​klenger.net

A somewhat new inverter transfer relay on the market is offered by Xantrex.  This relay is suitable for switching a single 15 amp circuit and is designed specifically for inverter applications as described here, and comes in a smaller and easier to install form factor than the traditional 30 amp transfer relays.  From the Xantrex description:  An easy to mount 15A Inline Transfer Relay provides switching between camp-ground and inverter AC source. It comes with a power plug for convenient connection to the inverter GFCI and a hardwire cord for the AC input and output interface.


Notes:

  • The 12 VDC converter must not be powered from the inverter because it will just burn up energy trying to charge the battery while running from the same battery.


  • Unless you are installing a very substantial solar electric system in the RV, you do not want to run high power appliances like the microwave from the inverter. Therefore, those appliances must be isolated from the inverter output, and powered directly from the 115 vac external power bus (see schematic).  A high-power inverter installation is beyond the scope of this page.


  • There is no point in running appliances from the inverter that can be run from propane. Examples are the water heater, refrigerator, and electric space heaters.


  • It is not necessary to connect the 115 vac inverter output through a circuit breaker because modern inverters have overload protection built into them. The inverter will shut down if overloaded.


  • If the inverter is more than 150 watts or so, the inverter should be installed as close to the battery as practical.


  • Connect the inverter to the battery and RV ground with adequate gauge wire. DC current draw by the inverter will be approximately 10 times the AC current it is delivering. A 1000 watt inverter will require 4 – 6 gauge wire.


  • Power from the battery to the inverter must be fused. A 1000 watt inverter can draw close to 100 amps, so do the math when selecting wire gauge and fuse size.  RV batteries can deliver hundreds of amps of current through a 6 gauge wire shorted to ground. 
    Fire or battery explosion could result.


  • The Xantrex XS(RS)-400 inverter shown here has provisions for a remote on-off switch, allowing the inverter to be turned off when not being used. If the inverter you select does not have this option, you can: leave the inverter running all the time as the idle current is less than 300 ma, or install the inverter in a location where you can access the on-off switch on the inverter.  A remote on-off option is always a must-have when I select an inverter.


  • Warning: Installing an AC inverter must be performed carefully as connections are made to high current DC sources and high voltage AC systems. Be sure to comply with all electrical codes and utilize high quality workmanship. If you are not sure if you are qualified to perform this installation, seek professional assistance.

​Click image for PDF drawing

A 115 vac inverter can be permanently installed in an RV, and connected through an automatic change-over relay. The relay is wired in such a way that the normally closed contacts are used for the inverter output, and the normally open contacts are used when external (camp ground or generator) power is available. By connecting this way, inverter power is not used to energize the relay coil, saving battery power. You will most likely need to do some 120 VDC re-wiring in the RV to isolate the wall receptacles that will be powered by the inverter from built-in appliances that require external power.  This discussion assumes an RV with 30 amp electrical service.  An inverter installation as described here can be done on an RV with 50 amp service, but a simple inverter as described here should only be connected to a single 120 VAC outlet circuit from the 50 Amp circuit breaker panel.

Xantrex XS(RS)-400 True Sine Wave Inverter (Example)

RV Inverter Installation