Corolla 1.6 16v 1990- Battery light is always lit ?

When you strip it to the essentials, it is a fairly simple device.

The regulator gets turned on by incoming power on a switched line, from the Ignition position - and through a 'Check Alternator' light bulb on some cars. If there's a problem, it grounds the line and lights the lamp.

When the regulator decides it needs to make electricity, and how much, it sends power through the + brush and slip-ring to the rotor coil, and then out of the rotor though the second brush and slip-ring to ground. The rotor is a simple electromagnet.

(You use two brushes because it is very bad to send electricity through a bearing. The electric current will cause arcing and will quickly erode the balls or rollers and the races, and the bearing will not last long.)

The windings are in the stationary part, and there are three sets of windings staggered around the stator.

The diode stack is three sets of diodes that rectifies the three phases of AC power from the windings into Direct Current power. Older cars have discrete diodes, newer ones it's a big IC with a built in heat sink.

The power coming out of the alternator will still have a lot of AC noise artifacts in it, known as Alternator Whine when it leaks into your AM Radio reception, because there is very little filtering after the rectifiers. The car battery acts as the big filter capacitor that makes it nice pure DC for the rest of the car.

And NEVER run an alternator equipped car engine without a battery in the circuit, in the car or while bench testing. If someone so much as suggests disconnecting the battery while your car is running "as a test of the alternator", THEY ARE MORE THAN LIKELY RECKLESS MORONS. Get Them Away From Your Car NOW, before they blow something very expensive up.

Some alternator designs (not all) will not self-regulate the output voltage without seeing a battery connected to the output leads, they will go 'full field' and can put out 50 to 150 volts on the output stud. Needless to say, this is not good for the other electrical parts in the car...

They might get away with doing it on their car with a 'Brand M' alternator, and they think they can do it on any car - then they try it on your car with a 'Brand N' alternator and all hell breaks loose.

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As we've come to expect from Bruce, a clear and understandable explanation!

Yes!!

Problem solved!!

Thanx for all the help guys!

/kaabdalis Gord Beaman wrote:

Thanx for the info!

/Kaabdalis

Bruce L. Bergman wrote: