An automotive alternator is 3-phase rectified, thus will have a fair
amount of ripple. Whether your inverter can cope will require a
"smoke" test ;-)
...Jim Thompson
Also most alternator regulators are designed to 'charge' a batter, and
expect that a battery is attached to the alternator. You may find
regulation is poor, especially at light loads with no battery.
What are you spinning the alternator with? Also, with no batery, you
need a self exciting (single wire) alternator and IIRC these require a
minimum RPM to activate, and that minimum speed is on the order of
2500 RPM.
For the ripple problem, I'd think a reasonable capacitor would help.
Since inverters are basically SMPS I don't think they expect totally
clean input voltage. but as Jim says: you can give it a test!