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Charging System Diagnostics

thiggy's Avatar

Join Date: May 2002
Posts: 718

05-25-02, 09:09 PM   #1  
Charging System Diagnostics

I have been told that one way to check if you have a defective alternator or generator is to crank the vehicle and disconnect the battery. If the engine continues to run, the alt/gen is OK. If it dies, the alt/gen or some component of the charging system is defective. Is this a reasonable test? Is there a more definitive way to check the charging system with a standard shop multi-tester? The car I am actually trying to resuscitate is a 1967 Datsun 411 with the 1600 cc engine. It has been parked for 4 - 5 years and required a major clean-up of gunk in the fuel line and gas tank before I could get fuel to the carbs. I finally got it running, but when I disconnect the battery the engine dies.

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the_tow_guy's Avatar
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Join Date: Feb 2001
Posts: 11,475

05-26-02, 07:43 AM   #2  
Some vehicles will run with the battery disconnected and others will not, so not really a valid test. With the engine running, check voltage at the battery. Depending on the vehicle and alternator you should probably be seeing somewhere around 13.5-14.5 volts. At that age it may have an external regulator which could also be the culprit of any chagring problems. This is not a definitive test because there is amperage invloved, too, but it's a start. I'm assuming you dropped a new battery in it during the revival?

Joe_F's Avatar
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05-26-02, 08:17 AM   #3  
Definitely not a valid test...in fact a great way to wipe out the diodes in the alternator.

TowGuy gave you a much better way to check it...and more accurate too.

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