Generator overvoltage scenarios
I'm reading about battery systems on https://www.kitplanes.com/understanding-lithium-batteries/ and it says this:
"Once bus voltage is sustained above 60 volts, the internal MOSFETS (metal oxide semiconductor field effect transistor) on the EarthX BMS may no longer be capable of maintaining protection. Some engines like the Rotax 912 are only capable of putting out 40 volts in their worst-case overvoltage condition, so not all aircraft charging systems need an automatic overvoltage protection circuit."
As I understand the Rotax has a 14.2±0.3V AC generator provides with a permanent magnet and self-excited field coil in the rotor, and the generator coils (plus the "magneto" coils and a coil for the tach, in the carb engines) in the stator. I have three questions about that worst case 40v overvoltage condition if anyone can answer them:
1. What condition or type of failure could cause the Rotax generator to produce such a high voltage?
2. Would it have any effect on the mag coils (I don't mean ignition coils) or only the generator ones?
3. For iS models which have dual generators instead of one generator and two mags, how do the ECUs respond?
Thanks!
