[C320-list] Alternator issues

[Warren Updike]

Dan, I'm not by any means an expert on this problem so these are just some thoughts. I assume you replaced the alt with a similar type: case grounded, internal regulator, 35-50A. If the PO had not made any changes, this is what would have been original equip. The Pos from the alt attaches to the battery post on the starter. That post is live to the batt when the master switch is on. The negative is via the alt case through the metal-to-metal surfaces to the engine block. Since both alts worked for a day, I'd check carefully the neg path to ground. Also, check the pos cable to the starter. Make sure the connectors on both ends are solidly attached to the cables. If there is a connector/cable issue, then the diodes could have blown if the battery or ground was faulted while the alt was working (same as switching off.)
Nigle Calder's book, "Boatowner's Mechanical and Electrical Manual" (or similar tome,) is a good source for troubleshooting charging issues. There are very detailed instructions that should reveal the problem.
Also, I have turned off the key while engine is running. This should not cause a problem as this also kills the field current so the alt just stops charging as if the engine had been stopped before the key is switched off. 
I know how frustrating, and costly, such problems can be. I hope you find the problem before calling in an expert at $75-100/hr.

Warren and Pattie Updike
1994 C320 "Warr de Mar" #62
Middle River, Chesapeake Bay

-----Original Message-----
From: dmcnamara3 at woh.rr.com [mailto:dmcnamara3 at woh.rr.com] 
Sent: Saturday, May 27, 2017 9:46 PM
To: c320-list at lists.catalina320.com
Subject: [C320-list] Alternator issues

Hello,
I had asked for assistance on this issue about a year ago, but my problem persists.  I have a 1994 Catalina 320 with a Perkins 30.  When I bought the boat 2 years ago the original alternator (Lucas 55 amp) was not functioning.  With the engine running,  there was no voltage output checked at the back of the alternator with a volt meter, and the alternator light was on and the tach was not functioning.  
- I went through and cleaned all of the electrical terminations on the terminal block. 
- Checked the large fuse on the back of the engine.
- Replaced the battery selector switch
- New batteries
- Replaced the old battery charger with a new one (also check polarity on the plug to the battery charger)
- Replaced the alternator with a new one
At this point I started the engine and the new alternator was putting out voltage (tach worked, charge light went out)
The next day alternator did not put out again,  replaced alternator with another new one.  Everything worked again until the next day, then nothing.
I'am not turning the battery switch off or turning the key off before stopping the engine.  I wait until the engine is totally stopped before turning the key off.
Using an Ohm meter set on the diode selection shows OL (positive lead on positive post of alternator) and 1.035 (negative lead on positive post of the alternator) If I read this correctly the diodes are not blown.
Sorry for such a long post, I thought I would try to solve this issue before I call in an electrician.
thanks
Dan