Alternator failure

[Jim Boltz]

I have been trying to solve issues with upper helm analog tach not receiving signal and my digital display at main helm blanking after an hour or so of engine run time. In the process of troubleshooting I discovered my port alternator was producing zero power. It is connected to a 2 alternator/3 battery isolator. Ordered and received a new alternator from Seaboard. Installed and tests good, 13.5 volt output. It also solved my blanking digital display and my analog tach. Happy as could be. Run boat and after a couple hours I notice analog tach becoming erratic, then digital dislpay blanks, and the alternator has stopped putting out power. I have a three wire alternator, the main output post, an exciter wire that brings 12V to the alternator and a third wire which i’m not sure what it does but runs to some sort of relay on above the engine fuel filter. Engine is 480CE. So question is what is killing my alternators?

Topic

[Tony Athens]

Diode Isolators : Far from old school and IMO, offer many advantages over the latest generation of automatic charging relays/combiners, especially with electronic engines that I feel should NEVER talk to each other unless in an special situation and the operator wants them to…………….But this is a controversial topic and also has a lot of old wives tales attached to it, all based on ignorance about diode isolators and how alternator actually charge & sense voltage as part of any discussion on the subject….

Tony

1 user thanked author for this post.

Jim Boltz

[Rob Schepis]

Battery Terminal Voltage

Not sure if you’ve seen this:

Installing Digital Volt Meters (DVM) on Your Boat

[Jim Boltz]

Thanks for the info and tips to improve what I’ve got now. My system does already keep the three batteries independent from each other (except for auto parallel during engine start). The system does have a single common ground. My left alternator has failed (twice now) due to something else going on in the system. I’m hoping it is the isolator as everything else tests normal with a voltmeter. Everything worked 100% (including analog tach and the digital display) right up until the new alternator failed. I am going to test the diodes on the isolator in the morning to see what’s really going on there. The right alternator has been keeping my entire system charged and has been for months as I just figured out that my left alternator has not been working for that long. I really like the idea of voltmeters on dash for all 3 batteries and will be installing that in the future. I’ve been told isolators are now considered old school and I should consider replacing with charging relay. I’ve looked into that briefly but its boating and fishing season and consider that a winter project.

[Tony Athens]

Jim,

Unfortunately, you are not suppling enough infor to sort this out (internal wiring of the diode isolator), how and where your alternator sensing leads from both alternators are hooked up, along with many other details…………. Also, with all that said, it would be impossible to really troubleshoot based on how it is supposedly wired and there is no way to tell what component is working or not working ( a bad diode/diode isolator, a non-working alternator, a bad relay, etc) , ……………..If this was my boat, I’d rewire all of this to a much more intuitive system, one that you understand and one can be isolated to sort out what may be working right or may not be working……………………….

#1 for all is you have to be able to MONITOR BATTERY TERMINAL voltage on all 3 banks individually whether an engine in running or not, and a way to shut of all paralleling and battery charger input. Personally I always use manual ON-OFF switches for all paralleling, I never rely on a relay..

Having two engines and 3 banks ( engine 1, engine 2, & the house bank) is the way to go as long as you can have all isolated except for ONE COMMON negative. If one engine alternator should go bad, or its starting bank, it should not affect anything else.. If the house go bad, it should not affect either engine…The way you have it set up, no one has a clue as what is affecting what..

Corey sent you a well thought out DC power distribution system diagram that is 100% long term proven and one that is simple to “see” if you have an issue and one that will allow you to pin-point” where it is.. When you size “ONE alternator in” with “2- bank output” (3 terminal) isolators, size them for at least 80-100AMP over your alternator output—I’d use 250 A unit for 160A alternators .. And be sure you hook the alternator sensing lead up to the one of the diode output terminals—We prefer a simple DPST switch ( 14ga wire) on that so you can “prioritize” the alternator output for either the starting bank or the house bank. With DVM’s at the dash, you will always “see” exactly what is going on—engine(s) off or on.

Your call as to how to move fwd, but IMO, I’d start fresh if you are in it for the long term..

Tony

[Jim Boltz]

Tested exciter wire with engines running. It’s a steady 13.8. The third wire appears to be something that runs from the alternator, not to it. My gut says problem is the isolator and voltage from the right alternator backing up into the port one as there is a voltage leak from isolator at the post where port alternator connects. Going to get new alternator repaired locally, plan to install a new isolator unless someone thinks it stems from elsewhere. Oh all batteries show 12 something static and 13.8 with engines running.

[Jim Boltz]

Tach

I was told my tach did not run off alternator but hard to believe it does not since it worked great as soon as new alternator was installed then failed as alternator quit. I don’t see a transducer on bell housing just 2 of the type pictured.

[Jim Boltz]

Pics

wiring diagram

[Jim Boltz]

Pics

Isolator and 3rd wire from alternator

[Jim Boltz]

I will run back down and take a pic of wiring diagram from owners manual. In the meantime I put a voltmeter on the post where the port alternator connects to the isolator. It reads initially 8 volts then counts down and reads a steady .5 volts. The stbd alternator post on the isolator reads zero until motor is started then reads 14.0. With stbd motor running I read about 2.5 volts on the post of the port alternator where it connects to isolator. It should be zero. I think I am getting voltage backing up the line to port alternator, can this cause the diodes on alternator to fail? Pics will follow.

[Corey Schmidt]

Jim, can you provide a simple sketch of how your DC distribution system is configured? Both YOU and us need to really understand this before we can jump in to help troubleshoot…

Also, are you clear as to what is driving your tach signal? is it the alternators or are you using magnetic pickups?

What exact diode isolator(s) are you using?

Here are some examples: https://www.sbmar.com/articles/typical-dc-power-distribution-example/

[Jim Boltz]

alternator diodes

After a bit of searching found this about diagnosing alternators, “Diode failures may also allow AC current to leak into the electrical system. AC voltage creates electrical “noise” that can confuse electronic modules and digital communications. A leaky diode also can allow current to drain out of the battery through the alternator when the vehicle is not being driven.” So I am pretty sure I own 2 alternators now with failed diodes, just need to figure out the cause. I’m not a whiz with electrical but the problem seems to be from 1 of the 3 wires, a backflow from the isolator, the exciter wire, or the third wire.

[Author]

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