engine and drivetrain 320 alt upgrade problem

[schliske]

I installed a rebuilt 320 alternator in my '70'02 and the battery seemed to lose charge occasionally. My dash warning light is out of action right now so I'm not sure if it is trying to warn me. I realized that at night when I start it the headlights and dash lights are a bit dim but when I rev it to 3000+ something happens and the lights get bright. They stay that way even at idle until I shut it down. If I make sure to do this every time I start it the battery stays charged. I know this isn't good for the engine. Voltage regulator? All connections and grounds are clean but the battery is getting old. Thanks- Michael

[c.d.iesel]

voltage at BATTERY WITH KEY off ? = ____________ v

voltage at BATTERY WITH MOTOR AT 3000 RPM ? = .___________v

PLEASE FILL IN THE BLANKS

[Mike Self]

your charging system. It actually has two positive leads going to it (vs a + and -). One positive lead comes from the battery and causes the light to illuminate when the ignition is on but the engine is off. The other lead comes from the alternator, and once the engine is running, its positive charge "cancels" the positive on the other side of the bulb, causing it to go out. On at least some 2002s, the charging system won't work if the bulb is burned out. At least, that's what I've been told.

Also, your 320 alternator has an internal voltage regulator, so you shouldn't be using the external one that came with your '02 (metal can just above the battery). Check the archives for proper wiring diagram for an E21 alternator used in a 2002...

cheers

mike

[SOUTHBAYeric]

There is an FAQ on the 320i alternator if you haven't already checked it out.

[trangieboy]

On internal regulated alt like yours the charge light IS needed.The current running thru the charge light also runs thru the alt and `excites` the alt to start it charging.OR as you have found out if you spin the alt fast enough it will `self excite`.

You can just rev the engine in 1st or 2nd gear after the engine is warmed up if you don`t want to replace the charge lamp.

Just check that your wiring is correct too.

Mal.

[ingraham]

I can confirm what the others have posted, since I studied this in detail a few weeks ago. After startup, the alternator field coil gets its current from the charge light. Blue wire!