help alternator red light in the dash

[deQuincey]

today i have come across an unexpected issue,

i drove my car this morning and it drove well, then after work i started the car and realised that the alternator red light in the dash was on more time than normal, but it finally went off

then a little later I noticed a little strange noise from the engine, opened the hood and i thought that it was something in the alternator area,or inthe steering pump, it was only a slightly different sound, not a click, or a bump or any other noise

then i realised that the alternator red light in the dash started lighting but very very low, you can hardly noticed it in the surrounding sun light, but in a shadowed area of the street you can see it glow

my voltmeter was still saying that i had more than14 volts, and that remained constant all the trip backhome

after some kilometers the glow dissapeared, still more than 14volts in the gauge, no change

then some km more and the glow came again and went away later

ideas ?

thanks

 

[deQuincey]

by the way
the alternator has only three years old, it is a new model from bmw, with regulator integrated

 

[adawil2002]

Check the plug on the back it could be loose. Though the alternator is new the wiring probably isn't. Vibration can fracture the wires at the ground connector under the insulation.

Had the same problem with my '02, fractured ground wire, that looked fine.

 

[Stevehose]

I have just been through this issue and I solved it but I don't really know what the cause was :-( I have a new 80 amp alternator and occasionally the red light would come on. My research indicated that if the red light is constant and/or the alternator whines, then a diode(s) in your alternator is bad. If it is random (like mine) then try adding a dedicated ground wire from the alternator case to the negative battery post, tightening the belt, and replacing the regulator with a german one not a chinese one like in mine - I did all 3 and problem solved but can't say defintively which worked so check the belt first! Assuming all electrical connections are clean and tight of course.

 

[rsporsche]

i think you have a ground problem. start the car at night with no lights on and see if the red light glows lightly. then turn on the lights, but leave the dash lights off ... does the red light glow slightly?

 

[deQuincey]

thanks for the ideas

my first thought was tightening the belt, as this can result in a erratic behaviour, i will check the ground issue and the contact in the dash too

the regulator, being an internal one and belonging to the new bosch alternator i assume it is not guilty

yesterday i could check that the connections in the alternator were ok, including the one for the idiot light, and the belt, well it can be tightened a little bit more...


i will try to go through them in the weekend,and comeback here with results

 

[x_atlas0]

Diodes would be my concern. The light can be lit but you still get 14+ V. Depending on which diode(s) are bad in the diode bridge, you will also get no charging.

 

[deQuincey]

Diodes would be my concern. The light can be lit but you still get 14+ V. Depending on which diode(s) are bad in the diode bridge, you will also get no charging.

i beg your pardon for my absolute lack of electric-auto knowledge

how can i check those diodes ? and more important where can i find them ? and how can they be removed to check, do i have to take the alternator out from the car ?

regrds

 

[61porsche]

Dq

Post a picture of your altenator. One wire or 3?

Where did you pick up the + for the volt meter?

 

[deQuincey]

Post a picture of your altenator. One wire or 3?

Where did you pick up the + for the volt meter?

i do not have a pic here, but they are two cables that came out from the alternator, the big one that goes directly to the battery (+), and the thin one to the red light in the dash,

i mentioned that the alternator has an internal regulator

as referred to the volt meter, the + has been taken straight from the battery connection

 

[MMercury]

i beg your pardon for my absolute lack of electric-auto knowledge
how can i check those diodes ? and more important where can i find them ? and how can they be removed to check, do i have to take the alternator out from the car ?
regrds

Diodes are typically press fit into a rigid assembly commonly referred to as a diode plate (No 6 Below) and internally mounted within the alternator. Diodes occasionally go bad and testing generally requires accessing them. Testing is generally for continuity.

Before removing and disassembling the alternator, consider double and triple checking your grounds - to engine block, body and battery.

http://www.audiurquattro.de/ralf/infos/pdf/Alternator.pdf

http://www.oichan.org/mods/alter/alter2.htm

http://www.e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/12316020.html

 

[DaveG]

The red light basically works like this...
When the engine is off, or the alternator is not charging, the voltage at the D+ terminal on the alternator is lower then the battery. So current flows from the instrument cluster, through the light, to the alternator, making the bulb light up.
When the alternator is charging, the voltage at the D+ terminal should be the same as the battery voltage and the light goes out. No current since there is no voltage difference.
If the alternator is working as your volt meter shows and the light still shines it usually means that the voltage at the instrument cluster is lower then the battery.
This is usually due to a bad connection somewhere in the power circuit to the instrument cluster.
Check Voltages starting at the ignition switch and working your way to the light looking for bad connections and you should be able to find the problem.
DaveG

 

[deQuincey]

The red light basically works like this...
When the engine is off, or the alternator is not charging, the voltage at the D+ terminal on the alternator is lower then the battery. So current flows from the instrument cluster, through the light, to the alternator, making the bulb light up.
When the alternator is charging, the voltage at the D+ terminal should be the same as the battery voltage and the light goes out. No current since there is no voltage difference.
If the alternator is working as your volt meter shows and the light still shines it usually means that the voltage at the instrument cluster is lower then the battery.
This is usually due to a bad connection somewhere in the power circuit to the instrument cluster.
Check Voltages starting at the ignition switch and working your way to the light looking for bad connections and you should be able to find the problem.
DaveG

thanks, nicely explained
now i understand the basics and it makes sense