It’s a long shot but……..Alternator 101 question

[KeelsonGraham]

Hi all,

My Victron BV702 is showing - 2a with the engine at 1200 RPM. Looking in the engine bay there's a brown wire from the alternator connected to nothing. I'm guessing this might be the issue, but I can't see anywhere obvious that it's come off. If anyone has a similar arrangement to mine (photo attached) could they please tell me where to look! Many thanks. KG.

[KWKloeber]

KG

The tan wire has nothing to do with the alternator.  It's the sending wire to the engine panel hi-temp alarm. The wire has pulled off from the hi-temp switch (8 o'clock in your photo.)  Zip tie the harness to eliminate strain on the terminal.  Westerbeke used a terrible switch with a "button" type terminal.  The mating terminal (female Packard 56 terminal) is a somewhat unusual one that doesn't belong on a marine engine.

FYI there's a replacement switch that has a 1/4" quick connect (which is one step above the OEM and as well doesn't belong on a marine engine.)

Unfortunately, I haven't been able to source a temp switch that has a secure, threaded terminal.

FYI Ron has opined many times on here about using a rubber terminal cover on the temp gauge sender (the other terminal that's on your thermostat cap.)  You could do the same on the hi-temp switch - remove the plastic insulator and use only the metal terminal and a terminal cover. 

You might have a bad alternator field excite. 
Under what conditions is the monitor showing 2a?  What's your battery SOC?

[mark_53]

What voltage are you reading?  If the voltage sense wire is disconnected, voltage will be about 17 volts.

[KeelsonGraham]

Many thanks KW.

-2a with the fridge running and a couple of lights on. Battery SOC is indicating 50% on the rather crude OEM gauge. 100% on the Victron because we've only just set that up (after a lengthy charging period). I suspect that the batteries are shot, but that doesn't account for zero alternator output.

Mark, voltage is just above 12. I.e. in the yellow band on the OEM battery gage.

Good to see an extensive alternator diagnosis section in Simon Calder's book. I'll work my way through that!