Re: [Classic Mustang] Alternator Light On-But Charging

Flick -

A diode _is_ a (solid-state) rectifier.   (A tube can be a rectifier too.)  Their wondrous properties are that they allow electricity to pass in one direction, but not the other. 

An alternator generates electricity (get this) in an alternating current.  (!)  A battery cannot use this because the net charge is 0 volts.  What the car needs is direct current ... so to convert an alternator's AC voltage to DC or Direct Current voltage, a rectifier is used to only allow the energy to go one-way. 

In most electrical equipment, the typical solution is to use a bridge rectifier.  This simple circuit requires 4 diodes to convert AC into DC.  Its pretty efficient, and when a large capacitor is added, the result can be very clean DC voltage.   But auto motive alternator manufacturers take a shortcut - they will typically put a single diode in series with the output of each of the three windings on the alternator's armature ... thereby saving a diode in the process.  The overall output is less, but so is the drag on the engine. (I suppose.)

USUALLY... when a diode fails, it burns out and creates an open circuit - so no voltage comes out.  On occasion, a diode can simply short closed ... and allow AC voltage to be sent out (and back again).  The net result is that the battery doesn't take a charge. 

I think this explains the case you've seen previously - and may be why we're seeing the idiot light in the presence of a positive voltage.

The diodes (@ $2.50) can be replaced... but most people simply swap the alternator and turn it in for a core charge.

My thots -
v/r,
Michael

Flick01@Aol.Com wrote:

I'm a bit rusty on the termonology but I ran into the same problem a long time ago. I'm sure someone can fill in the blanks but essentially one of the internal pieces of the alternator, I forgot if it's a rectifier or a diode, something has gone bad. What happens is the alternator produces the right voltage but doesn't have enough amperage. An electrical shop or a facility equipped with all the modern computerized diagnostic gizmos can probably hook up a few wires and tell you in a couple of minutes.

__._,_.___

Your email settings: Individual Email|Traditional
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe

__,_._,___