About 10 minutes after departing from my first anchorage under power, there
was a shrieking sound like a slipping alternator belt or bad bearing from
the engine area. I shut right down and investigated. Belt tension was
proper, no sign of rubber powder or wear. Started the engine up and it was
fine.

About half an hour later, static like chirping noises began coming from the
engine panel alarm speaker. These were intermittent and in a random
pattern. The best explanation I could come up with was that something was
trying intermittently to send an alarm signal to the panel but wasn't
getting enough power through to light an alarm light or fully engage the
buzzer. At the next anchorage, I rechecked the alternator belt tension and
verified that it wasn't the coolant alarm by disconnecting that sender unit.
I couldn't disconnect the oil pressure sender due to a corroded screw that
will have to wait until I take the oil filter off.

The prime suspect is the charging circuit. Battery voltage makes the alarm
sound and the light go on. The voltage regulator in the alternator sends
voltage through a diode to counteract this current. When they balance, the
light and buzzer are off. If they don't balance, the lights and alarms go
on. It seems therefore, that a slight imbalance occurring intermittently
could cause the annoying chirps in the buzzer. 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.

--
Roger Long

"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!

On Sat, 23 Aug 2008 22:31:15 -0400, "Roger Long"
wrote:

The big question is whether this is an early warning of
something going south in the alternator or voltage regulator.

An accurate voltmeter across your battery(s) is a good thing to have
for many reasons but one of the most important is monitoring your
alternator. With the engine runnning at cruising speed you should be
seeing somewhere between 13.8 and 14.2 volts. Anything less than 13.5
you definitely are not getting full output and should get it checked.

The problem you describe could also be a loose or corroded connection
between the alarm panel and alternator.

Thanks, I'll look into all that.

I have a volt meter on the panel and checked it frequently after this event.
It held steady at 14.0 but electric loads on my boat are about as minimal as
they get. No refridgeration or big screen TV. Half the interior lighting
and the anchor light are LED.

Question about belts. Mine is toothed (smooth pulleys). On airplanes, we
would check for belt slippage by feeling the belt and pulleys and finding
our fingers black from rubber dust. You mention belt polishing. My fingers
came away from both the pulleys and belt absolutely clean. Is the
formulation of the new belts different? (Remember, the FAA makes aircraft
use 30 - 50 year old technology for everything).

--
Roger Long

On Sat, 23 Aug 2008 22:31:15 -0400, "Roger Long"
wrote:

About 10 minutes after departing from my first anchorage under power, there
was a shrieking sound like a slipping alternator belt or bad bearing from
the engine area. I shut right down and investigated. Belt tension was
proper, no sign of rubber powder or wear. Started the engine up and it was
fine.


Check the fixing of all pulleys to shafts. We lost (and fixed) the raw
water cooling on last year's delivery from NI. In that case the pump
pulley was only attached by grub screws which had loosened. Sounded
like a bearing squeaking.. and then steam started coming out the blunt
end.

In article ,
says...
About 10 minutes after departing from my first anchorage under power, there
was a shrieking sound like a slipping alternator belt or bad bearing from
the engine area. I shut right down and investigated. Belt tension was
proper, no sign of rubber powder or wear. Started the engine up and it was
fine.

About half an hour later, static like chirping noises began coming from the
engine panel alarm speaker. These were intermittent and in a random
pattern. The best explanation I could come up with was that something was
trying intermittently to send an alarm signal to the panel but wasn't
getting enough power through to light an alarm light or fully engage the
buzzer. At the next anchorage, I rechecked the alternator belt tension and
verified that it wasn't the coolant alarm by disconnecting that sender unit.
I couldn't disconnect the oil pressure sender due to a corroded screw that
will have to wait until I take the oil filter off.

The prime suspect is the charging circuit. Battery voltage makes the alarm
sound and the light go on. The voltage regulator in the alternator sends
voltage through a diode to counteract this current. When they balance, the
light and buzzer are off. If they don't balance, the lights and alarms go
on. It seems therefore, that a slight imbalance occurring intermittently
could cause the annoying chirps in the buzzer. 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.


I've had this happen years ago with automobiles. Usually when the
lights, heater, wipers, etc., are all on and the load is nearly what the
generator could put out. I've also had it happen with a modern
alternator when the brushes got extremely worn.

You should have a system volt meter installed (I can't see how you can
live on battery power without one :-). If the alternator is putting out
correctly, and depending on the type of regulator you have, system
voltage should rise to 13.something. If it doesn't then you have either
a bad alternator or a bad regulator.

Of course, you can have a bad connection in the instrument wiring
harness. I had a Yanmar that had some corrosion in the connector where
the wiring harness comes off the engine. used to unplug it and plug it
back in a couple of times to wipe the terminals when things didn't work.

--
Cheers,

Bruce in Bangkok

"Roger Long" wrote in
:

Thanks, I'll look into all that.

I have a volt meter on the panel and checked it frequently after this
event. It held steady at 14.0 but electric loads on my boat are about
as minimal as they get. No refridgeration or big screen TV. Half the
interior lighting and the anchor light are LED.

Question about belts. Mine is toothed (smooth pulleys). On
airplanes, we would check for belt slippage by feeling the belt and
pulleys and finding our fingers black from rubber dust. You mention
belt polishing. My fingers came away from both the pulleys and belt
absolutely clean. Is the formulation of the new belts different?
(Remember, the FAA makes aircraft use 30 - 50 year old technology for
everything).

--
Roger Long


Your hands came away from the belt clean? Has the engine been started
since it was put on??....(c Belts grind their whole lives...planned
obsolescence. Get one of the 100A load testers for $15. That will tell
us.

What may have happened is a rectifier diode shorted during operation,
locking the now-shorted alternator making the belt squeal until the
shorted diode burned itself open due to the massive current from its own
coils and the now-shorted battery....for just a few seconds at most.
After that it wouldn't short anything because it's an open. You hardly
hear it in a car when it happens.

"Larry" wrote

Your hands came away from the belt clean? Has the engine been started
since it was put on??....(c Belts grind their whole lives...planned
obsolescence. Get one of the 100A load testers for $15. That will tell
us.


I went down this morning and tightened the belt up a bit and did get my
hands a little dirty. Nothing like I'm used to seeing though. I did notice
that the alternator pulley is nearly mirror polished inside. The belt on my
engine goes around the cast iron flywheel so no polishing there. This belt
has about 80 hours on it.

No strange radio sounds and the system seemed to charge perfectly over the
next 8 days. Is it still possible I have a burned out diode?

--
Roger Long

In article ,
says...
"Larry" wrote

Your hands came away from the belt clean? Has the engine been started
since it was put on??....(c Belts grind their whole lives...planned
obsolescence. Get one of the 100A load testers for $15. That will tell
us.


I went down this morning and tightened the belt up a bit and did get my
hands a little dirty. Nothing like I'm used to seeing though. I did notice
that the alternator pulley is nearly mirror polished inside. The belt on my
engine goes around the cast iron flywheel so no polishing there. This belt
has about 80 hours on it.

No strange radio sounds and the system seemed to charge perfectly over the
next 8 days. Is it still possible I have a burned out diode?

--
Roger Long


You said in a different post that system voltage was about 14 VDC which
indicates that the alternator is producing its rated output as otherwise
you will not be reading 14 volts.

However, why not just take the alternator off and take it to the
'lectric shop. there must be someplace in Maine that repairs alternators
and they all have test stands to test the output. If it is a normal
Yanmar alternator it has an internal regulator so the test will check
that also.

By the way, if the alternator is taken apart change the brushes. they
are cheap and changing them eliminates one more thing that might go
wrong next year :-)




--
Cheers,

Bruce in Bangkok

On Sun, 24 Aug 2008 04:51:57 +0000, Larry wrote:

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.

I have heard of AC clamp on meters that form a transformer when in
use. This doesn't seem to work with DC.

Casady