I have twin 5.7's on my older, but good shape Sea Ray Sedan Bridge. I have a feeling that the port engine needs an alternator replacement. when the boat is running, the port amp gauge shows 11 amps, and the starboard engine show 12-13 amps. What is the best way to test the alternator, using a volt meter to determing if it needs replacing. BTW; the batteries are almost new, and I doubt that is the issue. Any help is appreciated.
Aternator Testing
- Thread starter bobdeesr
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Why would you think a difference of 1 amp (which could be the gauge or shunt + or -) would involve changing the alternator?
From the description you have no problems with charging.
Unless you are having a problem not discused there appears to be nothing wrong?
Bill
From the description you have no problems with charging.
Unless you are having a problem not discused there appears to be nothing wrong?
Bill
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If indeed you are talking about AMP meters, then 11 to 13 amps means they are working and produce a charge
However, if your ate referring to the more common voltmeters then 11 volts means the alternator is not charging. On the other side, "12 to 13v" is meaningless since 13v is fine, but 12 would be too low
Easiest way to test is to use a multimeter at the battery terminal and measure voltage engine off then on. It should go up about a volt to a little over 13. Make sure you bump the idle a bit to 1200 or so as some alternators don't output much below 1000
However, if your ate referring to the more common voltmeters then 11 volts means the alternator is not charging. On the other side, "12 to 13v" is meaningless since 13v is fine, but 12 would be too low
Easiest way to test is to use a multimeter at the battery terminal and measure voltage engine off then on. It should go up about a volt to a little over 13. Make sure you bump the idle a bit to 1200 or so as some alternators don't output much below 1000
Pascal I re-read his post it's clear he says amps and port amps gauge vs starboard amps gauge.
If he is reading amps then I see nothing wrong unless he gets more descriptive or can tell us a problem he is having related to one side not charging.
Bill
If he is reading amps then I see nothing wrong unless he gets more descriptive or can tell us a problem he is having related to one side not charging.
Bill
If you have any doubts and they have been installed awhile, pull at least one before it goes bad. A good local alternator should be able to replace brushes and bearings at a reasonable price. Most damage (and costs) is done by short, arcing brushes or bad bearings. It should give you a good idea as to the status of the other one.
It sounds like you do have a problem. Follow alien1952's post to check the voltage at the alternators. If the the voltage is low at the alternator post then you probably have bad diodes in the alternator. Mke sure you run the engines past idle speed.
Either replace with a marinized alternator (not an automotive unit) or have the alternator you have rebuilt.
Bill
Either replace with a marinized alternator (not an automotive unit) or have the alternator you have rebuilt.
Bill
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I had a feeling he was talking volts... Very very few boats have amp meters at the helm...
You can measure at the alternator or at the batteries. I checking at the alternator be very careful not to short the post with the probe as the alt. case is metal. Safer at the battery although if you have a bad connection somewhere, alt may good but showing low at the battery
Never trust a gauge mounted voltmeter... Use it as reference to see a trend but not to rad an actual value.
You can measure at the alternator or at the batteries. I checking at the alternator be very careful not to short the post with the probe as the alt. case is metal. Safer at the battery although if you have a bad connection somewhere, alt may good but showing low at the battery
Never trust a gauge mounted voltmeter... Use it as reference to see a trend but not to rad an actual value.
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Turn on key - note the number.
Start engine - if number doesn't increase you have a problem.
Start engine - if number doesn't increase you have a problem.
That's as basic as it gets. If it doesn't increase then it's not charging. It doesn't mean its outputing the correct voltage, but is a good starting point. A battery in a hot engine room should be charging at about 13.9 volts. Most alternators will put out closer to 14.3 volts. The higher the temperature of the battery the lower the voltage is needed.
I would agree and add most are not conjoined. If they are it's done with the proper external cross-over charging device or emergency start only momemtary relay. Otherwise only 1 alternator does all of the work the other thinks no charging is needed.
Back on topic I would eliminate all wiring by checking the source (alternator) on each engine, only after they checked good would I start digging into the boats wiring system.
Bill