SaabCentral Forums banner

1 - 16 of 16 Posts

·
Registered
Joined
·
22 Posts
Discussion Starter #1
I am trying to diagnose an alternator issue for my 2003 Saab 9-3 ARC. My car is not warning me of a failing alternator via the SID system and yet I am not getting anything out of the alternator. I have read many things online including that these Bosch alternators "do not self-excite" (meaning I assume that they do not just generate a 14.6V unless they are getting the proper signal from the ECU or something about the the D+ and DF terminals not right). I found this helpful bit online too:

"There are four connections to the alternator itself. D+, DF,D-, and B+. If you look at the Haynes book, what is not readily apparent, but is true nevertheless, is that the set of diodes that connect to the D+ terminal are a duplicate set (except for lower curent rating) to the ones for the B+ terminal, which is the actual high current output of the alternator. The D+ terminal is therefore a duplicate output terminal of the alternator, with less current capability. The lower set of diodes on current track 80 is common to both the D+ and B+ functions, and forms the ground return for both the B+ and D+ outputs. The DF or "Dynamo Field" terminal connects to the ungrounded end of the alternator field winding, and is an input to the alternator. The current supplied to the DF terminal determines the strength of the magnetic field that penetrates the output windings, and thus controls the alternator's output. The D- terminal is connected to the alternator frame, and is the ground return for the voltage regulator. The other end of the field winding is also connected to ground at this point.
The Bosch alternator is incapable of self-excitation, or "boot-strapping" itself to an operating condition. Older DC generators and some U.S. alternators have residual magnetism retained in the core, or some other scheme to get enough field current to get themselves up and running. The Bosch alternator uses a different scheme. The charge warning lamp is connected between the ignition switch and the D+ terminal. When the car is first started, there is no output from the alternator at either the B+ or D+ terminals. The voltage regulator, sensing no output, is attempting to command maximum field current... it effectively shorts the D+ and DF terminals together. This places the D+ terminal close to ground potential, because the resistance of the field winding is not large. This means that there is +12 volts on one side of the charge warning lamp, and the other side of the lamp is grounded through the alternator field winding. Current thus flows through the lamp, lighting it. This same current, however, also flows through the alternator field winding, producing a magnetic field. This magnetic field is what the alternator needs to start up, and if everything is working correctly, that's exactly what happens. The alternator now begins to develop identical voltages at the D+ and B+ terminals. The D+ terminal is connected to one end of the charge warning lamp, while the other end of the lamp is connected to the battery via the ignition switch. Since the B+ terminal is hard-wired to the battery, and since both the D+ and B+ diodes are fed from the same set of windings in the alternator, no voltage difference can exist between these two points. The warning lamp goes out.
The voltage regulator "watches" the voltage at the D+ point, which should be the same as that applied to the battery. It now changes the short between the D+ and DF terminals into a variable resistance. This effectively controls the field current (whose source is now the output from the D+ terminal, and not the charge warning lamp) and thus regulates the output voltage of the alternator.
Fault conditions: When something happens to the charging system that causes it's output to be insufficient, the result is almost always a net voltage difference across the charge warning lamp, causing it to light. For example: Suppose an output (B+) diode opens. The efficiency of the main output is now considerably reduced. The voltage regulator does not know this, however, because it is looking at the D+ point. So, the B+ output is now lower than the D+ point and the warning lamp lights. Let's say that one of the D+ diodes failed: The D+ output is now reduced considerably. This means that the voltage regulator will have difficulty in maintaining sufficient field current for normal output. The field regulating resistance is low or short (between D+ and DF terminals) and the resulting load on the crippled D+ system drops it's voltage well below the battery voltage. Therefore, there is a net voltage difference across the charge warning lamp and it lights.

The bottom line is that in order for your light to light, you must have a net imbalance in the outputs of the D+ and B+ sections of the alternator (or between the D+ output and the battery voltage, which amounts to the same thing).
To trouble-shoot the problem, you need to check the various sections independently. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator. Note that this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes.
To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply (not the battery, as in the earlier check) and so checks the remainder of the circuitry. If this test puts the light out, then the alternator is good, and the trouble is elsewhere. If it doesn't, then the alternator is almost certainly bad, with one other possibility:


In the Bosch system, the size of the charge warning lamp bulb is critical. Too low a wattage bulb will not supply enough field current for "bootstrap" operation to be reliable. The Bosch book that I have states that the lamps must be at least 2 watts for 12 volt systems. If you have replaced your charge warning lamp recently, then too small a lamp may be your culprit.

My question is does anyone know where to find the DF and D+ terminals on the relay board to do this diagnostic?

Thanks,
 

·
Super Moderator
Joined
·
8,928 Posts
what is the voltage when you put a meter across the battery with the engine running..could also be the clutch in the pulley has failed..
 

·
Registered
Joined
·
22 Posts
Discussion Starter #5
By the way, I have had the alternator out and 1. replaced regulator, 2. replaced rectifier as well. 3. tested the rotor windings for error (Youtube video), 4. tested stator windings for continuity. Several of my local commercial autoparts stores tested the alternator after the repairs BUT they shoed an alternator failure with their machine. I could not believe it, so I had a local Latin American alternator shop test the output on the thing and I clearly saw the alternator generating 14.6 V!!
 

·
Registered
Joined
·
22 Posts
Discussion Starter #7
Could the tension on the pulley in the car be a variable that is different enough to cause NO voltage in the car BUT 14.6 on the bench..." IDTS.
 

·
Registered
Joined
·
22 Posts
Discussion Starter #9
I just tested for voltage at the DF terminal- the wire plug into the alternator...with the ignition on...and NO Voltage. Aha.

"Your next test is for Field voltage this is the small wire on the back of the alternator (usually green) marked DF. You should test this wire with the ignition on. You should find around 9 volts or so, but the main thing is you find some voltage if you have no voltage here your alternator will never start to charge. If this is your problem you will have to trace this circuit back through the battery light on your dash for this you should see your wiring diagram."

Anyone have the 2003 Saab 9-3 arc wiring diagram?
 

·
Registered
Joined
·
22 Posts
Discussion Starter #10
The DF or "Dynamo Field" terminal connects to the ungrounded end of the alternator field winding, and is an input to the alternator. The current supplied to the DF terminal determines the strength of the magnetic field that penetrates the output windings, and thus controls the alternator's output. The D- terminal is connected to the alternator frame, and is the ground return for the voltage regulator. The other end of the field winding is also connected to ground at this point.
 

·
Registered
Joined
·
22 Posts
Discussion Starter #11
With the car running I have tested the voltage at the alternator plug (the DF and ground). The one terminal (must be DF) has a 12V reading. So I guess that means the alternator IS getting the voltage it needs to start generating an out put. Yet it is not doing so. So... pulley? When I have the car running and unplug the alternator (DF and ground) THEN the computer (SID) finally alerts me with the BATTERY warning light. So I guess I cannot rely on the SID to alert me when the alternator is NOT generating any voltage. Time to install a voltmeter then. But before I remove the alternator for a third time I would still like to run this test:

The bottom line is that in order for your light to light, you must have a net imbalance in the outputs of the D+ and B+ sections of the alternator (or between the D+ output and the battery voltage, which amounts to the same thing).
To trouble-shoot the problem, you need to check the various sections independently. Thus the first check: Connect +12 volts from the battery to the DF terminal on the relay board. This is the maximum field current situation, and should result in maximum output of the alternator. Note that this checks the B+ diodes, the alternator windings, and the common diodes. It does NOT check the D+ diodes.
To check the D+ portion of the system, it is necessary to find out if the D+ output can produce enough current to drive the alternator to full output. To do this, short the D+ and DF terminals on the relay board. This will provide the maximum field current to the alternator that the alternator ITSELF can supply (not the battery, as in the earlier check) and so checks the remainder of the circuitry. If this test puts the light out, then the alternator is good, and the trouble is elsewhere. If it doesn't, then the alternator is almost certainly bad.

Does anyone know where to locate these terminals on the relay board?

Thank You.
 

·
Registered
Joined
·
22 Posts
Discussion Starter #12
By the way, when the car is running I can see inside the alternator that the rotor windings ARE spinning. Clearly the pulley is NOT fully shot and the alternator rotor is getting revolutions, and yet still absolutely no alternator output.
 

·
Registered
Joined
·
22 Posts
Discussion Starter #15
Bought a new OEM clutch pulley from Wagner Alternator out of Chino, CA. I was referred to them by IAT www.iat-usa.com/index.html
Bosch clutch pulley F 00M 991 139
Saab 12803493 - now obsolete
Litens brand is the equivalent I went with. The IAT part # is 391019

Will test alt with new pulley. The old pulley was able to spin BOTH directions, which it should not. I believe the reason the one shop was able to get the 14.6 V was that there is a sticking point still in the pulley, but likely not enough to make it generate while installed...

I will see once the new pulley gets here.
 

·
Registered
Joined
·
22 Posts
Discussion Starter #16
got the new pulley and installed it and successfully tested at Autozone. Installed the alt and it is functioning well , 14.4 or greater V.
 
1 - 16 of 16 Posts
Top