Yanmar 3YM30 burned out alternator and starter motor

[pugwash01]

Have heard that accidentally turning the 'ignition' key back to 0 with the engine still running can fry the alternator, but can it burn out both that and the starter motor? And if so how?

[boatbod]

No, turning the key off with the engine running will not burn out the alternator. To do that you'd need to turn off the battery switch with the engine running.

Usual suspect for burned out starter is either a stuck solenoid (starter runs continuously until dead) or water immersion.

[pugwash01]

...but both together at the same time?

[boatbod]

Originally Posted by pugwash01

...but both together at the same time?

Possible I suppose, but depends on the alternator. If the excite power shuts off first, loss of battery connection wouldn't be such a big deal. Loss of battery with the alternator still being excited means it's could go over voltage very quickly. The over voltage it's what damages the rectifier diodes.

[boeing1]

can you damage the alternator if you select from battery 1 to battery 2 or both while engine is running

[smac999]

If your switch is bad / weak. Otherwise it shouldn't

[boatbod]

Originally Posted by boeing1

can you damage the alternator if you select from battery 1 to battery 2 or both while engine is running

Usually those switches are "make before break" which would be ok. Damage usually only occurs if the battery gets disconnected while the alternator is running.

[topmast]

If you have only one bank and it is connected to either neither the off position is the same the unused terminal and the alternater can blow diodes . The other day a guy comes over and says 'Battery is dead, can I borrow portable jump start.? "Need help" ,Nope I'm good' Comes back a few minutes later, 'somethings wrong , your cables melted' He'd connected both cables to the positive battery terminal and the inline 175 amp fuse . So, ,,I learned that not everybody has an understanding of their stuff

[watevaworx]

Have you considered a lightning strike . We met some people on a cat crossing the Pacific and lightning had taken out both the starters and alternators on both engines

[mitiempo]

Alternator output should go directly to the house bank positive. Start battery is charged by an ACR or Echo Charge. This way it is both more efficient and there is no possibility of damaging the alternator with the main battery switch.

[Boatwright]

If this actually happened as described, I'd be looking for a loose connection on the battery cables -- open circuit caused the alternator to fry; big voltage drop caused the starter to overheat and fail or maybe the starter itself is OK but a poor connection is the problem.

[Elie]

Strange ... Can it simply be some sort of spike coming from the shore power or a lightening strike?. A bad alternator controller may generate a very high voltage. Not for long!. A starter or solenoïd switch may become sticky, and force the pour starter to run continualy, but that would obvious. Or simply that the two problems may not be related at all?...