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Beg to differ Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Thu, 23 Jan 2003 14:31:11
In Reply to: Another Question, JJ, Thu, 23 Jan 2003 05:09:09 Members do not see ads below this line. - Help Keep This Site Online - Signup |
The purpose of the Voltage Regulator is to, well, regulate the voltage.
The alternator creates current when the engine spins (via a belt) the armature in a magnetic field. That magnetic field is created by some electromagnets in the alternator called 'field coils'. The bigger the magnetic field, the higher the output voltage. The faster the armature spins, the higher the output voltage.
The voltage regulator controls the current into the field coils. At low speed (idle), the VR puts a lot of current into the field coils, so you get decent output at slow speed. As the engine speeds up, the alternator output increases, so the VR drops the field coil current to keep the output the same.
As you turn electrical loads on, it pulls current out of the alternator, so the voltage drops, and then the VR puts more current into the field coils to compensate. The same for turning loads off. But the VR can't work instantly, so for big loads, there will be minor voltage spikes and dips.
So when the VR is working right, the output voltage is pretty steady in the 13 volt range. The voltage changes with temperature - when things are cold, the output will be higher - as much as the low 14 volt range.
There are brushes to carry electricity from the rotating parts to the stationary parts. The brushes are built into the VR. Since all the current flows through the brushes, when they get worn and dirty, you get a voltage drop. So worn brushes can cause low output voltage, especially at idle.
There are diodes inside the alternator, as it produces AC voltage - it's a three-legged full-wave bridge, for those who care.
Seeing voltages in the 12 volt range - even 12.9 - at idle with loads on isn't a good thing, espeically in the winter when it's cold and the VR has a higher output. Once the voltage drops below 12.6, the alternator isn't providing current - it's the battery. That's not good. The alternator should provide ALL the car's electrical power requirements when the engine is running.
If you're seeing below 13.0 at idle, think about replacing the VR, as replacing it also replaces the brushes at the same time. It's easy to do on the 900.
posted by 192.249....
, Thu, 23 Jan 2003 14:31:11 <-- Viewing This Message, Thu, 23 Jan 2003 16:38:25
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