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Using an autoformer to compensate for campground low voltage

by Tom Jones

Much has been written in various RV-related forums about autoformers, some of it by uninformed folks &/or with lots of emotion. This article will attempt to explain, in simple terms, what an autoformer is and how/when it could/should be used.

The term autoformer is a blending of the words automatic and transformer, although there are manual versions of this equipment that are also called autoformer, albeit a misnomer.

Power supplied to the pedestal at a campsite might be 20A, 30A or 50A and 120V ac, the same voltage coming into a stick house. The 50A supply is actually two legs of 50A 120V.

Many older campgrounds often have wiring that is too small for the power-hogging RVs we hook up today. The result is that the voltage at the receptacle falls due to the voltage dropped along the campground wiring. If the voltage coming into an RV drops too low, motors such as the ones in air conditioners will draw additional current and could overheat.

There are various numbers touted for the "safe" voltage range, but it is generally accepted that air conditioners should not be run when the voltage is below 108V

A simple solution is to just not run the air conditioner(s) when the voltage drops below "safe" levels. However, not only will this be uncomfortable when it's hot, the voltage can actually rise again due to varying loads on the campground electrical circuits. An alternative is to use an autoformer to automatically step up the voltage in the RV when the pedestal voltage drops and automatically lower the voltage in the RV when the pedestal voltage increases, thereby keeping the voltage within a "safe" range.

Using an autoformer will adjust the voltage in the RV to a normal level and allow you to safely run appliances such as air conditioners which contain electric motors. The net result of using an autoformer will add very little additional load on the campground. This will be of the order of 1A to supply the electronics to automatically sense the voltage and adjust it accordingly.

One drawback - using air conditioning when one wouldn't otherwise - will result in increased load and lower voltage for everyone.

To be completed ...