Voltage Regulator for Permanent Magnet Alternator

Thread Starter


Joined Oct 31, 2020
Is there anyone here that has a detailed understanding of how subject voltage regulators actually work?

If not known, it is OK to not comment.



Joined Jan 23, 2018
I know how some of them work, and, in addition, I suggested a much better scheme to a person who used it ansd was very happy with it.
With the permanent magnet alternator on some motor cycles, the way that the voltage regulator works is that as the generated voltage exceeds some level, a high current Zener diode starts to conduct, and draws enough current so that the voltage does not continue to rise, because the Zener diode has become the main load on the alternator.
My suggestion was to use a common three terminal series voltage regulator instead., with adequate heat sinking.That worked very well and they did not have any more problems.


Joined Mar 14, 2008
My suggestion was to use a common three terminal series voltage regulator instead.
The problem with that is, some permanent magnet alternators can generate very high voltages at low currents and high engine speeds, which can blow a series regulator (and leave a slew of burnt lighting bulbs), or even break down the alternator winding insulation.
That's why some type of shunt regulator (e.g. Zener diode/emulator) is normally used.

The more sophisticated regulators use SCRs or MOSFETs to shunt the current to ground at each AC cycle when the voltage is exceeded, which reduces the power dissipated in the regulator.
Below is a circuit I created using MOSFETs (which dissipate less than SCRs) to work with modern 3-phase motorcycle alternators, as an example:
It works in simulation, but I didn't build a working model.

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