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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel > 20 years without knowing, So I thought I'd ask.
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Diesel This is a forum dedicated to diesel engines and their applicable accessories.


Thread: 20 years without knowing, So I thought I'd ask. Reply to Thread
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Topic Review (Newest First)
12-10-2011 07:51 PM
Capt Len As an aside to the potential damage to alternator, turning the key off prematurely will turn off oil alarm .So now you pull the stop cord or whatever you have. No way of knowing if engine has actually stopped what with all the partying going on in the cockpit and you release the cord early.Engine gives it's last gasp and bounces on compression sucking salt water into cylinder from manifold, bending one or more con rods I can hear you say "'Only an idiot would do that!" Fortunately the insurgency company paid me for my time and parts and the bruises on my butt are finally fading.
12-10-2011 07:00 PM
dabnis
Quote:
Originally Posted by Rockter View Post
Dan,

Many ships, like mine, need a live ignition to excite the alternator rotor. I have one of those early, and reliable, Ample Power regulators from 1992.

If I turn the ignition off though, I simply do not charge.

I am puzzled as to how any other system would work? How would the alternator be regulated without a power supply? How would it charge?

I don't think it does any harm to my system to turn it off when engine is running, but I simply try never to do it. It has happened every now and again. All that happens is that the alternator amperage just drops to zero.
.
From an earlier post:

#19 (permalink) 3 Weeks Ago - Add Post To Favorites
dabnis
Senior Member Join Date: Jul 2007
Posts: 528
Rep Power: 5


Quote:
Originally Posted by casey1999
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.

Dabnis
12-10-2011 07:00 PM
hellosailor Rockter, if you have a diesel engine that is also referred to as a "compression" engine, and there actually is no ignition system. So there's no "ignition" power to your alternator. Even in a spark engine (aka Otto Cycle or gasoline engine) there's no ignition power used for the alternator, really. All you need to to apply some volts to "excite" the alternator, and that doesn't have to come from the ignition system at all.
As to regulating the alternator, again, ignition has nothing to do with it. The regulator is connected to the battery (or kludged directly to the alternator output) and the regulator then varies the exciting current depending on what voltage it senses at the battery.
IF your system is one of the many that interrupt alternator field(?) current when it is "key off", and IF your alternator is one of the many that are not protected against this condition, the bottom line is that if you interrupt most alternators the wrong way, they will see this as "Gee, the battery got real low, I'd better go to full output power! Warp ten, Now!" and proudly burn themselves out in less than 30 seconds by attempting to deal with what they sense as a low battery.

In fact this is a common tactic used by shyster repair shops when drivers come in for a battery/alternator check. They'll disconnect the (field? sense?) critical lead for a minute while showing you how the voltage is fluctuating or something, and then they'll show you how the alternator (now) is really dead.

If you know how your system is wired, whether your alterantor is vulnerable, etc. then it may be perfectly safe to shut the key while the engine is running. As a rule of thumb? Oh, well, we always tell the kids to go play in the street, there's never any traffic to worry about. (Wham.) Better to get in the habit of erring on the safe side.
12-10-2011 04:53 PM
Rockter Dan,

Many ships, like mine, need a live ignition to excite the alternator rotor. I have one of those early, and reliable, Ample Power regulators from 1992.

If I turn the ignition off though, I simply do not charge.

I am puzzled as to how any other system would work? How would the alternator be regulated without a power supply? How would it charge?

I don't think it does any harm to my system to turn it off when engine is running, but I simply try never to do it. It has happened every now and again. All that happens is that the alternator amperage just drops to zero.
.
12-09-2011 06:01 AM
jcboyce I know the 2 & 3 GM20f or 30F better.
As I remember the warning concerns the alternator, and I think it reads don't shut the ignition off before shutting down the engine. It is in the opperating manual.
I got the manuals from the yanmar web sit under previous modles, you might get one there.
Boyce
11-28-2011 01:14 AM
donradclife Turning off the key with the engine running will disable the alternator (and the alternator-driven tach), but shouldn't damage them. I have done this countless times without problems--sometimes to reset my smart regulator, and sometimes to cut off radio noise.
11-21-2011 05:22 PM
hellosailor dan, it seems you've been lucky for 20 years. As Jeff warns, MANY boats are wired such that turning off the key will kill the alternator, so the bottom line is that "the prudent mariner" doesn't shut or remove the key until after the engine is off.

To paraphrase Napolean, I'd rather have a lucky mariner than the prudent one, but still... your habit would cause damage on many boats. Ignoring the question of whether it is going to disable alarms, as well. As long as you don't touch the key on any other boat, that's not a problem.
11-20-2011 09:36 PM
Capt Len Jumper cables ,,,ta da! Or my special rig to isolate start from house. an RV type solenoid can be controlled by key,oil pressure or external switch Two are automatic ,3rd should painted red and used only if starts fail you.
11-20-2011 09:06 PM
davidpm
Quote:
Originally Posted by btrayfors View Post
Much prefer to lead the alternator output directly to the house batteries, and use a voltage follower device like the EchoCharge or DuoCharge to maintain the start battery -- which doesn't require much charging anyway. Simple, reliable, relatively inexpensive, avoids any need to switch this or that (and, potentially, make a mistake doing so).
Sounds good but don't you need a switch to put the house bank in the starting circuit in case the starting battery fails?
11-20-2011 07:36 PM
bandaidmd dabnis, +1 for cap'n Lens reply, hes spot on.
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