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Posted by Ari [Email] (#2847) [Profile/Gallery] (more from Ari) on Mon, 7 Apr 2003 08:42:04 Share Post by Email
In Reply to: Change Voltage Reg. or Brushes??, Vladimir, Mon, 7 Apr 2003 01:58:00
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The brushes are part of the VR. They are soldered into the VR. It is possible to just solder in a new set, if you can find a set of brushes. I recommend putting in a new VR. You can always solder in a set of brushes to your old VR and keep it as a spare.

Of course, I'm going to ask how you know the alternator died. Before you go through the effort of rebuilding it, make sure that was the problem.

What were the symptoms? I'll bet the car just died, and you found out the battery wasn't charged. Stick a meter on, and there is no alternator output.

With a charged battery, if you turn the key to ON, do you get a BAT light? If not, your alternator may be just fine.

There is a wire that runs from the battery, through the ignition switch, through the BAT light, to the alternator. This is a thin, usually yellow or green wire, going to the back of the alternator.

The alternator needs a magnetic field to work. This field is created by electromagnets, called field coils. When you turn the key to ON, current flows through the switch, through the BAT light, through the green/yellow wire, and powers up the field coils. Because current flows, the BAT light glows. This creates a magnetic field in the alternator. Once the engine starts turning fast enough, the alternator start putting out voltage. The voltage regulator takes this voltage and powers the field coils by itself. Since there is no need for current from the battery, there is no current through the BAT light bulb, so it goes out.

If the alternator stops putting out voltage, the field coils look like ground. This pulls current through the BAT light, and it lights up.

If the wire is broken, or the BAT light bulb burns out, there will be no current to fire up the field coils, so the alternator never 'turns on'. You can spin it as fast as you want, but with no magnetic field, nothing comes out.

I would check that the BAT bulb and wire to the alternator are OK. With the key to ON, make sure the BAT light comes on. If not, find out why. Otherwise, you may rebuild the alternator for nothing.

If you do need to replace the BAT light bulb, get one from a dealer. It's a special wattage to make sure you get the exact right current for the field coils. Don't substitute.

Good luck!

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