Alternator Tech

One of the questions I have gotten on ocassion is why is my alternator is not putting out and what could be wrong.
If you can imagine after reading this article and then understanding it without the pictures relates to the daunting tasks I have faced, so with almost 2 disks worth of pictures and the dis-assembly and re-assembly of the spare alternator I carry for Fireball, hopefully the GM internally regulated alternator will be explained.
Understand that every make of alternator is different and there is no way I can devote the time to tear them all apart, so for now read into the insides of the most popular of Alternators;   The GM 12 SI (system integrated).
Warning:  There are a bunch of pics here so loading times will be slow.

One of the first daunting tasks that brings on confusion is Clocking, so here it is in a nutshell.  The Yellow Arrow points to the upper mounting flange and represents 12 o'clock.  The Red Arrow points to the regulator port and is at 3 o'clock.  That means this alternator is clocked at 3 o'clock.
If you don't get it, look at the next picture!



Place a mark on both sides of the case where a mounting bolt goes through.  Only mark one boss on each half of the case as shown.  This will tell you when you put it back together how it lines up.








There are 4 bolts that hold the two halves of the case together which are now removed.













With the bolts removed, the case must now be seperated and this is where attention to detail is important!   The case must be seperated with the Stator Assembly attached to the back half of the case.  Inserting a screwdriver and prying gently will accomplish this task.   As you seperate and ultimately remove the rear half from the front half, you may hear a couple of clicking sounds.   This is the brushes falling out of the brush assembly but don't go looking for pieces as the brushes are attached to the brush assembly.

Here we are looking into the back half of the alternator.   It may look a little daunting now but once we get through the dis-assembly and re-assembly process, this will look easy.










This is a look at the Rotor Assembly still attached to the front cover.   We did not feel the need to remove the pulley, fan, and cover from the rotor for this article.   If we had found the front bearing to be bad we would have finished the dis-assembly and replaced the bearings but since this is a fully functional alternator and we are more interested in showing you why an alternator would quit charging, rather than how to change bearings (which you would only do if the alternator was making noise) we will stay on track with the energy producing part.

Taking a closer look at the Rotor, we find that it is wound with many turns of insulated copper wire and then given a protective covering to help protect the inner covering.











This is the rotor contacts where the brushes ride.
I will explain how to test the Rotor later in the article.












We will dis-assemble the alternator and then show how it's put back together and what tests need to be done.   I do allot of articles with just re-assembly, but Alternators have some very touchy parts that break easy so I decided to do this both ways.
First we will remove the 3 nuts from the Rectifier Assembly and remove the Stator Wires, carefully prying the Stator Assembly loose from the back half of the case and setting it aside.

Next we will loosen the bolt on the Regulator/Brush Assembly ultimately removing the bolt along with the Connection Diode.   Note the Brushes hanging out of the Brush Assembly in the foreground.









Next we remove the other two bolts holding the Brush Assembly and Regulator to the case.
It is important to remember which 2 holes get the insulated bolts and which one doesn't.   Many alternators have burned up and caused electrical fires in the engine compartment by screwing this up.





Next is the removal of the Recifier which requires the removal of the large nut on the left and the two small bolts on the right the lower of which attaches to a capacitor or condensor which supresses ignition noise.








The large nut in the preceeding picture is attached to the Positive Lug on the Alternator where the Battery wires go.   This is removed and set aside.










Here is the Components of the Internally Regulated Alternator!
1. Rectifier Assembly
2. Regulator
3. Connection Diode
4. Brush Assembly.   Some of the other items are the attaching hardware of which you should already recognize from the dis-assembly.





We are now ready to test the Rectifier, but first we have a class of Insulator 101.
The recifier is actually two halves with 6 diodes terminating at 3 lugs.   The Yellow line shows the positive side of the assembly (note the red plus sign), while the blue line represents the ground or negative side (note the black negative sign).
Understanding this, we now have 6 tests to accomplish, first testing the positive side diodes and then the negative side diodes.
With an ohm meter set on 2k put the Black Negative lead of your ohm meter on the Positive side of the Recifier heat sink.   Probe the copper connector next to the first mounting lug until you get a reading as shown in the picture.
Infinity or 000 on the ohm meter is bad, but a reading between .400 and .600 is good.   If you get 000, double check your leads to make sure your connected right. If you get 000 in both directions the Diode is bad and the whole Rectifier needs replaced.   The following pictures show you the complete testing process and typical readings so looking at them carefully should explain the testing procedure.
Remember that when you test the Diodes on the Positive side, you need to reverse the leads on the ohm meter and move the Positive lead of the Ohm Meter to the Negative side of the Rectifier Block and then probe the diodes on that side with the Negative lead of the Ohm Meter.


Test the center and far right diodes in this fashion then switch leads connect to the Negative block with the positive lead and continue.   The following 3 pics show the procedure for the Negative Diodes as well as normal readings.







Once the Rectifier is tested and passed, turn it over and inspect the insulator and bolt hole (arrow) for breaks or weak spots that might cause the Rectifier to short out. The Negative side must ground to the case through the screw but the Positive side must be isolated from ground using the insulated Battery Post, and the insulator on the Rectifier.   The Large Nut makes the connection between the Rectifier and the Battery Post.   If you absolutely want to check to make sure there is no short, you can connect the Black probe of the Ohm Meter to the case, and the Red Probe to the Battery Lug and should get no reading with the Ohm Meter set on the 200 scale. You will get a resistance reading in the 2k, and 200k settings.   This is normal.   If you get a 000 reading in the 200 scale on the Ohm Meter you may have missed a shorted diode.   This test can be deceiving on some meters so unless your sure what your looking at, don't worry about this test, just pay attention to detail with the insulator on the Rectifier.

Now we are going to test the Stator Assembly.   This is also done with an Ohm Meter set on the 200 scale.   You should get a reading on each of the tests.   Below are the pics from these tests.   Note that polarity is not critical on these tests as you are just checking for continuity.









Once the Stator windings have been tested, we look at the windings very carefully to make sure there is no burnt spots, or missing insulation.   If this Alternator went into a full output state sometime in it's life or was shorted out for some reason, these wires will be burnt and the Stator will need to be replaced.




We will now look at the brush assembly and brushes.   If the brushes are worn down to within 3/16's of an inch it's time to replace the brush assembly.   We had over 3/8's of an inch of brush so we will re-use this set.
The brushes are then carefully put back in their housings and a round toothpick stuck through the holes in each end to hold the brushes in the housing for re-assembly.   This toothpick will remain in the assembly until the last step of re-assembly.

Now we inspect the Regulator or Heart of this Alternator.   We look for cracks, burnt spots, and bad or corroded connections.
We then test the regulator with an ohm meter looking for opens and shorts.   This is the most commonly failed part of the Alternator as it is easilly blown by spikes, overloads, and arcs mostly by using the vehicle to jump other vehicles.   If in doubt with the readings or condition of the Regulator, just replace it.   To test this, set your Ohm Meter to the 2k scale and perform the following tests as outlined in the pics below.











The last component test is the Connector Diode.   Check it with an ohm meter set in the 2k scale as shown in this picture and the picture below.













With all component tests done we now check the Rotor by connecting our Ohm Meter to the connections where the brushes ride.   Set the Ohm Meter for 200k and note the reading!   A reading of 000 on the 200 scale is OK also.   We are performing this test to confirm there is a connection between the windings.   If you get no reading, the Rotor is open and will need replacing.

With everything testing fine, we now start the re-assembly process starting with the Positive lug, and the rectifier assembly and attaching screws.   If you are using this article to build your own alternator, refer to the pics under the dis-assembly section for re-assembly reference.   The pictures are more expanded for the rest of the article to show the whole process as it is put back together.   Before you start, put a small dab of grease in the rear bearing to give it a new lease on life.   The front bearing is sealed and is self lubricated.


Rectifier installed and the bolts and Battery post nut tightened snug.


Brush and Regulator Assembly mated and installed with two of the bolts in the correct places.   Note the Red Arrow pointing to the Toothpick, holding the brushes in place.   This toothpick must extend out the back of the case far enough that you can get a hold of it for the final step.





Next the installation of the Connection Diode.   Note the correct placement of the insulating bolts in the Brush/Regulator Assembly.


Installation of the Stator and the placement of the 3 Stator Wires.   Note: The notches on the Stator Housing must be lined up with holes in the case.   If this step is missed, you may not get the bolts back in the case but worst of all it may mis-align the two case halves causing a binding problem once the final assembly is made.   Once alignment is made and the wires installed, screw on and snug the 3 nuts holding the Stator wires, and Connection Diode to the Rectifier.


Remember those clocking marks?   Now is the time to utilize the marks to correctly clock the two halves of the cases.


Remember the Toothpick?.....


.....Just grip it firmly and pull it straight out.   You should hear 2 clicks as you remove it and these are the sounds of the brushes seating with the Rotor Connections.


Finally, if your assembly is successful, you can easilly spin the Alternator.
Note:  If you can't spin it or it binds, the brushes missed seating and fell to the side, or something isn't assembled correctly. Disasseble and recheck your work, reset the brushes with the toothpick and try again.   If you follow the pictures, you should have sucess the first time.


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