Alternator troubleshoot

[Catalina007]

Excuse my basic question and be gentle please.
If my alternator is not showing any VDC output when I put a voltmeter on the  + post and - casing....
1. The field excite wire is not doing its job (should be providing 12v with ignition on
Or 2
Something else going on and I should take it in for bench testing.
Anything else?  Even if it was a loose belt it should be outputting something.
Tach is also not working (off AC Tap)

It is a newly installed Leece Neville 3 wire  type.

Assume wires are ok

[Stu Jackson]

>>>>>>>>>>>>>>>>
Tach is also not working (off AC Tap)

It is a newly installed Leece Neville 3 wire  type.

Assume wires are ok

No need for any excuses, we're here to help.  Need more info, though.

Tach not working usually confirms AO is not, too, but not always.

What does 3 wire mean?

Did it work when you first installed it?

Can't assume the "wires are OK," because while they may "look" fine, have you pulled on each and every one of them?  I've had factory crimps come apart on me soon after installing a new alternator - it was the regulator wires.

Internal or external regulation?  From what you said, I figure internal, because of the "excite" reference.

Are your batteries full from being plugged in and charging all the time? 

Help us to help you.

[mainesail]

It is a newly installed Leece Neville 3 wire  type.

Assume wires are ok

Going to need a model #....

[Catalina007]

I brought the old alternator to a local repair shop and it was declared dead.
I got a Mando 55 amp internal reg replacement for now which will keep us going until the end of the season in a few weeks.
Tach and Alt are working now and we are back in business. 
This winter will look at some battery and ext regulator etc

Question. How hot is normal for an alt to be while charging?  It was working hard  as the house bank had been drawn down, I measured
about 205 degree F.  If I put  a larger reg (say 72 amp)  would it work easier and cooler?
 
I did the new bracket, ammeter/voltmeter switch, new and increased wire sizes including from Alt to solenoid and battery cables.   



 
   

[Stu Jackson]

>>>>>>>>>>>>>>>>>>
I got a Mando 55 amp internal reg replacement for now which will keep us going until the end of the season in a few weeks.>>>>>>>>
>>>>>>>>>>>>>>>>>>>>>>>>>

Question. How hot is normal for an alt to be while charging?  It was working hard  as the house bank had been drawn down, I measured
about 205 degree F.  If I put  a larger reg (say 72 amp)  would it work easier and cooler?
 

How large is your house bank?  Do your boating activities take you to, say, anchoring overnight and depending on the alternator to replenish the bank from an overnight discharge?  Or do you daysail and plug in every night?  Do you have a fridge?

You bought essentially almost the smallest alternator you could.  Anything larger WILL work cooler.

[Catalina007]

Its light use with 2 x 100A house bank and 1  starting batt.  Daysailing occasional overnights.
Its impossible to get electrical or mechanical pro help. Just wanted to get functional right away for
remaining season and not out too much stress on a  35 yr old engine without more in depth analysis.
On a mooring no shore power. Have hooked up a 20v solar trickle charger also.   
She was probably running hot because the batts were drawn down so far and working hard. Hopefully they will come back up over 12v
but they are due for a change this winter anyway.  Might go to 72amp and keep this one for a spare.   
Prob upgrade the cabin panel to breakers as well - its still old agc fuses
And upgrade the engine wire harness
And new engine mounts
And..... 
   

[Ron Hill]

007 : From some of the things that you have mentioned you probably have a 1986 or 1987 C34. 

On you list of things to do I get the wiring harness upgrade done first - you have a FIRE hazard on board!!  You probably have a Ammeter on your engine panel!!

Most stock alternators with an internal regulator only charge at about 13.5 -15 V and a few amps!! So the max amp size doesn't really matter (cooling) because it will never charge at that Amp size because of its internal voltage regulator.  The wiring upgrade will help in charging because it will drastically reduce the wire length from the alternator to the batteries!!  Read Stu's wiring Electrical 101!!

A few thoughts

[Catalina007]

Hi   
On prior post I mentioned I did the ammeter/voltmeter switch out already
Also increased sizes all Batt cables and wire from ALT to Solenoid   
I want to replace the balance of the harness wires over the winter