I'm looking for a circuit that can clip the peaks of a sine wave source, typically the source is 40V peak to peak and should be clipped at about 13.8V. The circuit below does exactly this but to my knowledge there are no zeners that'll be able to handle the 50W or possible larger peaks. The idea will be use power mosfets or BJTs attached to a heatsink to clamp the peaks.

This will be used to clamp the generator output on a gasoline engine, the kind of regulators used on these generation of engines are pretty bad and cooks the battery, I'm attempting to fix this problem. The generator won't damaged by clamping the output.

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/EJh9o.png