Alternator Question

[Grant Lenahan]

Sounds like a very high impedance system.  I'd check ground first, B=  
n ext (its more complicated).

Grant
On Dec 9, 2007, at 5:28 PM, Vittorio Bares wrote:

> More diagnosis:
>
> Leaving it at idle for a while seems to bring the (system) voltage  
> back
> to the point where the gauge shows 14v (volt meter never shows more  
> than
> 14).
>
> Cooling fan, or headlights instantly bring the voltage down below 12v.
> Smaller accessories such as dome lights, blower or dash lights don't
> have much of an effect.
>
> Tried using booster cables to ground the radiator fan to the motor. No
> change.
>
> Engine revs have no effect on voltage once the system gets above  
> 12.5v.
> Took the car for a test run - went well enough for a while - voltage
> dipped a little when fan came on - but not bad. Then I tried the  
> lights,
> ok for a short spell, then the fan came on and basically killed the
> system. Charging well below 10v, car started running badly (not as  
> much
> power, lightly missing) - looks like I was running on battery only (?)
> and the extra juice from the lights on and the fan on sucked too much
> out of it.
>
> Made it back home - let it idle for a while, gradually the volt meter
> made it back into the normal range, around 14v.
>
> Right now, it would appear that the lights and the fan are running an
> unusually high load - what does that actually mean in practical  
> terms -
> what am I looking for?
>
> TIA,
>
> Vittorio -
>
>
> -----Original Message-----
> From: Grant Lenahan [mailto:glenahan at vfemail.net]
> Sent: Sunday, December 09, 2007 2:50 PM
> To: Vittorio Bares
> Cc: Mark R; Steve Sears; quattro at audifans.com
> Subject: Re: Alternator Question
>
> 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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