This is the voltage regulator I asked for suggestions about current limiting. The diagram shows the prototype without current limiting.
+-----------------+------+-----O +Batt | | | _/ | | 7.5v /^ 1K - blocking | | ^ diode | | | | | | | | +-----O Armature | | | | | | | | - freewheel | | ^ diode | | | V +---100K---------+-----O Field - | | | | | | | : | | | 1N4148 : | | | X10 : | | _| | | .01 | | V +----||---+---|| N channel - | | |_ mosfet | | | | | | c/ | +---R---+-------| NPN | | e\\ | Rtrim | | | | | +-----------------+------+------O GroundThe 100 K resistor and the 0.1 uF cap are for hysteresis, to keep heat down in the mosfet; I'm putting this circuit into a small, flat enclosure without fins so it can be installed in a motorcycle's battery compartment. The string of 1N4148 diodes are there so the regulator will have a temperature coefficient matching the charging characteristic of the battery. And that's another reason to keep heat down in the circuit. Similarly, I used a schottky for the blocking diode, which has to conduct all the charging current.
Generator configuration: One of the armature brushes is grounded. The other brush is wired to the A terminal on the outside of the generator and is also connected to one end of the field coils. The other end of the field is connected to the F terminal on the outside of the generator. It's called a floating field or "type A" arrangement, common on the old GM vehicles and Harleys.
Any current limiting scheme will probably involve a sense resistor in series with the blocking diode. Some discretes or an op amp will send a current the base of the NPN transistor controlling the mosfet that conducts field current, diverting the pullup resistor current and lowering the Vgs, thus reducing field current.
I'm still debating the easiest way to do it. I got some great ideas from Win and the others in the previous thread about this subject. But my failure to elucidate how how the regulator and generator work resulted in some confusion and I decided to post an explanation.