Some of you may already know about this, because some of the 1970s bevels had under-charging problems using 180W alternators, and replacement using the ST2 alternator has been discussed on websites. I am using the Super Pantah side cover on the F1/TT1 because it resembles the actual race bike part, and ignition pickups are on the outside. It also uses a thin "race" alternator; I think the original bikes used the Saprisa version, as found on some Moto Guzzis. But one of my problems was that I am using a Shorai Lithium battery, and want to keep it. But they need at least 13.1 volts to maintain a charge; every other brand of lithium Battery I check seems to need about the same.
Below are two versions of "race" alternators as sold by Ducati, and the ST2 version. The two on the left are similar, but one has three wires (like F1), and one has only two. The thicker version on the far right, with only two wires, is the ST2. Then there are differences in the stators; the two on the left are marked differently and are very weak when used as magnets. The one on the far right is marked same as the center one, but it can be picked up with a very large screwdriver with no problem!
When I used either versions with weak rotors the maximum DC volts at the battery were in the range of 12.85 to 13.05 --- barely above 13. And measuring AC volts using any combination of wires was in the range of 25 to 30 --- really low! I guess that is all they do, and that is not enough for a lithium battery. Using the strong rotor and the thick ST stator (I mixed and matched) I now get 14V+ all the time, and 65-70 AC volts; really what an early 916 or 748 were supposed to need as minimums. So now my battery is happy all the time, and reads about 13.4 volts the day after a track day. Based on my experience with this brand it will probably go another seven or eight years.
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