fla-gypsy wrote:
My understanding is sensitive appliances should not be operated at outside of +/- 10% of 120 volts. That would put the lower limit at 108 volts. When I have encountered this I switch everything else off or to LP and let the AC have all available power and monitor my voltage meter.
Yes you can run the A/C at 105 volts. And yes when below about 110 volts, switching the refrigerator over to gas will increase the voltage so slightly, and also have 3 less amps being used by the RV. The compressor motor will draw much more amperage at 105 volts than the normal 120 volts. And in reality, the "Nominal" voltage is 115 volts, so +10% is 126.5 volts and - 10% is 103.5 volts. Anything between 103 and 130 volts it will work. But it will work much better over 108 volts with less amp draw, thus less heat in the compressor winding, and the compressor will be happier, it will turn faster and you will have more cooling capacity at 122 volts than at 108 volt.
I built my own 120 to 132 volt transformer with a isolated 12 volt transformer rated at 40 amps (500 watts). Basically you wire the 120 volts to the transformer, then the 12 volt output to the black input wire and the 120 + 12 to the output black wire, carry the neutral through from input to output. With 120 volt input, you get 132 volt output. With 110 input, you get about 121 output. With 100 input, you get a acceptable 110 volt output.
I was in the pits at Bowling Green Raceway, with my brother's 1967 Dragster! It was exciting, but the humidity was around 100% with a slight rain in the air, and 85F out during Father's day weekend. I was plugged into a 20 amp receptacle without any fuses (well I guess the 00 wire on the pole was fused someplace). Many other motorhomes where plugged into the same receptacles. I had to double up, and set my transformer to +24 volts, as the input at the end of 100' of extension cords was less than 100 volts, and I wanted at least 115 for the A/C.
The Hughes Autoformer is the answer that you can use. It will boost the voltage by 3 volts all the time, and when it detects less than 112 volts it will automatically switch to the +13 volt coil, and boost the voltage to an acceptable level. Inside the RV you will enjoy the A/C and not know if it switched or not. The only problem is cost. $300 - $500 depending on the model. Normally because 50 amp parks do not suffer from low voltage, I would only buy a 30 amp model, as that is the likely time you will need it.
I built mine for about $200, the transformers are not cheap. Mine is manually adjusted, not automatic like Hughes.
Fred.
