Thread: Problem- Alternator or Battery

Originally Posted by mogindo

However, since me alternator is not charging properly, I would think that the battery light would stay on for longer.

Don't overthink things! The warning light goes out regardless of the alternator producing one amp or full output. It simply shows the difference in the voltage between the ignition switch and the internals of the alternator. It isn't "programmed" in any way, it is just a dumb light globe.

The reasons for an alternator not charging properly are many, including not enough revs, loose drive belts or a melted main power cable connector at the back of the alternator. You should check the alternator voltage at elevated revs if your battery has been flattened, say 2000 rpm. A flat battery at idle will not show a higher voltage.

so if my battery is flat (and it is) then when I rev up to 2000rpm, I should see elevated voltage at the Alternator, correct? I read that the voltage at the alternator should be about 13V at high rpm.

Will I also see elevated voltage at the battery terminals at 2000rpm?

(when I reved up last night, I didn't see more voltage at the battery)

I am not, over thinking, but also try to learn in the process, so thanks to all you guys for advices and opinions.

(luckily I called my mechanic and he still has the old original alternator, one I replaced with the new one. On;y because I wanted to fix jummpy tacho, but it didn't help. I think that old alternator is actually still good.)

Originally Posted by mogindo

so if my battery is flat (and it is) then when I rev up to 2000rpm, I should see elevated voltage at the Alternator, correct? I read that the voltage at the alternator should be about 13V at high rpm.

Will I also see elevated voltage at the battery terminals at 2000rpm?

(when I reved up last night, I didn't see more voltage at the battery)

If the voltage is significantly higher at the alternator than the battery then the connecting cable is faulty. There should be no more than 0.1 volts difference at full power. A big difference would mean you need to fix or duplicate the cable from the alternator to the battery.

My voltage at the alternator was lower than the battery !

Originally Posted by mogindo

My voltage at the alternator was lower than the battery !

That's likely because when you pulled the terminal off the battery the regulator backed off.

Well dumb me, for taking the terminal off. Grrr, Thanks Tombie, I am learning a lot form this.

Now, how do I reset the regulator?

Will putting a fully charged battery reset the regulator?

I have a feeling that its the battery is dead, but the alternator is fine. Batt is at least 4 year old Optima red top and Alt is $265 six months old.

You can't reset a regulator. It either works or is stuffed. There is no "computerese" involved in the regulator. It is strictly analogue.

My voltage at the alternator was lower than the battery !

Yes but what was the voltage with the engine running at 2000 rpm and the battery connected???? Is the drive belt tension correct?

Belt is not making any noises so I assume its correct tension.
i think i ran about 1500prm and the voltage at the alternator was 10.98V and at the battery 11.04V. It seemed that the battery voltage was dropping though the longer the car was running.

I ran it for about 10 minutes like this.

So what if I put new battery in. Will that make the Alternator charge more and regulator increase its band. Where is it anyway?

Thanks man for help.