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Discussion Starter #1
Is it common for a 77k alternator to die so fast?? Seriously, because mine did and I am kind of :confused: why, my dads car has over 105k and it still running strong... I took it to get checked at autozone and they told me that the diodes were bad and that I needed to changed them, if I had the money I would buy a new one. I had my old 95 engine for 77....K miles until it died on me and swaped an 03.. Alternator was sitting there for 3 months and I didnt had any problems before. What could it cause for the diodes to fail????:2huh:
 

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Luck of the draw. I used to rebuild starters, alternators, generators, etc. in the army. I put an alternator together and went through 5 bad regulators in a row.
 

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Someone said something about turning an alt while not under load will damage the diodes, but I'm kinda sceptical about that.
 

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Discussion Starter #4
Could an electrical problem in the car also kill it???? Since I swap an 03 and "IF" I messed up some cables, could that have cause it??? But wouldnt the cables also been fried if I had the cables wrong???
 

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Anything is possible. In it's most basic operation, an alternator has 2 wires, 3 if you count grounding it. One is the ignition wire which provides current to excite the windings in the rotor and the other is the power wire to the battery. With todays set ups and without perusing through a bunch of wiring diagrams I will not go into what all the other wires are for, i.e. voltmeter/idiot light.

To answer the question about hooking things up wrong, generally that fries regulators. Since the diodes only rectify A/C current to D/C current inside the alterator, not likely.
 

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If you have disconected the battery while the car was running then that will fry the alt. Do you have any heavy stereo or at least some kind of amp that would draw a good amount of current? I had a 300 wat stereo in an 88 Bronco II years ago and one night I had it cranked up with all the lights on and half way home I noticed the Alt light was on. The alt. fried internally. But, it was only a 95 amp alt. My cougar has a 130 amp alt; very durable. Or have you jump started anybody recently? Sometimes the current demand from another car can do that to a weak alternator.

Clay
 

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Diodes are quite durable. In the 1000's I've rebuilt, less than 5 percent needed diodes. Typical was regulator only. The others needed new rotors or stators from being overloaded and frying them. I do disagree about disconnecting that battery causing the alternator to fry. The alternator is regulated and will only provide the required power. It doesn't know if the battery is hooked up or not. It just knows that all of a sudden it doesn't need to put out as much current as it had and regulates itself. Kinda like if the battery is fully charged. Yes the car runs off the battery, and the battery is continually being charged by the alternator but the output is minimal at best when only the ignition system is in operation. Obviously higher as more accessories are turned on. A car does not need a battery to run continuosly. At start up (other than turning the engine over) it provides a small current to excite the rotor so the alternator can begin producing current, after that it is pretty much out of the picture other than storing electrical energy for the next start.
 

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Discussion Starter #8
CMAN, I never discconected the battery when car was on.. I did had 2 amps and my 12's subs, but I have a digital cap....

flewthecoupe, when I took it off my old 95 engine, the alt was working fine, when I finished swapping my 03 in and put the alt and connected the battery, sparks "jumperd" when I connected the negative charge, could that killed my alt??? After that, the car run, but my voltage gauge was very low, like 1/4 on the lines. Then all of the sudden the battery died on me and it was a NEW battery, took it to get it recharged and put it back on and happened the same thing. I took it off, took it to autozone and the diodes light came up on their machine.....
 
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