Michelle P writes:

Chuck,
You need to also measure the current the alternator is putting out at
the same time. The voltage alone will not tell the whole story.
If the alternator is putting out and the voltage is still low then there
is a big draw on the system. Likely the battery. Once it is satisfied
then the buss voltage will rise. The comment about the regulator is BS.
Likely from someone who does not understand them. They are adjustable.
13.7 is only slightly low for a 14V system. it should be 13.8-14.2.
If you can get a recording meter like a Fluke that would be best. If you
can get one that will do both AC and DC at the same time, this would be
good as well. This will tell you if a diode or two has or is dying.
Michelle

I second the line of thinking. Make more measurements. Use a scope
to look for bad diodes. Use a good DVM to measure the alternator
OUTPUT at the alternator. Big issue here is keeping body parts out
of the way of the people-chopper up front as you must be well above
idle.

Bad diodes are about the only {alternator} thing that keeps an
alternator+regulator+installation from making full output. Most of
the time, it's regulator or loose wiring issues that bite you on
the [banned by Mikey Powell]... err tailwheel.

GM auto alternators have a "full-field" tab. It lets you bypass
the regulator so you can see the alternator working full tilt.
This typically gets you 15+ volts DC, so if such can be done,
pull all the avionics feeds first......

In a car, I think the best belt test is your ears. Load the alternator
with headlights/blowers/heated seats etc. The belt should talk to
you but not howl/sing. I don't know if you can hear as well w/
aircraft.


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433