Rectifier Temperature

What Bill said. Nice job. :) 

Merry Christmas Bill

The Rotax regulator uses a switched full wave bridge to regulate the power.  It’s simply an SCR on/off switch, it’s not a shunt regulator. The heat generated by the regulator is proportional to the current though the regulator.  Low current draw equals low heat and maximum current draw equals maximum heat. 

Here is a simplified function diagram and a copy of the internal regulator schematic. There is no shunt. 

Hmmmmm,

It is a shunt regulator or is it a full wave bridge?

Checking. Maybe Rotax will weigh in.

Okay here you go,

Shunt on iS only and is a 3 phase

and

UL & ULS is a single phase system 

Hoping Bill Hertzel will chime in here...

I've been curious about the nature of the shunt regulator on the iS engine.  Because the available current output on a permanent magnet alternator is essentially constant, you might think that the total load on the alternator is always at max, and that the load is then divided between the connected aircraft load and the shunt regulator. However, I don't believe that to be the case.  This is what I believe, please feel free to punch holes in it!

The shunt regulator uses a type of fast switching device (usually an SCR) to short the alternator windings to one another for a portion of each electrical cycle when the setpoint voltage is exceeded.  The SCR’s are not variable in resistance, rather they are very fast switches that are either open or closed.  So, during the time the shunting device is closed, the voltage in the windings (being shunted) drops to near zero, essentially shutting it off.  And without voltage, no current will flow (except eddy currents). However, when the SCR is closed there is still a resistance across it as they are not perfect.  This typically results in a combined voltage across the SCRs of about 2 volts.  We know the rated output of the 912iS alternator is 30amps at 14.2 volts.  And since power = voltage x current (P=VI)  then 2 volts x 30 amps = 60 watts. So in summary, I don't believe that under any conditions the regulator will have to dissipate more than about 60 watts. But it still gets hot, in the same way a 60 watt light bulb does.

My point is that some folks seem concerned that the shunt regulator is a poor design because they think it fully loads the alternator at all times. However it does not, and a shunt regulator is actually a very good design when a permanent magnet alternator is used.