Another question about regulator vs alternator.

[Lmarche]

Last winter I replaced the battery for a new one. Recently, on a cool 46 f morning there wasn't enough current to start the engine. I took the battery for testing and charging. Battery checked ok and every thing was back to normal. A few days later, I rechecked the volts on the battery poles 12.2v ( a little low again ), then started the engine at idle with no equipment turned on and the battery clamps 12.3v ( again a little lower than the normal 12.5 to 14.0 range given by a 101 project for your 911 ). But what I didn't like at all, was the 11.6v reading with the a/c, stereo and headlamps on.
Is it correct to say that a regulator tries to control current below 14v at different rpms? ...a faulty regulator shows close to 17v? ...and a faulty alternator doesn't powers more than 12.5v?
911SC 1982 owned for a year.
Thanks for any help folks.

[Driver_X]

What were the readings @ 3,000 rpm?

[Bob Kontak]

Originally Posted by Lmarche

.......again a little lower than the normal 12.5 to 14.0 range given by a 101 project for your 911

A charged battery at rest should be 12.5 or above.

High 13's S/B your voltage when idling - no load - and it should only vary by a few hundredths of a volt steady state.

From my experience a regulator problem will exhibit voltage that varies at the battery posts. At a steady draw state it will vacillate a lot - a half volt or more - one way and another. It's confused, in short, for whatever reason V regs get tired. The alternator charging voltage is there but the v reg ain't doing it's job.

11.6 V with a draw on it tells me that your alternator is tired.

I'm not an expert but if the voltage is steady off the battery terminals and you are not getting enough charge under load, it's the alternator.

[S2GART]

A VR simply ensures that only 14 volts goes to the battery. No matter what the RPM, the voltage shouldn't exceed 14.1-14.3 volts. If your 1 yr old battery isn't able to start the engine, obviously it is not being charged. Pull the alternator and check the brushes on the VR and have the alternator tested.

[Lmarche]

Thanks for the comments, I'm going to recheck the volts at 3000 rpms with and without accesories on, and evaluate if the alternator or the regulator are starting to fail.

[Targalid]

Your alternator is not charging. The alternator is energized via pin #11 on your 14 pin connector, the blue wire, which is connected to the red alternator light on the instrument cluster. Do you see the red light on your dash when the key is turned to run? If not, you have a bad connection or your bulb has failed. The alternator will not charge without it. If all is well here, I suspect the voltage regulator but check connections first: dirty, poorly connected?

[yundar]

So... Should red Alt light come on with key every time as a check. I am not charging and I have no alternator light coming on but it does not come on with the key before I start the car either. Voltage is low so I a suspecting the alternator but could have a bad wire/ gauge light. Thanks, Andy.

[JoeyD911]

I had the same issue on my 82 SC. It ended up being the voltage regulator. I had same voltage issues as you at the battery. You need to put the new bulb in for the alt charge light first. nothing works W/O that, believe it or not. The bulb completes the circuit. I have a regulator that will fit if you're interested. It is not a Valeo unit and it is made to fit 928/911. I had an argument with the guy who sold me the unit, but it turned out that it would have fit in the end. i'll pass it on to you for 50.00 if you want it. If your car has fewer than 125K on the clock and has been stored indoors, I doubt it is the alternator.

[Targalid]

Yundar,
Yes, the red alternator light should come on every time you turn the key to run as you prepare to start the car. When the engine begins to turn, the light goes out as the alternator supplies voltage. The fault can be a bad bulb but more likely is a dirty connection between the light and the alternator. A good place to look for a dirty connection is at the 14 pin connector in the left rear of the engine next to the fuses.
Al

[Lmarche]

I haven't got the time to test it again. The car has started everytime since last post, but I haven't use the a/c or the headlamps. I checked the alternator lamp before starting the car and it's working.
Another thing I'm going to do is to clean the transmition ground, before investing on a alternator. Those anyone have the 95 amp alternator?
Is it a good idea to put more load on the old electrical system?

[Lmarche]

Another question, is it posible that rain water coming into the engine, can do the alternator hesitate?

[yundar]

Thanks Targa Lid. I was gone all weekend but I will try that.