Dual Alternators
Senior User
Joined: Jul 2006
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From: Hesperia, So Cal
im not sure if its the same with diesels,(i dont see why not) but if its is running and you disconnect the positive connection on your battery, and the motor dies, you have a bad altenator, your altenator when motor is started is supposed to charge and run the engine, so if the engine dies when you take off the + cables, it meansyour engine was running off the bateries and the altenator wasnt/isnt doing its job! hope this helpsDustin
i ain't rite
Joined: Mar 2005
Posts: 65,564
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From: Marlboro Mental Hospital.
to test the alternator, do a load test on it while running. that will tell you its condition.
and pulling a wire off the battery will not do anything but burn electrical components.
and pulling a wire off the battery will not do anything but burn electrical components.
Posting Guru
Joined: Oct 2005
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From: Powell River B.C.
Check the output at the battery terminal with a volt meter, not running battery voltage should be around 12.5, then with the truck running it should be 13.8-14.5 volts, even with the lights, fans, whatever else you can turn on on.
Post Fiend
Joined: Nov 2003
Posts: 21,285
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From: Nutter Fort, WV
Go by the local parts store and have them test the alternator.
Do a load test on the batteries first so they will need charged, then when they test the alternator output they can get both the voltage and the amperage the alternator is putting out.
I have had alternators that were putting out the correct voltage but no amperage. Truck always seemed like the batteries were dead, and it would not start.
The alternator test showed 14 volts and only 5 amps charge with low batteries and a 125 amp alternator.
Changed the alternator and the test showed 13.8 volts and 120 amps charge.
Problem fixed.
Do a load test on the batteries first so they will need charged, then when they test the alternator output they can get both the voltage and the amperage the alternator is putting out.
I have had alternators that were putting out the correct voltage but no amperage. Truck always seemed like the batteries were dead, and it would not start.
The alternator test showed 14 volts and only 5 amps charge with low batteries and a 125 amp alternator.
Changed the alternator and the test showed 13.8 volts and 120 amps charge.
Problem fixed.
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From: Prunedale CA
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From: Powell River B.C.
If you load up the system with all the electrical on you can, a volt meter check will let you know if the alternator putting out amperage. If not the voltage will drop the more you load up the system. Several faults with alternators, worn out brushes and commutator rings, the feild to ground resistance will wander all over when you turn the armature, or a burned out rotor will measure an open feild. These will take out the regulator. Another fault is the diodes burn out or the stator windings break, reducing the output capacity of the alternator, usually will show up as static on your am radio- if anyone listens to them any more!
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