So I think I have beaten this topic to death on this forum already, but anyways. I had a problem with my alternator not giving enough juice to the battery. So I figured buying a new and stronger alternator will help with the drop in voltage and bad idle. Did that, and now i have a 140 amp alternator with a 14.5 regulator in the alternator. So what happened?

Well at first it was doing its job great, took it for a drive around town to do some work. Well it starts up at 14.5 volts (i think) and when I break it doesn't drop the volts down like before (great). But now it seems like it will idle higher at sometimes ( it reached 1,100 rpms at one point at idle)

So i figured it will just go away. Now it seems that after awhile, it wont charge right and will stay at a little above 12 volts when breaking. I'm kinda confused because I thought the new alternator would keep the battery at 14.5 volts? Am i missing something here or is it that there is another problem I over looked as well?

 

What series car and what series alternator? What make of alternator? Mazda or???????

Series four need switched power to the black/white wire on the alternator and also very much needs to see voltage on the white/black wire on the alternator (excitation voltage).

Series five NEED a constant 24/7 power on one wire of the alternator and NEEDS to see voltgae on the other wire when the key is switched ON (exctiation voltage).

Ford alternators need stuff also.

Now someone is going to tell you to take it off and to the auto store where they will check it out for FREE! How excitiing. But it won't help you at all if your not seeing excitaion voltage when it's ON THE CAR. The free auto store checkout will NOT check that out for you.

This might be helpful: http://www.autoshop101.com/trainmodu...or/alt101.html I probably need to read that also.

 

Its for a s5 n/a, and i have a s5 alternator that was rebuilt to handle 140 amps. Can you explain more on how a s5 needs a 24/7 power on one wire and what exactly is excitation voltage?

 

Excitation voltage is fed to the alternator (on a series five) from the warning light assy to the alternator and inside the alternator it goes through something called slip rings and on to the ROTOR of the alternator. So that when the .....................ah heck, I'm no good at explaining things like this.

Sooo, try this link. http://www.alternatorparts.com/under...lternators.htm Go to it. Then look waay down the page and where there is a title saying FIELD CURRENT SUPPLY. There you will find the answer to the question.

So on a series five alt you have two wires in the small plug. One wire comes from the warning light assy and is the excitation voltage required for making the alternator put out. The other wire in that two wire plug is from the EGI fuse in the engine bay and is hot as long as there is a battery in the car. No key required. It's there 24/7 and feeds the regulator in the alternator.

About the excitation voltage.................even if the wire is not connected to the alt that should feed it excitation voltage, a alternator may very well SELF excite itself thru the residiual magnatizm in the rotor IF you rev the engine up high for a brief moment. Once excited it'll stay that way til the engine is killed.

I have no personal experience in this area.............but its been said that if the SERIES FIVE alt does not see voltage to the regulator 24/7, that the alt will deplete the battery overnight. Rumor that's probably true. I read it on this site so it must be true. Right?

 

OK i think I know where you are getting at here, but how is this going to solve my problem? lol? Are you trying to ask if, when I rev my car, does the voltage increase and stays at that level until it is used?

**An update to this problem, when I drive with the headlights on and press the brakes, the voltage drops bellow 12 volts?

 

SUBSCRIBED:
i have a series 5 N/A that has the same problem. let it sit overnight and the battery is dead. try to start the car 4 or 5 times, then the battery dies from full voltage. how are WE supposed to fix this problem?

 

Well I just got an update to this, I took it to autozone to get my alternator tested and it seems that the one I purchased is bad

This is probably why I had all of the above problems.

And blackrotary23, I think you have a complete different problem. It sounds like something is draining your battery. Have you tried checking your fuses?

 

If you had the boosted alternator tested, it failed because it's giving out more amps than the alternator was originally designed for. Put it back on the car and have it tested on the car. This will give you the readings coming from the battery. This way you know exactly what's getting to the battery

 

That's how I originally tested it at auto zone, and how I double checked with an old alternator tester.

and the seller is going to send me another one, but he told me to do this and I was wondering if any of you know what he is asking, "on the plug check for voltage wend you open the key" Is he asking to check the voltage when the key is on?

 

Pull the small alt plug off.

Key to ON.

Check both wires/terminals in the plug for voltage. Should be there on both.

One wire is White/Blue and is fed by the EGI fuse and should have batt voltage.

The other wire should be White/Black and should have voltage and is fed by the warning light assy in the car via the Meter fuse in the interior....I think.

Those are the colors on a 91 car according to the online FSM wiring diagrams.

 

Does your Battery light come on when you cycle the key for the "bulb check"? if it does not illuminate, and your alternator gets the power signal from the warning light assembly, then maybe the bulb is burnt out causing no signal power to get to the alternator.

 

I think i found the problem...

I think it has to do with low idle. I only think this because my car idles between 600-700, also everytime i go fron a gear to neutral it drops to 500 then back up. And while it drops so does the voltage.

So before i mess with the idle i wanted to see what you guys think of thos