Electrical System

The image above (larger version) shows the major concepts of the electrical system I’m planning on building into my RV.

The major goals are:

• Always on 120v power
• Off the grid
• No propane
• Comfortable HVAC System
• Mostly 120v instead of 12v

There’s a whole ton of items in the picture above, and they all serve a purpose.  I’m going to explain what they are and why I chose them in the paragraphs below.  These, of course, are my designs and plans as of today’s date; things can and will change.

The heart of the whole system is the 4000 watt Magnum Hybrid Inverter/Charger.  This might be the single most expensive piece of equipment in the RV, and it’s for good reason.  This powers and controls the entire 120v AC electrical system, and it does so more gracefully than any other inverter or charger I’ve seen yet.

The concept behind the Hybrid inverter is that you can “run larger loads off smaller generators.”  What this actually means is that the unit will very intelligently figure out where power is supposed to go under whatever situation it finds itself.

Let’s say you’re boondocking and running off of batteries alone.  In this mode, the unit simply functions as an inverter.  Easy as can be.

But, let’s say your batteries start running low and it’s time to turn on the generator.  If your generator is only capable of outputting 2000 watts, and you’re running the air conditioning and the fridge and lights and who-knows-what-else, then you might be drawing more than the generator can handle.  The inverter uses the power from the generator plus power from the batteries to keep everything running.  When the demand drops down, then the unit uses some of the generator power to run the house and the excess power to charge the batteries.  It does all of this smoothly, without requiring me to do anything.

Let’s put together another situation: let’s say you’re hooked up to shore power, but it’s a friend’s driveway and you’re running a long extension cord.  You can tell the unit to only draw up to 5 amps (or whatever number you choose), and that way you’re not going to overheat the extension cord nor are you going to blow fuses.  When demand is low, your batteries will be charging.  When demand is higher, the inverter supplements the shore power with battery power to make everything work.

With all of these capabilities, the net result is that power is on, 100% of the time (assuming you have some kind of power source), just like at home.  For me, that’s very important because I expect power to simply be on, all the time.

Because this particular inverter only runs on a 24v battery system, that dictated some of the other decisions in my rig.  The main battery bank is (8) Trojan T-105 batteries running at 6v each.  They’ll be wired in series-parallel to give me a total of 24 volts.  I looked into all the various battery technologies, and these are simply the cheapest per watt-hour, and since I can handle the size and weight, that’s what I’m going with.

Also connected to the batteries is an Outback solar charge controller wrangling the (5) 345-watt solar panels on the roof.  That’s a theoretical 1,725 watts of solar coming in under ideal conditions.  By my calculations, if I’m not using the heat or air conditioning much, that should be sufficient for all of my other daily activities, including taking a shower once a day.

In case the solar panels aren’t bringing in enough power, and I’m not hooked up to shore power somewhere, I’ll have a small inverter-style generator.  It’s important to use this type of inverter, even though they’re more expensive.  They’re much quieter and they produce a true sine-wave output.  Depending on how all the figures and efficiencies work out, one gallon of gas should completely fill up my batteries.  We’ll see how that works out in the real world.

Coming off of the magnificent Magnum Hybrid Inverter is the first 120v circuit breaker box.  This first box will be in the rear area of the RV, the utility area, and will have circuits for the A/C unit, and a few outlets back there.  There will be another huge circuit with some heavy-duty wiring that will lead to the second AC breaker box which will be located somewhere in the kitchen area.  I haven’t quite nailed down its placement yet.

The second breaker box will have a bunch of breakers for pretty much everything else in the RV.  I decided to go with two breaker boxes because the AC power source was in the rear of the unit and I didn’t want to run multiple romex from the rear of the RV to the front since they’ll need to pass around the soundproof bedroom area, and I don’t see that being an easy task.

A couple other oddities going on in the diagram is the orphaned 12v system on the far left.  Having a 12v battery on board might be a necessity given how many things run on 12v power sources in RVs.  Roof vents for example, seem to be 12v only, so I might have a few 12v lines running around.  There’s a couple different ways to charge the 12v battery, and my preferred way is with a small solar panel I’ll put on the roof.  Since the loads on this battery will be tiny, it’s recharging mechanism can be tiny too.

Full-time RVers might also notice a few other items hooked up to my 120v power that might seem odd: the fridge, water heater, and 2 water pumps.  I don’t like propane systems, of any kind.  They seem far too prone to fires and explosions than I’d like, plus there’s always the health-and-safety warnings to “crack open a window” when doing just about anything with propane.  I personally don’t like running a power source that sucks up the same oxygen I’m using and then could accidentally burn down my house if something jiggles loose out of place.  So, no propane.  Also, “luxury” RVs are going “all-electric” now, so there must be a reason, right?  (Technically, those luxury RVs are electric and diesel, but they like to call themselves all-electric.)

Since there’s no propane, the fridge, range, oven, hot water heater, and HVAC systems are all electric.  That’s one of the reasons for the huge battery bank and solar array.

I had some options with the water pumps, but since I had 120v power very close to where they were going to be located, it made sense to just pick out some 120v water pumps.

When I first start out, I’m likely to skip buying the generator to save on upfront costs.  It’ll be a good test of just how good the rest of the system is, and I really love the idea of not having a generator running.  (Of course, I’m planning on muffling the sound of the generator as much as possible, so even if it is running, it shouldn’t be much of a nuisance anyways.)

The 12v system may or may not be installed, and I might choose to go with a simple battery-tender instead of an extra solar panel and charge controller, but those things will evolve on an as-needed basis.

Speaking of things evolving, it’s very likely that I’ll upgrade the battery system at some point to a giant lithium-ion based system, but that certainly won’t happen immediately.  To meet my electrical needs, a current lithium-ion system (just the batteries) would have cost me $6,000 the last time I checked, and that was just a bit too rich for me right now.  Eventually these batteries will die, and hopefully lithium-ion batteries will be less expensive by then.