e9 alternator.

[Simufly]

Got a problem with the alternator or controller. Standard 55amp Bosch Alternator and external VCU.
Symptoms. When running, the voltage at the battery varies quickly (2-3 pulses per second) between 13.8 and 14.4v. Very noticeable with the lights on as they too pulse.
Checked all the earths and connections, all fine.
Have the alternator on the bench and notice there is an extra terminal D+.
The blue book suggests this should be earthed but can see no evidence that it has ever been connected and there is no brown within the loom that might be utilised.
SO is it the alternator or the controller and what is D+ for.
Any help much appreciated.

 

[HB Chris]

D+ is the terminal for the Alternator warning light on the dash, don't ground it. Since you have a voltage regulator it isn't used, it is tapped into the regulator plug at the regulator.

 

[Simufly]

Alternator

Thanks for the info. Any ideas as to what is causing the pulsing?

 

[adawil2002]

Could be worn brushes or failing diodes causing the pulsing. Probably time for a replacement or rebuild.

 

[jmackro]

Probably time for a replacement or rebuild.

Yup. And unless you are a real stickler for authenticity, replace it with a later alternator with an internal regulator - less stuff to go wrong.

 

[Simufly]

Alternator

Ok seems that a later one would be a better prospect so which lead do I splice into to put the warning light out?

 

[Mike Goble]

It's a blue wire - pin 8 of the test connector. The warning light is grounded by this wire when the alternator isn't producing juice. When the alternator is working properly, there is 12v on either side of the warning light and it is extinguished.

http://www.e9-driven.com/Wiring_Diagram.pdf

I put a GM alternator in my Bav, 100+ amps for not much money.

 

[HB Chris]

Or, the blue wire from the dash that ends at the voltage regulator where it is in the triple plug can be cut and then run to D+ on new Alt.

 

[sfdon]

You might consider installing a resistor in parallel with the bulb.
Keeps the alternator working with the bulb burned out.

 

[Stevehose]

Can you ellaborate on this - what value resistor, where to install, etc.

You might consider installing a resistor in parallel with the bulb.
Keeps the alternator working with the bulb burned out.

 

[Mike Goble]

Can you ellaborate on this - what value resistor, where to install, etc.

As I read the diagram, between pins 2 and 8 of the test plug. It takes very little current to tickle the alternator, if I was putting a resistor in it would be at least 1K.