Sorry but D+ is half wave rectified and so it is always much lower than B+ or battery, even with all 3 perfect diodes.

This is in opposite of Rob's overcharging in post #9.

The 3-diode voltage D+ is connected to vr +61, and so if this negative feedback is lowered then they VR should command the Alt to generate more D+ and B+, isn't it?

But then if one or more of these diode is opened, the D+ also has lower current capacity, so even if the VR tried to force more current into the Alt rotor field to generate more B+, it cannot do so with a weaker D+.
So only either you or Rob is correct.

Sapote,

Thank you for highlighting my error in basic electrical theory that I was taught in high school in 1966 and still remember today. Unfortunately, I forgot and misspoke while providing input to this post.

1. Equal voltage sources in series will increases voltage source.

2. Equal voltage sources in parallel stays the same.

3. Current in series circuit stays the same.

4. Current sources in parallel increase current in circuit.

5. V=I X R, I drops at D+ due to open exciter diode in parallel with other two exciter diodes will effect the feedback to DF and output from alternator.

The outputs to DF and B+ are 3-phase AC voltages. The schematic below is used to simulate the operation of the alternator. The RC circuits on each end of the schematic are used to measure the DC voltage at the respective outputs.

The schematic can be used to simulate the shorting of one diode or open circuit diode.

Resistors R1 and R4 can short or open D4.
Resistors R9 and R12 can short or open D9.
Resistors R5 and R8 can short or open D3.


http://forums.pelicanparts.com/uploa...1549371463.jpg

This sim run has all diodes working properly.

Notice the DC voltage of VREG (regulator) and VBAT (battery) are identical. The regulator sees the same voltage as the battery.

http://forums.pelicanparts.com/uploa...1549371854.jpg

Here's what happens when one of the diodes powering the voltage regulator opens. R1 is changed from 0.001 ohm to 1e15 ohms.

Now the voltage reaching D+ has a loss of voltage from the winding represented by voltage V1. The average DC voltage present at the voltage regulator is now about 11V instead of 13.5V in the normal case. The voltage applied to the battery is still 13.5V.

If the lower voltage of 11V is applied to the voltage regulator, the regulator sensing low voltage would increase the armature current to raise the voltage up to its normal value.

In this case, 11V would have to be raised to 13.5V via the VR. If the DF voltage is raised to 13.5V, then the battery voltage would rise to about 16V.

http://forums.pelicanparts.com/uploa...1549372538.jpg

Hi Pat,

You're right that those 3 diodes only add more current and the peak voltage stay the same even if one diode was bad. Therefore the B+ charging voltage should be lowered if one or more diodes were bad, not higher.

Brian

Hi Spoke,

Thank you for taking time to show me that I was wrong in saying D+ is lower than B+. I forgot that the D- (ground) is referenced to the 3 diode Anodes, therefore voltage from D+ to D- is a full wave rectified and not half as I said before, and D+ = B+ . (And the voltage from D+ to the neutral point of the 3-phase field is a half wave rectified but we don't care about that.)

Edited: Cathodes changed to Anodes.

Brian

You hit the nail on the head with the 1/2 wave rectification. I was wrong on that one. Here's the contribution of voltage supply V1 to the output voltage. It's clearly 1/2 wave rectified but the addition of the 2 other phases results in a full-wave operation.



http://forums.pelicanparts.com/uploa...1549389782.jpg

The photo shows the back has : D+, D-, +61, D, DF. However the VR plug only shows 3 wires, so where the 3 wires connected to the Alt back?
1) DF, D-, +61 , or
2) DF, D-, D

The old Motorola SEV Alt doesn't use the 3 exciter diodes, but it has the larger 7th diode for gating the charging voltage B+, and the voltage from the full-wave 6-diode bridge is +61 which only connected to the VR's +61 post.

Since your Alt has the +61 post but no D+, I wonder if it is the older 7-diode type or the newer 9-diode type.

About the Brown wire, for sure it should have very low resistance from the plug to the wire end connector (which I assume connected to the Alt D-). No?

Hi Pat,

2) in this case, since each of the diodes only had the output voltage at certain time only (they are 120* out of phase), therefore if one of these parallel sources (diodes) is opened, then the average DC voltage is reduced but the peak voltage at D+ is unchanged. (Connecting 3 AAA cells in parallel and remove one cell, the output is still 1.5V unchanged because the 3 sources are DC and not out of phase.)

Found the problem!!
 

Finally found the problem this morning as to the cause of the over-voltage issue.
Well it seems like I caused it.
When I was re-taping my wiring harness, I cut the plug that went to the Heater Blower motor not realizing that the two brown wires that tied into the plug also went from the Voltage Regulator to the Alternator.
It was driving me nuts as to the cause as the alternator checked good an I had tried several voltage regulators. So I started back tracking thinking about what I had done and while checking the wiring diagram I realized what I had did.
Soldered the wires back together and back to proper charging.

The wires I had cut
http://forums.pelicanparts.com/uploa...1549737045.JPG

Diagram

http://forums.pelicanparts.com/uploa...1549737254.JPG

Thanks for all the troubleshooting advice

Scott

We have all made decisions that bite us in the behind later. Glad that you finally figured it out and you learned something in the process. I am happy for you but I have to ask why would you cut and remove the heater fan plug? It would seem to me that leaving the plug unconnected to a heater blower would be logical and at any time you could install the heater blower if you choose. Porsche leaves wiring in the harnesses that may not be an option for the year and model. Rear fog light comes to mind. Option on ROW cars.

Removed Plug
 

Targa80,
I was not going to hook up that blower fan again since I backdated the heating.
I should have just left the plug it was not hurting anything.
So much for my stupidly!!

Lesson learned, just leave it alone.

Wow, very interesting that a break in the D- to the regulator caused the over charging. We all learned from from this one. Thanks for the feedback.
Rob

Imagine this VR is an old mechanical relay type, which depends on the current flows through the relay coil to cut off or energize the Alt rotor field-- more relay current means less rotor current and less relay current means more rotor current which results higher charging voltage. Without the D- connection from VR to Alt then there was no relay coil current or weak current (flows from VR chassis to Alt chassis). The newer transistor VR works in similar way.