Potential damage to alternator diodes

[Scott T-Bird]

Yesterday, I was pushing my boat along at WOT for about a 5-minute spell and I detected slightly different engine sound. I also thought I detected an unusual smell, like something electrical or mechanical could be cooking. I noticed slightly higher rpm but more importantly, the voltage guage showed just around 12.5 v. I went below and looked at the Balmar battery monitor and could see immediately that the batteries weren't charging. This triggered my recollection that I had recently disconnected the alternator at the service disconnect switch that I have installed. I switched it on (while the engine was still going at WOT) & everything appeared to go back to normal. The voltage gauge showed 14+ volts and the monitor climbed to over 40 amps when I stopped watching. As I finished motoring to home port, it seemed like the faint smell from earlier had completely dissipated. I had to leave for home in a hurry so I didn't bother checking under the engine cover.

I'm wondering if I did any damage to the alternator diodes or belt. I have a high-output alternator (not the original but it is at least 20 years old) and a new Balmar MC-618 external regulator. The belt is a new serpentine belt installed with an adaptor kit to change the pulleys. I'm pretty sure I wired the disconnect switch and regulator correctly with the regulator power wire on the alternator side of the disconnect switch. Also, my alternator has some sort of jumper between the positive and negative posts that I guess is some kind of alternator protection device. I have no idea if it is any good.

Everything seemed to return to normal. Since I don't have a photographic memory of my wiring diagrams, I'm going to make a point of verifying every connection and create accurate wiring diagrams for reference.

 

[dLj]

Doesn't sound like you have done anything to damage you alternator. Hard to say what the smell may have been. But since everything started charging correctly after switching the system.back on - you certainly haven't blown your diodes...

dj

 

[dlochner]

The belt probably should be replaced. It went from no load to a full load in seconds as a result some of the belt is now the belt dust on the alternator.

If the diodes were blown or any of the other electronics in the alternator were damaged, the alternator would not be charging the battery.

 

[colemj]

That jumper between the terminals is a TVS diode to help mitigate a voltage spike on disconnect.

If the alternator is working, its diodes are fine.

Belt damage on a serpentine should be obvious.

Mark

 

[Davidasailor26]

The usual cause of burning out diodes is cutting the load while the alternator is pushing many amps. You didn’t do that, so your diodes are probably still fine, as evidenced by the fact that the batteries still charged fine when reconnected. If you didn’t hear any belt squeal when you turned the switch, and you don’t see any unusual belt dust I probably wouldn’t worry about the belt. The pulleys were already spinning so it’s not like a stopped pulley got put on the moving belt.

 

[Scott T-Bird]

The usual cause of burning out diodes is cutting the load while the alternator is pushing many amps. You didn’t do that, so your diodes are probably still fine, as evidenced by the fact that the batteries still charged fine when reconnected. If you didn’t hear any belt squeal when you turned the switch, and you don’t see any unusual belt dust I probably wouldn’t worry about the belt. The pulleys were already spinning so it’s not like a stopped pulley got put on the moving belt.

That's what I thought. There was not any sign or noise of distress once I switched the alternator on. The sound of the engine seemed normal and the rpms dropped about 100. That photo was taken 5 years ago when I removed the alternator and replaced the standard v-belt pullies. The belt dust blackened the entire engine compartment. There has not been any belt dust since I installed the serpentine belt. I haven't looked at the belt yet since this episode. I do have a spare, but I figured I will never need it.

I thought the smell might be from the belt freewheeling. In any case, the smell was very faint and seemed to disappear when the alternator was loaded. Once there is a smell in your nose, it seems, it lingers for a while so it is hard to tell when it disappears.

 

[Stu Jackson]

This triggered my recollection that I had recently disconnected the alternator at the service disconnect switch that I have installed. I switched it on (while the engine was still going at WOT) & everything appeared to go back to normal

Dave and david are both right. If your house bank was pretty full there is more than anecdotal information that says with low amps diodes can and do survive.
I have previously noted that I depend on removing the AO fuse and hadn't gotten around to installing a switch. Reading this makes me understand why I never will: it is hard(er) to forget when the saloon seat cover that houses the battery bank and fuse are off than a simple switch somewhere. Of course, it's always argued that in case of emergency a switch is easier. While that's true, to turn of my AO I just turn the ignition switch off, engine keeps running. That's because it provides power to my MC-612 external regulator.
Glad things are working for you, Scotty. A good report. Don't forget to let us know what the SOC of your house bank was when this happened; always helpful info to know when discussing alternator output (AO). I didn't want to assume this happened when you were leaving your slip after just unplugging with a full house bank. What work were you doing that prompted you to use that switch? Just curious about use patterns.

 

[marcham]

Just a few thoughts...
a) Engine RPMs should not change with alternator loading up/down. The noise will change. When you move the lever, you are setting the governor RPM, not opening/close a throttle body. The governor then feeds fuel to match that RPM. A change of sound is normal with a change in load, but the RPMs should not change. It might have a slight RPM change (bump) but should go back to it's previous setting.

b) Does the alternator service disconnect also shut off the regulator? If so, no problem for the connection while the engine is running. If the regulator was powered and the alternator output was not connected to anything, it certainly would have worked pretty hard.... that may be the odd / new smell. Does everything work? If so, keep an eye on things, as you may have shortened the life of the regulator or alternator components. Ideally, the alternator disconnect also depowers the external regulator or disconnects the field wire (still not a good idea to open the switch while the engine is running). Some battery switches have a separate power lead for the external regulator to avoid these kinds of issues. If it is inadvertently switched to OFF, it will disconnect the alternator field wire before disconnecting the alternator output from the battery. https://www.bluesea.com/products/3001/HD-Series_Heavy_Duty_On-Off_Battery_Switch_with_AFD

 

[Scott T-Bird]

Don't forget to let us know what the SOC of your house bank was when this happened; always helpful info to know when discussing alternator output (AO). I didn't want to assume this happened when you were leaving your slip after just unplugging with a full house bank. What work were you doing that prompted you to use that switch? Just curious about use patterns.

Yes, batts were fully charged when I left the dock. I had been out for the day and anchored for a while before returning home so there was discharge for the day, but not very much. Fridge, chartplotter & instruments running, with some autopilot. During my difficulties earlier this summer, I discovered a failed spade connector underneath a rat's nest buried in electrical tape. The failed connector kept me from starting the engine! At the time, I just crimped the failed connector with a pliers to get me going. Later, I replaced the connector with a secure butt connection. Since I had to work with tools in close proximity to the back of the alternator, I shut it off for safety. As I have recently learned, the safety aspect is a bit more complicated as I will discuss in a follow-up to the post by @marcham above.

 

[Scott T-Bird]

Just a few thoughts...
a) Engine RPMs should not change with alternator loading up/down. The noise will change. When you move the lever, you are setting the governor RPM, not opening/close a throttle body. The governor then feeds fuel to match that RPM. A change of sound is normal with a change in load, but the RPMs should not change. It might have a slight RPM change (bump) but should go back to it's previous setting.

b) Does the alternator service disconnect also shut off the regulator? If so, no problem for the connection while the engine is running. If the regulator was powered and the alternator output was not connected to anything, it certainly would have worked pretty hard.... that may be the odd / new smell. Does everything work? If so, keep an eye on things, as you may have shortened the life of the regulator or alternator components. Ideally, the alternator disconnect also depowers the external regulator or disconnects the field wire (still not a good idea to open the switch while the engine is running). Some battery switches have a separate power lead for the external regulator to avoid these kinds of issues. If it is inadvertently switched to OFF, it will disconnect the alternator field wire before disconnecting the alternator output from the battery. https://www.bluesea.com/products/3001/HD-Series_Heavy_Duty_On-Off_Battery_Switch_with_AFD

Thanks for these comments. I recently read an article by @Maine Sail discussing the correct way to power the regulator and I'm pretty sure that I've got it wrong. I haven't been back to inspect but it is now a high priority. After I bought the boat, I replaced the MC-614 regulator with a new MC-618 regulator. Since the wiring was already in place, I'm pretty sure I just connected the power lead in the same manner as it was done before. The previous owner didn't have an ADS and that was my addition. I'll bet the regulator power lead was open. Obviously, this is a safety concern, so I'm not sorry this came to light.

I have a keyed ADS so I believe it is the m-series 6004 from Blue Sea.