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ceeclipz

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"hello everyone...I Want to th

"hello everyone...I Want to thank all of you for all your help..we are in the water as of last weekend...

I have a concern..on my 89 4.3 mercruiser the alternator was running at about 14 on land, then 13..on sun when I took the boat out it was at about 12....does this mean that its done...what should I do...Should I rebuild it, if so which kind of shop does that work, or is it easier to replace it....

Thanks"
 
How long did you run the engin

How long did you run the engine on Sunday?

What other loads were running on Sunday that weren't running the other times?

I'm not convinced there is anything wrong with the alternator or regulator.
 
"the engine ran for about 1 ho

"the engine ran for about 1 hour, the only thing that ran on sunday was two batteries opposed to only one, when it was running on land...."
 
"Belt tight? If it is chargin

"Belt tight? If it is charging two batteries then it is probably OK. Disconnect all the batteries; now remove and clean the alt. wire ends with fine emery cloth or sandpaper. Also clean the bases where the wire ends attach including the batteries and switch.

If you change alternators, consider upgrading to a 90-100 amp alt. You will have to change the alt. output wire to handle the increased current load. It is now probably a 10 ga. wire and would need to be replaced w/an 8 ga. or prefferably a 6 ga. FINE STRANDED COPPER wire. Battery wire is not fine stranded; get it from an electronic stereo shop or electric repair shop. The wire requirement is probably on the installation instructions."
 
"You didn't mention what y

"You didn't mention what you were using to measure voltage. If it was the volt meter on the boat the information in your post is probably not accurate. Get a digital multimeter.
Measure the battery voltage with the engine off.
Start the engine, measure the battery voltage.
If you read 13. to 14.5 volts, your alternator is fine."
 
"I am using the volt meter on

"I am using the volt meter on the post....How would I measure the battery voltage, just on the battery posts or on the alternator as well.

thanks"
 
Ceeclipz:

Use a digital vol

Ceeclipz:

Use a digital voltmeter to check the battery terminals after the engine has reached operating temp. The battery should be fully charged and the meter should read approx. 14.0 VDC. w/the engine at 2000 RPMs. WRITE DOWN THE READING FOR REFERENCE IN THE NEXT TEST. If it is more than 14.4 VDC the alternator regulator is not working.

The next test is easier w/gator clip voltmeter leads. YOU MUST NOT WEAR A LONG SLEEVED SHIRT OR JACKET TO GET CAUGHT IN THE PULLEYS. The back of the alt. has several wires connected to it unless it is a single wire system. The orange wire is B+ and the black wire is B-. Connect the positive meter test lead to the B+ and the negative test lead to B- connections. W/the engine at 2000 RPMs the meter should read between 14.0 and 14.4 VDC AND only be 0.04 volts LESS than the reading YOU WROTE DOWN at the battery. IF THE DIFFERENCE IN VOLTAGE READINGS IS LESS THAN 0.02 vdc THE BATTER CABLES ARE GOOD.

If you remove the alt. make sure you tag each wire with the correct label for reinstallation.
 
""If it is more than 14.4

""If it is more than 14.4 VDC the alternator regulator is not working. "

Guy, would it be the same if the reading on the conection to the alternator would read less than 13.6..."
 
"The indicated voltage is goin

"The indicated voltage is going to vary, depending on the condition (state of charge) of the battery(s) and the load on the system.
I would bet the 12vdc you saw on Sunday is a result of one of the two batteries not being quite up to snuff, or there is a high resistance connection in there somewhere... take a good look at all the battery cable termination points (both ends of all the cables). Anything loose, frayed, discolored or corroded, and hardened or brittle insulation would be cause for rejection."
 
"Here's a simple test.
Us

"Here's a simple test.
Using the panel voltmeter, the reading should be around 12 with the ignition on, not running, and no other loads.
When cranking it may drop down to 8 or 9 volts.
Once started, it should almost immediately jump up by 2 volts or better to around 14 volts.
If you don't see a jump of 2 volts or better when it starts, you likely have an alt or regulator failure.

Rod"
 
"The boys have spoken.

&#34

"The boys have spoken.

"if the reading on the conection to the alternator would read less than 13.6..."

If it reads at the alternator posts less than 14.0 volts at 2000 RPM, then the alternator is failing. An open circuit diode would drop the output voltage.

The boys explained the important point; the alternator has to respond to a drop in battery voltage and turn itself off when the battery has reached 14.4 volts.

Note: If the alt. is putting out 14.04 volts at the B+ terminal, then the battery terminals MUST read at least 14.0 volts. If it reads 13.9 volts then the battery cable or the alt. cable has high resistance and need to be changed.

To determine which is the culprit, follow the voltage path from the alt. to the starter then to the battery. If the alt. is putting out 14.04 volts and the voltage at the starter and the battery is 13.9 volts, then the bad cable is the alternator output wire. If the starter post reads the same as the alt. B+ volts. such as 14.04 volts and the battery reads 13.9 volts, then the battery cable is bad.

Confused?
uhoh.gif
"
 
"Rod said:

"Once starte

"Rod said:

"Once started, it should almost immediately jump up by 2 volts or better to around 14 volts.
If you don't see a jump of 2 volts or better when it starts, you likely have an alt or regulator failure. "

Rod.... I noticed last year that I only get the 2 volt jump after giving the boat a little gas. But I do get the jump. Is that normal at all?"
 
"Rick;
The older single wire

"Rick;
The older single wire alternators typically needed to rev up a bit to say 1000 RPM before they would kick in, but the newer 3 wire units seem to produce a voltage kick at lower RPM's.

If yours kicks in with a small increase in RPM, then I would say its working fine.

Rod"
 
"No small hiatus... just been

"No small hiatus... just been busy. New job, new house, a million excuses to keep the boat from getting wet!"
 
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