I have a '69 A-108 van (that's an A body right?). I did the standard battery/alternator test. Put the multi meter across the bat terminals. Engine off reads 13 volts. Engine running . still 13 volts What does this indicate? I know the voltage should go up with the engine running. Thanks.
Charging system question
- Thread starter cult colt
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Yup. Sure is.
But probabaly should be under electric rather than engines...
That's the quick and dirty test but there may have been surface charge on the battery.
Flip the lights on for a couple seconds, turn off, and remeasure the battery voltage.
Battery should be 12.5-12.8 V
Flip the lights on and see what it reads. After the surface charge is removed it shouldn't drop much with just lights on for a minute or less.
When the lights are on, the ammeter should show the battery is discharging 5- 10 amps.
Start the engine. The ammeter should immediately show battery charging, especially when the engine is on fast idle.
Voltage at battery should read 13.8- 14.2 depending on temperature and regulator setpoint.
Voltage between alternator output stud and ground should be the same.
When the battery is recharged, the ammeter will be centered.
Flip on the parking lights, the ammeter should stay centered. With the headlights on, it may show slight battery discharge until you increase rpm above idle.
If you are seeing battery discharge while running, or running with just the parking lights on, measure the voltage at battery and at the alternator output.
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67Dart273
Well-Known Member
If it is idling quite slow, it may not show additional voltage at dead slow idle. But a slight increase in idle speed should result in a voltage increase to about 14. VR is temperature compensated. It should read different when hot or cold. "Warmed up" is nominally 13.8---14.2 with battery normalized
Measuring voltage at the alternator output terminal might show you if there is a harness problem, such as a bad connection in the bulkhead / firewall connector
"The quick and dirty" test for a no charge situation (check belt tension) is to jumper power to the alternator field terminal after disconnecting the green field wire, then run the engine, increase RPM and see if battery voltage starts to go up
Measuring voltage at the alternator output terminal might show you if there is a harness problem, such as a bad connection in the bulkhead / firewall connector
"The quick and dirty" test for a no charge situation (check belt tension) is to jumper power to the alternator field terminal after disconnecting the green field wire, then run the engine, increase RPM and see if battery voltage starts to go up
Is there a magnetic field at the rear center cap of the alt while running?
512Stroker
We are all here because we are not all there.
Plan and simple your charging system is dead.
Could be the alternator and/or the voltage regular.
Have the alternator tested at a competent shop, if it tests good you know the answer.
Assuming your wiring is correct and in good shape.
Good luck its not rockect surgery.
Not really understanding the question.
Electric current through windings of wire create an electromagnet field. The field is weaker the further it is from the windings.
A brief description on this page: Magnetic Field around a coil of wire
Here's the back of a 1969 roundback alternator.
In the center, circled in yellow, is a pressed in needle bearing.
This is the rotor. The yellow line show where bearing cup goes.
Orange arrows show the path of electricity from the voltage regulator into the rotor windings, and then out to the ground brush.
The windings are in the interior and cant be seen due to the shadow.
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Inside the rear housing with the stator.
The spinning magnetic field of the rotor induces alternating current in the stator.
The diodes rectify current flowing out into direct current.
The can at 12'o'clock is a capacitor
The spinning magnetic field of the rotor induces alternating current in the stator.
The diodes rectify current flowing out into direct current.
The can at 12'o'clock is a capacitor
67Dart273
Well-Known Member
The rotor does generate a magnetic field. I've seen "quickie" tests where someone puts a screwdriver across the rear of the alternator, this is supposed to prove the rotor is active.
But that really doesn't PROVE anything. There is so much more that can go wrong with a charging system, it really matters not whether the rotor is producing a field.
I tend to "group" the charging system:
The output circuit which "on these cars" encompasses the alternator output, through the bulkhead, through the ammeter, back out the bulkhead, to the battery. There are at least several major connections in there that can drop the charge path
The components, the alternator and the VR
The field circuit, from the ignition "run" circuit, through the VR and the green field wire, and the brushes, through the field.
Any part or more than one of all of that can be defective
But that really doesn't PROVE anything. There is so much more that can go wrong with a charging system, it really matters not whether the rotor is producing a field.
I tend to "group" the charging system:
The output circuit which "on these cars" encompasses the alternator output, through the bulkhead, through the ammeter, back out the bulkhead, to the battery. There are at least several major connections in there that can drop the charge path
The components, the alternator and the VR
The field circuit, from the ignition "run" circuit, through the VR and the green field wire, and the brushes, through the field.
Any part or more than one of all of that can be defective
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