Yes the RPM ratings for altenator output is for the altenator, not the engine speed. And yes the altenator does spin faster than the engine due to the pulley sizes, and yes the wiring to the 7 pin plug is usually too small.
But, most of the specs I have seen rate them in the 4000+ range.
And motors with fuel injection don't idle at 800 rpm nowadays.
My last 3 TVs idled at less than 600 rpm.
That will be too slow for charging any substantial amps at idle.
Now what maybe could be done is some pulley size changes. Not sure if that would result in a overspeed condition when driving though.
