1985-1998 [Subscribe to Daily Digest] |
 | [Main 9000 Bulletin Board | BBFAQ |
Prev by Date | Next by Date | Post Followup ]
Member Login / Signup - Members see fewer ads. - Latest Member Gallery Photos
Re: help with the alt charging system Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 12 Feb 2004 08:05:34
In Reply to: help with the alt charging system, abc, Wed, 11 Feb 2004 22:21:55 Members do not see ads below this line. - Help Keep This Site Online - Signup |
First off, you need to have both wires to the alternator in place - the big, fat wire from the battery, and the thin (usually yellow or green) wire that runs to the alternator from the Batter light in the dash. You don't want to run the alternator unloaded.
Even if the battery was fully discharged, charging it won't pull a good alternator down to 10 volts.
I assume you used the voltage regulator that was in the good alternator. If you didn't, stick it in. Next, disconnect the THIN wire (yellow or green) from the back of the alternator, and turn the car to ON. The Batt light should be OUT, and if you measure that wire with a meter referenced to ground, it should show battery voltage. If the light is still on with the thin wire disconnected or you see zero volts (or nearly so), then find out where the wire is shorted to ground. THat's your problem, not the alternator.
If the battery light goes out when you disconnect it from the alternator, make sure you're sticking it onto the right terminal on the alternator. Sorry to have to say that.
Start the car - I'm assuming you've either recharged the battery or jumped it. If the battery light is on and the voltage is low (less than 13 volts), rev the engine. If the light goes out and the voltage jumps up into the 13 volt range, great. If the voltage stays low, measure the voltage between the Alternator CASE and battery negative, while the engine is running. To do this, I suggest you shut off the engine, hook up a clip lead to a mounting lug of the alternator, and hook up the meter before you restart the engine. Reaching into the engine while it's running is a sure nomination to the Darwin awards. The voltage difference between the alternator case and battery ground should be only a few tens of millivolts - less than 0.050 volts or so. If you're seeing a volt or more, then the alternator ground is bad.
My guess is that the thin wire from the bulb is either shorting to ground or hooked up to the wrong terminal. The alternator is a generator that uses electromagnets to generate a magnetic field. When you first start the car, electrical current flows from the battery, through the BATT light bulb, down the thin wire, and into the field coils of the alternator, making a magnetic field. Since current is flowing through the bulb, it lights up. As the alternator armature spins in that field, it creates its own current, and using the Voltage Regulator, takes over driving the field coils. Basically, it puts voltage on the alternator side of the wire from the BATT light, about the same as the battery voltage. Since the bulb has battery voltage on both leads, no current flows, so the light goes out.
If that wire is shorted to ground, the bulb will be on, but no current flows into the field coils. No current, no magnetic field, and the alternator has no output. All you'll see is battery voltage.
posted by 192.249....
, Thu, 12 Feb 2004 08:05:34 <-- Viewing This Message
No Site Registration is Required to Post - Site Membership is optional (Member Features List), but helps to keep the site online
for all Saabers. If the site helps you, please consider helping the site by becoming a member.
 |
 |
 |
 |
 |
