20 years without knowing, So I thought I'd ask. - Page 2 - SailNet Community
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post #11 of 42 Old 11-14-2011
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This panel is designed to be run with the ignition switched on. When your key switch is turned off after starting the engine you disable the alarms so that you will never know if it overheats or loses oil pressure as you have switched these off.

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post #12 of 42 Old 11-14-2011
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Quote:
Originally Posted by NCboatrx View Post
This panel is designed to be run with the ignition switched on. When your key switch is turned off after starting the engine you disable the alarms so that you will never know if it overheats or loses oil pressure as you have switched these off.
Agree,
I also have a 3GMD and wired according to the yanmar manual. I can turn the ignition of after the engine starts, but I would not have any alarms powered and therefore an overheat or low oil pressure would not alarm. The alternator is still wired in as the alternator is wired directly to the battery. If I disconnected the battery with the engine running I would damage the alternator diodes. Even with battery disconnected the engine would run, although now with a damged alternator and no warning alarms. Maybe your panel was modified- with the engine running test your alarms with the panel test switch.
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post #13 of 42 Old 11-14-2011
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My key is purposely broken off in the ignition switch (can't lose it over the side that way). I use a stubby flat screwdriver to operate the switch. I turn it on just prior to starting the engine. I turn it off when the engine is shut down.

My alarm panel is powered through the switch and the low LO pressure alarm sounds continuously if the switch is left on.

If the switch were left ON, the starting battery would run down if the battery selector were left ON. Both are OFF when the boat is at dock. The hotel battery bank is selected when at sea, and the ignition switch is still OFF.

No reason to leave it on.
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post #14 of 42 Old 11-14-2011
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Quote:
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My key is purposely broken off in the ignition switch (can't lose it over the side that way). I use a stubby flat screwdriver to operate the switch. I turn it on just prior to starting the engine. I turn it off when the engine is shut down.

My alarm panel is powered through the switch and the low LO pressure alarm sounds continuously if the switch is left on.

If the switch were left ON, the starting battery would run down if the battery selector were left ON. Both are OFF when the boat is at dock. The hotel battery bank is selected when at sea, and the ignition switch is still OFF.

No reason to leave it on.
I think I am lost.

"I turn it on just prior to starting the engine. I turn it off when the engine is shut down." "No reason to leave it on"

Am I missing something?

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post #15 of 42 Old 11-16-2011
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Engine running with panel off? No engine alarms!! Probably no alternator output either. My fire and bilge alarms (3 separate stations) are on a different panel which bypasses the either neither both switch and is separately fused.Your hard wired GPS likely has a system voltage reading if there is no volt/amp meter in the existing panel.
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post #16 of 42 Old 11-16-2011
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Am I missing something...

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I think I am lost.

"I turn it on just prior to starting the engine. I turn it off when the engine is shut down." "No reason to leave it on"

Am I missing something?

Dabnis
Just trying to point out that my ignition switch is always on when the engine is running and always off when the engine is not running.

The switch routes power to the starting solenoid, to the alternator field circuit, and to the instrument panel...needed to start or run the engine, and not needed when it is shut down.

The OP seemed to be questioning the oft-stated guidance to keep the switch on at all times with the engine running in order to avoid damaging the alternator. He routinely turns his switch off when underway.

I'm not an expert on this, to be sure, but I know enough to know that my alternator is excited from the battery at start up, and self-excites when running, either of which is a suitable way of exciting the alternator.

My concern is that with the engine running, if the switch is turned off, power to the instrument panel is interrupted and I no longer have low lube oil or high temperature alarms to warn me of a pending or existing unsafe condition. That's the primary reason the switch stays on until the engine is stopped.
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post #17 of 42 Old 11-16-2011
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Quote:
Originally Posted by fryewe View Post
Just trying to point out that my ignition switch is always on when the engine is running and always off when the engine is not running.

The switch routes power to the starting solenoid, to the alternator field circuit, and to the instrument panel...needed to start or run the engine, and not needed when it is shut down.

The OP seemed to be questioning the oft-stated guidance to keep the switch on at all times with the engine running in order to avoid damaging the alternator. He routinely turns his switch off when underway.

I'm not an expert on this, to be sure, but I know enough to know that my alternator is excited from the battery at start up, and self-excites when running, either of which is a suitable way of exciting the alternator.

My concern is that with the engine running, if the switch is turned off, power to the instrument panel is interrupted and I no longer have low lube oil or high temperature alarms to warn me of a pending or existing unsafe condition. That's the primary reason the switch stays on until the engine is stopped.
Got it, thanks for the clarification. As I asked earlier, what is the down side to leaving it on as the OP seemed to be concerned about?

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post #18 of 42 Old 11-17-2011
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The Yanmar manual states (and I think most engine manuals) the alternator can be damaged (rectifier I think gets damaged) if the alternator is disconnected from the battery when the alternator is spinning. Can this happen even if your alternator is self exciting? How is the rectifier actually damaged?
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post #19 of 42 Old 11-17-2011
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The Yanmar manual states (and I think most engine manuals) the alternator can be damaged (rectifier I think gets damaged) if the alternator is disconnected from the battery when the alternator is spinning. Can this happen even if your alternator is self exciting? How is the rectifier actually damaged?
Two possibilities, I think?

1. If the alternator doesn't "see" battery it won't charge, no damage?

2. If it "sees" battery and tries to charge into a "no load" condition the diodes, (rectifier) can be damaged?

By mistake I ran an alternator "open" for a short time and got away with it. from what I have read I was lucky.

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post #20 of 42 Old 11-17-2011
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Quote:
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Two possibilities, I think?

1. If the alternator doesn't "see" battery it won't charge, no damage?

2. If it "sees" battery and tries to charge into a "no load" condition the diodes, (rectifier) can be damaged?

By mistake I ran an alternator "open" for a short time and got away with it. from what I have read I was lucky.

Dabnis
I blew the alternator turning the "ignition" key off while the engine is running. No doubt about it. I knew as the tachometer stopped working immediately.

On some engines the fuel pump will be off with the key off.

On most engines the alarms are off.

So we've established beyond doubt that it's bad practice to turn the key off while the engine is running, so regardless of the fact it hasn't done any harm yet, it's time to get into a good habit, in case you sail another boat someday.

Bristol 31.1, San Francisco Bay
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