Alternator, charging ?

gtfireftr

gtfireftr

Member
Oct 9, 2014
292
Westport MA
Boat Info
1997 Sea Ray Sundancer 290
Engines
Twin 4.3 liter w/Alpha Drives
So we were out last night... I noticed the Port engine charging gauge hovering around 12v...
Stb gauge was normal at around 14v...
Any advice as to the best way to test the alternator? belt is good...
Thanks
 
Are you sure it's not the battery itself? How old is it? If it's lead acid, check the water levels. The battery could be getting old and not holding a charge.
 
Not sure... It's 3rd year with the boat, so at least 4-5 yrs old.....
If alt was charging wouldn't it still show 14v on gauge?
 
Normally it would if the battery was still good. A dead cell could be drawing high current .
My guess the alt just went bad
 
Pretty easy to check. Do you have a "Fluke" or similar voltage tester ? If you don't , I'm sure a fellow boater would have one. Anyway, start by checking battery in question with the engine not running. A good battery should read between 12.8-- 13.5/13.7 volts DC. Next, start engine, go down in the engine compartment, be careful because serpentine belt will be going around on the front of the engine. Locate the alternator, on the top rear find the main wire (will be under a small rubber cover) connected to the alternator. You may want to locate this before you start the engine just so you know where its at. With the Fluke, check the output voltage of the alternator, Black probe to a ground, Red probe to the main wire connection. At idle, you should get a reading of about 13.2 volts or greater. Next,, increase the engine RPM to about 2000 or so. Check the alternator output voltage again. You should get a reading of @ 14.2> volts DC. If the voltage reading does not increase with an increase of engine rpm, your alternator is probably bad. However, keep in mind, make sure all electrical connections are clean (no corrosion), and tight. This includes the battery connection also. While your down there, it would be a good idea to remove both batteries cable connections and clean and grease them not only for good maintenance, but just so you know they are good. If you do determine the alternator is not putting out the necessary voltage, you can have it rebuilt locally if you have rebuild shop nearby..just make sure the rebuild shop knows it is for marine applications,,Not for an auto. Good luck,,,, this is an easy DIY job. Oh, just FYI, if you do tackle this yourself, take a quick picture of the serpentine belt routing around all the pulleys. It will save you a little aggravation later.

good luck,,,Garry
 
GCHOG said:
Pretty easy to check. Do you have a "Fluke" or similar voltage tester ? If you don't , I'm sure a fellow boater would have one. Anyway, start by checking battery in question with the engine not running. A good battery should read between 12.8-- 13.5/13.7 volts DC. Next, start engine, go down in the engine compartment, be careful because serpentine belt will be going around on the front of the engine. Locate the alternator, on the top rear find the main wire (will be under a small rubber cover) connected to the alternator. You may want to locate this before you start the engine just so you know where its at. With the Fluke, check the output voltage of the alternator, Black probe to a ground, Red probe to the main wire connection. At idle, you should get a reading of about 13.2 volts or greater. Next,, increase the engine RPM to about 2000 or so. Check the alternator output voltage again. You should get a reading of @ 14.2> volts DC. If the voltage reading does not increase with an increase of engine rpm, your alternator is probably bad. However, keep in mind, make sure all electrical connections are clean (no corrosion), and tight. This includes the battery connection also. While your down there, it would be a good idea to remove both batteries cable connections and clean and grease them not only for good maintenance, but just so you know they are good. If you do determine the alternator is not putting out the necessary voltage, you can have it rebuilt locally if you have rebuild shop nearby..just make sure the rebuild shop knows it is for marine applications,,Not for an auto. Good luck,,,, this is an easy DIY job. Oh, just FYI, if you do tackle this yourself, take a quick picture of the serpentine belt routing around all the pulleys. It will save you a little aggravation later.

good luck,,,Garry
Click to expand...

I'm not an expert so I'm asking for my own knowledge too... could the same be accomplished by connecting the tester to the battery terminals vs. the alternator's main connection? Also, if the tester reads ~14.2 at the battery, would putting a load on the battery (turning in the radio and other battery operated accessories) also test if the alternator is kicking in and charging effectively?
 
start at the alt feed post, engine off, should read battery voltage(with no isolator in the circuit)
start engine , voltage should increase, do the same test hooked up to the battery

start at the alt feed post, engine off no voltage (isolator in the circuit)
start engine voltage should be approx 14.6 V, shut engine off
go to battery and attach meter, record battery voltage
start engine to 1500 rom, read battery voltage, if increases isolator working, if no increase isolator bad.
 
Bt Doctur said:
Normally it would if the battery was still good. A dead cell could be drawing high current .
My guess the alt just went bad
Click to expand...

Why would you guess at something that can be tested? It all starts with the battery's. They can be tested and so can the Alt. I will never understand this theory .
 
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