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Old 07-19-2018, 05:09 PM   #1
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Perkins 6.354 Alternator and harness

It's the gift that keeps on giving!


The post I originated last year, and is currently 'stuck' to the top of the list, finished with my reporting that I had taken the MRBF post fuses out of the engine start cabling and replaced 'em with mechanics' sockets. At least as good as a penny in an old-style house fusebox, but the AYBC does not require fuses in the starting circuits.


I did not report that, while the port engine will start, the starboard engine's alternator idiot light lights as soon as the battery switch is 'on'. The engine will start, but the idiot light remains on and the ammeter does not budge from zero. When we replaced the battery wires at the starter, the + stud turned. I assumed that we'd damaged a connection within the starter (solenoid equivalent is within the starter).


I got my ever-willing, flexible son back aboard today and he discovered that all the large wire's insulation between the starter and the alternator was melted. We removed the alternator and found that it was an 'aftermarket' unit from Slovakia, had been thoroughly wet and was covered with corrosion. We removed the wiring harness and found that there was no fuse where the port engine has one. Presumably, the PO's 'mechanic' had thought it unnecessary.


I had started to make a new harness and thought it reasonable to measure and trace the wires so that the new one matches the Perkins original. I'm quite sure, and remain quite surprised that the fuse is on the ground side of the alternator wiring. That is, the alternators' own case is not the ground; it has a separate fused ground tagged onto the starter motor mounting bolts.


Pics show the harness and the end that tags onto the alternator. Thoroughly corroded at the connection.



I'm looking for your readings on your baloney meters. I'm self-medicating with Goslings and Tonic.
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Old 07-19-2018, 08:33 PM   #2
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Ouch! That doesn't look like fun.

When I recabled, I dropped the dual-use start cable function (charge from the alternator and start load) with the small wire running to the alternator. I ran my alternator charge directly to the battery banks with large cable. The load cables are all run separately to switches outside the ER, then to the distribution panels. I lost the function of the analog ammeters but replaced them with a SOC meter.

I wanted more control over the load without affecting the charge...and vice versa. I can still deselect charge with my keyed start switches without affecting the loads. I've been very pleased with the arrangement.
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Old 07-20-2018, 04:30 PM   #3
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Wow! Are you certain it actually used to work? Bad alternators sometimes get hidden by battery chargers and generator use. One day the genny craps out and they find a main engine won't start.
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Old 07-21-2018, 09:52 AM   #4
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I believe the alternator quit/shorted at about the time I replaced the battery primary wires. Seems a totally unfair intervention of the gods! That might well be why my MRBF fuses blew even with 300amp fuses installed.
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Old 07-22-2018, 05:56 PM   #5
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Further thoughts and a rewrite of my adventure:


Woo hoo! More fun is being had. When last I posted, I had said that the 300amp fuse in my port engine MRBF had allowed one start before it blew. I assumed that the fuse simply was not big enough to cope with the initial load of a starting motor. So, I put a mechanics' socket in the fuse holder which brings me back to where I was: an unfused starter circuit. I then did the same on the starboard engine's fuseholder.

Went back to the helm position and the port engine started normally. The starboard engine's alternator idiot light lit just as soon as I turned the battery switch on for that engine. Obviously not normal. Being inordinately stupid at more times than I could wish to admit, I tried starting that engine. It started but the ammeter read zero and the idiot light remained on. Happily, it shut down instantly.

I thought back to my attempts to start the engines with 200amp fuses: again, I got one start out of the port engine and its fuse. No start out of the starboard then, and the fuse was blown. But wait! There's more!

I have posted previously that I've changed the engine start battery wiring and battery switches so that I could start either engine from either or both batteries. Additionally, I arranged that the either or both start batteries could be switched to serve as 'bank 2' at the 12v panel and its switch, and that I could start either engine using the house bank '1'.

As I was fiddling with the three switches in my first attempts to operate my new wiring system, having got one engine start out of the port engine's fuse, I noticed a smell of hot insulation. I thought it was from around the 12v panel switch but nothing was warm to the touch (the digital temp meter had the switch studs at about 4 deg warmer. Turns out that that switch is rated for only 150 amps, so I ascribed the smell to it.

Beware the thickening plot! When my son installed the battery wires to the starboard starter, he noted that the + stud had turned and that he could not tighten the connection as tightly as he'd wished. He'd left before I finished the wiring for the first try. When I had the no-start problem we decided that perhaps he'd turned the stud enough to damage/disconnect something within the starter.

He came back aboard on Thursday with the intention of pulling the starter and having a look at the stud in the light of day. Instead, he discovered that the wiring harness between alternator and starter had melted insulation from one end to the other. When he went to remove the wiring from the alternator, the ground side wire connection broke. He pulled the alternator and it was heavily covered in corrosion as was the melted wire.

We took the alternator to have it tested but the folks at an auto parts store and another at a marine service facility said to not bother, it being obvious that the thing was toast. And neither had a replacement. I've bought one from a Perkins parts supplier.

Current problem is to make a new wiring harness for the melted one and I might as well make another for the port engine. The port engine has its original alternator but a new starter of the sort that has an external relay. The starboard has a Slovakian alternator but has its original starter of the sort that has an internal relay. The port engine has had its alternator wiring messed with for the connections but has a fuse on the alternator hot side; additionally, the alternator ground is through a wire leading to a starter mounting bolt. The starboard engine has its original wiring but the fuse had been removed. Additionally, the Slovakian alternator appears (hard to get a good connection with my voltmeter...) to be to be grounded through its case. The installer appears to have used the original ground wire for power to the starter and the original power wire with the fuse removed for the ground side in addition to the case.

So! Why would the ground side wire be melted?
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Old 07-24-2018, 12:08 AM   #6
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Maybe it's time to hire a pro electrician? There's no telling what fried from your socket fuse.
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Old 07-25-2018, 11:45 AM   #7
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Quote:
Originally Posted by FlyWright View Post
Maybe it's time to hire a pro electrician? There's no telling what fried from your socket fuse.

You're right about socket fuses. Very high capacity. But clearly not at fault since an ABYC-compliant setup, no fuse, would have the same capacity. The fault lay in the serendipitous failure of the alternator and its wire corroded by slopped engine-cooling-system-cleaning stuff. Additionally, that replacement alternator was installed without the fuse that the harness originally had.



As for for hiring a pro marine electrician...I remain confident that I can do relatively simple things. I've wired two complete houses, one old car and important parts of two other cars, and done major work to three boats. (With sufficient drink taken, I'll confess the very few faults...) Electronics? Quite another thing.


I've made new wiring harnesses for the alternators of both engines and the replacement alternator has arrived. Had I not 'thrown my back out' carrying a shop vac from the basement to the LR, where I'm restoring 160-year-old windows to operable, I'd be down at the boat with my ever-willing son to put it all back together.
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Old 08-02-2018, 07:44 AM   #8
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The saga continues! Put alternator in. No joy (alternator idiot light lights when battery switch is on). Troubleshot. No joy (same). Took alternator out and to three places before finding someone who could verify that it's OK. Put it in and troubleshot some more. No joy (same). Finally connected the starboard's wiring and panel to the port engine: all normal. Connected the port's engine wiring to starboard and no joy (same). Thus isolated the current problem to the starboard engine's on-engine wiring harness. Removed same. I'll diagnose and repair it tomorrow. Nuri may return tomorrow afternoon to reinstall it. Still, therefore don't know what the real initial failure was.
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Old 08-04-2018, 09:26 AM   #9
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Light at the end of the tunnel!


I recorded the on-engine harness that we removed. I cut the tape wrapping open, inspected every conductor, cleaned the old tape goo off the wires, and rewrapped it.


Nuri swapped alternators from engine to engine. New alternator worked fine on port.


We reinstalled the wiring harness on starboard...after a discussion about connections at the starter motor: whether the several brown wires are + or - and the several black wires are - or +. I cast the deciding vote in my role as captain: brown are + and black are -. I had Nuri convinced that black is - by having him look at the port engine and checking continuity from the black wire at the readily, painlessly accessible start injector. Yup, black is -.


Turns out he'd wired all the smaller brown wires to the - post on the starter, and all the black wires to the + post. Give him a break! I can't get there at all. And he did it all by feel the first time (nearly two months ago). He forced himself further into the hellhole and made sure that everything was where my surveyed wiring diagram said it should be.


Upon trial, all instruments and idiot lights behaved correctly but the starter would not crank. Much troubleshooting ensued by checking that the 35 year old relays were not faulty (traded 'em from port) and that there was 12v at the (internal) starter solenoid on the CAV45.


Given that that starter worked just days ago, we presumably damaged some internal connection to the solenoid when a stud turned instead of the nut coming off.


Utterly exhausted and discouraged after two days and about 14 hours, we left the boat. Gotta' pull the starter and devour it in daylight. I presume it's the reverse-turning engine so correcting the starter, or having it rebuilt is the way forward. Sheesh!


Maybe Flyright was right, but stubborn counts for something, too.
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