Gordon wrote in
m:
Calling all you electrical aces!
I took the boat 60 nm north to have a hard top dodger installed.
When I left the home dock, the charging rate was 13.6 and doing
well.
Several hours into the trip I noticed the charging rate was down and
dropping at 12.3. Ammeter showing zilch. Turned off all electrical
with
no help and continued on in. Drove up a few days later to work on the
problem, but when I started the engine, all was normal. Good current
and
voltage.
Picked up the boat a week later and same thing occurred. Worked good
for first few hours and gradually fell off.
This alternator uses a separate regulator. So it appears either the
alternator or the regulator is going south when it warms up.
So which is it or could it be something different?
Thanks
G
Swapping the regulator is the easiest test, but I think you're missing
just one diode in the 3-phase rectifier stack, intermittently, caused by
the diodes getting hot on a bad diode, the ones pressed into the heat
sink inside the alternator by the stators. If one diode opens, you get
one phase, instead of 3 and current goes way down, not keeping up with
the loads. The output with one diode open looks like this:
_____^_____^_____^_____^_____^ instead of a constant current output
caused by the phases overlapping each other. This will cause the radios
hooked to these batteries to whine at zero volume as the pulses of
current pulse the battery pretty hard because the regulator has the
rotor current running wide open trying to get up to its regulator
voltage.
Your regulator should float the charged batteries at 14.2 to 14.4 volts.
13.8 volts is the natural battery voltage at 1.260 specific gravity of
all the good cells. At 13.6, the battery will not top off....A full
battery will discharge a good bit to the 13.6V level. This is another
indication it's running on one phase....You get some charging current to
raise the battery voltage after starting but it falls off bad when the
load current exceeds the ability of the one phase to keep up with the
demands.
Take the alternator to Autozone or any car electric shop that has an
alternator test set. The best place is one that repairs diesel truck
electrics. He can test monsters like yours.
Your electrical loads may be exceeding the capabilities of the
intermittently rated cheap alternator on your boat. Skip completely
cooked a brand new alternator that WASN'T rated for CONTINUOUS DUTY on
Flying Pig from a electric dealer in Charleston. I found out from his
experience most alternators are INTERMITTENT duty, designed to recharge
starting batteries, not power full time electrical loads. Those
cheaper, open frame, car-type alternators are all intermittent duty.
They'll put out 120Amps....for 10 minutes before overheating....not 54
hours on a voyage. The current rating is simply the maximum current to
expect, PEAK CURRENT, not average.
Continuous Duty alternators, of course, COST SERIOUS MONEY. Look he
http://www.alphatrononline.com/Large...lternators.cfm
http://www.alphatrononline.com/image...p9-10_0811.pdf
Make SURE you're seated and leaning back against something solid when
they quote you the prices.....