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Go Back   SailNet Community > On Board > Gear & Maintenance
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  #1  
Old 07-07-2008
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Engine ON/Switch OFF

The engine panel for our relatively new Yanmar 3YM30 (<100 hrs) is mounted on the cockpit-facing wall of the bridge deck in our Pearson 323. This puts the key in the path of crew's feet as they climb in or out of the companionway. While we were motoring the other evening, someone's foot must have brushed against the key, moving it to the "off" position. The engine kept running, but the tach froze at whatever RPM we were running at the time. The tach sensor is connected to a signal from the alternator. Does this mean the charging circuitry was also turned off? Likewise the engine hour meter? I assume any alarm circuits (high temp, low oil pressure, etc.) are also shut of when running this way. This sounds risky, but otherwise not threatening. Are there other dangers when running this way?

TIA
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Old 07-07-2008
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You'd probably need to consult your installation manual/wiring diagram to get the full extent of what the switch provides power to sensor wise.

I'm assuming your normal shut down is via a fuel cutoff?
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Old 07-07-2008
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The switch in the key circuit is an electrical switch. Diesel engines need no electricity to run, high pressure causes the ignition of the fuel. Turning off the switch will usually shut down all things electrical except the alternator. As long as the alternator is turning (motor running) it is producing power. Depending upon how the circuitry is done, this usually means that power has no place to go, so it will fry the diodes on your alternator.
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Just like Ragtime says, but most likely will keep chargin your batteries, unless you have an electronic switching system that disconect it from the keys (I've never saw this config) .... and yes, you loose all the alarms too.
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Old 07-07-2008
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I would suspect you have fried your alternator. You should check the output with a multimeter.

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It's all in how it's wired up. Generally, the power for the tach and gauges gets turned on when 1. the switch is on AND 2. when there is more than 5 pounds of oil pressure. As to how the alternator is wired, it might not need that signal from the oil pressure switch to come on. My old Perkins does. No oil pressure, no field voltage, no tach, no hour meter.

The same is true on the big boat's Volvo. Everything is a function of the keyswitch and the oil pressure switch. Nothing moves until those two conditions are met.

As for your alarms, I wouldn't put a huge bet on them working, either. Nearly everything electrical/electronic on more modern engines is predicated on having the 'ignition' switch on.
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Old 07-07-2008
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When I turned the switch back to the ON position, the tach came back to life, which indicates that the alternator is still sending its sense signal, and the voltmeter I have connected to the battery banks jumped to 14+ volts, so I don't think I fried anything. These took a few moments to come back on, as the regulator has a built-in startup delay.

I have a system like doggie's, i.e. BlueSeas dual circuit switch, ARS battery combiner, Balmar 90A alternator with ASRIII external smart regulator. I will check to see how it's wired, though.

Thanks,
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Old 07-07-2008
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Quote:
Originally Posted by jbondy View Post
Does this mean the charging circuitry was also turned off?
Yes, but it will turn off the field windings, so it won't do any harm. Imagine how silly it would be to have a switch that went through a position where it could damage your alternator.
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Old 07-07-2008
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most main four-position battery switches do--off.
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Originally Posted by BigNige View Post
Yes, but it will turn off the field windings, so it won't do any harm. Imagine how silly it would be to have a switch that went through a position where it could damage your alternator.
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Old 07-07-2008
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Quote:
Originally Posted by sailingdog View Post
most main four-position battery switches do--off.

Yeah, OK, and so is disconnecting the leads. But we are talking about a switch that has to go past "off" to "stop" every time you use it.
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