battery drain

[ian <iann@domain.elided>]

Greg Hermann wrote in response to a battery drain diagnosis:

""  Your logic sounds fine. The 3 amps sounds
suspiciously like the field
current that the rotor of the alternator would
draw, and it would thus
appear to me that the regulator is putting full
battery voltage to the
field when the engine is shut off. ""

I concur, and by the way good job in isolating the symptom Kevin.  I
would suspect the "diode bridge" (rectifier) internally mounted in the
alternator.  Basically it's function is to convert the alternating
current produced by the alternator into DC voltage by filtering the
voltage cycle with a series of diodes.  The diode is designed to allow
current to pass one direction only.  When they fail, and they do so for
a number of reasons, its like leaving a gate open and the current is
free to flow in both directions.  If memory serves me I believe that the
diode bridge typically involves 6? diodes, but it's been a long time
since I disassembled a Bosch alternator.  I am thinking that if the pass
through current is not excessive that the alternator would still be
capable of rectifying the current and charging the battery, however I
would not put off repair too long.

Regards,

Ian

(ducking for cover should Fred Di not agree)

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