Originally Posted by Wotname
I don't think the tach wiring
has anything to do with the fault but I could be wrong!
The voltage dropping from 14 to 12.7 suggests
the alternator output is going to zero volts (zero current) and the voltmeter is faithfully showing the fully charged battery
voltage for that second or so. As soon as the alternator is producing current
again, the voltmeter is faithfully showing the 14V of the alternator output.
The tach feed from the alternator is the AC voltage across one stator winding. So if the alternator stops producing current
then the AC volts on that stator winding will be also zero which is why the tach is dipping. At higher RPM
, the hysteresis inside tach doesn't let the tach needle to drop before the AC tach feed comes live again. Again supposition only!
I think you are seeing the alternator output going to zero for 1 second every 18 seconds.
I am assuming the alternator is internally regulated and internally sensed
- the resolution schematic you posted earlier is too low for my eyes to make out the fine detail.
Can you transpose the alternators between the engines to see if the fault is internal to the alternator or external to it?
Are there any other charging
sources (solar panels
etc) connected to that battery
of that engine
Is there any unusual load of that alternator / engine
that might be cycling on and off every 18 seconds that is messing with the regulator or the alternate output?
It is a curly one for sure!
So general update: I ran a new test ground from the Tach to the battery directly. This didn't resolve the issue.
Yes, so the alternator is internally regulated and sensed. I can swap alternators between the engines, which is what I plan on doing hopefully sometime today.
As far as other charging
sources I have shore power
. I've disconnected both during test runs and the issue remains.
I've also purposefully discharged the batteries
to around 50% and tried with all other sources of charging off and the issue remains.
I've also tried to run the engine with all loads off at the panel and the issue remains.
During all these test cases the starboard engine works great. (Both are Westerbeke
44A's with Bosch alternators.)
At this point I dunno what else it could be, so I'm going to swap them sometime today hopefully.