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Alternator Issue

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Guy Mayer

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So i have a 1978 280Z and im having an issue with my alternator. Im not actually sure what the problem is.... Ive had my alternator rebuilt and tested. Ive also had my battery replaced and tested. Both work, but the alternator is still not charging the battery. Once the car is started it will run, but as soon as I cut it off and try and restart it... the battery is dead. So it must be a wiring issue, but im just wondering if this has happened to anyone els.... if so, What is the problem???:mad::mad:

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I like to do my own testing of equipment. So I have a battery load tester and a very good digital volt ohm meter. Sometimes those auto parts stores don't know what they're doing. If you check the voltage at the + terminal of the alt. While it's running should be above 14v at around 2000rpm. If that checks out and don't have at least 14v at the battery, then your issue is a wiring or if u have a voltage regulator between the altternator and battery.

Just for kicks, if you check the voltage at the alternator, put the meter to AC to check the ripple current. It should be less than 500mv in my experience.This makes sure the bridge rectifier is doing its job converting a sine wave to square for dc voltage.

I'm not an electrical engineer so this is just from experience not education.

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If the battery is really dead, I would recommend providing it a full charge with a battery charger. Alternators are really designed to maintain a charge, but not actually charge a dead battery.  I just went th.rough this with my son's 2001 VW Jetta

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