Hello, I'm having problem with my.. idk is it alternator or the battery.

First, my alternator has blown 2 of 6 diode and it can't charge battery, have to jump start for many time in the 2 week. Then I get it to repair shop for rebuild mine. It seem to be work but not really(?).

At the repair shop, it shown 13.5Vdc at the battery terminal on idle. Haven't check at alternator yet. I drive for long distance then shut off for just 5 minute and the battery suddenly drop to 10Vdc when try to crank the engine. After jump start (again) I drive home, shut off engine then measure battery it got around 12.6Vdc. Then I pull it out to charge it up and clean up the terminal.

In the morning, battery voltage is around 13.4Vdc. The car start fine, measured at battery terminal while engine running and I get 13.9Vdc on both battery and alternator. But, after engine get hot, the voltage drop to around 13.1-13.2Vdc on both terminal on idle, revving at 2000 rpm, driving. I try turn on and off AC/Light/everything but it still remain steady at 13.1-13.2Vdc on all condition.

I measure between + terminal of battery and alternator and got around 0.17Vdc different.
And - terminal of battery and alternator housing and got 0.1Vdc different.

No battery indication light up at all time.

The question is mine battery are done? Or the alternator rebuild is bad?

Thanks

 

All sounds normal.
Battery votage while running should be anywere from 12.6 to 14.4v
The alternator will changes its output depending on the load of voltage needed.
While cranking a car the battery normally drops down to around 10-11v. Then it returns to normal battery/alternator voltage.

 

Thanks xile6, I just found the invoice from my last battery change and it got almost 3 years now, so I decided to replace the battery. Lighting, AC seem to be more stable, no dimming. Charging voltage get a bit higher to around 14V when cold and 13.4V when hot on cruising. Since you mention that mine (when at 13.2V) is normal then nothing to worry now. Thanks again.