Will I kill my alternator?

[Carmelo]

I have a question about my alternator - sorry I am a bit clueless about this stuff.

It is a Hitachi LR180-03a fitted to a yanmar 4jh2e. I stop the engine with a manual stop cable (no solenoid). I know that if I (or more likely a non-regular crew member) turns of the ignition key on the yanmar panel this will not stop the engine but will kill the alternator. My questions are:
1. How quickly will the damage be done? Is it just a few seconds or longer?
2. Is there anything I can do to prevent this risk? I have read that it is possible to fit some kind of diode or similar to protect the alternator. In fact I think I have heard that modern alternators in cars come with this protection. Is there any chance that my Hitachi has it so I don't need to worry?

Thanks

[DeepFrz]

I think you may have confused turning your battery switch to off while the engine is running. This will kill your alternator, and you wont have to wait for it. Turning the ignition switch to off probably will not kill your engine.

[sailorboy1]

I haven't looked at the engine wiring diagram on my new boat, but on the last one all the engine key turned off once the engine was running was power to the gauges/tach/panel alarms and panel lights.

[djmarchand]

Turning the key off on your Yanmar kills power to the alternator "ignition" wire as well as engine instruments. This ignition wire turns off the Hitachi's internal regulator and stops the alternator from producing current.

This will have no affect on the engine or alternator. The engine being entirely mechanical (including the stop cable) will continue to run. Other devices- lights, sailing instruments, etc will be powered by the ship's batteries and will ultimately run down, but this is no different than while sailing.

As others have said, this is very different from disconnecting the batteries while the engine is running. If you do that the alternator which was producing charging amps suddenly has no place to put those amps. This causes a momentary voltage spke which blows the alternator's internal diodes. A Zap-Stop device, another diode, can prevent this from happening.

David

[senormechanico]

dmarchand has it exactly right.

[Sailmonkey]

turning the key off is fine, but you never want to turn off the battery switch. If this was a problem thousands of yanmar owners would be without alternators.