Originally Posted by wrapperman
The biggest issue with the Franks Autotransformer is it robs Peter to pay Paul affect. You may be okay but your neighbors are paying the price. It robs them of amperage and voltage and makes their power issues worse.
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I am not an Electrical Engineer (but did Minor in Physics), but I do know that the pedestal is fused at 30 amps and I can never pull more power than that without tripping the circuit breaker.
What comes into the autotransformer is whatever voltage is available at 30 amps draw maximum.
What the autotransformer does is take some of that 30 amps (about an amp at full boost; leaving 29 amps available to the camper) and convert it to voltage to boost the voltage delivered to the camper. So if you are "stealing" from anyone you are stealing from yourself.
Because you are paying for 30 amp service you are "taking" nothing away from your neighbors and you are only helping yourself.
While you may have less available amperage, your inductive equipment (Air Conditioner and Microwave) needs less amperage to run than trying to operate it at the lower voltage. (Watts=Volts times Amps with Watts fixed in an inductive circuit)
Example: A 12 RA (running amp) at 120 volt air conditioner needs 1440 Watts to run with 120 volts supplied. Since that 1440 Watts is a fixed number in an inductive load; if the voltage drops to 100 volts, the RA increases to 14.4 amps. This can trip the internal thermal protection in the compressor or eventually burn up the compressor motor. We won't even BEGIN to talk about the momentary start up amps required as even at 120 volts that number can exceed 25 amps for a few seconds (not enough; long enough; to trip the air conditioner's 20 amp breaker).
There is benefit to your resistive loads as well (like your water heater as an example). Since the resistance is fixed in a resistive load circuit, the power of the circuit varies by the voltage available.
For example, water heater element with 10 ohms of resistance at 120 volts will use 12 amps (1440 Watts). If the incoming voltage drops to 100 it will drop the amperage used to 10 (1000 Watts effective heating). (V/R=I then P=V*I)
This means your water heater has to stay ON longer to heat the water to the shutoff temperature.