Air conditioners put a load on electrical systems. That can mean voltage drops which are not good for motors. There are a number of devices designed for RV’s that will compensate for voltage drops. They are usually an autoformer controlled by a voltage sensing circuit that switches in a 10% voltage boost when the park voltage drops to under 110v. The autoformer windings also provide some surge protection and there may be over and under voltage shutdown circuits as well as indicator lights for common power problems.
The best known are the Hughes models and the Franks’s. Less well known are the TRC Surge Guard and the Dynamo. Frank’s autoformer is a two step design for 8% and 16% boost while the others are usually single step 10% boost devices.
The basic 3600 watt unit for 30 amp 110v trailer type service runs about $400 and weighs about 14 pounds. The 50 amp 220v version runs about twice the weight and price.
There is a myth that these pull excess power from the park power grid. While the autoformers are not 100% efficient, they do not consume much power in themselves and their voltage compensation will likely increase the efficiency of air conditioners in the RV. There is little net effect in actual power usage with a voltage compensator.
What will happen, though, is that the upstream current will be higher than that provided to the RV. That is because power is the product of voltage and current. The voltage compensator increases voltage which means it decreases current to meet the power needs of the RV. What that means is that the circuit breakers on the pedestal the voltage compensator is plugged into will trip at lower power draws. Circuit breakers depend upon current and just assume a nominal voltage.
These voltage compensators tend to be valuable devices outside the RV. That means they are targets for thieves. You can usually install them in an RV compartment to prevent theft or you can chain the handle on the device to the park pedestal.
Another issue that puzzles some folks is whether to put a power conditioner in front of or behind a voltage compensator. It seems like overkill to use both but the likely best choice would be to have the conditioner ahead of the compensator. A ‘whole RV’ conditioner is also usually a rather expensive device and will have indicators for power conditions and faults that might be hidden by the autoformer.
A voltage compensator is one of those things you probably don’t need but the exceptions are likely to be when you really need it. Know your options and always check park power for voltage and correct wiring before connecting your RV.
UPDATE: another one at RV Performance Products – good price and warranty; appears to be the standard item with no special features of any significance. (thanks to snyders27 at Escapees)