Alternator: charges at idle: discharges as RPMs increase???
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Alternator: charges at idle: discharges as RPMs increase???
I have an '82 SD. The car wouldn't start. The new battery, less than three months old, was tested as "bad" and replaced. Two days later, it died again. This time they said the alternator was "bad" and was replaced. Two days later the car wouldn't start. Battery was good. The alternator was good at idle--about 10 amps--but at any increase in RPM, the ALTERNATOR STARTS DISCHARGING. They assumed alternator was bad and replaced it with a new one. Same thing--charges at idle but discharges at higher RPMs.
Two coincidental and probably irrelevant things: Over this same period of time I have replaced the a/c blower fan fuse about 10 times. I assumed I needed a new fan unit and replaced it. After about three days of usage, it blew again. Second, my clock stopped working yesterday.
All I get from my shop is "the machanic's shrug." Help!!
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Memphis10c
'82 300SD 110K
'04 BMW 530i
Two coincidental and probably irrelevant things: Over this same period of time I have replaced the a/c blower fan fuse about 10 times. I assumed I needed a new fan unit and replaced it. After about three days of usage, it blew again. Second, my clock stopped working yesterday.
All I get from my shop is "the machanic's shrug." Help!!
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Memphis10c
'82 300SD 110K
'04 BMW 530i
Member
Joined: Jul 2007
Posts: 242
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From: NJ, USA
2004 E500 4matic
I'm a electrician and I fix moving stock, however its diesel Locomotives. 
so form a electrical stand point it soulds like something is drawing high amperage when the rpm rises. did you try pulling the A/C blower fuse and increase the RPM to see if the voltage drop across the battery below 12v? bc if the you notice the voltage don't drops below 12v. you have a problem with your blower circuit. with out looking at the print the thing is to do what you did. that is change out the blower and fan. However since that did not work, your best bet is to look at the other components on that blown fuse circuit. however you will need a print (wiring diagram) for that.
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Memphis10c
'82 300SD 110K
'04 BMW 530i[/QUOTE]
so form a electrical stand point it soulds like something is drawing high amperage when the rpm rises. did you try pulling the A/C blower fuse and increase the RPM to see if the voltage drop across the battery below 12v? bc if the you notice the voltage don't drops below 12v. you have a problem with your blower circuit. with out looking at the print the thing is to do what you did. that is change out the blower and fan. However since that did not work, your best bet is to look at the other components on that blown fuse circuit. however you will need a print (wiring diagram) for that.
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Memphis10c
'82 300SD 110K
'04 BMW 530i[/QUOTE]
MBWorld Fanatic!
Joined: Mar 2006
Posts: 3,254
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From: Louisiana
03 E500 and Corvette
Possible to have the diodes breaking down with heat as the load increases. If you could do a wave form analysis of the output you might see it. I have seen a regulator fail under heat after it runs a while at high loads. Don't rule out the regulator/alternator as defective. Jim
