How does AC ATV regulator work?

[hal9001]

Whats the circuit inside 2 phase AC regulators for ATVs like the one in the picture? Are they efficient?
All pictures have the regulators closed.

[TheMG]

In such vehicles that typically have a permanent magnet alternator, the regulator is a shunt regulator. Literally just clamps the voltage to a max value, excess energy being dissipated as heat.

Not very efficient at all but simple reliable and effective, and has negligible impact on the engine of the vehicle since it's a relatively low power alternator to begin with, and at lower RPMs the output of the alternator is often below the regulation point anyways.

Often these shunt regulator modules will also have a separate DC regulator for battery charging output.

[hal9001]

thanks!

[floobydust]

Small engines like moped and ATV use a shunt regulator which wastes the excess voltage as heat.
Better designs use a couple SCRs as a series regulator, like the Kubota one.
Thread on the subject with a few schematics: https://www.eevblog.com/forum/projects/ac-generatoralternator-charger-rs1105-replacement/