looking to go off grid and looking for input

simply stated Watts = Amps * Volts... therefore 3500W = 12V * 291.66666666...7

So if you want to use 35000W you have to figure out how to get ~ 300A from all those parallel 12 VOLT batteries and that would need some very large wires!

Crazy_Wolf1234 said:

oh one thing I meant to ask about that DC to AC converter, when it produces the 3500 watt of power, what is it's draw on the battery? is it drawing just the 12 volts or is it drawing the amps as well when hooked to a refrigerator pulling 1000 watts. in other words if the power goes out and I want to hook one up to my fridge to save my food from spoiling, how long will one car battery last running that fridge before the low power warning kicks in and shuts off the unit?

The draw in Amps in a perfect world is as westbranch stated, 291 amps at 12 volts. But inverters are not perfect and I think the peak efficiency of the one you linked is 90%, so closer to 320 amps. This is all part of the basic formula watts = amps × volts.

A single car battery (the wrong chemistry for deep cycle use!) Would not last very long. Car batteries are designed to give a big punch of power all at once. They are usually Lead Calcium (in the US), Deep cycle tend to be Lead Antimony. Car batteries don't do well with 'deep cycling'. Marine batteries are often lead calcium with thicker plates, though we are seeing some Lead Selenium as well, a better choice and a common car starting battery in Europe with better cycling. We usually recommend golf cart batteries for people starting out with small systems. All Lead acid batteries are made up of 2.12 volt cells, so a 12 volt lead acid battery is just a string of 6 cells. A 6 volt golf cart battery, 3 cells. This is easy to see when you get to forklift batteries as each cell is connected in plain view.

Things that use a thermostat, are hard loads to pin down. Fridge's, Freezers, and air conditioners will have varying loads. The amount of energy they use will vary with the atmosphere they are in. My fridge runs nearly constantly during the summer when the kitchen is in the high 80's and low 90's, I would guess that the 16 year old design is drawing 3kwh's by it's self in the summer! I had a very well insulated cabin 10 x 16, 6" insulated walls, 8-10 inches in the floor, built in the shade. I could cool it down in a couple hours and the compressor would only run 30-40% of the time on the hottest day's. I now have a 'tin can' (mobile home) with 3 1/2 inch walls, but tightly built. back bedroom has less cubic feet than the cabin, but the air run's constantly near 90% duty cycle. If you are setup and living in a place, it's best and easy to check loads with a Kill-A-Watt meter.

I mentioned it before, but perhaps in a post you mostly ignored, due to the tone, but the inverter you linked to is a Modified Sine Wave (MSW) inverter. This type of inverter is hard on motors, typically they will use more wattage and run hotter. A Pure Sine Wave will be easier on motors and some electronics.