An RV converter and inverter are named almost identically and do opposite things. A converter takes alternating current from shore power or a generator and produces direct current to run the coach’s lights, pumps and fans and to charge the battery. An inverter takes direct current from the battery and produces alternating current so household appliances work without shore power. Confusing the two leads to some memorably frustrating troubleshooting.
What the converter is doing all the time you are plugged in
Most of an RV’s everyday systems run on direct current: interior lighting, the water pump, furnace blower and ignition, vent fans, the refrigerator’s control board and the propane detector. When you connect to shore power, the converter supplies all of that and simultaneously charges the house battery. That is why a coach plugged in with a dead battery still works, and why a converter failure produces the confusing symptom of a coach that seems fine on battery but dies after a day at a campground with everything connected. This is also why a coach with a failed converter still lights up briefly on battery before going dark, which misleads people into blaming the battery.
What the inverter is doing when you are not
An inverter runs the other direction, drawing heavily from the battery to produce household voltage for outlets, a microwave or a television. Because it is converting stored energy, it consumes battery capacity quickly, and because conversion has losses, more energy leaves the battery than reaches the appliance. Inverters also draw a standby current simply by being switched on with nothing connected, which over a weekend can be a meaningful drain. Many installations feed only selected outlets from the inverter rather than the whole coach, which is deliberate. Pure sine wave output matters for some appliances and electronics, while modified sine units are cheaper and less universally compatible.
Why a converter-charger is not necessarily a good charger
Older converters were simple supplies that held a single voltage regardless of what the battery needed, which meant chronic overcharging on long hookups and chronic undercharging in short ones. Modern units are multi-stage chargers with bulk, absorption and float behavior, and better ones allow the charging profile to be set for the battery chemistry installed. If a coach has been upgraded to lithium or absorbed glass mat batteries, the converter is one of the components that must be confirmed suitable or replaced, because the original may have no appropriate profile at all. Some units also allow the charging current to be limited, which is useful when running from a generator with modest capacity.
Combined units and transfer behavior
An inverter-charger packages both functions and adds an automatic transfer switch, so the coach runs from shore power when connected and from the battery when not, switching over without intervention. That convenience introduces the same neutral-to-ground bonding question that boats face: the bond must exist at exactly one point for whichever source is active, and the transfer arrangement has to handle it. It is not a detail to improvise. Follow the manufacturer’s installation instructions and applicable requirements rather than assuming a household approach translates. An inverter feeding the whole coach can also backfeed the converter, which then tries to charge the battery from the inverter’s own output.
Sizing both to the actual loads
Converter output should comfortably cover the coach’s direct current loads plus a sensible charging current for the battery bank, otherwise the battery charges only when everything else is off. Inverter size should reflect the largest appliance you genuinely intend to run and its surge demand, since motors and compressors draw far more at startup than while running. Equally important is the cable between the battery and the inverter, which carries very large current at low voltage and must be short, generously sized and fused close to the battery. Ventilation around both units matters as well, since each dissipates heat in proportion to what it is converting.
What to check before you act
- Confirm the converter’s charging profile suits your battery chemistry.
- Account for inverter standby draw when leaving it switched on.
- Size inverter cabling for the real current and fuse it near the battery.
- Verify neutral-to-ground bonding is correct for each source in a transfer setup.
Common questions
Can an inverter charge my RV battery?
A plain inverter cannot; it only draws from the battery. An inverter-charger includes a charging function, but that is a separate circuit inside the same box.
Why does my battery go flat while plugged in?
Commonly a failed or unsuitable converter. If it is not charging, the coach runs the battery down even though shore power is connected.
The practical takeaway
Keep the direction straight: converter in, inverter out. Verify the converter actually charges and that its profile matches your batteries, size the inverter and its cabling for real surge loads, and treat neutral bonding in any transfer arrangement as a matter for the manufacturer’s instructions.
References and further reading
- Department of Energy: estimating the energy appliances actually consume
- NFPA: code treatment of separately derived systems, bonding and grounding
- OSHA: wiring design, protection and grounding requirements
Numerical scenarios are illustrative unless identified otherwise. Follow the exact product instructions; component ratings and local installation requirements can differ.
