Output voltage from the stator is directly proportional to RPM. The faster the magnet spins inside the stator, the more EMF is generated. At idle the AC will only be around 20 volts AC or so, at 2000 RPM maybe around 30 - 45 volts, 3000 RPM around 60, 5000 RPM probably around a hundred or so. Sorry, do not have exacting figures, and it will vary some from stator to stator, and bike to bike depending on just how strong of a charge it is on the magnet.
The idea is as RPM increases, so does AC voltage, and the readings want to be fairly close on all 3 windings...