Charging Issues...Please Help!

-
N

Nelson7604

Active Member
Joined
Apr 30, 2014
Messages
40
Reaction score
0
Location
Beaumont, CA
Ok...Well here's the skinny...I got a brand new alternator, but I ended up breaking one of the brushes. I got a new set of brushes for it and when I fired it up again, one of the field wires nearly melted off along with the new brush.

I diagnosed that as my impatience when I noticed I put the two field wires on backwards (if that makes a difference; I followed my wiring diagram as I'm not familiar with how alternators work). I then tore the harness apart and replaced the damaged wire(and new brush), fired it back up and no charge.

I fired it up again after I got headers, didn't pay attention and melted through the ignition wiring harness with the headers! I cut the bad wire out and spliced every wire again with solid connections (Still no charge).

After about a couple weeks, it finally started to charge out of the blue. Thinking it might have been a loose/bad connection that I fixed somewhere along the line I kept an eye on it with a voltage meter (getting around 15v at idle). Sweet! all taken care of!

NOT!! Fired it up to move around in driveway and alternator was smoking like crazy and same field wire was getting hot. I shut it all down, disconnected wire and battery and there it sits...

Am I missing anything? Other than patience... Should I get another alternator or did something short out during all of my stupidity that I need to replace?

Anything will help at this point. Thanks in advance.
 
As above. You probably need to pull out the brushes carefully and figure out where the short is. It may well be on the brush holder opposite to the one with the hot wire so don't look at just one brush; both need to be ungrounded for things to work in your 1972 system. Here is the reason:

In your car, 12v is fed via a blue wire to one field terminal (brush) on the alternator. The other field terminal (brush) connects via a green wire to the regulator. The regulator applies what can be thought of as a variable resistance to ground; in turn, this varies the current flowing from 12v and through the field winding and brushes to regulate the system voltage.

If you get a short to ground at the brush to which the green wire connects, then the 12v connected at the other brush sends full, uncontrolled field current through the field winding to that grounded brush, and the alternator charges like crazy and you can get a lot of smoke.

You could also have a short to ground in the green wire somewhere. If the brushes are not shorted and the wires are not shorted to ground, then the regulator is next to suspect. But the brushes and wires are the likely problem areas.

You may have had this problem all along if you had 15v or more at low idle; that is too high. The system should put out only 13.7-14.3 volts warmed up and at FAST idle (maybe a few tenths more when cold and fast idle), and lower voltage at low idle. You just made it really show up when you revved up the engine to move it around.

BTW, it does not matter to which the blue and green wires connect. So reversing them is not an issue.
 
Hi,

NM9's pretty much has the technical issues covered. I'll only add, do you have a ohms or continuity position on your meter you are using to measure voltage? And, can you post some close up pictures of the brush holder area of your alternator (off the engine) so we can see what you have.

I agree that you very likely have a shorted brush or holder, you just need to find out why.
 
nm9stheham said:
As above. You probably need to pull out the brushes carefully and figure out where the short is. It may well be on the brush holder opposite to the one with the hot wire so don't look at just one brush; both need to be ungrounded for things to work in your 1972 system. Here is the reason:

In your car, 12v is fed via a blue wire to one field terminal (brush) on the alternator. The other field terminal (brush) connects via a green wire to the regulator. The regulator applies what can be thought of as a variable resistance to ground; in turn, this varies the current flowing from 12v and through the field winding and brushes to regulate the system voltage.

If you get a short to ground at the brush to which the green wire connects, then the 12v connected at the other brush sends full, uncontrolled field current through the field winding to that grounded brush, and the alternator charges like crazy and you can get a lot of smoke.

You could also have a short to ground in the green wire somewhere. If the brushes are not shorted and the wires are not shorted to ground, then the regulator is next to suspect. But the brushes and wires are the likely problem areas.

You may have had this problem all along if you had 15v or more at low idle; that is too high. The system should put out only 13.7-14.3 volts warmed up and at FAST idle (maybe a few tenths more when cold and fast idle), and lower voltage at low idle. You just made it really show up when you revved up the engine to move it around.

BTW, it does not matter to which the blue and green wires connect. So reversing them is not an issue.
Click to expand...

I think you are right about the fact that it typically doesn't matter which wire connects to which terminal, but if the hot wire is connected to the brush that is grounded then you would have a dead short to ground (hence the melting of the wire) by reversing the wires it would send the alternator into a full charge situation (hence 15 volts at idle). I agree that one of the brushes are probably not installed correctly and is grounded. Take them out and inspect carefully. Good Luck
 
superchargeddrt said:
I think you are right about the fact that it typically doesn't matter which wire connects to which terminal, but if the hot wire is connected to the brush that is grounded then you would have a dead short to ground (hence the melting of the wire) by reversing the wires it would send the alternator into a full charge situation (hence 15 volts at idle). I agree that one of the brushes are probably not installed correctly and is grounded. Take them out and inspect carefully. Good Luck
Click to expand...
A good point.... and I can't say why it did not charge for a while and then did!
 
nm9stheham said:
A good point.... and I can't say why it did not charge for a while and then did!
Click to expand...

Because anything can happen if you take something apart, break it, reassemble it wrong and fry stuff?
I'm at a loss also.#-o
 
nm9stheham said:
A good point.... and I can't say why it did not charge for a while and then did!
Click to expand...

Try taking the brushes back out and examine them. If one of them were shorted to ground and then was connected to hot wire there would be an extreme current draw and the brush would show signs of damage. You can buy new brushes and very possibly fix your problem.
 
Ok. Thanks for the quick replies.

I checked the brushes with an ohm meter and sure enough one was grounded.
I took it out and it doesn't appear to be damaged.
The part inside the alternator that the brush rides against (I don't know what it is called) is grounded out.
Is this reason for another new alternator?
 
If you ohmed it out while installed, you would need to read the meter very carefully. With all wires disconnected, and ohming brush to brush you are going through the armature which could easily be misread as a short.
If you ohm either brush to case and get any reading, that would be a short and either bad alternator, or a shorted(almost impossible)brush. The brush holder would have to be broken.

Now heres a wildcard
Is it possible to install a brush holder from an isolated field alt into a non-isolated alt, in such a way that a short is pretty much precluded?
 
Those are called the slip rings and if one is grounded to the case, then yes, that needs to be replaced. With your year alternator, the field, the slips rings and the brushes should show high resistance readings to the case.

I am sure you did this, but make sure that there is no grounding lug at the one brush. Sometimes those are added to ground a brush and make the alternator work for the older regulation system where one brush was grounded inside the alternator.
 
Take both brushes out and measure resistance from each slip ring to the case. If you measure anything appreciable (say <1000 ohm), the armature (rotating part) is probably bad. The FSM shows removing it and running a saw blade between each copper contact rectangle. That insures that none are electrically bridged and that the insulator doesn't protude to block the contacts (or I might be recalling the starter motor). But, alternators are so cheap, most just replace them.
 
You must log in or register to reply here.
-

Back
Top