wilies13
Active Member
Before the next trip I would check voltage...should be something between 13V and 14V...just to avoid an breakdown during the trip.... 
Voltage regulator symptoms
- Thread starter Boobouna
- Start date
Good advice. I have a USB socket on the console that has a voltage meter built into it, so I always see my voltage.
Luis -- Pictures do help. Indeed, they explain our difference of opinion.
In the external regulator schematic, all three terminals from the field rotor in the alternator are connected, each via a diode, to terminal D+. In the internal regulator diagram, only two of the three terminals are connected to terminal 61, and importantly, the terminal that is not connected to terminal 61 is the connection to the voltage regulator circuit.
I found this same wiring diagram in my blue binders, but I don’t think internally regulated alternators are wired this way. In the schematic posted above (and contained in my binders), only one diode is shown as connecting to the voltage regulator. I think all three connection points in the field rotor are connected, via a “triad” of diodes, to the voltage regulator “sensing” connection in the internally regulated alternator just as they are with the externally regulated alternator. This is consistent with your statement that “there are 3 small diodes, separate from the high current power rectifier diodes, dedicated to this purpose (voltage regulation).” And I think your picture of the voltage regulator supports my conclusion. In your diode plate picture there are three diodes connected to the diode plate, and to the U shaped springy metal contact. So I conclude that the node between your internal voltage sense red circle and the diode on that wire is a connection point (which should be indicated by a black circle, rather than by crossed lines indicating no connection), in the same manner as it is in the external regulator alternator.
In addition, I think the blue wire from the dash light is connected to the “sensing” point on the regulator in both types of alternators.
As to the external regulator, the schematic shows both the output from the field rotor at D+ on the alternator and the blue wire to the dash light are connected at terminal D+ on the voltage regulator. If the voltage through the dash light blue wire is less than the voltage through the triad of diodes connecting to the field rotor, voltage will be drawn away from the terminal D+ junction on the voltage regulator and the voltage that the voltage regulator “senses” will be reduced. In this manner, the voltage through the blue wire does influence the operation of the voltage regulator.
As to the internal regulator, if you were to add in the connection point at the node I mention above in order to correct the schematic as it applies to the three field rotor diodes, this would also indicate a connection between the “triad” output and the blue wire. And if you look at the picture of your voltage regulator, you can see that the terminal 61 spade lug assembly includes a connection to the diode plate.
One other thing that indicates that the internal regulator schematic picture posted above cannot be correct. Whereas the three smaller “sensing” diodes would allow flow to the regulator and on to through the brush assembly to the field windings in the field rotor, the flow can only come through this path if there is current induced in the stator and through the power rectifier diodes because the high current power rectifier diodes prevent current flow from the battery. This induced current must arise from the magnetic field generated around the field rotor, which only arises when a flow of electricity through the windings exists. So, the field windings need to be “excited” in order for the alternator to begin to function, and this initial charge must come from the battery. Again, adding the black circle connection I suggest above to the node between your internal voltage sense red circle and the diode on that wire, making this a connection point, provides a path for the electricity needed to excite the field rotor through the blue dash light wire connection to the terminal 61 connection. If this node is not a connection point, there is no source to enable the initial charging of the field rotor windings in that diagram.
In the external regulator schematic, all three terminals from the field rotor in the alternator are connected, each via a diode, to terminal D+. In the internal regulator diagram, only two of the three terminals are connected to terminal 61, and importantly, the terminal that is not connected to terminal 61 is the connection to the voltage regulator circuit.
I found this same wiring diagram in my blue binders, but I don’t think internally regulated alternators are wired this way. In the schematic posted above (and contained in my binders), only one diode is shown as connecting to the voltage regulator. I think all three connection points in the field rotor are connected, via a “triad” of diodes, to the voltage regulator “sensing” connection in the internally regulated alternator just as they are with the externally regulated alternator. This is consistent with your statement that “there are 3 small diodes, separate from the high current power rectifier diodes, dedicated to this purpose (voltage regulation).” And I think your picture of the voltage regulator supports my conclusion. In your diode plate picture there are three diodes connected to the diode plate, and to the U shaped springy metal contact. So I conclude that the node between your internal voltage sense red circle and the diode on that wire is a connection point (which should be indicated by a black circle, rather than by crossed lines indicating no connection), in the same manner as it is in the external regulator alternator.
In addition, I think the blue wire from the dash light is connected to the “sensing” point on the regulator in both types of alternators.
As to the external regulator, the schematic shows both the output from the field rotor at D+ on the alternator and the blue wire to the dash light are connected at terminal D+ on the voltage regulator. If the voltage through the dash light blue wire is less than the voltage through the triad of diodes connecting to the field rotor, voltage will be drawn away from the terminal D+ junction on the voltage regulator and the voltage that the voltage regulator “senses” will be reduced. In this manner, the voltage through the blue wire does influence the operation of the voltage regulator.
As to the internal regulator, if you were to add in the connection point at the node I mention above in order to correct the schematic as it applies to the three field rotor diodes, this would also indicate a connection between the “triad” output and the blue wire. And if you look at the picture of your voltage regulator, you can see that the terminal 61 spade lug assembly includes a connection to the diode plate.
One other thing that indicates that the internal regulator schematic picture posted above cannot be correct. Whereas the three smaller “sensing” diodes would allow flow to the regulator and on to through the brush assembly to the field windings in the field rotor, the flow can only come through this path if there is current induced in the stator and through the power rectifier diodes because the high current power rectifier diodes prevent current flow from the battery. This induced current must arise from the magnetic field generated around the field rotor, which only arises when a flow of electricity through the windings exists. So, the field windings need to be “excited” in order for the alternator to begin to function, and this initial charge must come from the battery. Again, adding the black circle connection I suggest above to the node between your internal voltage sense red circle and the diode on that wire, making this a connection point, provides a path for the electricity needed to excite the field rotor through the blue dash light wire connection to the terminal 61 connection. If this node is not a connection point, there is no source to enable the initial charging of the field rotor windings in that diagram.
Chris, Everything you said above regarding the BMW wiring diagram (internally regulated) is correct. BMW made a mistake and it should be as below where the pen points --a "dot", or node, tying all three small diodes together.
What is not correct is to say that the voltage is "drawn away" at the regulator/alternator by a lower voltage on the far side of the blue wire, between the dash bulb and the fuse box/battery point. The regulator senses the voltage right at that node pointed by the pen above, where all 3 small diodes come together. If the battery voltage is low then the bulb glows responding to the voltage difference. The voltage at the regulator side of the blue wire is always what is seen at the output of the 3 small diodes. It does not get "drawn away" by what happens on the other side of the bulb, between the bulb and the battery/fuse box. It's Kirchoff's voltage law; look it up.
What is not correct is to say that the voltage is "drawn away" at the regulator/alternator by a lower voltage on the far side of the blue wire, between the dash bulb and the fuse box/battery point. The regulator senses the voltage right at that node pointed by the pen above, where all 3 small diodes come together. If the battery voltage is low then the bulb glows responding to the voltage difference. The voltage at the regulator side of the blue wire is always what is seen at the output of the 3 small diodes. It does not get "drawn away" by what happens on the other side of the bulb, between the bulb and the battery/fuse box. It's Kirchoff's voltage law; look it up.