Can field short to ground fry alternater?

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69DartGTConv

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New alternator was working and now 2 vdc @ input to reg. Only thing I found was frayed field wire touching valve cover.

thx
 
The alt is probably fine, the voltage regulator, that's another thing.

BUT FIRST.

20 QUESTIONS TIME....

  1. what car
  2. What year
  3. What engine
  4. What alternator ( "1 wire", 1 field wire, 2 field wires)
  5. What voltage regulator (electronic with "V" shaped connector, or mechanical clip on / screw on connector)
  6. What wiring modifications
  7. Anything else you can think of
 
69 Dart GT
413 with 1 field wire alt & mechanical reg
Wiring is stock again except upgraded dist wiring

Yesterday I measured 0 vdc output at the field connector and 2 at the input to reg
 
You broke the VR. I you can "fix" things remove the cover and see if there is a "broken wire" which is actually a fuse. You can't replace it but you might be able t bypass it
 
and '69 the ignition feed wire was run from the bulkhead to the VR first, then to the ballast resistor. If the engine is running there's more than 2 Volts feeding the ballast resistor. Might pay to recheck the measuments and do a visual inspection of the junctions.
 
per the wiring diagrams I have looked at, the field wire from alt goes direct to input side of VR. I get 0 volts at the field terminal with the wire detached.
image000000 (12).jpg
 
I think your thinking about it backwards.

The power flows INTO the alternator field terminal FROM the voltage regulator.


The path is:
Power source(12v) to voltage regulator (12v)
Output of voltage regulator (6 to 10v) to field terminal of alternator(6 to 10v), when running and charging.

Screenshot_20220526-191546.png
 
Close.
When the engine is running, the alternator is the power source. So most of the time the ignition terminal of the regulator should be around 14 Volts.
But this is why its worth measing the alternator's output voltage, and/or the votlage difference between the alternator output (Bat terminal) and the regulator input. Then there is no question as to the voltage the regulator should be seeing.

When the regulator input is lower than set point, the regulator allows a direct connection to the field terminal. The field terminal voltage should be virtually the same as the input voltage.

However as soon as the voltage on the ignition terminal rises, the regulator's points open forcing the electricity to go through a resistor.
When the votlage rises higher, that connection is opened and no power is available at the field terminal.
The hot trick would be to view it on scope.
 
Close.
When the engine is running, the alternator is the power source.

field wire from alt goes direct to input side of VR. I get 0 volts at the field terminal with the wire detached

My point is that the alternator is not OUTPUTING voltage on the field terminal.
It is receiving voltage from the VR.

IGN is the "input" to the VR
FLD is the "output" from the VR, and will be less than "nominal" 12V when the alternator is charging (unless the alternator is charging at full rated output current)
FLD terminal ON the alternator receives "input" from the VR.


Screenshot_20220526-191546.png


BTW The voltages I listed were just nominal, not measured.

The op most likely fried the VR with the shorted field wire. As the photo of the VR states "DO NOT SHORT ANY TERMINALS TO GROUND"

Not trying to be definsive here, just setting the op straight on what the field path is and what he should expect in terms of voltage when it is running correctly.


These videos are worth their weight in gold!
 
My point is that the alternator is not OUTPUTING voltage on the field terminal.
It is receiving voltage from the VR.
thumbs_up-gif.gif


BTW The voltages I listed were just nominal, not measured.

The op most likely fried the VR with the shorted field wire. As the photo of the VR states "DO NOT SHORT ANY TERMINALS TO GROUND"

Not trying to be definsive here, just setting the op straight on what the field path is and what he should expect in terms of voltage when it is running correctly.
beer-gif.gif


These videos are worth their weight in gold!
Yup. Good stuff!
food-20-21-gif.gif
 
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