Did My Alternator Just Blow?

[fallingeggs]

Hello!

We had a bit of an exciting start to our sail from Dominca for Martinique this morning. While motoring out of the anchorage due to low winds, I noticed an abnormal high pitch whine coming from the engine. Belt tension looked fine. Checked the engine instruments; voltage is reading rather low at high 11, but Victron is reading closer to 13. Go back below to look at the engine and notice smoke with a bit of an electric smell. Shut down engine immediately. Quickly realize we have zero power to the electronics, except for the bilge pump.

Thankfully we already had our main raised and were able to maintain steerage with the light wind. After calming the nerves, I removed everything off the batteries and around the engine. Other than the main battery fuse being blown, I can't find the source of the smoke or any short. Replaced the fuse and everything powered right back up. We are now racing off to Martinique.

I am thinking the issue is an internal short of the alternator, but unsure how to confirm this. Anyone have tips? It is the original, 35 year old 55 amp alt, so I wouldn't be surprised.

I also don't have anyway to isolate the alt while the engine is running other than cutting the positive wire. If I do this, should I be able to run the engine without fear of blowing the main fuse? I don't depend on the alt for charging and can put up with no RPM until it is replaced.

Or maybe I'm on the wrong path completely. Any tips to test other parts of the system are welcome!

[travellerw]

Originally Posted by fallingeggs

Hello!

We had a bit of an exciting start to our sail from Dominca for Martinique this morning. While motoring out of the anchorage due to low winds, I noticed an abnormal high pitch whine coming from the engine. Belt tension looked fine. Checked the engine instruments; voltage is reading rather low at high 11, but Victron is reading closer to 13. Go back below to look at the engine and notice smoke with a bit of an electric smell. Shut down engine immediately. Quickly realize we have zero power to the electronics, except for the bilge pump.

Thankfully we already had our main raised and were able to maintain steerage with the light wind. After calming the nerves, I removed everything off the batteries and around the engine. Other than the main battery fuse being blown, I can't find the source of the smoke or any short. Replaced the fuse and everything powered right back up. We are now racing off to Martinique.

I am thinking the issue is an internal short of the alternator, but unsure how to confirm this. Anyone have tips? It is the original, 35 year old 55 amp alt, so I wouldn't be surprised.

I also don't have anyway to isolate the alt while the engine is running other than cutting the positive wire. If I do this, should I be able to run the engine without fear of blowing the main fuse? I don't depend on the alt for charging and can put up with no RPM until it is replaced.

Or maybe I'm on the wrong path completely. Any tips to test other parts of the system are welcome!

Do you have the pinout for the alternator? If you do, then you should be able to simply disconnect the "field" wire and that will render the alternator disabled. At that point you can disconnect the positive wire from the alternator and it should be nothing but a spinning belt pulley.


Once you get here (Martinique), there are a couple of places that can test it for you. Le Marin is your best bet, but there is good automotive services in Fort de France. I even think there is somewhere that will rewind it, but not sure it would be worth it. Probably makes more sense to replace it if its failed.

P.S. Based on your description, I'm pretty sure your alternator has failed with an internal short.

[txg]

I would suppose coming to le marin as well. We're here for two weeks now and compared to most other caribbean places (maybe except St. Martin) it is so much easier to get things done, you can buy and get service for nearly everything here

[fallingeggs]

Thanks to the both of you. Safely anchored in Saint Pierre. Will move on down to Le Marin in a few days. Will also attempt to disconnect the positive and field (if I have one... would a self exciting alt have a field wire? Could mine be self exciting? I have dug around before and thought I only saw the positive).
Cheers.

[travellerw]

Originally Posted by fallingeggs

Thanks to the both of you. Safely anchored in Saint Pierre. Will move on down to Le Marin in a few days. Will also attempt to disconnect the positive and field (if I have one... would a self exciting alt have a field wire? Could mine be self exciting? I have dug around before and thought I only saw the positive).
Cheers.

Yes, "self exciting" alternators are actually a thing. If you do have a "self exciting" alternator, then just unhooking the positive wire will completely disable the alternator.

It would be a good idea to get it disabled as you will most likely need your motor when you come around diamond rock. The 11 miles between diamond rock and St. Anne can be brutal. Our friend tried to "sail" it yesterday and it took him 10 hours of "no cheat" sailing (yes for just those 11 miles). However, in his defense he didn't have a foresail as he blew it out.

I would head directly for Le Marin and not anchor out in St. Anne. Although St. Anne is MUCH nicer, it makes for a long wet, rough dinghy ride into Le Marin. Its pretty quiet around here so I don't think you will have an issue finding a spot to anchor in Le Marin.

P.S. How was the run across the Dominica-Martinique Channel? That is one of my least favorite channels and can be darn rough in the wrong conditions.

[fallingeggs]

Originally Posted by travellerw

Yes, "self exciting" alternators are actually a thing. If you do have a "self exciting" alternator, then just unhooking the positive wire will completely disable the alternator.

It would be a good idea to get it disabled as you will most likely need your motor when you come around diamond rock. The 11 miles between diamond rock and St. Anne can be brutal. Our friend tried to "sail" it yesterday and it took him 10 hours of "no cheat" sailing (yes for just those 11 miles). However, in his defense he didn't have a foresail as he blew it out.

I would head directly for Le Marin and not anchor out in St. Anne. Although St. Anne is MUCH nicer, it makes for a long wet, rough dinghy ride into Le Marin. Its pretty quiet around here so I don't think you will have an issue finding a spot to anchor in Le Marin.

P.S. How was the run across the Dominica-Martinique Channel? That is one of my least favorite channels and can be darn rough in the wrong conditions.

Great info thanks. I generally try not to cheat, but when the wind is 6-7knots, the motor is on.

The sail today was fun. We saw 18-20 knots (on our 56' mast) at 85-90 true. The waves on the south of Dominica and north of Martinique did noticable pick up (7'-), but the angle was off the nose to avoid slamming into them.

[fallingeggs]

Buggers. Disconnected the alternator and started the engine. Blew the fuse again without even a crank. By passed the fuse and tried to crank, nothing. Guess the starter was the issue or the alt blew it up too. Good thing I have been carrying a replacement for the last three years! Starter is original, so, again, not surprised. Just more work to do.

[travellerw]

Originally Posted by fallingeggs

Buggers. Disconnected the alternator and started the engine. Blew the fuse again without even a crank. By passed the fuse and tried to crank, nothing. Guess the starter was the issue or the alt blew it up too. Good thing I have been carrying a replacement for the last three years! Starter is original, so, again, not surprised. Just more work to do.

On the upside you probably found the culprit. I'm willing to bet your alternator is fine.

Look forward to seeing you in Le Marin (or maybe St. Anne if you don't have to go in for repairs now). There is a potluck on the beach in St. Anne. Usually starts around 1:00pm and ends at 5:30 or so.

[fallingeggs]

Great. Got the starter in and engine starts up. Will leave the alt disconnected until I get a few more fuses. Will look out for you. Cheers.

[ZULU40]

Originally Posted by travellerw

On the upside you probably found the culprit. I'm willing to bet your alternator is fine.

Similar to switching battery banks while the engine is running,
Engine running no battery connection and ,,,,, phffft

Im thinking the diodes in the alternator have probably blown by now

[Cadence]

Originally Posted by fallingeggs

Hello!

We had a bit of an exciting start to our sail from Dominca for Martinique this morning. While motoring out of the anchorage due to low winds, I noticed an abnormal high pitch whine coming from the engine. Belt tension looked fine. Checked the engine instruments; voltage is reading rather low at high 11, but Victron is reading closer to 13. Go back below to look at the engine and notice smoke with a bit of an electric smell. Shut down engine immediately. Quickly realize we have zero power to the electronics, except for the bilge pump.

Thankfully we already had our main raised and were able to maintain steerage with the light wind. After calming the nerves, I removed everything off the batteries and around the engine. Other than the main battery fuse being blown, I can't find the source of the smoke or any short. Replaced the fuse and everything powered right back up. We are now racing off to Martinique.

I am thinking the issue is an internal short of the alternator, but unsure how to confirm this. Anyone have tips? It is the original, 35 year old 55 amp alt, so I wouldn't be surprised.

I also don't have anyway to isolate the alt while the engine is running other than cutting the positive wire. If I do this, should I be able to run the engine without fear of blowing the main fuse? I don't depend on the alt for charging and can put up with no RPM until it is replaced.

Or maybe I'm on the wrong path completely. Any tips to test other parts of the system are welcome!

Give the alt. a sniff test. See is it smells. I'd hazard a guess a bearing has worn enough the rotor and stator came into contact.

[Dove1955]

Originally Posted by travellerw

Do you have the pinout for the alternator? If you do, then you should be able to simply disconnect the "field" wire and that will render the alternator disabled. At that point you can disconnect the positive wire from the alternator and it should be nothing but a spinning belt pulley.


Once you get here (Martinique), there are a couple of places that can test it for you. Le Marin is your best bet, but there is good automotive services in Fort de France. I even think there is somewhere that will rewind it, but not sure it would be worth it. Probably makes more sense to replace it if its failed.

P.S. Based on your description, I'm pretty sure your alternator has failed with an internal short.

If there is an internal short in an alternator, then the hot lead out has a direct to ground short. If you have a multimeter, with the engine off, use the ohm selection with one probe on the
hot and the other one to the frame of the alternator. There should be no reading if everything is ok. Any reading at all means there is a short.

[travellerw]

Originally Posted by ZULU40

Similar to switching battery banks while the engine is running,
Engine running no battery connection and ,,,,, phffft

Im thinking the diodes in the alternator have probably blown by now

If its a self exciting alternater, then I will bet it hasn't.

[travellerw]

Originally Posted by Dove1955

If there is an internal short in an alternator, then the hot lead out has a direct to ground short. If you have a multimeter, with the engine off, use the ohm selection with one probe on the
hot and the other one to the frame of the alternator. There should be no reading if everything is ok. Any reading at all means there is a short.

Sure.. Except he already posted it was a starter short..

[fallingeggs]

Originally Posted by travellerw

If its a self exciting alternater, then I will bet it hasn't.

Turns out I was mistaken. Removed three wires. Third, I guess, being the tap for the tac.