Nissan Repair: Nissan Sunny Alternator, nissan sunny, alternator

Question
Hi Von.

Hope that you can help. I have a 1994 Nissan Sunny Van 1.7D. The battery has been flattened several times and it turns out that it is due to the Alternator not charging it sufficiently.
When I turn the ignition on and the van is in idle the voltage across the battery is approx 11.4V Which to me suggests that the Batt is not being charged. A charging voltage of 14.5V (Approx) is only present when I rev the engine to between 3 to 4 thousand rpm. The voltage is increased to 14.5 and stays at this level even during idle.
The battery light on the dash is not working but when I disconnect the plug at the alternator and take to ground the light comes on.
Also there seems to be a hydraulic pump on the back end of the alternator, do you know what this is for and can I remove it along with the alternator withour spuing hydraulics everywhere.

Do you know why the alternator would only charge the battery after hitting high revs?

Thank you

Kind regards

Royston

Answer
Royston,

Yes, the alternator is defective and whould be replaced.  The combination pump needs to be removed to get the alternator out and that makes your alternator a little more expensive.  I would check around for prices on rebuilt units and see if you can come out for less money if you had yours rebuilt.  You need 14 volts around 1000 RPMS.  So, yours is gone.  Higher revs put out more voltage in generators and alternators.  The reason that we use alternators is that they develop more voltage at lower RPMS.