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Go Back   SailNet Community > On Board > Gear & Maintenance > Engines > Diesel
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Diesel This is a new forum dedicated to diesel engines and their applicable accessories.


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  #21  
Old 11-17-2011
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Quote:
Originally Posted by MarkSF View Post
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.
Mark,

Curious to know if it blew because it was turning with no exiter (battery) present or if turning the key off disconnected the load. I can imagine there are as many wiring options as one can think about out there.

Thanks, Dabnis
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  #22  
Old 11-17-2011
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Quote:
Originally Posted by dabnis View Post
Mark,

Curious to know if it blew because it was turning with no exiter (battery) present or if turning the key off disconnected the load. I can imagine there are as many wiring options as one can think about out there.

Thanks, Dabnis
The wiring is the stock setup straight out of the Universal manual. The key turns off the exciter, but does not disconnect the load.
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  #23  
Old 11-17-2011
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As noted above, there are different ways of wiring engines.

Most engines have the starter solenoid wired thru the ignition key, some with a separate starter button.

Most engines have the temp and oil sensors wired thru the ignition key.

Most engines have the guages wired thru the ignition key.

Many engines have the alternator field coil wired thru the ignition key...this provides excitation to the alternator for those which are not self-exciting.

Other accessories may also be wired thru the ignition key on some boats.

With diesels, in general, it is good practice to follow these steps when starting or stopping the engine:

(when starting the engine)

1. Turn on the ignition key
2. Start the engine, either with the ignition key or a separate starter button
3. Check the exhaust to be sure water is coming out
4. Check the oil guage to be sure you have oil pressure
5. Leave the ignition key ON

(when stopping the engine)

6. Press the STOP button or pull the STOP lever
7. When the engine stops, listen for the oil alarm -- it should go off when oil pressure drops -- this tells you that the low oil pressure alarm is working OK
8. Turn off the ignition key

Mark...on most boats, turning off the key with the engine running should not blow the diodes on the alternator; it should merely remove the field current which would stop the alternator output. However, it's still not good practice to turn the key off while the engine is running.

Breaking the connection between the alternator and the batteries, however, will definitely blow the alternator diodes very quickly if the alternator was putting out any appreciable current when the connection was broken. On many boats with the alternator wired thru the battery switch, this is much too easy to do, e.g., by switching the 1-2-Both-Off switch to the OFF position, intentionally or otherwise.

Dockbumdan: you've been a very lucky camper for the past 20 years. Time to mend your evil ways and see if you can do it right for the next 20 :-) And, who knows....if your dockmates on the Sassafras see you doing it right for awhile, they might just invite you along for a sail on their boats!

Bill

Last edited by btrayfors; 11-17-2011 at 02:58 PM.
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  #24  
Old 11-17-2011
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Bill, that's a good summary.

I've been told before that what I did should not have blown the alternator. However, it did. I've also heard from others that have had the same experience. Therefore my conclusion has to be that it can blow the alternator but it's a rare occurrence.
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  #25  
Old 11-17-2011
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Quote:
Originally Posted by btrayfors View Post
As noted above, there are different ways of wiring engines.

Most engines have the starter solenoid wired thru the ignition key, some with a separate starter button.

Most engines have the temp and oil sensors wired thru the ignition key.

Most engines have the guages wired thru the ignition key.

Many engines have the alternator field coil wired thru the ignition key...this provides excitation to the alternator for those which are not self-exciting.

Other accessories may also be wired thru the ignition key on some boats.

With diesels, in general, it is good practice to follow these steps when starting or stopping the engine:

(when starting the engine)

1. Turn on the ignition key
2. Start the engine, either with the ignition key or a separate starter button
3. Check the exhaust to be sure water is coming out
4. Check the oil guage to be sure you have oil pressure
5. Leave the ignition key ON

(when stopping the engine)

6. Press the STOP button or pull the STOP lever
7. When the engine stops, listen for the oil alarm -- it should go off when oil pressure drops -- this tells you that the low oil pressure alarm is working OK
8. Turn off the ignition key

Mark...on most boats, turning off the key with the engine running should not blow the diodes on the alternator; it should merely remove the field current which would stop the alternator output. However, it's still not good practice to turn the key off while the engine is running.

Breaking the connection between the alternator and the batteries, however, will definitely blow the alternator diodes very quickly if the alternator was putting out any appreciable current when the connection was broken. On many boats with the alternator wired thru the battery switch, this is much too easy to do, e.g., by switching the 1-2-Both-Off switch to the OFF position, intentionally or otherwise.

Dockbumdan: you've been a very lucky camper for the past 20 years. Time to mend your evil ways and see if you can do it right for the next 20 :-) And, who knows....if your dockmates on the Sassafras see you doing it right for awhile, they might just invite you along for a sail on their boats!

Bill
Bill,

Good explanation!! To prevent an accidental "open" what about having the alternator output hard wired to the starting battery and with a lead from a battery isolater device going to the 1-2-Both- off switch?

Dabnis
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  #26  
Old 11-17-2011
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Quote:
Originally Posted by dabnis View Post
Bill,

Good explanation!! To prevent an accidental "open" what about having the alternator output hard wired to the starting battery and with a lead from a battery isolater device going to the 1-2-Both- off switch?

Dabnis
Depends, of course, how your boat is wired. However, I don't like it, and I don't much like battery isolators either (i.e., the ones with diodes and/or active relays).

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).

Just be sure to include an appropriate type and size fuse or high AIC breaker in the alternator output cable, located close to the batteries. Size it for at least 150% the maximum output of the alternator. I prefer ANL fuses for this purpose.

BTW, many charging setups can be improved by running a ground wire -- same size as the positive charge wire -- directly from the alternator ground lug to the house battery bank. Grounding the alternator through the engine isn't quite the same thing, but is the situation I find on many boats.

Bill
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  #27  
Old 11-17-2011
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Quote:
Originally Posted by btrayfors View Post
Depends, of course, how your boat is wired. However, I don't like it, and I don't much like battery isolators either (i.e., the ones with diodes and/or active relays).

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).

Just be sure to include an appropriate type and size fuse or high AIC breaker in the alternator output cable, located close to the batteries. Size it for at least 150% the maximum output of the alternator. I prefer ANL fuses for this purpose.

BTW, many charging setups can be improved by running a ground wire -- same size as the positive charge wire -- directly from the alternator ground lug to the house battery bank. Grounding the alternator through the engine isn't quite the same thing, but is the situation I find on many boats.

Bill
OK, sounds better. It appears that with your setup one wouldn't need the 1-2-both-off switch, a lot simpler. Good point on the separate ground wire, lots of amps running around. Thanks for the feedback.

Dabnis
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  #28  
Old 11-17-2011
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The designated ground from alt groundlug to bat - terminal is certainly a good idea. Allows alt to read correct voltage. The other common source of voltage loss is the either neither switch If you are in doubt about v readings put a voltmeter across the backside bolts and look for ie drop. Also look for potential difference between bolt and wire terminal .These points are just as important as the battery post clamps but are usually in the locker with the wet gear. May not be popular but I've isolated starting bank with a continuous run solenoid (rv stuff) . When oil pressure is up, all three banks are ganged in parallel and the solenoid valve on the water cooled muffler is shut. Shut down is simple; pull handle, hear alarm, turn key raise a glass to all the women I've known.
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  #29  
Old 11-19-2011
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Dan, Diesels don't have a "choke", stopping the engine is done by turning off the fuel supply within the injector pump by a manual cable or electrical solenoid. Its surprising that your hour meter worked with your habit of key off operation.
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Old 11-20-2011
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Quote:
Originally Posted by bandaidmd View Post
Dan, Diesels don't have a "choke", stopping the engine is done by turning off the fuel supply within the injector pump by a manual cable or electrical solenoid. Its surprising that your hour meter worked with your habit of key off operation.
Some diesels may have a "plate" or other device that blocks off the air flow. Many years back we had a 3-71 Detroit diesel in a commercial salmon troller. IIRC, I think it had that sort of arrangement, possibly in addition to a fuel shut off cable?

Dabnis
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