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Alternator Not Charging At Idle


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I've had two datsun alternators do this. You could rev the piss out of the engine and they'd charge at idle for a while but that trick wouldn't work very long. Sounds like replacement is in the near future.

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  • 2 months later...

I have this exact issue with my 74` B210...


Its a fairly new rebuild on the alt, done just last year bu the PO, (have the recept) earlier when i noticed the positive wire had broken off of its terminal i also noticed that the white clip that plugs into the back of the alt was a little loose. When i pushed it in to get a good connection it sparked slightly. I traced the wire to what looks like the voltage regulator mounted by my coil.


So putting things together im assuming that my regulator is shot now?

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Another common cause of not charging at low RPM is the brushes in the alternator worn out.  At low RPM, the rotor in the alternator needs a full 12 volts to charge.  As the RPM goes up, the voltage regulator put a resistor in series with the rotor, to cut back on the current, and this regulates the voltage.  If the alternator is turning really fast, the voltage regulator may disconnect the alternator rotor completely.

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