Originally Posted by safrog
Quick question. Does a 2000 W inverter draw the full 2000 watts or only what is needed o run what is running off the inverter?
Only what you plug in up to the 2000 watt rating; BUT
and its a big one; you are dependant on the battery(s) to supply the amperage to "make" the wattage. Once you start pulling serious amps, the capacity to supply amps drops rapidly. This will pull down the voltage and put the inverter into alarm and it will shut down.
Suppose you have a 2000 watt inverter and you run a 1500 watt microwave; you also have a single 12 volt 100 AH battery (will supply 5 amps for 20 hours = 100AH).
1500 watts of AC requires (about) 1500 watts of DC through the inverter or 1500 watts divided by a nominal 12 volts or 125 amps.
The problem is something called the Peukert Effect which is a characteristic of deep cycle batteries that makes it "hard" to get amps out of the thick storage plates. This will reduce the "real capacity" to a tiny fraction of the 5 amp load capacity (see chart - OFF THE CHARTS! - extrapolated to about 15AH).
You can run that 1500 watt microwave (or coffeemaker) for about 7 minutes before it kills a fully charged 100 AH battery and the inverter alarms.
So how do you fix that? Add batteries. That way the 125 amps is "shared" across multiple batteries and no single one sees that much demand.
4 - 100AH 12 volt batteries (Each "sees" 31 amps) so each batteries capacity is only reduced to 55AH (BANK Capacity 220AH or you can run the microwave at 1500 watts for 220/125 or about 105 minutes).
My 2 battery 150AH system can only "feed" a 400 watt inverter and still have enough juice to use other DC items in the camper. (I DO have a 1000 watt inverter BUT I never use much more than 300 watts of its capability when boondocking (Watch TV for a few hours, lights, water pump, maybe some nighttime heat). I still need to recharge my batteries the next day.
Inverter size above the capability of the battery stack is wasted money better spent on a better (smaller) inverter and another battery.
Hope that helps.