Alternator Question

[Grant Lenahan]

Good advice from Mark.
Just a "2nd that" to separate the wheat from the chaff as they say :-)

Grant
On Dec 10, 2007, at 4:02 PM, Mark R wrote:

> You know the alternator is good (can output 14V at load), so if you're
> having a voltage drop, the issue is in your primary wiring.
>
> The only other situation that can mimic the conditions is a dead-short
> inside the battery (across one of the plates), but you'd be  
> unlikely to see
> 12V when "fully charged."  Of course, a free battery test will rule  
> that
> out.
>
> As for continuity, what you described was a test for amperage, not
> continuity (which is the OHMs scale, not milliamp scale).  Might  
> want to
> confirm or scan in the bentley pages and I'll write you a procedure.
>
> Bad primary wiring is common with older VAG products.  Primary  
> wiring I'm
> talking about it battery to starter, starter to alternator, fusible  
> links...
> basically anything large diameter under the hood.
>
> Quick test:
> Hook up voltmeter across battery.
> Voltage: (should be about 12.5 volts)
> Start car.  Idle Voltage:  (should be higher, about 14V)
> Put a load on the alternator (fans, high beams, etc.)  Voltage  
> (should be
> the same as above).
>
> Hope I've helped more,
> Mark Rosenkrantz
>
> On Dec 9, 2007 2:25 PM, Vittorio Bares <Vittorio.Bares at nuance.com>  
> 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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