it's not amperage! ITS CURRENT!!!!
in this case R is your lights and any other losses so that's pretty much constant, or not in the case of the dimming lights
so V varies with the MMF (magnito moto force) of the flywheel speed. this also increases current, I, and leads to blown light bulbs.
now someone mentioned watts... watts = power P=VI or in 3 phase S=VI*
regulators tend to help, but never completely solve the issue as I still blow bulbs with my trailtech dial a bright regulator set on low.