[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.

[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]

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]

wiring diagram

[Jim Boltz]

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.

[Jim Boltz]

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.

[Jim Boltz]

two pics one after starting with good data then after failure. If I shut down and restart data will show again then fail.

[Jim Boltz]

Cleaned connections, swapped computers, swapped last section of data wire to the display, and displays themselves, all no help. When key is turned system ok displayed with good data. Start and all indications appear normal. Then one by one all the data turns to dashes with flashing data inactive message. Each time the key is turned off and then back on it works for a short period then fails. Puzzling.

[Jim Boltz]

A cummins engine manual will have all the recommended maintenance items listed by engine hours. Combine that with what you can read here and you should be all right. I have been cleaning my aftercoolers every two years. Its a fairly simple job and Tony has a nice write up on how to do it.

[Jim Boltz]

I was told they are 24×31. they are acme. I don’t see any real discernible black smoke getting on plane. I can make 2600 rpm wot with full fuel and a couple of guys. I’m waiting to see what happens with warmer air and loaded for offshore. I have stock tabs and nose is a bit high but I don’t push tabs down much. I have seen guys discussing tabs on the Carolina classic owners forum.

[Jim Boltz]

Thanks, I will start on that next time I’m down there. Hopefully that is all that is required.

[Jim Boltz]

Went down this morn to troubleshoot. Turned key, system test ok, no data link inactive message. Started motor and let idle for over 5 minutes, all is normal. Yesterday I didn’t notice the problem until motors had been running for about 5 hours, mostly at idle. I suspect an elevated engine room temp may be causing the problem. Does the data link signal originate from the engine computer? If problem arises again should I swap computers in attempt to trouble shoot?

[Author]

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