Voltage Regulator and low output from Alternator

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jhdeval

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I know I should know this but for whatever reason I just can not remember nor can I find it. I am getting about 11.8 volts out of the alternator on the charge lug. On the voltage regulator I am getting nothing out of the field and about 12 volts on the input side. I do have a 2 field alternator. I am using an old style regulator with the electronics not the multi-field regulator.

Is it my regulator or alternator that is blown? I am leaning towards the regulator.
 
Did you ground the second field terminal?

Basically this is a simple circuit

The regulator MUST be grounded. MUST!!!

The regulator has two connections, IGN and FIELD

IGN goes to switched 12V from the ignition switch, and this is subject to "suspected" voltage drop

FIELD goes to either field terminal of the newer style alternator

The remaining field terminal must be grounded.
 
Yes the second field is grounded as is the regulator. I am getting voltage on the ignition side because I am able to start the car but the battery is not charging most likely from the low output from the alternator.
 
OK, sounds like a defective regulator OR MIGHT BE you have a shorted field in the alternator

Since this MIGHT be a problem, I'd be cautious. Might be worth your time to yank the alternator off there

You have a multimeter? Pull green wire

OFF AT THE REGULATOR FIELD

The reason for this is you do not want to disturb anything down at the alternator in case this is some intermittent deal. "You want to find the problem"

Post back if you have trouble. Set your multimeter up for LOW resistance measurement. Clip one meter probe to a GOOD engine block ground, and firmly stab the other probe into the green wire connector. You want to be CERTAIN you have a good connection for this. Carefully measure the resistance.

It should be MORE THAN a dead short.

The alternator field might draw (older) around 3A, or (newer) more like 4, and there has been reports of as much as 6 amp draw.

So using "one end" at 3A and the top end of 6A you can plug this into ohms law at 12V and this give you a resistance of around 4 ohms to 2 ohms

(R = E / I )

If it measures close to "a dead short"

Then either the green wire (unlikely) is shorted to ground

or the alternator has a problem. This is common with rebuilds, as common as having wrong or missing insulator washers in the brushes

IT JUST MIGHT BE that the field is shorted and has taken out your regulator. If this is so, remove the cover and see if you can find an open fuse inside. It might be an "open" piece of tiny wire
 
On the other hand if your resistance readings look "good" it might just be that you simply have a bad (defective) regulator
 
Sounds to me like the regulator is fried for sure. Disconnect it and see what the voltage measures from the charge lug to ground. If it ain't at least 13.5V the alternator is fried as well. Unregulated alternator output should be 14.5-16.5V...
 
If its a square back dual field alternator, just upgrade to the superior electronic regulator. You are half way there anyway. Run original blue hot wire to top of triangle plug of electronic voltage regulator and then down to one field and then other regulator wire to other field. done! Electronic regulator doesnt allow voltage to swing as wide asold points did.
latealt.JPG
 
That's true. To upgrade to the newer 70 / later regulator, all you need is "one more wire."
 
I guess its time to upgrade. I misread initially what 67Dart273 said and I measured from the field on the alternator to ground and I got exactly 0 resistance or complete short. I also tested the output on the lug and got about 11.94.

Well time to shop what year did the new voltage regulator start on?77 or newer?
 
jhdeval said:
I guess its time to upgrade. I misread initially what 67Dart273 said and I measured from the field on the alternator to ground and I got exactly 0 resistance or complete short.
Click to expand...

You need to stop right there and yank the alternator and check it out NEITHER field connection on an isolated field unit should show any continuity to ground.

That is, if you jumpered one field connection to ground, remove that and check them each to ground.

Pull the alternator and post a good photo of the rear view.
 
Ok so I did forget to remove the second field connection which was to ground. I tested again after and I got open from field 1 to ground and field 2 to ground. Based on what your original post asked me to do you want me to measure the resistance on the wire from regulator field to field connection. I have replaced that wire a year or so ago I expect it should be minimal although I have not tested it as of yet.

Its to dark to pull the alternator now it will have to wait till tomorrow.
 
We are confusing each other. Let's step back

You need to get this thing on the bench (if you do not) and check it

Check EACH brush to ground that is the alternator case. Should be "open," or infinity

Now check from one brush to the other. It should NOT be a dead short, but rather up in the 2--4 ohms or so between the two brushes

What I'm very concerned about is that one brush is either UNintentionally grounded, or has an intermittent ground. This could have ruined your VR, and may ruin another or worse, burn up some wiring. That circuit IS NOT fused
 
So I pulled the alternator off and I get open on the each ground to field and about 22.4-22.9 ohms of resistance from field to field. I double checked the voltage out again and it is still floating around 11.7-11.9. I am ground on the thermostat body bolt. I checked across the lugs of the battery and positive to the bolt and the voltage was within a couple of point .2 to .3 variance. I feel confident that I am using a good ground.
 
Ok, with what you've done, sounds like the field is OK. If you can post a good photo. Inspect the brushes carefully, best to pull them out. You are looking for anything that could cause an unwanted ground (short) from one brush to the case

IF you can confirm that this is not likely, next put it back on the car and do a simple test

If you are going to continue to use the 69/ earlier regulator, ground one field terminal. Clip the remaining field to a battery source such as the starter relay big stud

Start engine, bring up RPM and see if it charges. If not check voltage at alternator output stud and see where it sits at "a good fast idle."
 
I just bit the bullet and replaced the alternator and voltage regulator with the newer late model "square" backs. I am getting good charging and PLENTY of amps. I went with a 78 amp unit.
 
Make sure to warm it up, let it normalize, and check running battery voltage. Should be 13.8--14.2, and in no case less than 13.5 or more than 14.5
 
That's a bit low, but..........

battery might still be a bit low, or might not have been clear warmed up
 
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