Alternator Issues (12 volt conversion)

[jh19900]

My Gen II alternator started experiencing intermittent overvoltage so I finally started looking at the charging system.

The Gen I alternator has no positive lead attached so it does not appear to be part of the charging circuit at the moment.

Both batteries are charging at the exact same voltage so the they must be wired in parallel with the Gen II alternator.

The Gen II alternator has only the exciter leads and the positive lead attached. This must mean it is case grounded and therefore not an isolated ground alternator.

Is there a way to test an alternator for an isolated ground without tearing it apart?

It seems for an easy fix I could buy a case grounded alternator like the one from an 84 eldorado or buy an isolated ground alternator and attach a ground wire to the frame.

Am I correct in my thinking? Anything I should look out for?

 

[Recovry4x4]

On the back of your alternator, there are six slotted vents. At the end of one of these vents, will be a stud if the alternator is isolated ground. In the absence of this, your alt is case grounded.

 

[Warthog]

Here is a picture of a stock alternator..

It would help to post a picture of your setup so we can possible tell how your truck is wired.

 

[jh19900]

Thanks for the help! I'll try to get some pictures up. The Gen II alternator that I took out the other day was the same model as the 84 eldorado alternator. I'm just going to replace it with another case grounded alternator. When I have some more time I will try to convert it back to the stock 24 volt system.

 

[jh19900]

Here is a quick video after install. https://youtu.be/y9j1bg4pmIA

The positive terminal of the driver side alternator is not even connected. Is there any reason I should leave this alternator on the truck?

The passenger side alternator is just a case grounded 84 eldorado alternator. The two batteries are connected in parallel.

 

[jh19900]

Well, the fun isn't over yet. The new alternator is fine at idle and low speeds but as soon as I get on the highway it is outputting 16+ volts. Looks like I got a bad alternator from napa.

 

[6x6guy]

What size wire do you have between the alternator post and the positive terminal.
Check the negative post and make sure you have contact on the frame, body and motor area and even perhaps the alternator it self, a uneven electronic flow of electrons between the ground and positive areas will cause a problem with the
alternator over or under charging at times depending on the RPM of the armature.

 

[jh19900]

What size wire do you have between the alternator post and the positive terminal.
Check the negative post and make sure you have contact on the frame, body and motor area and even perhaps the alternator it self, a uneven electronic flow of electrons between the ground and positive areas will cause a problem with the
alternator over or under charging at times depending on the RPM of the armature.

This is interesting as it is only at 13 or so volts at idle so it is acting like you described. There is no negative post, it is only grounded through the case. I'm not sure of the exact size of the positive wire but it didn't strike me as being too small.

The last alternator was the exact same model (case grounded eldorado) and it was always at ~14 volts at idle and not much higher on the highway. Something is definitely wrong.

 

[Warthog]

Sounds like it could be a bad voltage regulator in the new alternator.

 

[6x6guy]

Contacts such as ground can be affected by grease and or rust preventing a good negative ground affecting the performance ( out put ) of your alternator- and causing a intermittent ground and undesirable operating conditions.

 

[6x6guy]

The RPMs of a alternator will change the voltage output of the device - most common alternator regulators will engage at approximately 800 to 1000 RPM depending on the stator which will excite the regulator and elevate to voltage to 14 volts ( charging Voltage ) assuming that a good ground and equal flow of electrons ( size of both wires are of equal resistance and not causing warm to touch wiring or a unbalanced system).