Alternator & Voltage Regulator Explanation

[ctaylor738]

I am getting a charging light when the engine is running, and no charge to the battery.  I have always wondered how you determine if the problem is the regulator or the alternator.  I haven't quite figured that out, but I did come across this article which explains how the pieces work.

It is written for BMW motorcycles, but I believe that the principles are the same as our cars.

http://www.buchanan1.net/charge.shtml

Chuck Taylor
1970 280SL #14076
Falls Church VA

[ctaylor738]

So from the article and diagram, I figured out that the test is that if there is approximately battery voltage at D+ with the engine running, then the alternator is OK and the voltage regulator is bad.  If there is substantially, less, then the alternator is bad.

So I did this test by sticking a short piece of wire into the D+ socket, plugging the voltage regulator back in,  and attaching the meter to the other end of the wire.  Started the engine and found 12.86 volts.  Replaced the voltage regulator, and all is well.

The D+ socket has red/blue and blue wires running to it.  The red/blue is from the alternator, and the blue goes to the dash light.



Chuck Taylor
1970 280SL #14076
Falls Church VA