CHARGING SYSTEM

March 15 2011 - March 16 2011

This week we learned the alternator off car testing and the charging system on-car testing.

ALTERNATOR OFF CAR TESTING

First day we disassembled an alternator to see how it works and tested all important parts of the alternator.

Equipments are, adigital multimeter, alternator, screw drivers, sockets.

To disassemble an alternator, we need to follow the directions in a service manual just like the procedure in our pratical book.

After we removed the rear cover, brush holder, rectifier, and regulator, we tested the rotor winding to ground and the rotor winding internal resistance.

To test the rotor winding to ground, we set the meter on 2k ohms, place black lead on the centre of the rotor shaft and red lead on the positive slip ring, the meter reads infinity, because there should be an open circuit otherwise the rotor winding has shorted to ground need to replace it.

Then we set the meter on 200 ohms to test the internal resistance of the rotor winding by place one end of each lead on each slip rings, the meter reading was 3.5 ohms, we can find the reading specification is 2 to 6 ohms.

Next we removed the back cover of the alternator, found there are four terminals. First we need to find the common point which is the terminal has most wires attached, then we measured the resistance of each stator winding by touching each terminal and the common point, the actual reading are 0.2 ohms for all three terminals, within the spec reading, means there is no problem of the stator winding.

After that we tested if the stator winding contected to the ground by place the meter leads on the common point and the alternator body, there should be no circuit between the winding and ground. The reading was infinite which is a pass.

Once we done that, we moved on to test the rectifier. Diodes in the rectifier makes the current only can go one direction. Faulty diodes in an rectifier reduce current and voltage output.

There are two sets of diodes in one rectifier, positve diodes and negative diodes. As we know the current in a working diode should only can go one direction. We set the meter on diode test mode, to test the positive didoes,  place the common lead on output terminal and positive lead on each input terminal, the resistance was low, around 0.52VD, when we reverse that, the reading was infinite. To test the negative didoes, we found readings were opposite to the positive diodes, the reading tells us all the diodes on the rectifier are working good.

The next testing was the voltage regulator, the voltage regulator controls the output of the alternator by controlling the strength of the magnetic field produced by the rotor. Procedure for testing the voltage regulator, first we need to find out the regulator spec's, the one I was testing the part number is 0170, field setting A, Voltage 12V, and Set point spec 14.5V. Then contected the regulator on to the tester by refer to the diagram for this regulator, after we turn the tester on, the short circuit light was off, warning ligh was stay on, field light flash continuously, and set point voltage reading was 14.5V, that means this regulator is working properly.

The last thing we did was measure the brush protrusion length, it is important because if the protrusions are too short, brush springs can not apply enough pressure to maintain the contact, may reduces the output of the alternator. To measuring that we just use an ruler to measure the length of the brush protursion, both protrusions on the brush we tested was 9.0mm which are more than the minimum length of 4.0mm.

After tested all the parts of the alternator, we assemble the alternator back on and tested it to see if it is working properly.


CHARGING SYSTEM ON-CAR TESTING

Second day of this week we tested and learned how the charging system works on-car.

From the charts in the workshop, we found the charging system that we used from a MAZDA 323 1981-1985.

First thing we need to do was remove the sureface charge of the battery by turn the fan on for serval minutes. Then we contect the voltmeter across the terminals of the battery, with the engine off. The reading was 12.5V whick means the battery in good condition and fully charged.

After that, we start  the engine and let it run at about 1500rpm - 2000 rpm, contect the voltmeter across the terminals of the battery got a no-load voltage reading 14.5V. As we know the no-load voltage increases should between 0.5 to 2.0 volts. If the reading higher than that, means something wrong with the regulator, if the reading same as the open circuit voltage, means the charging system not working properly.

Once we finished the no-load test, we contected a load test onto the battery with engine running at about 2000rpm, increased the load  in the system to 100amps dc, the voltage dropped to 13.0V and the amp meter reading was 29.1amps, which told us the charging system is supply current to the electrical units and charging the battery.

The last test was the voltage drop test. we used the voltmeter tested the voltage drop before and after the alternator when the engine was running to see if there is any resistance in the system. the reading was 0.017V between battery postive to the alternator output, and 0.02V between battery negative and alternator body. Then we calculated the total volts droped 0.037V, within the maximum allowed 0.40V.