Watt Usage for Converter (220 volts to 110; South America)

[rockandroll]

Gents,

I'm headed to the land of 220 volts in the next couple months. I will need a transformer (220 to 110) and am not sure which size (watts) we'll need. I'm aware of the "Watts = Amps x Volts" equation but the 110 vs 220 vs 12 volts is throwing me off.

In 12 volt mode running off the camper battery, we don't (can't) run the camper A/C and the 3-way fridge is run off of propane. We use very little amps. I just don't know how many amps we pull when plugged into shore power (110 volts). Any help with the estimates would be helpful.

I've found [ame="http://www.amazon.com/Power-Bright-VC500W-Voltage-Transformer/dp/B000MX1QXA"]this[/ame] 500 W Power Bright transformer. But does this mean I'll get only 4.5 amps!? (500 watts / 110 volts). I'm sure we're under 15 amps (because we regularly plug into 15 amp outlets, but this would mean a 1,800 watt converter.

The AC is a Carrier Air V (I believe to be ~ 11,000 BTU). The fridge is a Dometic 3 Cu. Ft. 3-Way

 

[cwsqbm]

Watts stay relatively constant. For example, to run a 11,000 BTU Dometic A/C unit would require around 800W, regardless of the supplies voltage - 6.8A at 115V, 3.7A at 220V, (taken from Dometic's website) or 66A at 12V.

For an A/C unit, this makes sense. The only difference between the different A/C units is the type of motor that runs the compressor and fans. The motor has to do the same amount of work to cool the same amount, and work (per unit time) is power, measured here in watts.

If you look around, now you'll see why 2000W inverters or portable generators are popular for people trying to run A/C (and some still have issues starting up, since start-up current is even higher).

 

[rockandroll]

Very helpful! Looks like I'm going to need something in the 1500-2000 watt range. I'll start looking.