alternator test - diesel engine

parvenu · #1 (**permalink**) 09-08-2005

How do I test my alternator to test whether or not it''s charging my battery?

I have a diesel engine (Westerbeke 27).

Someone suggested that I disconnect the positive terminals of my batteries. If the engine keeps running, that means it''s not working off the batteries. Problem with that, in my mind, is that a diesel engine doesn''t depend upon sparkplugs as a gas engine does. So what would disconnecting the terminals tell you?

So any suggestions?

Thanks.

George

PaulBl · #2 (**permalink**) 09-08-2005

<So what would disconnecting the terminals tell you?>

Nothing important.

dman · #3 (**permalink**) 09-09-2005

Pulling the cable off your battery will blow your alternator if it is working.The current has to go somewhere,even jumping it and running on a dead battery can damage it.If you need to check the alternator, all you need is a voltmeter. Make sure you have a good battery. Start the engine and set the voltmeter on DC voltage. Take the red lead of the voltmeter and put it on the large red wire at the alternator. Put the black lead on the alternator housing. With the engine at high idle, you should have a reading of 14.2 - 14.6 volts. Take the voltmeter to the battery and place the red lead on positive and the black on negative. You should be reading 14.2 - 14.6 volts. If not, you have a wiring problem to the battery. If you do have 14.2 - 14.6 volts and you still have problems, test the battery.Also remember that the diodes in the alternator can flow backwards when they malfunction,draining it when it isn`t running.

sundown2 · #4 (**permalink**) 10-20-2005

a real simple test to check an alternator is to take a piece of metal (screwdriver etc) and hold close to the back of the alternator while it is running. If it is producing electricity it will be creating a magnetic field and you will be able to feel the pull on the metal. (be careful not to hit the output post).
The surest way to test output though is with a multimeter ( Radio Shack about $25). with the alternator running check from the output (+) to ground (-). reading should be above 13.5.

GordMay · #5 (**permalink**) 10-21-2005

Goto: CruisersForum.com
and check out “BASIC Alternator Testing”
http://cruisersforum.com/showthread.php?s=&threadid=375&highlight=alternato r+test