Why would you want a separate AC alternator?
There are two ways to produce usable AC power: (a) run an alternator at a constant speed; (b) run a DC alternator (alternator with rectifier) and run the power through an inverter.
(a) is unfeasible for our purposes.
(b) just duplicates the function that most of us already have.
An normal inverter is much more useful and versatile than one built into a separate unit just for use when the engine is running.
If you need AC power on board, just put on a large alternator, better a second school
bus alternator with dual belts, separate from the regular alternator. And install a regular inverter.
Then you have AC power produced from battery
power when the engine is off, and not just from when the engine is running.
I looked at the Unipower site. First of all, you can't generate 6kW with a "fan belt". That's a serious amount of power which requires serious power transmission
. Read $$$$. Your engine won't pull that at idle, either. Secondly, who needs 6kW? That's 52 amps at 115 volts. Looks like massive overkill to me. Even on my big boat full of electrical
conveniences, a 3000 kVA inverter (which practically gives more like 2.5kW or even less) is plenty. This is paired with a 110 amp x 24v school
bus alternator, which produces theoretically 2.6kW and practically around 2kW over a wide RPM range.
I can even run a washer/dryer off this inverter when the engine is running. If the alternator is not producing quite enough power, the shortfall is merely made up for out of the battery
This is a much more versatile and useful setup than a dedicated engine-mounted AC alternator.