I would like to get some advice regarding the following scenario: I want to build a cheap, small generator for an energy harvesting application. There are magnets on a rotating shaft and off-the-shelf inductor(s) are positioned (fixed) near this shaft. After the inductors the voltage is rectified and then a power management IC takes over (boost/buck, storage).
At 1000 rpm the system should provide enough power (~10 mW) for the circuit behind it. But the rpm can vary between 1000 and 20000. Once the rpm are higher than 1000 there is excess energy. Therefore I have a find a way to deal with this excess energy. Either get rid of the excess energy or maybe prevent the generation in the frist place.
Using multiple inductors and switch them on/off depending on the rpm was an idea. But this would take quite some effort with rpm detection and circuitry, depending on how many inductors I would use. So I am looking for easier solutions.
A mechanical solution to increase the gap between the inductors and magnets is not possible, bc both are fixed in place and there is not much room at all.
Zener diodes could be a thing, but dissipating the energy as heat may not be the most suitable way, bc the thermal conductivity of surrounding materials is not good.
Do you guys have any ideas how to deal with this issue?