Did I ruin my alternator?

[donradcliffe]

Some engines are wired so that the stop solenoid needs the key on, some aren't. Some alternators need the key on to start charging, but can continue without it.

[tdoster]

Originally Posted by double u

...no charterboat would have a working alternator...none!

There is absolute truth. Can't count the number of calls "We turned the switch off, but the engine is still running, what should we do."

[seabreez]

Originally Posted by Jerry Woodward

I accidentally turned the key off while my Yanmar 2gm20 was running (I have two of them on my cat and turned the wrong key off). I kept it running in neutral and I increased the RPM to about 2000 for 5 min or so before I noticed the key was off, yikes! I shut down the engine, turned the key on and it energized and the engine started just fine.

What is the likelihood that I ruined my alternator? What is the best way to check to see if it is charging ok? If so, is it an easy fix, i.e. replacing diodes, or am I looking at a new alternator?

If you only shut the key, you removed the energizer or the power to the stator and no magnetism is present to charge and the alternator turns freely. If you disconnect the battery, then the overload has to go some where or it fries the diodes.

[seabreez]

Originally Posted by Jerry Woodward

I accidentally turned the key off while my Yanmar 2gm20 was running (I have two of them on my cat and turned the wrong key off). I kept it running in neutral and I increased the RPM to about 2000 for 5 min or so before I noticed the key was off, yikes! I shut down the engine, turned the key on and it energized and the engine started just fine.

What is the likelihood that I ruined my alternator? What is the best way to check to see if it is charging ok? If so, is it an easy fix, i.e. replacing diodes, or am I looking at a new alternator?

I forgot to mention how to test the alternator... engine off, check the voltage at the big wire at the rear of the alternator. You should read battery voltage of 12.9 volts. Then start the engine and test the voltage, this time the voltage should have increased. If the alternator is good you should read 13.2 to 14.7 volts.

[GrowleyMonster]

What they said. You are probably fine, but check the rectifier.

Disconnecting the batteries from a running alternator with the battery switch, I believe, fries the diodes because the regulator has no sense input and puts out a tremendous voltage spike. I might be wrong. But every time someone has come to me and asked me what the problem might be when the batteries run down instead of charging, or the alternator gets really really hot, I tell them check the rectifier. (diodes). Always, they are toast. Knock on wood.

If things are wired properly, turning the key off shouldn't hurt anything. But check those diodes anyway.

[double u]

Originally Posted by tdoster

There is absolute truth. Can't count the number of calls "We turned the switch off, but the engine is still running, what should we do."

they ALL do it like in their cars, multiple times during each charter. (& I don't think it de-energizes the alternator, as there would be some remaining magnetism even after shutting off excitation)
in general I learned during my years as basemanager:
if it doesn't break in charter - it's really, really good stuff!

[Matsubob]

The Field Coils must have current flowing to them, is the reason you don't want to power down before the armature quits spinning. This is why you don't move the battery switch between 1,2 and Both while it is turning, because even that split second is enough to spike it and blow a diode.
Balmar has a feature on their charge controller for a switch to take the alternator offline, for the purpose of allowing the engine to develop full power. Theoretically, when that switch is in the off position it shouldn't hurt the alternator to change the battery switch position, but I sure don't want to try it!

[Elie]

Tunrning the key off will stop the alternator charging,while off. But back on and everything will return to its previous state. I often use that trick to force my Balmar smart alternator regulator(612H) to restart a cycle of high bulk charging. So don't worry, be happy!

[Stu Jackson]

Before you think you're out of the woods:

IT ALL DEPENDS ON HOW IT'S WIRED

You didn't tell us anything about your wiring so all the good intentions of the respondents could well be incorrect!!!

IF your alternator output is wired through the C post of a 1-2-B switch, which is common on most production boats, then turning off your switch with the engine running WILL usually kill the diodes if there is a substantial load on the alternator at that time.

If the AO is run to the house bank, which makes the 1-2-B switch a USE ONLY switch and NOT a charge and use switch, you could turn the switch off with the engine running and not do any damage, because the alternator output (AO) is always going to a battery and would remain uninterrupted.

In MOST cases the key switch only activates the regulator on the alternator, so turning it off only turns the alternator off.

Is it still working? What are your voltages when it's running? Do you know how to figure that out? Do you have a voltmeter installed? Do you have a DVM?

But, unless YOU know how your boat is wired, all answers are speculation.

I suggest you learn more about the subject to confirm what is installed on YOUR boat.

[Dauntlessny]

Originally Posted by Dockhead

If I had a dollar for every time I'd done this . . .


Never hurt my alternator. Doubt if it hurt yours. Don't worry; be happy!

Me too. First time I did it, I thought I had a runaway diesel, as the key powers the fuel shutoff solenoid.

[Jerry Woodward]

Originally Posted by Stu Jackson

Before you think you're out of the woods:

IT ALL DEPENDS ON HOW IT'S WIRED

You didn't tell us anything about your wiring so all the good intentions of the respondents could well be incorrect!!!

IF your alternator output is wired through the C post of a 1-2-B switch, which is common on most production boats, then turning off your switch with the engine running WILL usually kill the diodes if there is a substantial load on the alternator at that time.

If the AO is run to the house bank, which makes the 1-2-B switch a USE ONLY switch and NOT a charge and use switch, you could turn the switch off with the engine running and not do any damage, because the alternator output (AO) is always going to a battery and would remain uninterrupted.

In MOST cases the key switch only activates the regulator on the alternator, so turning it off only turns the alternator off.

Is it still working? What are your voltages when it's running? Do you know how to figure that out? Do you have a voltmeter installed? Do you have a DVM?

But, unless YOU know how your boat is wired, all answers are speculation.

I suggest you learn more about the subject to confirm what is installed on YOUR boat.

I did not touch the 1-2-B switch, only the "key" switch so I'm hoping that, as you and others have said, that this switch does not control the load and thus would not damage the alternator when turned off. I've only owned the boat for a month and she is now on the hard. I will definitely be checking the alternator charging and mapping the electrical system as you suggest when I get back to the boat in November.