electrical AC/DC
When you’re planning on living off grid one of the most important systems in your conversion is the electrical system. What type do you choose, batteries and how many, solar and how many panels, charge controllers, then you have to pick a brand. With all the false information on the internet you still have to decide what’s true and what’s just internet. I have had so many people bring me buses they converted and ask me to “fix” them because they listened to some you tube internet person that doesn’t have a clue what they are doing. So lets break. This down. First I’m not paid by any company to endorse their brand. I use the brand i use because i have tested them and i know they work in my conversions. We just finished bus build 217 as I’m writing this article. So I have quiet a bit of experience in converting both OTR buses and school buses.
What we use is as much 12 VDC as possible so we use dc electric refrigerators, LED lights
DC-propane appliances. Our stove oven combinations use propane with a 12 VDC ignition, water heater/boilers use 12 VDC and propane. Our in house built Pellet/wood hybrid heating stoves have a 12 VDC auger to feed pellets and we use 12 VDC fans and pumps for the hydraulic systems. Our washer and hydronic dryers use 120 VAC for the agitation and tumbler. Our washer will wash a load of 8 pairs of jeans on as little as 500 watts. The clothes dryer uses 120 VAC to turn the tumbler and hydronic heat to dry. The dryer uses 100 watts. The dry can also use propane if for some reason hydronic heat isn’t available. The microwave if the coach has one is also 120 VAC. The purpose in using as much 12 VDC as possible is to keep the power lose of converting to AC as low as possible. A good example of this is to run a 120 volt AC refrigerator with a inverter that draws 7 amps AC at 120 volts will draw 49 DC amps from the battery with a Xantrex 458 inverter, the inverter DC draw will very depending on brand and what dc voltage it uses. But a refrigerator running on 12 VDC power will draw 5.5 for the brand we use. So you save 43.5 amps per hour using 12 VDC over inverting to AC power. Some may argue that if you use a 48 VDC inverter then you’re more efficient and it does use less DC amps but still more than double of what the DC refrigerator uses. So by not having to convert to AC except for a couple of loads you can really stretch your power out. So in the last build we call “BIg Dog” I have 1800 watts solar , 1000 watts wind and a hydro generator thats 550 watts. So most full sun mornings will have my batteries from 12.1 VDC morning voltage after the night to charged at 14.1 in two hours. We use thick plate lead/carbon AMG batteries. And I know some
are saying why not lithium? So here are the numbers. I can discharge to 50% on my batteries without worrying about sulfating the plates. I have 200 amp hours per battery, with two battles in each bus. So a total of 400 amp hours. To get 400 amp hours in lithium it would cost $3500 with the cheapest battles I know of. The batteries I use cost me $750 so for the money I’ll stick with my AGM carbon plate batteries. The only down side is weight they are heavy. But weigh isn’t ne’er as fuel robbing as aerodynamics.
So what we do when determining what the electrical system will be is total the amps and add 40% for cloudy and windless days to be safe. This gives us a base line to work from.
The DC side of things we use a AC/DC master panel that has monitoring capabilities as well as circuit protection.
We have DC to DC chargers to tie the coach batteries into the system for charge when the coach batteries get to a preset voltage the solar will charge them back to a preset voltage and then disconnect from the coach batteries. We do the same thing for the generator start battery.
Use like to use USB chargers all over the bus to keep the life saving personal devices charged.
Some interesting facts about the Big Dog bus is that we spent the entire winter in Wickenburg Arizona we used around a 1000 watts in 24 hours thats it. All living systems including TV, satellite, refrigeration, lighting, appliances and water systems all operating the batteries never dropped below 12.0 between wind and solar they stayed charged no matter how much we used the system. So to keep your system efficient. Use as much 12VDC as possible.
One thing to always remember is to clean your panels often, what we do to make this easier is we have a facet on the roof. I have a quick connect on the facet to plug a coiled water hose into the facet, then I can wash the panels with water from the water system. Makes cleaning panels very easy as I don’t have to climb the ladder with anything as everything is on the roof. We have a anti-freeze valve ( this valve automatically dumps the water and shuts off the feed) on the water line that feeds the roof mounted facet just in case it gets freezing one night. So I don’t have to keep a constant eye on the ever changing weather.