Cooking a regulator/rectifier

Question... I just had my work on KF 1200 gone over by my tech advisor. Likes what I have between panel and firewall. Much relieved. But curious about master switch only shutting off battery power. Feels that would damage rectifier/regulator if engine continues to run with the master switch off. I had that experience with a rectifier on a motorcycle. But, I read in one of the many discussions on this forum that it is technically not an alternator but a dynamo. I have no idea what that suggests regarding this issue.
I also think I read in a thread that rectifiers had been damaged when masters cut out the battery with the engine running.
If so, could a solution be a relay controlled by the master switch that disconnects both wires coming from the alternator to the rectifier ?
Could a switch in the "C" lead from the rectifier have an effect on separating the rectifier input from the alternator?
There are so many of you knowledgeable about this stuff I thought I would ask before trying some tests.
OK now for fuselage covering.
Bud

Correct. Never shut the master off before grounding the ignition modules if talking about a Rotax engine. No solution involving a relay needed as long as you do your shutdown in the proper order.

Shutdown order:
1. Avionics master off if you have one.
2. Ground ignition modules to stop engine ( turn off key or flip both ignition switches to off).
3. Master off.

Start up takes care of itself as the starter solenoid will not and should not energize until the master switch is engaged.

Ground into me in my flight training, years ago, in order, the shutdown checklist:

1. M Miscellaneous (all electrical switches)

2. M Mixture (Not applicable to a 912)

3. M Magnetos (Ignition grounding)

4. M Master.


Shutting the master off with the engine running is the most common cause of death in our ($200) regulator-rectifiers.

OK... Understood. Now let's consider an in flight electrical fire , or some other electrical anomaly that demands shutting down the electrical system but requires continued flight. Unless I am mistaken, this engine, the 912 I have, will run without the battery or rectifier . So in an inflight electrical emergency I can fly to a safe emergency landing IF I can isolate the rectifier. Is this not a consideration?
With my Ford V6 application I had both a circuit breaker and switch that could isolate the alternator if it should run away, which, by the way, destroyed the computers in a car I had. Does anyone feel it is a mistake to be able to isolate the rectifier?
I am not trying to be argumentative, but merely testing an idea. I can easily accept the advice regarding the engine shutdown procedure suggested.
Bud

The ignition system on a 912 uses two separate dedicated generating sources on the flywheel to operate the ignitions, totally independent from the charging system. The main reason 200 crank rpm is needed to start the engine.

In your example of an inflight fire, wrecking the voltage regulator is the least of your worries. Seriously.

I don't think anyone would fault you if you chose to set up some type of relay or DPST switch system to cut off the yellow AC voltage source wires to regulator. This would just add additional complexity where it really isn't needed.

I used Bob Nuckolls' Z-16 diagram from his "AeroElectric Connection" book as a basic starting point for my electrical system. I have a master switch that provides the same functionality as a typical split master switch and allows operation with battery only or battery & alternator. It controls a small single pole relay that makes & breaks one of the two yellow wires coming from the Rotax dynamo. In addition there is a crowbar over-voltage module that will switch to ground & trip a 5 amp circuit breaker that is feeding that relay coil through the master switch. So you actually have 2 ways to kill the dynamo output - with the master switch (leaving the "master solenoid" on and hence the battery still connected to the system, or turning off everything, as you wish), or by pulling the circuit breaker. Either way disables the output from the dynamo. It's really quite simple, plus you have OV protection. If you don't have a copy of the AeroElectric Connection, it is available online for free.