Alternator Question

[Grant Lenahan]

I'm not sure where to start, and excuse me if you know all this, but  
a few comments and questions come to mind:

1. You say it shows 12.5V running at idle.  It should be 14+V. This  
suggests the voltage is too low, preventing the regulator from working.

2. You also say it is dropping when revving the motor. Is this  
correct? Current - and thus ability to maintain voltage across any  
given load - should rise with RPMs.  Yet it is falling. The only  
explanation I can think of is that the load is rising - faster than  
the rpms.  So what draws power more at high rpms?  Under normal  
operating conditions, nothign I can think of.

So this is a long-winded prep to "stop trying to fix the alternator  
and go find the unusually high load".

Or, of course, find out if something is current limiting the  
alternator, which might look similar.

3. If the diagnostic display now reads 12v - regardless of actual  
voltage - it suggests that something is amiss in he dash cluster.

4. Could these be related? Or might the dash cluster simply be  
inaccurate when working from a B+ voltage that is out of range. I  
dont know, but I've seen that in the past. Way int he past.

Good luck in your quest.

Grant
On Dec 9, 2007, at 2:25 PM, Vittorio Bares wrote:

> Back at it - I've replaced the alternator w/a refurbished one - I now
> have 2 fully working units (tested at AutoZone) :\.
>
> Went back an cleaned contacts behind the snub nose (alternator  
> bracket).
> Cleaned contacts to adjustment bracket.
>
> Voltage is dropping when revving the motor.
>
> The diagnostic display for voltage on the climates control remains at
> 12.0 (channel 11). This is regardless of what the needle on the  
> gauge is
> doing. It used to properly indicate the voltage.
>
> Needle shows just over 12v on idle. Verified w/volt meter.
>
> Voltage off of the alternator (+ post to engine ground) is about 12.5v
> (seems low). I presume (it has a 14v regulator) it should read 14v  
> from
> somewhere - anyone know where to measure that from?
>
> Anyone know how to check continuity of exciter wire (blue) from
> alternator? Bentley says to check current across wire to alternator
> exciter post - I set my multi-meter to DC 250ma and the needle shot  
> over
> max (?) Bentley says it should be between 150-180ma - indicates if its
> low to replace climate control board - doesn't say anything if its  
> above
> ?
>
> Steve suggests in the attached thread to check voltage from the  
> battery
> - since the battery is charged via ground (I believe), would one  
> try to
> directly from one of the alternator mounting brackets to the negative
> post on the battery (a direct ground)?
>
> BTW - this is on a 1990 Audi 200 avant.
>
> Thanks!
>
> Vittorio -
>
>
> -----Original Message-----
> From: quattro-bounces at audifans.com [mailto:quattro- 
> bounces at audifans.com]
> On Behalf Of Mark R
> Sent: Monday, September 24, 2007 1:36 PM
> To: Steve Sears
> Cc: quattro at audifans.com
> Subject: Re: Alternator Question
>
> Steve's got it right... often overlooked is the primary wiring.  Audi
> didn't use the greatest wiring when new, and now you'll often find
> corrosion under the sheath due to moisture wicking.  Remember, the
> alternator has to have the ability to get the current (amperage)  
> out as
> well.
>
> Another quick and dirty test is to check voltage at the battery versus
> the alternator post (if available when engine is running).  Set up the
> wiring before starting the engine.  If you see a voltage change (drop
> along the wiring), you'll need some attention there.
>
> Cheers!
> Mark Rosenkrantz
>
>
> On 9/24/07, Steve Sears <steve.sears at soil-mat.on.ca> wrote:
>>
>> Vittorio,
>> If the alternator is one of those 110 amp units, then the two bolt
>> pivot is correct.  If it is the 90 amp unit, then it should have a
>> long bolt and nut at the pivot.  If you were to hook a long jumper
>> cable directly between the snubber mount to the battery ground, would
>> you get a different reading?
>> (The engine ground to chassis across one of the engine mounts may be
> bad).
>> You might also check the condition of the battery cable splice.
>> Cheers!
>> Steve Sears
>> 1962 and '64 Auto Union DKW Junior deLuxes 1980 Audi 5000
>> 1987 Audi 5000 Turbo Quattro
>>
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