wouldnt the voltage from the dyno feeding 30ish V AC into the regulator be enough to start the regulator?
GOOD question. Well of course. "It Depends"...
What it depends ON is the electronics question..
Most regulation systems have some chip that has to start up for anything to work. Usually there is some internal voltage regulator for the voltage regulator. IF that runs off the battery to-be-regulated and that battery is not there the circuit may never start up. In the Kubota system there is a rectifier that SHOULD supply DC power from the "Dynamo" AC generator as you suggest. But if there's NO battery or other load, the voltage may go high enough to cause a shutdown. Wish we had a diagram of what's IN the 4-wire Black Box of the Kubota regulator.
The easy test is any-old 12V battery to test with..
BAttery charging has become very complex with all the new types of batteries and safety regulations. I had dinner with my son and his wife last night. He designs energy management systems (Wind AND solar)
(For THESE Guys) used in many countries. He had a go-round with the designers of a new battery charging chip from Analog Devices co. "Our regulator can do anything, you can customize it"..
-- OK, I need to use lead-acid batteries.
- Um, NOBODY uses lead-acid anymore.. there are great Lithium and other types.
-- I NEED to be able to charge the batteries when they are at -20F on a mountain top. Look it up. NONE of those Lithium based batteries can be charged at all at -20F.
- OH
It's really great ! When most of your kids know more than you do about lots of stuff