Did I fry the alternator ?

[barrett bonden]

Fried alternator ?
Turned key, no response from starter. Cleaned some connections, turned key and now starter engages but will not shut off. Jiggled key, hit starter button, starter still will not stop; so knowing full well the sin I might be committing I turned the battery switch to off. Disconnected starter switch (thinking it might be the push button switch shorted), turned battery on and again starter engaged and would not stop till I turned battery switch to off.
Called mechanic, who suggested hitting starter lightly – this worked and now the starting sequence is normal – but what if any damage to alternator?
Voltmeter on battery #1 shows 12.36 with no charge going in when engine is running.
Shut down engine, switched to battery # 2.
Voltmeter on # 2 shows 12.30 going up to 13.4 – looks good.
Shut down, back to # 1 , again no input from alt
Back to # 2 – now no input from alternator – holding at 12.3. What’s going on ?
To # 1 – same. No juice going in
To # 2 – and now it looks good – up to almost 14 when I rev the engine
Engine off – wait a bit – and Back to # 1 – again nothing.
Back to # 2 and now nothing also.
In other words both batteries can start the boat, #1 never gets a charge going in and # 2 does half the time. Do I assume I fried the alternator ?

[ndutton]

No alternator damage as a result of the scenario you reported. Diode damage results from turning off the battery to a running engine at RPM sufficient for the alternator to excite. Time to look at connections and isolator/combiner if any for the problem.

[barrett bonden]

I was hoping this was the case, & good to hear. What led me to pull the alternator 2 hours ago is there’s no isolator/combiner; just a 30 (?) year old (older ?) big red manual 1,2,All switch. I cant imagine a connection issue that would allow #1 to start the engine but not accept a charge. This plus the rest of the symptoms seem to point to a bad voltage regulator on the alternator ?

[ndutton]

No, I do not see any indication of a regulator problem. As this is intermittent it suggests to me a loose or otherwise poor connection(s) somewhere in the battery cabling system up to and including the alternator output and all grounds.

[JOHN COOKSON]

I presume the belt is not worn and the belt tension is correct???
Be sure the pulley is not slipping on the alternator shaft. Any "funny" noises from the alternator?

TRUE GRIT

[barrett bonden]

I took the alternator in and was pleased to hear it tested fine – and was told that it’s low output of 35 amps (the info plate was so worn I no idea what I had) *might* account for some of the symptoms I described.
Mindful of the suggestions here I sandpapered all connections well during the re-install, and worked especially hard getting as much slack out of the belt as I could. Truly, gentlemen, I would tell you the connections were clean prior to the re-install – I’ve seen much more oxidized connections on this boat work perfectly well - and that the belt was tight enough to spin the sheave well in the first place - but also I must say that both batteries are now charging fine.
What is to be learned here ? That “some slack but the alternator sheave is spinning” is not good enough ?
Many thanks for your help.

[ndutton]

Our host offers a spring loaded belt tensioner that applies proper, calibrated tension every time. No more prying, no more trying. Bolt it on, turn the adjustment nut as instructed and you're done.

http://www.moyermarine.com/cgi-bin/s...=OVEL_04.1_546

Even though MMI didn't make a big deal out of it the tensioner features a significant improvement since the catalog picture was taken and at zero additional cost (gotta love MMI). The two angle brackets are now CNC machined marine grade aluminum rather than artisan shop produced painted steel.

[toddster]

Yeah, I had a similar episode a couple of years ago, when I mindlessly turned the switch to "off" at idle. No serious damage ensued. The problem was, the boat was 100 miles away and I couldn't test it before the next big delivery. So now I have this shiny new spare alternator...

Actually, the biggest problem with my setup is still the huge voltage drop over the small-gauge wire going up to the cockpit ammeter and back. Yes, I'll definitely fix that this weekend. Or next weekend. Well, sometime when there's no wind...

[hanleyclifford]

Originally Posted by ndutton

Our host offers a spring loaded belt tensioner that applies proper, calibrated tension every time. No more prying, no more trying. Bolt it on, turn the adjustment nut as instructed and you're done.

http://www.moyermarine.com/cgi-bin/s...=OVEL_04.1_546

Even though MMI didn't make a big deal out of it the tensioner features a significant improvement since the catalog picture was taken and at zero additional cost (gotta love MMI). The two angle brackets are now CNC machined marine grade aluminum rather than artisan shop produced painted steel.

The tensioner is one of those "install and forget it" kind of items. Every cruiser should have one. Mine has 2 round trips to Florida under it's belt () and I don't even think about squealing, slipping or alternator bearings.

[JOHN COOKSON]

barrett

I've got one more wire for you to check. Check the other end of the wire that goes to the alternator field coil. (I think it's called the exciter winding now days) It's most likely attached to coil +. If this wire or the connector is corroded it will not transmit a full amount of electricity and the alternator will be sort of slugish.
Also if there is a quick disconnect in the wire somewhere check it out too as it might be corroded.

TRUE GRIT