"Roger Long" wrote in
:

This didn't re-occur during
the remaining 7 days of the cruise but I'm curious if anyone has
experience anything like this or if one of our battery and alternator
experts can make anything of it. The big question is whether this is
an early warning of something going south in the alternator or voltage
regulator.



We need a hand held ammeter you can buy at any auto parts place like
NAPA. It reads -100-0-+100 amps. The meter runs off the magnetic field
that surrounds a DC wire with current flowing through it proportional to
the curren flow. It clamps over the wire to the batteries, for
instance, but any wire will do, even if the clamps are too big.

What I want you to do is to run the diesel about 1500 RPM while watching
your voltmeter and this little ammeter (or your charging ammeter if the
boat has one). Turn every 12V load in the place on and see what happens
to the DC voltage with the alternator heavily loaded, and loading the
belt hard driving it.

Even a tight belt will slip under heavy load when its surface gets
polished from the slippage they all go through. The alternator with the
slipping belt will make that squealing noise when something heavy, like
a load on an inverter, refridgeration or an intermittent short goes on
the load.

The other possibility we are checking for is ONE open alternator
rectifier diode, reducing us from 6 phases to one if one is open. The
belt will squeal like hell as the shorted diode locks the alternator
until the diode guts melt open and reduce the load to near nothingness.
If ONE diode is open, there are two indications. Instead of SIX power
pulses per revolution, you get ONE, which will make the stereo and
radios "whine" at a frequency dependent on RPM of the
engine....alternator whine. The other indication is it can't hold its
voltage on a charged battery UNDER LOAD on a CHARGED battery. Once the
house battery charges, no matter what the load up to the capacity of the
alternator, its output voltage should stay near float voltage when the
regulator goes into voltage regulation at 14.2VDC, or there abouts.
Heavily loaded, it'll drop to 13.9 or so due to internal resistances and
the usual corroded connections. If ONE diode is open, the load simply
overwhelms the poor charging current of one phase and battery voltage
drops off sharply as if the engine weren't running at all.

If you have a built-in ammeter, disregard my hand-held magnetic and use
yours.

Harbor Freight, the Chinese machine tool outlet stores, has a dandy LOAD
tester for cheap:
http://www.harborfreight.com/cpi/cta...emnumber=90636
It's a 100 amp nichrome resistor (nice electric heater) with a quite
accurate, but simple, built-in voltmeter you watch while loading and
unloading the running alternator. There are scales for alternator
testing as well as uncharging battery testing at 0 and 100 amps.

only $15! Everyone should have one!

While you're there, buy a few of their $3 red DIGITAL multimeters!
These multimeters test everything from transistors and diodes to
amps/volts/resistance...very accurately. The meter leads that come with
them are MORE EXPENSIVE than the whole multimeter/leads and all at Radio
Shack. I buy them just to get the meter leads and give the meters away!