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Alternator amperage question

Jul 6, 2019
15
Catalina Catalina 30, MKII 1987 Tom Holt Bellingham
I have an 1987 Catalina 30 mk2 and have been fixing the electrical deficiencies associated with the ammeter and trailer connectors in the harness. The boat has not experienced any obvious problems but I want to be safe and proactive.
First of all I changed the ammeter to a voltmeter and disconnected the Orange #10 wire the ran from the alternator through the harness to the cockpit console ammeter. Next I jumped the out put from the alternator to the starter solenoid based upon some input from the previous owner and information he left with the boat. Everything seems fine with operation of the boat including charging, however, today I noticed that the back of my alternator was getting very warm. I tested it with a clamp ammeter and detected 4 amps flowing between the solenoid and alternator when the engine is off. I’ve disconnected this jumper until I can figure out what is going on. Any input would be appreciated. Thanks.
 
May 20, 2016
2,808
Catalina 36 MK1 Everett, WA
Lots of good resources here also - what engine M25?? Take the original diagram mark it up to let us know what you changed and we can help.

I have a M25 - best resource on the web is @Stu Jackson s C34.org web site. Stu is our sailing for next few weeks with limited/no internet access.
 
Jul 6, 2019
15
Catalina Catalina 30, MKII 1987 Tom Holt Bellingham
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I have an Universal M25xp engine. I’m still figuring out the wiring, batteries, and charging system. The only changes I made besides the jumper were at the console. I documented the changes but am not a draftsman. Apologies in advance. There is a before (with color) and after. Thank you.
 

Attachments

Jul 6, 2019
15
Catalina Catalina 30, MKII 1987 Tom Holt Bellingham
The issue was the long run from the alternator to the cockpit and back through #10 wire and trailer connectors. This has been noted as a potential fire hazard in other posts (resistance, voltage drop and heavy current flow).
 
May 7, 2011
171
Catalina 30 3573 Lake Norman
Tk
I’ve done several harness upgrades and drop-in plug n play replacements on m25s XPs 30s 34s.
I don’t usually monitor over here so much but I’ve started a (draft) Harness 101 primer on the C30 forum Wiki site that might be of value to you. Basically an extension/update of the one I wrote for the 34 folks.
Research is important but you don’t need to do it blind or reinvent the wheel, there’s tons of resources (not dock neighbor hearsay or folks that like to tell you how they’d spend your money LOL). I just helped a c30-er reverse the mistakes he made by going it alone and listening to boat buddies.
 
May 20, 2016
2,808
Catalina 36 MK1 Everett, WA
don’t know why you would have current running to the alternator output - I didn’t see anything wrong with the wiring except the choice of color a PO used when replacing some wires, and some duplicate, unnecessary wires.

Les
 
Jul 6, 2019
15
Catalina Catalina 30, MKII 1987 Tom Holt Bellingham
I have some more things to try but I’m leaving for a week inland. Thanks for checking the diagrams. I may put the removed amp meter temporarily between the alternator output and the starter to see if amp flow changes direction with the engine running. What do you think?
 

Maine Sail

Moderator
Feb 6, 1998
11,037
Canadian Sailcraft 36T Casco Bay, ME
If amperage is back flowing into the alternator from the alternator B+/Alt Output stud then you have a bad diode/diodes in the rectifier.

If the current is flowing to the regulator on the "excite" wire this is powering the regulators field output and drawwing current when the alt is not spinning. 4A +/- of field current, into a stalled rotor, is within the correct range for this kind of oops... You need to figure out where the current is flowing, on which wire, and by disconnecting the alternator excite wire from the vessel (unless your alt is self exciting) this can differentiate the problem to the B+/Alt Output terminal or the regulator excitation wire.
 
Jul 6, 2019
15
Catalina Catalina 30, MKII 1987 Tom Holt Bellingham
This is helpful. Thank you for your input. Happy sailing!
 
May 7, 2011
171
Catalina 30 3573 Lake Norman
I have some more things to try \
Check the C34 forum, in the past I put in an "ALERT" that I found one of "our" OEM alternators wired incorrectly with the excite wired to the tach output. The excite might be wired in place of the charge wire, not with the excite wired to the key switch???
That was Catalina factory OEM, not a PO mod. You may be in that "boat."
Post a picture of the back of your alternator and/or a schematic of the wiring.
 
Jul 6, 2019
15
Catalina Catalina 30, MKII 1987 Tom Holt Bellingham
This a picture of my alternator. I removed the orange wire on the right that went to the “trailer plugs” and jumped from that terminal to my starter solenoid. Now I observe 5 A flowing from the starter back to my alternator.
 

Attachments

May 7, 2011
171
Catalina 30 3573 Lake Norman
No issue I can see with the wiring so I’d pull and take it to a reputable rebuild shop.
Mainesail likely pinpointed the diode problem.
Let us know.
 

Maine Sail

Moderator
Feb 6, 1998
11,037
Canadian Sailcraft 36T Casco Bay, ME
This a picture of my alternator. I removed the orange wire on the right that went to the “trailer plugs” and jumped from that terminal to my starter solenoid. Now I observe 5 A flowing from the starter back to my alternator.
Sounds like blow diodes in the rectifier.. The yellow sticker on the alternator should always be observed. Rotating the battery switch, with the engine running, is the number one cause we see of blown alternator diodes.
 
Jul 6, 2019
15
Catalina Catalina 30, MKII 1987 Tom Holt Bellingham
I agree. Will post an update once I have it.
 
Jul 6, 2019
15
Catalina Catalina 30, MKII 1987 Tom Holt Bellingham
Ended up having alternator rebuilt with a matched regulator. Works great now. The rebuild shop said there was ac leakage and the voltage regulator had been “customized”. The direct wiring from the starter solenoid to the alternator is complete and working.
 
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May 7, 2011
171
Catalina 30 3573 Lake Norman
What do you mean "matched" -- what reg no is it?
There is a regulator available that has external V sense and adjustable set point, which "our" OEMs did not. a noce step above what we have.