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Old 09-02-2010, 01:41 PM   #9
Lil bastard
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Quote:
Originally Posted by socalsharky
Thanks for the detailed reply. I just take small issue with your statement about "using the car as you describe...."

I am an engineer (though not an EE) so I totally understand the electrical circuitry of the car. My point was that I operated the car for the first three years of its life exactly as was intended by the manufacturer (other than not driving it everyday, which I'll grant you could be significant). When I realized that the battery was dead, I did not attempt to jump it, but rather bought a new battery. When that battery discharged, again I did not jump it, but hooked it up to a charger, in order to save the wear and tear on the alternator. So other than using a battery tender since the car was new, or driving it a lot more frequently, there was really nothing better that I could have done, right?
Well, that's right. I'm not slamming you at all, but have to say that these habits (infrequent driving, no maintainer) are less than ideal. Just explaining how your habits could contribute to the issue.

Again though, you are describing a battery which is drained because it would not start the car and discounting the cumulative effect (3+ yrs. in your case) of operating a battery which was at arbitrarily say, 60-70% (or whatever) a good portion of the time.

Both the battery and the alternator, each separately and together, suffer from this for the reasons I described. Realize that batteries are fairly precise - a healthy cell in a 6 cell automotive wet cell battery will produce between 2.1 and 2.2 VDC. This means a healthy battery will output between 12.6-13.2 VDC on a DMM (ign. off, key out) - this battery is 100% charged. If you measure only 12.45 VDC, the battery is only 75% charged. At 12.06 VDC, the battery is only 25% charged, yet most people think that this battery is OK because it's putting out 12 volts.

To measure the alternator, use a DMM set to VDC and read across the battery terminals engine running. The Bosch alternator spec is: 13.5-14.5 VDC.

3 Yrs. is the short side of a battery's life, though just beginning to enter the 'normal' reliable life expectancy zone. But, if it turns out your alternator is also kaput, 3 yrs. is definitely a premature death.

Something caused this. It could all be that the alternator was faulty to begin with and the battery too. Or that a sudden shock to the battery (pothole, speedbump, extreme environment, etc.) degraded it contributing to alt. failure. But, these are unusual. If the car were driven 3 times a week, 15+ miles/trip, these things would outweigh the possibility that a less than optimal battery was the culprit.

As an engineer, you are fully aware that machines in general tend to predominately fail at one of two points - their infancy or old age. The former because of a fault in material, design or manufacture, installation or application the latter because they simply wore out. If the failure occurs in-between, there is usually an external cause.

IIRC, the ign. off current drain is 60 mA after 10 min. (when the lights and such turn off). This is easily measured at the battery terminals w/ a DMM - disconnect one terminal and connect the DMM to the cable and the battery terminal. If the draw is higher than 60mA, suspect relays which are stuck on, other components like the radio (1 guy reported a 700mA current draw and it turned out to be his radio), even a bad diode in the alternator can cause ign. off current draw. To isolate the cause, start pulling fuses and relays one by one and notice any effect on the DMM value.

Again, using a DMM w/ AC capability, switch to AC and check voltage across the battery terminals with the car running. If you get any value other than zero, one or more of the diodes is bad and allowing current to reverse flow, even with the car off. Another check if you don't have an AC capable DMM is simply to measure the battery and then disconnect the negative terminal and leave it a day, then come back and take the measurement again. If it is the same, there is an issue with the car, if lower, the issue is with the battery.

Cheers!
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Last edited by Lil bastard; 09-02-2010 at 06:54 PM.
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