Regulator to Alternator Wiring

Stu Jackson · January 21, 2007, 08:25:35 AM

Ten months after the installation of our new alternator and regulator (see Nov. 2006 Mainsheet Tech Notes) I took Aquavite for a fuel fill up about a mile and a half from our slip. After fueling up (with "only" 11.939 gallons for the past 30 hours engine hours) we headed back. The tachometer had its usual 45 second delay, which turned into 46, 47, 48...seconds. It just didn't go on. I checked below and saw that the lights on the regulator were off and the volt meter showed that there was no charging from the alternator to the batteries.

I read the regulator manual on the way back to our slip which listed the "Troubleshooting" recommendations, including a page of tests of the wiring to the harness on the regulator. I prepared a list of "Symptoms" on a piece of paper, and planned out what the results of the voltmeter investigation would show.

But first, the connections. I checked the back of the alternator, and everything looked and felt fine. The large new #2 alternator output red wire was firmly in place, and the Zap Stop and the red power to the alternator from the regulator with the 10A automotive fuse were both in place. But, but, but...I'd remembered (and had documented in a wiring diagram) putting a fourth wire with a 1A automotive fuse on last April, and just couldn't find that fuse holder. I checked the regulator installation manual again, and confirmed that the "fourth" wire was the sense wire with the 1A fuse. I'd been working through the small alternator access door in the head, so I popped the top of the engine compartment and fished down and found the fourth wire.

It was laying on the floor of the engine compartment. The ring terminal was still on the positive post of the alternator, but the wire had completely disconnected and fallen off its ring terminal.

Of the four wires on the alternator positive post, this was the ONLY one that had been made "professionally" – it had come from the regulator manufacturer with the ring terminal installed with heat shrink and a foot or so of wire to the fuse holder. The other connections, listed above, had been field built when we did our upgrade. I was surprised to see the only factory-built connection fail. I installed a new ring terminal, used Liquid 'Lectrical Tape to seal it, and everything's working again.

Whenever something electrical doesn't work, remember to check the connections first!

Stu Jackson · January 30, 2011, 07:02:53 PM

A little update: Four years later "professionally installed" stuff is STILL falling off the back of the alternator!

Tach stopped working.

The ring terminal goes from the back of the alternator to a short wire that goes into an automotive ATO fuse holder, 10A. The wire sheared right off at the fuse holder.

I installed a new in-line old glass fuse holder for this power wire from the alternator to the regulator and a new ring terminal to the alternator post.

The tach works just fine again.

Here's a link to the wiring diagrams.

http://c34.org/bbs/index.php/topic,4548.0.html

If your tach unexpectedly stops, guess what to do.

Good reason to have electrical tools (wire stripper, ratchet crimper, wire, etc.) and fuse holder spares on the boat.

Bobg · January 31, 2011, 10:34:32 AM

Thanks for the update, everytime I see a post with Alternator in it I get interested as I still can't determine why my new 55 amp Mondo Alternator gets so hot it siezes when I charge my new T105's, the T105's have twice been professionally checked to be good, the Alternator brought back to Blue Circle and determined good, all items disconnected except the batteries,
Alternator charges and runs cool when connected to my start/reserve battery, or any other battery I bring aboard, just won't do the T105's either 2 at a time or all 4. Size 2 charging wire and ground. I finally gave up and do all the house bank charging thru shore power or my honda 1000 while at anchor. and just use the alt to maintain my start/reserve battery located behind the engine. Even the old marina mechanic gave up, "ideas anyone?"

Ken Juul · January 31, 2011, 11:43:48 AM

Since you know you can charge your start reserve battery. Why don't you temporarily move a pair of the T105's back there and try to charge them. If it works, then you know the problem is somewhere in the wiring to the main battery box.
I'd guess there is a short somewhere (probably out of sight) causing the alt to stay at full charging output.

Mike and Joanne Stimmler · January 31, 2011, 12:00:30 PM

Bobg,
One question. If you start off with fully charged T105 batteries from the dock, will the alternator maintain the charge or will it still overheat?
My best guess is a faulty connection somewhere between the alternator and the battery.
Is the wire direct or does it go through the 1-2-B switch?
One thing you could try, to prove a point(but it might be a pain)is to disconnect the alternator charging wire from the T105's and bring your other start/reserve battery to that same wire, connect it and see if it still overheats using the same exact charging wire as the T105's.

A few ideas

Bobg · January 31, 2011, 09:28:51 PM

Thank you for your help, I have started out with fully charged battery's, like a week on the shore charger and the Alt doesn't seem to overheat, but any use at all of the batteries, like a afternoon on the hook,and the Alt will heat, and heat within a minute of running.
I have disconnected all the house wiring to trouble shoot, nothing to the 12B switch, simply the batteries and the Alternator. The Alt puts out 13.8volts and slowly works it's way to 14 but overheats before it gets there. My start and a test 12 volt battery from my car doesn't do that, the Alt puts out 14.4 or so volts when starting and stays cool. I have not moved my house batteries to the start battery location to test that circuit yet because of space and weight, but that is a good Idea and will try something like that this spring.
One thing comes to mind as I sit here, I don't think I bypassed my ground wire from the house battery box under the cabin sole to the rear of the engine. I did replace the ring terminals on that wire. (The ground from the start battery has it's own ground wire.) I did use the old house ground wire when testing with my car battery and it worked, It did work once with 2 of the new T105's but 15 minutes later we tried the same battery's again and it overheated, I suppose it is possible the wire may have a intermittent short and will work with the smaller battery but not with the 4 T105's, I dunno, I'll try that in the spring.
What makes it frustrating is that the whole system with old T105's used to work until I changed out my Alternator from the Motorola to the Mando.

( I thought my Motorola was bad because it wasn't putting out anything, Harvey from Blue Circle tested it and said it was bad, so I bought the Mando with exchange, after that,I found a burnt through charging wire in the wiring harness from the Alt at the instrument panel prompting a wiring harness upgrade, I asked him to test my old Alt again, he still had it, and he said it was putting out some if he tapped on it, but by that time the new Mando was in) and here I am with the problem
Question: Does anyone think the Alt could be bad even if it tests good? Maybe it is being tested with a fully charged battery in the shop but if it has to "work," like on my boat, it overheats. Enough of this for now I'll get back to it in the spring, Thanks again for your help Bob

Stu Jackson · February 01, 2011, 08:47:06 AM

What makes it frustrating is that the whole system with old T105's used to work until I changed out my Alternator from the Motorola to the Mando.

If the new alternator is rated higher than the old one, you need to enlarge the ground wire, too, in addition to the alternator output.

Bobg, I recall earlier discussions when you provided your wiring diagram, which, IIRC, seemed to be OK with some comments. I'll have to go back and search for that discussion later.

Stu Jackson · February 01, 2011, 09:56:00 AM

Found it: Sizzling New Alternator here: http://c34.org/bbs/index.php/topic,5751.0.html with a link to a later discussion on page 3.

Bob, did you ever get your T-105 batteries tested?

I think there are a lot of suggestions on those two threads.

John Langford · February 01, 2011, 10:48:57 AM

Stu, I have had much the same thing happen to one of the fused lines from my smart charger. In my case, the connection within the in line fuse holder went south, taking the regulator with it. Took me quite a while to find the problem. But I agree, applying Occam's razor means checking connections first.

Stu Jackson · February 01, 2011, 11:19:08 AM

Good point, John. Sorry you lost your regulator, I'm surprised mine hasn't fried yet with all those factory connectors dropping off!!! I relocated one of the regulator's fuse holders from behind the alternator to back near the regulator (battery sense). Saturday's work just installed a new fuse holder behind the regulator, but with a large loop of wire for better support and moved it further away from the alternator (power wire with fuse holder). I really should have moved it further back to under the head sink, but the wire to the regulator went into the loom, so I felt that the extra wire loop would suffice. Perhaps next trip to the boat...