running an air conditioner on 250 feet of cord

Hi Mex,

A roll of #4 would be verrrrrrrrrrrry pricey now. I know it would be best.

Hi w8,

Thanks for the calculations. 1.6 volts I could live with and no autoformer.

There are other HOTEL loads involved. I was not pleased to have to purchase a 250' roll of 4 gauge wire. Lucky for me it was a different era and surplus wire was available. My connection site was in a boat yard 300' from the ocean. I was working on a 60' Chris Craft and did not have time to experiment. Anything smaller would have screwed me.

I use #10 for 100 ft runs and I have 122V at the end of the cord. In your case, I would use #8 to "make up" for a not so good source.

Using an autoformer epically with a 15 amp outlet will get you the click of darkness or a risk of a house call from a company that still does those (Fire Dept). Hopefully not the house call.

I would run it off a 20 amp outlet with at least 10ga wire if not 8ga wire. Let me do the calculations.
250 foot run is 500 feet round trip. Here are voltage drops figures for 10 amps of load, Most A/C's run a bit more than that.

10GA 1.6 volt (That should do it)
8GA .3141 (even better)
6ga .2 (Still better)

I rounded slightly

Information source Powerstream dot com chart

I did this once in a boatyard in Los Angeles. 235' from the receptacle. I was forced to use FOUR GAUGE coupled to a 30-amp twist lock receptacle*. Even then with the A/C I had to watch voltage carefully. The refrigerator was OK but not with low batteries in addition or a water heater element.

*Mating the two was a real exercise.

Hi smk,

I have considered doing double conversion as well--and replacing the msw inverter with a pure sine wave unit. I'd probably have to bump up to a bigger converter to do it long term.

250', #10 wire, 12 amps, drops about 6.5 volts. If the supply is good you should have no trouble. Voltage booster has its place but will draw more amps to make up for lost voltage. This could have your 12 amp draw too close to 15 amp to avoid tripping a breaker. True 20a should work either way. Continuous wire would be preferred over five EHD extension cords cobbled together.

I do wonder how long your solar/converter/inverter would hold up running the air.

You could consider running 240 volts to a step down transformer to 120 volts.
This would basically cut voltage drop in half.
At the rig end install transformer and distribution panel with 30-TT receptacle.

In my experience, the 15 amp outlet slowly drops voltage. After about 10 minutes it's typically lower than I would be comfy with. maybe I could have dropped more stuff out of the circuit before hand though. If I were you, I would consider a hard start capacitor, running the fan on low, and even consider the fan delay circuit that smkettner shared here a couple years ago.