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Alternator woes



 
 
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  #1  
Old February 8th 05, 05:01 PM
Mike
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Default Alternator woes

Hey guys, I'm having a charging system problem that I hope you guys can help
me out with.

Now, I know the charging system is simple enough in my 1986 GTI that I
shouldn't need a lot of help, but, well, whatever.

My car has ceased to charge itself. The battery and its related cabling,
fusible links, etc are all fine, as indicated by the fact that if the
battery is charged externally (by trickle charger or jumper cables) the car
runs just fine, until the battery runs down and the car dies. So I picked
up an alternator from Advance Auto, swapped it in, and I still have no
charging effect.

Now, I have a couple issues with the new alternator that bother me.

First, the old alternator has a small plastic box screwed to the back, with
a black wire connecting it to a spade terminal on the alternator marked +.
The plastic box is marked with a bunch of stuff, including a line reading
"2.2uF 100V", indicating it's a smoothing capacitor of some sort. The new
alternator does not have this piece. If it's just a smoothing cap, is this
critical? i.e. would lacking this part cause the new alternator not to
charge my battery? If it is critical, does this part have a name? I have
not seen it referenced anywhere, in the Bentley manual or on the web.
Should my new alternator have come with it?

Second, the old alternator had the blue wire for the idiot light connected
to a spade terminal labelled D. The new alternator has an empty hole marked
D with no spade terminal, and a different hole marked W that _does_ have a
spade terminal. What gives? Am I supposed to hook up the blue wire to the
W terminal now? I suspect not... Regardless, seeing as how it's just for
the idiot lights, I left it unconnected until I can verify how it needs to
be hooked up.

So basically, I now have the new alternator in the car with only the red
wire from the starter cable connected to it, and it grounds through the
engine. Ive done a little checking with a voltmeter, and I've got good
clean continuity from the Battery + to the alternator B+ (through the
starter), and good clean continuity from the Battery - to the alternator
housing. Still no charging effect, and I'm not sure where to look next.

Sorry for the long-winded question, thank you all in advance for any
assistance you might provide.

Mike


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  #2  
Old February 8th 05, 07:02 PM
Randolph
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Default


Mike wrote:

<snip>

> First, the old alternator has a small plastic box screwed to the back, with
> a black wire connecting it to a spade terminal on the alternator marked +.
> The plastic box is marked with a bunch of stuff, including a line reading
> "2.2uF 100V", indicating it's a smoothing capacitor of some sort. The new
> alternator does not have this piece. If it's just a smoothing cap, is this
> critical? i.e. would lacking this part cause the new alternator not to
> charge my battery? If it is critical, does this part have a name? I have
> not seen it referenced anywhere, in the Bentley manual or on the web.
> Should my new alternator have come with it?


I haven't looked at my '87 alternator lately, but I know the voltage
regulator is replaceable. It almost seems like your new alternator came
without a voltage regulator. Do you still have the old alternator?

> Second, the old alternator had the blue wire for the idiot light connected
> to a spade terminal labelled D. The new alternator has an empty hole marked
> D with no spade terminal, and a different hole marked W that _does_ have a
> spade terminal.


The blue wire goes to the idiot light, but its presence is absolutely
critical to the charging system. Alternators can not deliverer any power
unless the field winding is energized, and the field winding does not
get energized unless the alternator is delivering power. To overcome
this, if the alternator is not delivering enough power to energize the
field winding, the current that goes through the idiot light and the
blue wire is used to energize the field winding until the alternator
starts putting out current. So, disconnected blue wire = no power from
alternator. Again, it seems like your new alternator has a dummy plate
put in in place of the voltage regulator.

The W terminal is used for the tachometer on diesel engines. Since there
is no ignition system on diesels, is was common to take a signal from
the alternator, before the diodes, to run the tachometer. These days,
they probably use crank sensors like on a gas engine.
  #3  
Old February 8th 05, 09:14 PM
Brian Running
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Posts: n/a
Default

> First, the old alternator has a small plastic box screwed to the back, with
> a black wire connecting it to a spade terminal on the alternator marked +.
> The plastic box is marked with a bunch of stuff, including a line reading
> "2.2uF 100V", indicating it's a smoothing capacitor of some sort. The new
> alternator does not have this piece. If it's just a smoothing cap, is this
> critical? i.e. would lacking this part cause the new alternator not to
> charge my battery? If it is critical, does this part have a name? I have
> not seen it referenced anywhere, in the Bentley manual or on the web.
> Should my new alternator have come with it?


Mike, that little plastic box is the rectifier/voltage regulator, I
believe, and without it, your alternator doesn't make DC current, which
is what your car needs to run. Swap in the old one off your old
alternator, or buy a new one, they're not real expensive.
  #4  
Old February 8th 05, 09:27 PM
Mike
external usenet poster
 
Posts: n/a
Default

Magically delicious!

> The blue wire goes to the idiot light, but its presence is absolutely
> critical to the charging system.


This turned out to be the culprit. I didn't have it hooked up to begin with
because the hole marked D where the blue wire should've hooked up to was
empty, there was no spade terminal to clip the wire to. Well, upon what had
to be my 12th inspection, I noticed that the new alternator had a second
large cable connector (as in, threaded stud with a nut just like the stud
for the starter cable) that i had previously been ignoring. This large stud
is marked D+, and had a tiny spade terminal sticking out of the back side of
it where I hadn't noticed before. Hooked it up, jumped it, and it works
beautifully.

Thank you very much, Randolph!

Mike


  #5  
Old February 9th 05, 12:55 AM
Nate Nagel
external usenet poster
 
Posts: n/a
Default

Mike wrote:

> Hey guys, I'm having a charging system problem that I hope you guys can help
> me out with.
>
> Now, I know the charging system is simple enough in my 1986 GTI that I
> shouldn't need a lot of help, but, well, whatever.
>
> My car has ceased to charge itself. The battery and its related cabling,
> fusible links, etc are all fine, as indicated by the fact that if the
> battery is charged externally (by trickle charger or jumper cables) the car
> runs just fine, until the battery runs down and the car dies. So I picked
> up an alternator from Advance Auto, swapped it in, and I still have no
> charging effect.
>
> Now, I have a couple issues with the new alternator that bother me.
>
> First, the old alternator has a small plastic box screwed to the back, with
> a black wire connecting it to a spade terminal on the alternator marked +.
> The plastic box is marked with a bunch of stuff, including a line reading
> "2.2uF 100V", indicating it's a smoothing capacitor of some sort. The new
> alternator does not have this piece. If it's just a smoothing cap, is this
> critical? i.e. would lacking this part cause the new alternator not to
> charge my battery? If it is critical, does this part have a name? I have
> not seen it referenced anywhere, in the Bentley manual or on the web.
> Should my new alternator have come with it?
>
> Second, the old alternator had the blue wire for the idiot light connected
> to a spade terminal labelled D. The new alternator has an empty hole marked
> D with no spade terminal, and a different hole marked W that _does_ have a
> spade terminal. What gives? Am I supposed to hook up the blue wire to the
> W terminal now? I suspect not... Regardless, seeing as how it's just for
> the idiot lights, I left it unconnected until I can verify how it needs to
> be hooked up.
>
> So basically, I now have the new alternator in the car with only the red
> wire from the starter cable connected to it, and it grounds through the
> engine. Ive done a little checking with a voltmeter, and I've got good
> clean continuity from the Battery + to the alternator B+ (through the
> starter), and good clean continuity from the Battery - to the alternator
> housing. Still no charging effect, and I'm not sure where to look next.
>
> Sorry for the long-winded question, thank you all in advance for any
> assistance you might provide.
>
> Mike
>
>


If the new alternator does not have the "D" terminal you are screwed,
that terminal is the excitation for the regulator. Someone screwed up
in the alternator factory. THat's why the new one is not charging. I
believe the "W" terminal is a connection for a tachometer for Diesels.

Do you still have the old one? Unless the bearings are going, a new
regulator is 90% of the time all you need.

good luck,

nate

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