Solid State Switch for magnet DC Generator
I'm not sure using an N-channel MOSFET for Q1 makes a lot of sense in this application. For one thing, you're going to have to be careful that you don't exceed the maximum gate-source voltage &mdash; pulling the gate to +120V while the source is held at less than +22V is almost certainly too much. Any pulling the gate all the way to ground with +22V on the source may also be too much.

You'd probably be better off to use a P-channel MOSFET in this application, connecting its source to the generator, putting a 15V zener diode between the source and gate, and then pulling the gate down through a resistor when you want to enable (rather than disable) the charging.