RV Converters and Inverters

What's the difference between converters and inverters and why should you care?  You may hear fellow RVers using these terms and often they may be using them interchangeably and incorrectly.  Why should you care?  Most RVs are equipped with a converter and many also have an inverter.  You need to know what you have and how to use each one properly to get the most out of your equipment and avoid depleting your batteries.  Both have to do with managing the coach electrical system.  Each device provides a valuable and distinct function for your RV.  So, what is the difference and why does it matter?   Converters and inverters actually perform opposite functions.

A converter converts 120-volt AC power to 12-volt DC power.  This powers the 12-volt lights and appliances in an RV when it is connected to shore power or when the generator is running instead of running down the batteries.   The converter usually includes or is located near the fuse or breaker panel.  Converters usually include a battery-charging circuit to recharge coach batteries whenever 120-volt power is available.  However, these are usually intended only for light charging to maintain batteries when the coach is in storage and they're not very good at re-charging depleted batteries.  If your converter doesn't include a good multi-stage charger, you may want to add an automatic, automotive battery charger.  This solution is usually easier, less expensive, and more effective than upgrading the internal charger in a converter.   And I confirmed that with an engineer at one of the converter manufacturers.  I had called because the charging circuit on my converter gone bad and was putting out about 18 volts and boiling my batteries.  Rather than repair or upgrade the converter, the engineer suggested I disable the charging circuit (and instructed me how to do it) and install an automatic car battery charger.  It worked very well for a long time -- until I upgraded the whole system to an Intellipower converter with Charge Wizard from Progressive Dynamics.  Still, the fastest way to recharge your batteries will likely be running your vehicle engine.  The vehicle alternator has a higher, regulated output and will usually re-charge batteries faster and safer than any converter or plug-in charger.  Gas consumption with the engine at idle will probably be about the same as running the on board generator, so there is no obvious fuel savings to using the generator, even though it has a smaller engine.  Running the vehicle at or slightly above idle should be sufficient to charge your batteries.  Another advantage to running the vehicle engine is that it will recharge the starting battery as well as the house batteries.  Replacing an existing converter may be as simple as unplugging and disconnecting the old one and connecting and plugging in the new one.  However, if the old converter is an integral part of the power panel that includes the 120 volt breakers, the installation will be more difficult and complicated.  You will need to remove all the components of the old converter without messing up the 120 volt power panel, then connect the input to a 120 volt source and the output of new converter to the supply side of the 12-volt fuse panel.

An inverter does just the opposite from a converter: it changes 12-volt DC power from your batteries into 120-volt AC power to run AC appliances.  Inverters come in a variety of sizes and with a wide range of effectiveness.  Cheap inverters create a "modified sine wave" AC power.   These may be OK for some AC appliances, but any sensitive electronics will require a "true sine wave" output to function properly.  Inverters may be small and inexpensive and plug into a 12-volt cigarette lighter style receptacle.  These may be adequate to power small appliances, even a laptop computer, and charge cell phones (if the output is "clean" enough).  I have found my cell phones charge faster using a 120 volt charger plugged into an inverter plugged into the cigarette lighter than they do using a 12-volt car charger directly .   Larger units are hard wired into the battery bank and may power several outlets or circuits in the RV.   Anytime you're using an inverter, remember the 120-volt wattage draw will be 10 times the same wattage draw for 12-volt appliances of similar amperage.  What does that mean to you?  It means your batteries will run down at least 10 times as fast running a 120-volt 10-amp appliance as they will running a 12-volt 10-amp appliance.  Appliances are usually rated in watts.  For those of you who may not remember your high school physics, watts = amps * volts.   A 10-amp, 12-volt appliance uses 120 watts.   A 10-amp, 120-volt appliances uses 1200 watts. Batteries are often rated in amp-hours.  That determines the number of hours they can deliver 1 amp at 12-volts.  That means a 12-volt deep cycle RV battery bank with a rating of 850 amp-hours, theoretically, could run a 1-amp load for 850 hours or a 10-amp load for 85 hours or an 850 amp load for 1 hour.  That same battery powering 120-volt appliances through an inverter would run a 10-amp 120-volt load for only 8.5 hours or less.   Inverters are quiet so they can be used to power TVs and other entertainment systems past allowable generator hours -- IF you have a large enough battery bank.  Inverters are not typically used to run the electric side of a refrigerator (although some monster luxury motorhomes with really huge battery banks may have that capability).  They are best used for short periods of time for discreet functions, like running the microwave for a few minutes or making coffee. If you have sufficient battery capacity, they can be used effectively to run TVs and entertainment systems during "quiet hours".   They can be used to power electric lights but since incandescent lights are about 10% efficient as lights and 90% efficient as heaters, it is not an efficient use of battery power.   Just using the regular 12-volt lights would be more efficient since there is some loss of power in changing 12-volt DC to 120-volt AC in the inverter.  Or, better yet, use gas or battery powered portable lanterns and save your batteries altogether.  If you install an inverter be sure to use the proper gauge wiring for both connections to the battery bank.  The higher the converter output, the bigger wire you will need.  A handy trick for connecting a converter is to buy a set of heavy duty automotive battery jumper cables and cut the ends off.  Add terminals to the battery ends.  Large inverters usually have screw connectors that clamp down on the bare conductor itself.  If you connect the inverter output to outlets in your RV, be sure the wiring is of the proper size.

Some inverter units include a powerful multi-stage battery charger.  Battery charging is NOT a direct function of an inverter, but is rather an additional function that is sometimes included in a unit to be able to recharge the batteries that are needed to power the inverter whenever there is shore or generator power available.   Small, plug-in units won't have a battery charging function. Large, permanently installed units might.

Installation.   Both converters and inverters generate heat and need to be installed in an area with adequate ventilation.  They may also contain relays that can spark so make sure they aren't in the same compartment with flammable liquids or gasses.  Off-gassing from charging lead-acid batteries creates hydrogen gas,  which is highly flammable.  That is what caused the famous Hindenburg disaster.  They also draw a lot of current so make sure you connect them with adequate wiring.  My son, who is an electrician, suggested using a set of #6 gauge battery jumper cables to connect our 2500 watt inverter.  The jumper cables are the right gauge and the bonded wiring makes running the wires and identifying the proper polarity for the connections much easier.   Be aware that there are cheap jumper cables that are much smaller than #6 wires, so make sure you get the right ones.

Inverter use.  Always make sure inverter is disconnected when using your generator or shore power.  OEM installations will have a switch that only connect the inverter or the power from the 120-volt panel.  If the inverter is connected along with another power source it can burn out the inverter.

Maintenance.  Converters and inverters require little maintenance.   There are usually no user-servicable internal parts.  They both require adequate ventilation to avoid over-heating so don't use their cabinets for storage and keep all vents clear and occasionally remove any accumulated dust and lint from the cooling fins and vents.  It is a good idea to periodically check all the electrical connections.   Road vibration may cause connections to loosen.   Loose connections may cause arcing which will result in poor or intermittent performance and could cause a fire.  With proper care and usage both converters and inverters should last many years in normal service.  Output circuits from a convertor are usually distributed through a fuse panel.   If any circuit stops working, be sure to check to see that the fuse is securely in place and has not been blown.

Converter, inverter is definitely NOT like Po-tay-to, po-tah-to, or even Po-tay-to, To-may-to; the difference is more like the difference between dogs and cats.