Last January we installed a “whole house” inverter by Xantrex, and it really changed the way we live when we are boondocking. The inverter, a very full-featured 2,000 watt “pure sine” model, is so powerful that it can run our microwave oven, or a toaster or other typical appliance. Most of the time we use it to watch movies on the big screen during dark lonely nights out in the southwester desert somewhere.

(I’ve been reminded by an eagle-eyed reader that this Xantrex Freedom HFS is actually a combination inverter/converter.  That means it also charges the batteries of the Airstream when we are plugged in.  But for the purposes of this discussion I’m going to just call it an “inverter” since that’s the function I’m talking about.)

There have been two problems with it, however.  Both of them are the result of how the inverter was installed, rather than the device itself.  The installer decided that rather than putting in an electrical subpanel (I’ll explain in a moment) he would wire the inverter directly to the main electrical bus. This saved him some work but it gave us a headache.

If that’s gibberish to you, let me make it simple.  His way of wiring meant that every AC appliance in the Airstream is connected to the inverter—including the air conditioner and refrigerator.  That’s not great because it means that when we are plugged in to power at a campground with the air conditioner running, and there’s a momentary power loss (or someone unplugs our trailer, which happened this summer), the inverter automatically will try to power everything by itself—which it can’t do.

So instead it goes into overload and shuts off AC power, with an alarm shrieking until someone comes along and resets it. Even if the air conditioner is off and the inverter doesn’t overload we’ll still have a problem because the inverter will provide AC power to the refrigerator.  That means instead of switching automatically to propane, the refrigerator will drain the trailer batteries instead, in just a matter of a few hours.

I realized this not long after the inverter was installed, and worked around the problem all summer by manually shutting down the inverter entirely whenever we were plugged into shore power.  But it was a nuisance, and sometimes I forgot, with predictable consequences.

The bigger problem became apparent in May when we tried to plug into a regular household 15-amp power outlet while “driveway camping” at someone’s house. The Ground Fault Circuit Interrupter (GFCI) in the household outlet tripped instantly. Most outdoor outlets have GFCI built in these days, and so we were unable to get power from the house.

It turns out that the fix for all these issues is to wire the inverter up properly, which I guess should be no surprise.  Xantrex has issued a technical bulletin to explain why our wiring scheme trips GFCIs, and how to do it correctly. It took me quite a while to find the Xantrex bulletin so I’m posting it here for anyone who also has a similar set of problems.

The solution is to install a second electrical breaker panel (called a “subpanel”) to which you wire all the AC-powered devices that the inverter should power. In our case this includes the wall outlets, microwave, and TV.  Things that the inverter should not power, like air conditioner, refrigerator, or electric water heater, stay wired into the main panel.  Then you connect the inverter AC input to the main panel on a separate circuit breaker and connect the inverter AC output to the subpanel.

With this arrangement, everything gets juice when the Airstream is connected to shore power, either from the main panel or the subpanel.  The transfer switch built into the inverter simply passes the AC power it receives through to the subpanel.  When the shore power is removed, the main panel has no power so the air con and fridge don’t run, but the inverter will turn on automatically and supply the subpanel using battery power.  For a bit more detail on this, click here.

Not only does this prevent the problem of the inverter accidentally powering things it shouldn’t, but this arrangement also fixes the electrical quirk that causes GFCI outlets to trip when you plug the trailer into them.

I haven’t gotten around to this project yet but I will later in January.  Once I have the parts in hand it should be a fairly easy fix, since there’s plenty of room in the compartment when I have to work (near the existing breaker panel) and there’s no need to run additional wires.  I’ll document it with photos at that time.  Meanwhile, if anyone else has already done this upgrade I’d be interested to hear from you.