I am trying to design a brushless DC generator system for portable use of charging batteries and if suitable possible hybrid power system of an aircraft.
The "BLDC" motor/generator will be connected to a 1.5KW, 2.011HP and 10,000RPM Max water cooled engine. The reason for a brusheless motor is due to its ratios of weight to power and many are water cooled to make further use of a pre-existing cooling system already in place.
The brushless motor i have found that seems to be best suited to the specification and water cooled is this Turnigy AquaStar 4084-620KV Water Cooled Brushless Motor on Hobby-King the voltage is desire is 12V DC if i use the engine specifications of 1.5kW = 1500Watts we can say 1500Watts / 12V = 125Amps this is a lot of current to handle.
The motor/generator is rated for a maximum voltage of 37 Volts and 105 Amps that is 37 x 105 = 3885w or 3.9kw which is slightly overrated for my engine, to drive this I intend to use a pulley system to drive the generator at 21,700 rpm which will generate approximately 35v (obviously kv = rpm/volt is not exact but pretty close and less when in use as a generator) I then intend to transform this to a 12v dc at 125 amps or as close as.
Obviously if anyone can improve my calculations above and design you are welcome to input but my question is what is now the best method to transform to my desired output with regulation so that engine speed is proportional to current not voltage if possible.
Idea 1: A dc - dc buck converter could be used but either multiple or a large unit would have to be used to deal with the high current and will be expensive.
Idea 2: use a 3 phase transformer to convert to 12 volts before rectification however this will not add any regulation.
Obviously the 1.5kw of my engine is mechanical power and my estimated values may get me less as losses add up through rectification, heat, copper losses ect.