Low charge on 68 Cuda

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KitCarlson said:
So what happens when you remove the blue and green wires from regulator and connect them together ? That would give full field, to test alternator, the alternator post voltage should increase. Do not rev engine, the voltage and current may go too high. Your battery is very low on charge, the voltage may tale a few minutes to increase.
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I assume that if I get the higher voltage 15V + or - that will show the "new" VR is bad? or could it be something else?
OK I will give it a shot tomorrow and let you know what happens. Thank You
 
An unloaded alternator at full field and high RPM could reach 50V, that may be enough to exceed reverse voltage rating on diodes. The battery typically holds the voltage down if good, but have heard voltage can exceed 20V, that is enough to damage radio and other components.

The connection of blue to green wires is to test if the wiring and alternator is working. As others have suggested the VR could have been damaged due to incorrect connections in your first attempts.
 
Some alternators can put out over 100v if you put a full 12 volts on the field with no current limiting and rev them up!
 
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mrose said:
Ok Guys here's what it is reading at the VR....Going to the blue lead at the VR-11.91V and at the green - 4.67V
Let me know what you think.
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The VR looks to be working and trying to push more current into the alternator's field to get the alternator output up. The fact that the VR is putting out over 4 volts shows this. (Although it is possible that the 4.67 volts is from residual magnetism in the field core which is putting the voltage back out of the field terminal.) The more likely problem looks to be that that the alternator is not working, or somehow, the alternator's output is not getting to the battery. Try the test that Kit suggests above; I'd measure this right at the alternator output terminal and you ought to see if jump up some immediately when you short those wires together (after removing them from the VR).
 
nm9stheham said:
The VR looks to be working and trying to push more current into the alternator's field to get the alternator output up. The fact that the VR is putting out over 4 volts shows this. (Although it is possible that the 4.67 volts is from residual magnetism in the field core which is putting the voltage back out of the field terminal.) The more likely problem looks to be that that the alternator is not working, or somehow, the alternator's output is not getting to the battery. Try the test that Kit suggests above; I'd measure this right at the alternator output terminal and you ought to see if jump up some immediately when you short those wires together (after removing them from the VR).
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I don't understand your logic, here. 4V at the field connection, if that's what we have, is very very low, and would not result in very much alternator output. Since it's not charging, I would expect that figure to be nearly full battery voltage.

Likewise, if there's an open in the alternator output (charge line) the VR field connection WOULD STILL be very high because the VR is sensing low battery voltage.

It still sounds to me like a bad VR, but what the OP needs to do FIRST is as Kit/ Dave suggests and jumper "full battery" to the field by jumpering the two VR wires together. Slowly bring up engine RPM with a voltmeter on the battery and watch for an increase, and also watch the ammeter for charge.

So far as an unloaded alternator, they can put out MORE than 100V. There used to be switchboxes sold that advertised "you could get 115V" out of an alternator. These were a cheap switchbox with a 120V outlet. The switch "full fielded" the alternator and disconnected the output, ran it to the outlet. Very hard on alternators and diodes
 
From what I have measured in the old single field wire setup, the VR puts out about 2-3 volts normally That puts enough current into the filed winding to produce 13-14 volts. 4 to 5 volts says that the VR is trying to push more current into the field..... assuming it is able to which is indeed questionable.

And yes on the alternator switched systems for power tools.... you are one who knows what I was referring to. They were hard on drills too but it beat having nothing in the wilderness. I never tried a TV on one LOL
 
Keep it going fellas this is a great thread for those that want to learn something.
 
Sorry guys, I have'nt been able to do the VR blue and green wire together test yet.
I hope to get to it tomorrow morning.
Thanks for the help.
 
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