Lost on the math yes I am

[WeCheat]

Ok I am not getting anywhere looking at inverters for my truck. What I don’t know is how much I need from the truck. For example I have 14vdc making 70amp I get 980 watts right? They say most inverters are 80% efficient so when you run that 980watts DC in the inverter to turn it into AC I would get how many watts AC? Also whats the formula for this to convert DC to AC? Some say if you have like a 2500watt inverter you need 250amp DC to make it work.
Thanks for your time and help!!!

[rfwyzard]

Volts times Amps equals Watts. 14 volts times 70 amps = 980 watts. Times .8 for 80% = 784. Divided by 120 volts equals 6.5 amps. Truck battery, ignition and computers need power to keep the truck running. You didn't say how much power you need for your accessory but if it's much more than 4 or 5 amps especially on a long term basis you're going to need a MUCH bigger alternator. A second unit would be a good idea. Or maybe a generator in the back, then you wouldn't need to run the truck. A second battery with an isolator is a good idea also. Check out a trailer or RV store. They can tell you exactly what you need.

[bharbour]

output power in watts = input current * input voltage * efficiency in percent/100.

If you want that output power converted to current, divide it by the output voltage (120 or 240). This is a bit of an oversimplification because it ignores power factor, but that is another critter. Be aware that startup currents on motors can be 5x the operating current. Similarly, startup current on incandescent bulbs can be 3X the operating current. An inverter needs to be able to supply the startup current without sagging or exploding.

BobH

[WeCheat]

Thanks that is what I needed. You are great!