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I have a 64, which when I purchased, the previous owner told me that there was a short somewhere drawing the battery dead. I have owned the car for two years, all the while just using the battery cutoff on the negative cable after driving. It is time to figure out what the real problem is. I pulled the fuses, left the battery cable attached over night and the battery was dead the next morning. After recharging the battery and driving the last three weeks, I thought to try the obvious, I disconnected the battery lead to the alternator and after two days of leaving the battery connected nomally (no cutoff) she starts right up. Did I find the problem? Thanks in advance for any responses.
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Re: C2 battery draw down
Mike,
Make sure that the battery case is clean and dry. Sometimes a circuit can be established between the + and - terminals by moisture and a salt.
Joe -
Re: C2 battery draw down
About 75% of the time it is a bad diode in the alternator.Comment
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Re: C2 battery draw down
It looks like 2 diodes in the alternator would have to go bad to get a connection to ground; the diodes would be the first things to check.Comment
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Re: C2 battery draw down
I have a later year model and different car but it was alternator equipped with the same problem. I was alerted to the problem you describe by the red light on the dash illuminating after I turned the key off. I unplugged the alternator, and the light went out. Replaced a part in the alternator and on the road again. Starter/Gen independent shop owner locally I have used for two alternator repairs and each time it was just $20.00. Internal alternator parts are available to repair the alternator yourself. You can purchase a rebuilt alternator for your 64 for a very reasonable price from Auto Zone with warranty length depending on how much you pay, however if your alternator is a numbers matching unit, do not trade it in for the core charge. The internals except the bearings can be easily installed from a rebuilt into your alternator.Comment
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Not really....
the diode bridge consists of six diodes paired two together in a 'three-phase' circuit topology. All it takes is for one diode to be faulty to drain the battery.
Diodes fail in three ways:
(1) Open circuit
(2) Short circuit
(3) Junction puncture (leaking)
To get an alternator to drain the battery during engine shut down, all you need is #2 or #3... Plus, due to the charging system's montoring circuit topology, the ammeter will NOT indicate battery discharge from a faulty alternator diode bridge and the alt will still run and re-charge the battery with the other operable phases of its rectifying bridge (simply won't deliver its fully rated current flow)!
Detecting condition #3 can be tricky since a diode that's suffered EOS (electrical overstress) and has junction puncture, can give Jeckyl & Hyde symptoms... They can temporarily 'heal' themselves when voltage is removed and then re-open the puncture(s) when reconnected and exercised.
You determine #3 in one of two ways:
(1) Run each of the diodes on a curve tracer and view their actual reverse bias performance profile.
(2) Mount the alternator on a bench tester, exercise it (making SURE to run it long enough to get it hot), and view the output waveform on an oscilloscope (helps to have the main smoothing capacitor disconnected). The 'lumpy' DC waveforms generated are individually contributed by three individual diode pairs and they should all have reasonably the same shape. If one waveform is decidely different in appearance, that's where your failed or damaged diode resides...Comment
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Re: Not really....
From what I can see, for one failed (shorted) diode to drain the battery, it would have to be the diode that connects to the field relay.Comment
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Thanks for all the responses *NM*
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