[urq] Voltage regulator and idiot light question

[fdekat]

Hell Louis-Alain:


> 
> Message: 1
> Date: Wed, 19 Nov 2008 13:12:51 -0500
> From: "Louis-Alain Richard" <larichard at plguide.com>
> Subject: [urq] Voltage regulator and idiot light question
> To: <urq at audifans.com>,	<quattro at audifans.com>
> Message-ID: <009401c94a72$6ff9aa50$4fecfef0$@com>
> Content-Type: text/plain;	charset="US-ASCII"
> 
> Hi there,> 
> My car, an 1983 urQuattro with a Bosch 90A alternator and a battery under
> the rear seat, had a voltage regulator problem last week. The problem
(+16V)
> made the battery boil and lose half of its water, and made the driver a bit
> dizzy. More, when the driver stopped, the car wouldn't restart, no more
> juice at all. But, the problem was not the dead battery : I've installed a
> SPARCO safety electrical cut-off switch between the front seats, and it
> looks that it melted internally, preventing current flow. 
> 
>  
> 
> But why the ALT idiot light never lit ?   
> 
> Isn't it suppose to show any problem, no charge or overcharge ?


Not quite..  It only shows 'not charging'.

In essence, when they ign is on (but the motor not running), the alternator
regulator circuit is powered via the warning lamp. No alternator output, so
current flows through light, supplying regulator circuit power. Think of it
as the regulator circuit is 'sort of' suppling ground for the warning lamp.

Once the alterntor starts spinning, it 'self powers' the regulator circuit,
and puts it's own 12V on the 'small blue wire' terminal of the alternator.
Warning light now sees 12v from ign on one side, and 12V from alternator on
the other side, (same voltage on both sides of the light) so light goes out.

That's about all the light will do. 

That's also why, if the warning light is burnt out, (or the blue wire breaks)
that you may not get charging to start in the first place. 

Regards,

=Frank de Kat=