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Electrical Problems

Old Apr 8, 2012 | 02:54 PM
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4_whl_hvn
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Question Electrical Problems

Hello,
I have an '88 F-250 2wd 5-speed. My problem is that the truck drains the battery in less than twelve hours. I put a new battery in it yesterday, and it is almost dead this afternoon. There are no obvious things on such as a light, radio, ...etc, but something is draining the battery. This is something that has just occurred, as the truck sat all winter then started with full cranking power this spring.
I am fairly electrical savvy, but before I go through the trouble of tracing every wire to find the one that is drawing the juice and then tracing that circuit to the device drawing the power, I was thinking maybe someone has had this problem before and could make some suggestions that I could check into first.

Thanks,
Matthias
 
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Old Apr 8, 2012 | 03:35 PM
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CletusSnow
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I've heard of shorted alternators sucking down power before, why not unhook it, wait 12 hours and see.
 
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Old Apr 8, 2012 | 06:34 PM
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I had given that some thought, but with truck running I had 14.4vdc. But, the truck does not charge enough to keep truck running with the lights on. So if it is the alternator, it would make some sense.
I report back tomorrow.
 
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Old Apr 8, 2012 | 06:39 PM
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Originally Posted by CletusSnow
I've heard of shorted alternators sucking down power before, why not unhook it, wait 12 hours and see.
What he said.....

One of the bridge diodes can short causing a a constant drain on the battery without the engine running. A shorted diode in the bridge will result in low charging output (half-wave). A view on an oscilloscope of the output will show if that is the cause in a few seconds. A quick check with a DVM will typically show a large AC component of what should be a DC output. Pull the alternator and have it tested if you do not have access to those kinds of tools.
 
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Old Apr 8, 2012 | 06:45 PM
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If you take it somewhere to be tested, test it on the truck. When they bench test, they don't test for amperage output, just voltage, whereas on the truck, they will also test for amperage. But given what you've said, probably the alternator diode pack has gone bad.
 
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Old Apr 10, 2012 | 06:51 PM
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Well, It turns out that it is the alternator that is bad. Unplugged it and 2 days later battery still charged.

Thanks a bunch
 
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