IOD problem, 98 Intrepid ES

The battery will be completely drained in about 18 hours of 'just
sitting there'.

No aftermarket audio, lighting, or other electronics. Everything is
Mighty Mopar and pretty much as it was when new.

I think that I've eliminated the primary cables and charging circuits
as a problem. Everything is clean and tight. The battery is a new
NAPA/Exide spiral wound, 800cca unit. The primary +- cables bave been
replaced with 4ga from the battery to the jumper posts, the starter,
the PDC, and the alternator. The alternator fusible link is fine. New
battery clamps were put on with the new cables. The starter runs fine,
the solenoid contacts are clean, don't stick, don't arc.

When the car is running, everything is well, no dimming or brightening
of the headlights. The EVIC, ATC, radio / CD changer all work fine
etc, etc. Interior lights including the trunk light all turn off (and
on) when expected.

No dash lights or codes.

The next step is to get an ammeter on the battery and start pulling
fuses to try and isolate the drain.

Question: Are there internal components (diodes) in the alternator
that might have gone bad causing the drain? As I understand it, these
'alternators' are really externally controlled/excited generators that
run from the ECM. Are the diodes in the ECM itself or on the
generator? I've had the alternator out and tested at the local
O'Reillys. Other than a slightly rough bearing, it passed the machine
test.

thanks

 

Yes, and the system depends on the diodes blocking reverse current flow
to prevent a drain when the alternator is off. If a diode fails, you can
get a drain through the alternator when the engine isn't running.

As I understand it, these

No, they are alternators. The basic architecture is EXACTLY like the
gigantic 3-phase alternators in powerplants. The rotor driven by the
belt is magnetized by a variable DC current (controlled by the voltage
regulator inside the ECM). The rotating magnetic field induces
alternating current in the stator windings. Depending on the alternator,
there may be 3 or more 'phases' in the winding. Then a pair of diodes
per phase (for a total of 6 diodes in a 3-phase alternator) rectify the
alternating current to direct current before the wires are brought out
of the alternator. The rectifier bank (aka the "diodes") live in the
back housing of the Nippondenso alternator that most Mopars now use.

An alternator with a leaky diode will still put out a lot of current
when running. the correct test to apply is to see how much current the
alternator will "leak" backward when it is NOT being rotated. You can
put the positive terminal of an ohmmeter on the "bat" connection of the
alternator and the negative terminal on the housing. You should see a
nearly infinite reading. The problem with this test is that most
ohmmeters only apply a couple of volts (at most) to do this test. You
really need to apply a full 12 volts the the "bat" terminal, and then
measure how much current is flowing. If ANY measurable current is
flowing into the "bat" terminal, the alternator has a leaky diode (or
diodes). If you have a current meter that you can put in-line with the
battery, you can see if the leakage current goes away when you
disconnect the alternator, or you can put your current meter in-line
with the alternator "bat" connection and see if a current shows up.

 

SImple disconnect the alt & see if the battery still goes dead !!!!

 

Thanks for the info on teh alternator internals.

Is the rectifier bank replaceable?? This is a stock 120 amp
alternator.

 

its called a draw. diconnect the neg. bat cable..with a TEST LIGHT connect
one end to the neg bat connection and the other to the battery. if you
have a draw the light will be bright. start pulling fuses. when the light
dims....thats the draw. change the fuse an check the curcuit.