Alternator ?
Thread Starter
Instructor
Joined: Feb 2006
Posts: 117
Likes: 0
From: Elyria Ohio
Alternator ?
What is the normal output from the alt. when running at idel ?
Is there always voltage at the alt., even when key is off ?
I am pushing about 12.92 volts when running at idel at the alt. , and 12.58 volts at the battery.
Is there always voltage at the alt., even when key is off ?
I am pushing about 12.92 volts when running at idel at the alt. , and 12.58 volts at the battery.
Melting Slicks
Joined: May 1999
Posts: 2,897
Likes: 0
From: Moon Township PA
In my experience, GM alternators should run at about 12.5 volts +/- at the battery with the engine off. Idle voltage will slightly higher but you should see around 14.3 volts +/- when the engine is running above idle. What is your voltage at, say, 1500 rpm?
Relying on memory but you can check the battery at the alternator with the key off. That post is always hot, iirc.
Relying on memory but you can check the battery at the alternator with the key off. That post is always hot, iirc.
Le Mans Master
Joined: Oct 2007
Posts: 7,453
Likes: 976
From: RI, Now Franklin/Nashville TN
Stock alternators should show 13.5 volts or higher at idle and should not move much when the rpm's are raised. High output alternators are a different story. My 120 Amp alternator does not produce much voltage above 12.5-13.0 volts at idle but will go just shy of the red zone on the gauge if full charge is required. The high output alternator also will put out 14.8-15.0 volts under heavy load such as when my euro halogen lights pull current especially with the 100 watt halogen high beams on. The manufacturer of the high output alternator (and I have seen from other sources) state that the gen light flickering with HO alternators at idle is normal, which mine can do at times. The original alternator showed very consistent voltage on the guage and my Tach/Dwell meter (ps-the gauge in my car is very accurate).
Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
Do you still have the separate voltage regulator? In other words not internal regulator like the 69 has.If you do you can test the alternator separately.
edit-On the back of the alt. remove the plug with 2 wires in it.Make a little jumper to go from the "F" terminal to the "Batt" term.One end of the jumper will be a female connector and the other end will just be bare wire.Dont put the jumper on yet.Get your voltmeter hooked up,start the engine,set your idle to 1500,now put the jumper on the "F" term. and touch the bare wire end to the Batt term on the alternator(DONT GROUND THE JUMPER).Watch the voltmeter and see if your voltage starts to rise above 14v.Dont let your voltage get above 16v (alt is unregulated with the jumper in place).If your voltage went up then chances are the alt is ok and you have a voltage regulator problem or a wiring problem.Make sure your voltage regulator has a good ground.
edit-On the back of the alt. remove the plug with 2 wires in it.Make a little jumper to go from the "F" terminal to the "Batt" term.One end of the jumper will be a female connector and the other end will just be bare wire.Dont put the jumper on yet.Get your voltmeter hooked up,start the engine,set your idle to 1500,now put the jumper on the "F" term. and touch the bare wire end to the Batt term on the alternator(DONT GROUND THE JUMPER).Watch the voltmeter and see if your voltage starts to rise above 14v.Dont let your voltage get above 16v (alt is unregulated with the jumper in place).If your voltage went up then chances are the alt is ok and you have a voltage regulator problem or a wiring problem.Make sure your voltage regulator has a good ground.
Last edited by ...Roger...; Sep 28, 2008 at 03:47 PM.
Thread Starter
Instructor
Joined: Feb 2006
Posts: 117
Likes: 0
From: Elyria Ohio
This alt. is not orig. it is a newer type with 1 post, the regulator is seperate. I just started car and then disconnected the + post on the battery, and my volt meter on the alt. post and am getting about 10 volts, does this show anything?
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Race Director
Joined: May 2006
Posts: 16,528
Likes: 53
From: Dayton, Ohio
As far as your 10 volts coming from a 1 wire alt. probably means no alt. output but I dont think that alt. will have output unless its connected to the battery.....I believe thats how it regulates itself.
Why are you asking these questions? Do you think you have a problem?Is your battery not staying up? One seat of the pants test I use is to watch the interior light,turn on the headlights and it should dim and then go bright again.If not raise the rpms a little and see how it reacts then.
Last edited by ...Roger...; Sep 29, 2008 at 06:28 PM.
Racer
Joined: Mar 2008
Posts: 428
Likes: 0
Voltage at idle should be a minimum of 1 volt above battery voltage.
Voltage output can vary between 13.6 to 15.5 volts depending on the electrical needs of the vehicle. But, with a voltage higher than 15.5v, bulbs start to cook.
I agree with DWncchs, one wire alternators should have an internal regulator. Have the alternator tested.