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Curtis B.
Curtis B., Technician
Category: Construction and Road Equipment
Satisfied Customers: 988
Experience:  Technican turned service manager with multiple lines of equipment and rental units.
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JD 319d.........new battery, new alternator and alternator

Customer Question

JD 319d.........new battery, new alternator and alternator diode. not charging at the alternator and only showing 12.2V on display.......12.74V before starting........lights pull the display voltage to 11.7V while running regardless of engine rpm
Submitted: 1 month ago.
Category: Construction and Road Equipment
Expert:  Curtis B. replied 1 month ago.

Hello! Let's see if we can work together and come to a satisfactory conclusion!

Expert:  Curtis B. replied 1 month ago.

The alternator has to have 12 volts to the field coil , to activate the alternator. Is there voltage to the field terminal on the alternator?

Customer: replied 1 month ago.
do you mean with the unit not running?............if you mean while running yes i have 12.2V or so
Expert:  Curtis B. replied 1 month ago.

No, with key on and running, the field terminal has to have battery voltage to energize and start the alternator charge cycle.

Customer: replied 1 month ago.
i have the orig alternator on hand...........the machine is 150 mi away and wont be back to it till next thursday. Any thoughts on a course of action if I:
1- have 12 V at the field term with it running
2- dont have 12V at the F term with it running
its a bosch alternator just wondering which term if the "F" terminal?
thanks i can stay in touch with you if that is possible??
thanks Curtis!
Scott
Expert:  Curtis B. replied 1 month ago.

Looking at the alternator, the upper plug or the lower plug has to be the energizing terminal. as the large terminal is the output, which has to read battery voltage, and has to rise when the alternator is energized. Energizing terminal only gets voltage when key is on and and engine starts. Once energized, the output becomes greater than battery voltage, and charges the battery.

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