UPDATE--OK I did some tests out in the trailer comparing my 150w inverter with my 3000w inverter. The story has a surprise ending! Read on---
First we need to isolate what is actually inverter idle draw from any load draw. So shore power from stick house unplugged, converter off, no 120v loads on any circuit, no inverters on.
Trimetric baseline amps -00.2
Next turn on inverters (separately one only at a time)with nothing plugged in them. 150w only has a 12v plug so it goes in the Winegard socket. The 3000w inverter is on the battery bank out front on short fat wires.
So: test event, 150w amps, 3000w amps
-Inverter on no load, -00.3, -00.4 (150 up .1, 3000 up .2 from baseline)
-With shore power plugged in, breakers off except Main, -00.3,-00.5
-all breakers on, no loads on circuits, -00.6, -00.7 (I believe it is the GFCIs that draw some power?)
-all on, turn on 120v CFL lamp, -1.7a, -1.7a (150w draws 0.1 more)
-all on CFL out, now 60w regular bulb, -6.4, -5.8 (150 draws 0.6 more)
What? you ask? Apparently (voltage not actually measured to prove this) the way the 150w inverter is on the battery via long DC and longer 120v wires means it has higher voltage drop, which means it needs more amps to do the same watts (same 60w bulb)
So the test shows:
A. the idle draw of the 150w inverter was a titch less than the 3000w (by 00.1 amp)
B. the whole argument of which is more efficient goes out the window because in real life it is all about inverter-battery wiring and its voltage drop.
It might be fair to generalize that, as in my case, the big inverter will have less voltage drop (because of its specified short fat wiring) and so be able to run things--even small things--at lower amps to make the same watts.
