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Old 25-06-2014, 06:03   #1
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Did I burn out a circut

Yanmar 2GM15 and dual battery bank. Previous owner said NEVER turn off ignition key until I have turned off engine using the throttle. Guess what I did.

Now engine starts but I don't know if that is just because the batteries are still reasonably full. I don't know if the alternator is charging the batteries.

Also my shore power (which was not connected at the time of the 1 second long mishap) can be connected to a trickle charger for the batteries but it has stopped working.

Any ideas or experiences with such
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Old 25-06-2014, 06:09   #2
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Re: Did I burn out a circut

Real easy to tell, measure battery voltage, then crank it and run it at high idle, if the battery voltage increases to above 13.5 or so, your charging system is fine.
Don't have a clue about shore power though, I'd start by looking at circuit breakers
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Old 25-06-2014, 06:13   #3
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Re: Did I burn out a circut

Probably not. This myth prevails about many engine configurations when it is not the case...and gets repeated. Test as suggested to confirm. The way you blow diodes in an alternator is to eliminate a path to battery for the juice produced by the alternator. For example by turning the battery disconnect switch to off while the motor is running. Turning off the ignition on most diesel engine configurations does not so this.

Highly unlikely there is any causal relationship to the shore power issue. I would treat them as seperate problems. Apply good old structured problem solving to the shore power issue...start at the shore side connection and test every component in between. Be careful of course since you will be working with an AC circuit, or get someone involved who is more experienced with that.
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Old 26-06-2014, 07:11   #4
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Re: Did I burn out a circut

Thanks for the replies. I have learned a bit. One is that I do not believe I created any damages even though both a book I have and the previous owner say to not turn off the key while the engine is running. Maybe because it was so quick or maybe I was lucky.

Anyway, the alternator seems to be fine as the panel light for indicating charging is working fine. More importantly, I read the volts across the battery and alternator. Battery with no charging occuring - 12.3v. Battery with charging occuring - 14.36v. Across the alternator 14.5v. This tells me charging is occuring. Am I missing anything?

The shore power issue was as you identified a separate issue that occurred at the same time. At this point it is my understanding that source to the outlets on the dock was compromised. That was fixed and my shore power recharger seems to be operating correctly now. So I'm thinking everything is currently (pardon my pun) good to go.

On top of all that I learned more about my boat!
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Old 26-06-2014, 23:31   #5
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Re: Did I burn out a circut

I don't think the ign key is going to do anything. definatly not to the alt. turning off the battery switch probably will depending on how it's wired.
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Old 27-06-2014, 07:31   #6
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Re: Did I burn out a circut

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Thanks for the replies. I have learned a bit. One is that I do not believe I created any damages even though both a book I have and the previous owner say to not turn off the key while the engine is running. Maybe because it was so quick or maybe I was lucky.

Anyway, the alternator seems to be fine as the panel light for indicating charging is working fine. More importantly, I read the volts across the battery and alternator. Battery with no charging occuring - 12.3v. Battery with charging occuring - 14.36v. Across the alternator 14.5v. This tells me charging is occuring. Am I missing anything?

....
I suspect that if you investigate further you will learn that turning off the ignition has no effect on your engine except to depower the control panel. That's typical. What make/model of engine? Maybe owners here can confirm. Is there an electric fuel pump installed?

Looks like its charging just fine. Flooded cell batteries I assume?
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Old 27-06-2014, 07:50   #7
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Re: Did I burn out a circut

Different strokes/different folks, but the procedure on our boat(s) with the same/similar engine is to always turn off the key first. That way I don't have to listen to all the alarms going off. Happy to do it when starting, lets me know they are working, but no reason to hear them when stopping. And with the diesel Yanmars/Volvos/Betas in most boats all it does is power down the control panel and the alternator field circuit, both of which are not a problem.
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Old 27-06-2014, 07:51   #8
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Re: Did I burn out a circut

Yanmar manuals that I have seen stress this sequence - stop button first, then key off. I don't recall the specifics but without the voltage presented through the key switch to the alternator's internal regulator, the wrong voltage might be output - either too much or too little. So running it with the key off for an extended period of time could be bad for the battery, but for a short time should not.
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Old 27-06-2014, 07:53   #9
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Re: Did I burn out a circut

I like to hear the alarms at shutdown so we leave the key on. That way if they aren't working it doesn't ruin my morning sail. It may cause deprivation of a sundowner though.
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Old 27-06-2014, 08:49   #10
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Re: Did I burn out a circut

Some engines are wired so that the stop solenoid is powered by the ignition switch, and some are not.
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Old 27-06-2014, 12:58   #11
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Re: Did I burn out a circut

Does anybody have a comment on this this note I received

Direct Current Generators to produce a direct flow to batteries. The problem with them is that they are not a efficient as the newer Alternators. The alternators on the other hand do produce Alternating Current that needs to be modified to Direct Current before being sent to the batteries. I understand there are three diodes that are designed to cut off the half of the current that "flows backwards". When the engine ignition is turned off before the alternator a back flash of current can destroy some or all of the diodes. IF this happens they can be replaced quite easily. I have found a local expert who became so used to my problem that his price for repair was significantly reduced. The diodes themselves are worth very little, -it is the time to take the unit apart and test it that costs.

The alternator itself is in good shape. My friend actually, on one occasion improved its output by adding, I believe, some permanent magnets to its casing. Someone in the business can actually do the diode replacement in less than an hour.


It is probable that at least one of the diodes is dead and should be replaced. Only someone who knows the business and has a test bench can actually tell you the condition of the output.

As you said the engine will continue to start as long as there is power in the startiing battery. If you have power at your mooring, the battery charger can be left on to keep the battery up to power. If you were to spend too much time at a mooring, you may be without starting capability.
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Old 27-06-2014, 14:52   #12
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Re: Did I burn out a circut

I've personally had the alternator blow when I turned the key off before stopping the engine. I checked the wiring diagram and all this would do is remove the alternator field / excite connection. Maybe running for a while without excite can cause the alternator to put out excessive voltage? I don't know, but I won't be conducting the experiment again as it was rather expensive. There is now a sign by the ignition key : "Do not turn off while engine is running. Push throttle forward to stop engine", partly as a reminder to myself.

Maybe the books have it right?
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Old 27-06-2014, 16:44   #13
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Re: Did I burn out a circut

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Some engines are wired so that the stop solenoid is powered by the ignition switch, and some are not.
Yes, in that case it matters.
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Old 27-06-2014, 16:45   #14
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Re: Did I burn out a circut

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I like to hear the alarms at shutdown so we leave the key on. That way if they aren't working it doesn't ruin my morning sail. It may cause deprivation of a sundowner though.
I do the same to confirm alarms are working.
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Old 27-06-2014, 16:50   #15
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Re: Did I burn out a circut

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I've personally had the alternator blow when I turned the key off before stopping the engine. I checked the wiring diagram and all this would do is remove the alternator field / excite connection. Maybe running for a while without excite can cause the alternator to put out excessive voltage? I don't know, but I won't be conducting the experiment again as it was rather expensive. There is now a sign by the ignition key : "Do not turn off while engine is running. Push throttle forward to stop engine", partly as a reminder to myself.

Maybe the books have it right?
Just removing field voltage will cause it to produce no output and will not blow the diodes. Something else is going on there.
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