I guess I'm really dumb. To me, you shouldn't care about RPM of the turbine. At a certain output voltage the heater should start to turn on. Now I know that it takes a certain blade RPM to make that voltage, but some how you need to figure out what that RPM is. But that RPM is just a number, the voltage is the important thing. Once the voltage reaches your high limit you need a way to slow down or brake the turbine to lower the speed of the blades.
A window comparator circuit will do this for you. Under the low limit and no voltage would go to your heater, the blades would turn with no load. In the "window" (between low and high limits) the heater gets power. Once it goes into the high limit, the heater power shuts down and the gen stator coils are short circuited to each other to put the brakes on the turbine.
All of this done with out knowing any RPMs. Just the safe voltages for certain fan speeds.
A window comparator circuit will do this for you. Under the low limit and no voltage would go to your heater, the blades would turn with no load. In the "window" (between low and high limits) the heater gets power. Once it goes into the high limit, the heater power shuts down and the gen stator coils are short circuited to each other to put the brakes on the turbine.
All of this done with out knowing any RPMs. Just the safe voltages for certain fan speeds.