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Alternator/Voltage regulator/wiring Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Fri, 30 Apr 2004 06:33:49
In Reply to: battery warning light (sorry-long), JJW, Thu, 29 Apr 2004 18:01:03 Members do not see ads below this line. - Help Keep This Site Online - Signup |
First off, get a better meter, or replce the voltage regulator on you 900 IMMEDIATELY! No car battery will be at 15 volts no load. And a 17.5 volt output from an alternator will (1) cook the battery, and (2) burn out your electronics. Since the car is still running, I suspect the meter.
All the battery does is supply enough power to start the car. And keep the radio memory alive. After that, it's dead weight. The alternator's job is to supply all the power the car needs when the engine is running, and to replace the battery charge lost to running.
A normal battery, engine off, is around 12 volts or so, depending on state of charge. When you start the car, and if the alternator is working properly, the voltage will be 13.0 to 14.2, depending on engine speed, electrical load, and ambient temperature.
Everything off, the battery voltage is the No load voltage, high 11's to and ideal 12.6 for a fully charged battery. In order to charge the battery, the alternator needs to supply a voltage higher than the no load voltage, so current flows INTO the battery, charging it. So since the voltage isn't greater than 12.6 when the engine is running, check the alternator.
Now, it probably isn't the alternator itself. The alternator is just a bunch of spinning wire. About the only thing that can go wrong with it is a broken wire, or a blown diode. Bad wires are very rare, and blown diodes more common but still rare. The most likely culprit is the voltage regulator, which bolts into the back of the alternator. If that fails, the alternator won't work. You don't need to replace the entire alternator - just a $50 voltage regulator will do the trick.
However, there is one last thing to check - the wire from the BATT bulb to the alternator. It's a thin wire, usually yellow or green. If that wire shorts to ground, not only will the BATT light be on, but the alternator won't work. Look at the back of the alternator for the thin wire (the fat red one goes to the battery). Make sure the wire is in good shape, and hasn't rubbed up against anything and shorted out.
Most likely a bad VR. And get a better meter.
posted by 192.249....
, Fri, 30 Apr 2004 06:33:49 <-- Viewing This Message
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