Thread: Idle voltage....Alternator?

I have been keeping an eye on my voltage ever since I changed my tensioner 2 weeks ago. I noticed while the trans is engaged the voltage drops to just above 12v. I increase my rpms to see if that would help. As of right now I am idling at 750rpms. As soon as I hit the gas it goes up to 13.8 and slowly climbs to mid 14s. The volts are 14.6 when I cruise and 15volts at cold start up. I do have a electric water pump and an intercooler, but that should not be enough draw. I also have a stage 1 zzp alternator booster.

What do you guys think this is pointing at? voltage regulator, alternator or is this normal? Just want to be prepared for the possible cost before I bring it to autozone for testing.

Electric motors pull more power more amps then you think.
The volt buster is not helping much either. From what i remember it takes away from ampers.

I would not worry about it untill you car starts to see below 12.5 while driving. Have your battery checked out. Your cars electrical really mainly runs off the battery. Alt is to charge the system

Originally Posted by Toofastgs

Your cars electrical really mainly runs off the battery. Alt is to charge the system

Incorrect. When the engine is running the alternator is powering all systems at around 14.4V.

The battery is a 12V battery so it just sits there getting charged. It's potential is not enough to make it a power source in a 14.4V system, only a draw to be charged.

If the battery is what powers things, why can I take the battery out of a running car and it doesn't even notice?

Are you sure the alt booster takes away from amps?

I did some reading and I think i am going to do the big 3. I have some older power wire from about 5 years ago that I used with an old system. Should be enough to do it.

Originally Posted by jasonball

make sure the wire is still good. 5 years is old. can get alot of condensation and mess up stuff inside the wrap.

I assume just look for little water spots?

12-14 volts is normal

lol...ok so what I am experiancing is not ideal when it is in the 12s but it is acceptable

Im not so sure that is normal at idle. In order to charge, the alternator has to put out more voltage than the battery voltage of 12 volts. I dont recall ever seeing an alternator put out less than 13 volts at idle, normally its around 13.6 or so. With a voltage booster it should be putting out even more at idle.

Originally Posted by TDCRacing

I understand. But, There is no car in stock form that idles at 700 rpm's. I have a stage 2 voltage booster and still see right around that. No problems for over a year now. I'm sure if he would put the stock idle tables back he would be seeing the correct amount of voltage

Dude, my car idles stock at 650RPM. Most 3800s I've come across idle at ~700 +/-50 depending on the weather and cleanliness of the IAC.

Originally Posted by TDCRacing

Ok then you tell us what the problem is.

Faulty voltage regulator in the alternator or faulty alternator. It's simply having trouble maintaining voltage at idle. My car can maintain up to 15+ volts if the battery is low at 650-700RPMs idle. If it isn't giving you problems while driving, then it really isn't a big deal.

Though, I've seen this be a prelude to an alternator that just gives out. Can't say exactly when or even if. But it's possible.

The way to test if it is alt.

1. Test battery voltage at pos and neg
2. Test voltage at the alt output, more then a half a volt difference you got a bad alt or bad wiring going to alt.

On both test use the same ground point

Originally Posted by Toofastgs

The way to test if it is alt.

1. Test battery voltage at pos and neg
2. Test voltage at the alt output, more then a half a volt difference you got a bad alt or bad wiring going to alt.

On both test use the same ground point

I will check later today when I get home. I think the reason for my issue might be the 2 pumps going constantly with my headlights on at night. I rather find the issue prior to something dieing. Like TDRacing said, his has been like that for a year now. I just noticed it and I could be in the same boat