Bad Alternator, Batteries - PowerStrokeNation : Ford Powerstroke Diesel Forum
 
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post #1 of 5 (permalink) Old 04-23-2010, 06:23 PM Thread Starter
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Bad Alternator, Batteries

Well one of my batteries went dead so I took it out and have been runnin one battery, well the truck started actin funny again and had to get it jumped. So i took it to advance auto and got the alternator tested and all. The test said Diode Open and so my alternator is bad. Well I am wonderin what would cause all of this to happen at once? Also, how reliable is that Advance Auto test?

-John-
1996 F-250 Ext Cab Long Bed 4x4 w/ a few mods
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post #2 of 5 (permalink) Old 04-23-2010, 06:41 PM
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Re: Bad Alternator, Batteries

Well if your alternator wasn't chargin then thats why your batteries went dead. So thats why it all happened at once. Get a charge on your batteries and get a new alternator and BAM! problem solved.

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post #3 of 5 (permalink) Old 04-24-2010, 05:00 PM
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Re: Bad Alternator, Batteries

A bad diode lets the battery discharge as current leaks back through the windings from the battery to my understanding.

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post #4 of 5 (permalink) Old 04-24-2010, 11:58 PM
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Re: Bad Alternator, Batteries

^ That is a dead on accurate statement. a diode is designed to only allow the current to flow in one direction. If the diode is open then current can flow both ways, like toms said, current is back flowing through the alternator windings to field(ground). That is what killed the batteries. New alternator and charge up both batteries real good and that will solve your problem. DO NOT try to charge the batteries from the alternator when they are that dead. You will most likely burn up the new alternator.

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post #5 of 5 (permalink) Old 04-25-2010, 12:50 AM Thread Starter
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Re: Bad Alternator, Batteries

Well ended up gettin a new alternator and 2 new batteries. Went ahead and bench tested the alternator and it was puttin out like 17 or 18 volts. Got 2 batteries cause i charged one and it was still bad after charging. She runs good now. Thanks for the input

-John-
1996 F-250 Ext Cab Long Bed 4x4 w/ a few mods
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