voltage issue
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Senior User
Joined: Oct 2008
Posts: 276
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From: Denmark,WI
voltage issue
for the past few days when i start my truck in the morning i noticed it would crank a bit slow, i figured oh well its not broke yet. last night when i went to leave work i went to start my truck and it cranked over really slow once or twice and then just clicked. had a buddy come and give me a jump and it started like a top. after i got it started everything worked good, lights, radio, ect. this morning i took it to advance and had them do a test on the battery and alternator and they both came back good other than the battery being at about 12.1V at the time. (the guy said that was low). he said the only issue i have is a battery that needs charging. after the truck is jumped everything works as it should, but something is draining 1/2 amp from it. has anyone had this issue? i need a place to start...i hate wiring!! 2001 5.4 scab 4x4. like i said, everything works as it should once its jumped. nothing is dim or anything. thanks!
Lead Driver
Joined: Sep 2006
Posts: 7,907
Likes: 143
Before you go off in 6 different directions at once get some basics about the charging system.
First make sure both battery cables are in good condition and the ends are clean and the other ends are tight.
The battery posts are clean.
Test battery capacity.
When these are checked for, start the motor and use a voltmeter to observe the voltage at the battery just after starting.
Is it at least 15.5 to 16 volts?
If yes, the alternator is charging proper.
Does the voltage drop down to about 14 volts after about 5 minutes (assuming a good battery)?
If yes the regulator on the alternator is working properly.
Next , if you have a run down condition like over light, suspect the alternator stack of having a shorted diode even though it still charges ok, it would be a fault.
Then see if the problem is cleared.
A battery with some age at about 12 to 12.5 volts without the motor running is normal, (6 cells times 2.15 volts each = 12.9 volts.
If not come back here.
Good luck.
First make sure both battery cables are in good condition and the ends are clean and the other ends are tight.
The battery posts are clean.
Test battery capacity.
When these are checked for, start the motor and use a voltmeter to observe the voltage at the battery just after starting.
Is it at least 15.5 to 16 volts?
If yes, the alternator is charging proper.
Does the voltage drop down to about 14 volts after about 5 minutes (assuming a good battery)?
If yes the regulator on the alternator is working properly.
Next , if you have a run down condition like over light, suspect the alternator stack of having a shorted diode even though it still charges ok, it would be a fault.
Then see if the problem is cleared.
A battery with some age at about 12 to 12.5 volts without the motor running is normal, (6 cells times 2.15 volts each = 12.9 volts.
If not come back here.
Good luck.
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