When on inverter am I using the batteries?

msturtz wrote:

In 99% of the lower end motorhomes the inverters and most combined inverter converters have automatic transfer switches that will select external power when available. This is separate and distinct from the generator automatic transfer switch. In general there is an automatic transfer switch between shore power and the generator (some coach manufacturers bias the generator power when available) and then power is routed to the inverter incoming AC power supply inputs (not the DC side) if power is present on the incoming AC supply line for the inverter that closes an internal relay which turns off the inverter circuit and disconnects the inverter power circuits from the coach. This means the power provided to those outlets is provided by incoming shore power. There are a few variations that are very uncommon some especially older coaches had designated “inverter only” outlets that were only powered by the inverter. This method is very common in the towable market because they generally don’t have onboard generators. Another uncommon system is to have a phase locked paralleled inverter system. These combination inverter converters are generally referred to as “hybrid” inverter systems that will sync their line phase to the incoming AC if available. The inverter and associated EMS system manage the demand by load shedding. This means the inverter may come online and start powering certain circuits if the instant demand exceeds the available AC power supplied. For example, if a coach has 3 15K BTU AC units and the customer starts running the microwave the EMS system may direct the hybrid inverter to start powering the microwave by drawing power from the batteries at the same time it commands the battery charger (also called a converter) to stop charging. This is especially useful if the coach is plugged into a 15, 20, or 30 AMP shore power connection and 50 AMP split phase power is not available. These systems are generally only available on very high end coaches. It is also important to note that most inverters on most coaches provide square wave otherwise known as modified sine wave power not pure sinewave power. Many things do not work well with MSW power.

The problem is with your original comment, you made the assumption that is was a factory installed inverter/charger and had the transfer option.

His comment about plugging into the "inverter outlet" under the fridge initially supported the idea that it might be a stand alone unit.

For all we know, a prior owner installed a stand alone inverter (quite common), so it could easily have lead him to an incorrect assumption.

I was just clarifying for others who might take your blanket response to heart and have issues.