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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

Reply to
phreak
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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.

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Reply to
Steve

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

Reply to
sqdancerLynn

Thanks for the info on teh alternator internals.

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

Steve wrote:

Reply to
phreak

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.

Reply to
mac1833

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