Electrical Circuits

INDIVIDUAL CIRCUITS

The task that had to do be done was to wire up a individual circuit on a circuit board, an individual circuit is a electrical circuit that has only one consumer which in this case is the light bulb, by getting a power pack and setting it around 12.7-12.8 volts the same as a fully charged car battery this gives a realistic view on how circuits behave in an automotive electrical circuit.

Once the individual circuit had been wired the available voltage at different points of the circuit were measured, available voltage is how much voltage is left to be used in a circuit. To measure available voltage get a multimeter and set it to DCV(direct current voltage) and take the measurements along different points of the circuit. The first place that availble voltage was measured was the positive power supply to chech how much voltage is ready to be supplied, then the terminal before and after the switch were measure this was done to check whether there was any resistance in the wires which cause a voltage to be used up before it reaches any consumers and whether the switch is consuming any power due to resistance. Then measure the terminal before the light bulb to see how much voltage is available for the light bulb to consume. Then measure the terminal after the light bulb this should be zero as voltage must be zero by the time it reaches ground or earth. Then the terminal after the light bulb and the negative supply of the battery were measured both were zero volts.

Voltage drop was next to be measured, voltage drop is the voltage consumed by a consumer like a light bulb. Voltage drops were measure form the power supply to the switch from the switch to the input of the light bulb which were all 0volts it was when the input of the bulb to the output of the bulb were measured that there was a reading on the multimeter of 12.7 volts showing that the light bulb was consuming all the voltage before it goes to ground when voltage must be zero.

The difference between voltage drops and available voltage is that voltage drop readings tell you how much voltage a component is using and available voltage tells you how much voltage is left to be used in a circuit

Next the current or amperage was measured this is done by setting the multimeter to DCA (Direct Current Amperage)  10 amps then measuring at different points at the circuit, current flow should not change throughout the circuit. Then using ohm's law and power law some calculations were done to work out the resistance in the light bulb and how many watts the bulb was using.

The next task was to wire up a individual circuit with a larger light bulb then measure voltage drops at different points along the circuit some parts of the circuit had voltage drops other than the light bulb like the switch this indicates that there could be a poor connection and this is creating resistance meaning some voltage is used to move through the circuit. Then the amperage of the circuit was measured this came up higher than the smaller bulb circuit, this is because the larger bulb has less resistance and therefore allows current to move more freely and because the larger bulb has less resistance this means that the bulb is much brighter than the small bulb circuit. Then using ohm's law to calculate the resistance of the large bulb circuit the equation showed that the large bulb circuit had half the resistance of the small bulb.

SERIES CIRCUITS

A series circuit is a circuit were one consumer is hooked up after another, there is only one path for current to flow so voltage is shared but necessarily equally, but depending on varying resistances of the consumers in the circuit.

The first task was to measure volage drops across the circuit how to measure voltage drops using the voltmeter or multimeter is seen in the image below. Measuring voltage drops is done by placing the ends of the probes at the input and output of the consumer to get the voltage drop.

The two biggest consumers were the light bulbs both consuming 6 volts and the switch was consuming 0.7 volts indicating that there is resistance within the switch. This reading was to be expected as consumers in a series circuit must share the voltage. Then the amperage in the circuit was measured this did not change through out the circuit. The difference between the individual circuit and the series circuit amperages is that there is less current in the series as there is more resistance created from the two consumers. Then using ohm's law the resistance of the circuit was calculated and using voltage drops on the light bulbs the wattage was calculated for the bulbs. How to measure amperage is seen in the image below, amperage is measured by becoming part of the cicuit with multimeter to amps and taking the reading. It does not matter where in the circuit the ampmeter is hooked up so long as it is not hooked up to the power supply as amperage does not change in a circuit.

Then a three bulb series circuit was created first measuring the voltage drops across the circuit each bulb using about 4 volts this varied a bit due to different bulb sizes, this figure is lower than the two bulb circuit because now the voltage must be shared across three bulbs as opposed to two bulbs and each light bulb now gets less voltage than before. Next the amperage was measured along the circuit this came up lower than the 2 bulb circuit, this is because another bulb being added increases the resistance in the circuit and the current is reduced. Then using ohm's law the resistance was calculated this came up higher in the three bulb circuit as there is more consumer's adding more resistance to the circuit, then using the power law the watttage was calculated and the watts were lower in the three bulb circuit because the voltage or power is being shared among three bulbs now and not two. Next available voltage was measured across the circuit starting from the battery or power supply which was 12.7 volts the figures steadily went down through the circuit until voltage was zero by the time it reached the negative supply. 

 

 

PARALLEL CIRCUITS

A parallel cicuit is a circuit that has more than one input and output, each consumer therefore has its own input and output however this means that current draw is high for these circuits.

The first task was to wire up a two bulb parallel circuit and then measure the availble voltage before the two bulbs then measure voltage drops the readings were roughly the same as expected both bulbs get their own 12 volt power source and do not have to share it like they do in series circuits. Then the current flow was measured through both lightbulbs and added together to get the total amperage of the circuit this came up much higher than the series and individual circuits this is because more current is required to power both light bulbs to give them the full 12 volts. Then using power law the watts used by each light bulb was calculate dthis came up much higher than the series circuit because each bulb is getting its own power source rather than it needing to be shared like a series circuit, it is as if each bulb is in an individual circuit.

When a third bulb was added to the circuit the total amps flowing through the circuit increased this is because the more bulbs or consumers you add in a parallel circuit the less resistance there is the resistance of a cicuit can be worked out by working out the resistance of each light bulb and putting it in this equation 1/RT = 1/R1 + 1/R2 + 1/R3 this is if there is three bulbs in the circuit, this equation showed that there was less resistance in the 3 bulb cicuit than what there is in the two bulb circuit. Measuring the available voltage and voltage drops did not change for the 3 bulb circuit because each bulb is in an individual circuit they each get their own power supply this means there is no less or no more voltage for the bulbs to consume when the third bulb was added.

COMPOUND CIRCUITS



Compound circuits are circuits that are part series and part parallel circuit combinations.

The first measurement to be done was available votage and this showed that the two parallel light bulbs where only using  0.6 volts and the largest voltage drop was across the series light bulb. Then the current flow was measured this showed that current was split in the parallel circuit but still added up to the overall current flow this shows that the parallel cicuit acts as a single consumer. This means that the series light bulb is brighter than the bulbs in parallel as the current is divided for the parallel unit and the series bulb gets the full current thus showing that the parallel units are much dimmer than the series light bulb as the series bulb is getting all the current. As the parallel bulbs only use 0.6 volts this means that the series bulb gets to consume the left over 12 volts. The reason the parallel unit only uses 0.6 volts is that it has much less resistance than the series bulb and requires very little voltage to pass through that part of the circuit. This means that the series bulb must use the leftover 12 volts before it reaches ground.

RELAYS

The next task to do was to wire up a relay cicuit with three bulbs in parallel, a relay is a cicuit that is controlled using a winding that produces a magnetic field and a piece of magnetic steel that acts as switching points to switch on and off a circuit or to switch between circuits this can be seen below.

The magnetic field that is created by current flowing from 86 to 85 pulls down the switching points that come from 30 this switches the voltage from going to 87A and going no where and creates a circuit for current to flow through the light bulbs, this is activated when the switch to point 86 is switched on. 87A can also have a cicuit hooked up to so that current flow can switch between to different circuits.

Once the relay circuit had been wired up the next task was to measure available voltage at different points with the relay circuit on and off to see where voltage is going between the two circuits. With the relay circuit off the voltage from the power supply went through 30 and stopped at 87A there was no available voltage anywhere else except at these two points the available voltage would change in places if the circuit was nagatively switched that is if the switch was on the negative side of the circuit but the circuit that was wired up was positively switched. With the relay circuit on the voltage from the power supply flowed through to 86 and was consumed by the winding to produce a magnetic field, then the current and voltage flowed down to 87 and did not go to 87A as it is now a open circuit and 87 is now a closed circuit however because 87 is now a closed circuit and there are three bulbs to power this creates load on the cicuit and the available voltage is less than what the power supply is putting out. However this load on the cicuit does not effect the winding as it only uses 0.15 amps.

RESISTORS

The task to do was to select six resisitors, then using the resistor colour chart and using the resistor colour bands determine the resistance of the resistor in ohm's, and checking the resistors tolerance variations, then using a multimeter check that the calculations were done correctly and that the correct resistances were noted down. Then selecting two resistors and wiring them up in series meausure the total resistance of the resistors in series, then wire them up in parallel to and measure the resistance just like the series circuit using a multimeter set on ohm's and take the reading in the case of the parallel resistors the total resistance should be lower than the lowest resistance this is because as more consumers are added to a parallel cicuit the resistance goes down and the current increases, but as series circuits only have one path to follow all the resistances add up meaning that there is high resistance to current flow and the current flow is therefore very small.

TESTING DIODES

The task was to test a normal diode that was given to us the first test was to set the multimeter to 2K ohm's and test the resistance through the diode going from both positive to negative and negative to positive. In both cases the reading should be open circuit as there the meter does not produce enough voltage to push through the bindery layer of the diode. The output of the multimeter can be tested by putting one multimeter on 2k ohm's and using another meter put it on DC volts then using the reading from the DC volts this will be the voltage supplied from the meter which should be about 0.25 volts however lod meters can produce larger amounts of voltage and as the diode requires 0.6 volts to turn on this means there is not enough voltage for current to flow through the diode.

Then putting the multimeter on diode test test the diode from positive to negative this should give a of around 0.5 to 0.7 volts then test the other way negative to positve this should come up open circuit as a diode only allows current to flow one way which is conventional current flow direction meaning it should only flow from positive to negative. If there is reading this would indicate a faulty diode, then using a resistor and the diode wire them up in series then measure voltage drop across the resistor and the diode the resistor should have the largest voltage drop as the diode only requires 0.6 volts if it gets to much more then it will burn out. This means that the resistor will use the other 11.4 volts if the power source is producing 12 volts. Then the amperage reading was taken this reading should be very small as the resistor has to slow down alot of current so that the diode does not burn out. The high resistance to current flow is also because the circuit is in series and the current only has one path to flow through so there is low current flow. If a higher value resistor was put in the voltage drop values would be very similar however amperage would be even lower.

Next an L.E.D was tested on diode test on the multimeter, it was also tested to make sure current does not flow in the wrong direction, the l.e.d should have a greater voltage drop as the l.e.d produces the output of light and therefore more voltage is required to allow current to flow through the l.e.d, then wire up the l.e.d with a resistor in series and take voltage drop readings across the resistor and the l.e.d the resistor should be using less voltage as the l.e.d requires more voltage to allow current to flow this is also because when wired in series consumers share the voltage.

CAPACITORS

There was only one task to do, it was to wire up a capacitor with a resistor in series with a bridging wire before the capacitor going to earth, then hook up a multimeter on DCV to the capacitor, then remove the bridging wire and every 10 seconds record the voltage for 210 seconds, then graph the results, this should show that as time increases the voltage should begin slowing down, at the beginning the charge going into the capacitor will be increasing very quickly untill after the first minute then the charge will begin to slow and gradually increased, This is because of potential difference, because initially there was alot of potential difference there was not much opposing pressure and voltage or charge increases quickly then as charge increases the pressure from the capacitor increases as potential difference equalizes the charge gradually increases the charge will eventually stop increasing when it reaches the voltage of the power source this is when there will be no potential difference.

Starter Motor bench repair and on car testing

BENCH REPAIR

The task to be done was to strip down a starter motor and test the individual components of the motor to make sure they still worked, then rebuild the motor to condition that it can put back on a car.

First we tested starter motors off car by doing a no load test to make sure the motor worked then stripped the motor down to test the internal components of the starter motor, first was the no load test to make sure the starter was working properly before it was stripped down and tested.

The starter motor I worked on passed the test as it was above the minimum voltage requirement and was within amp draw specification. After the starter had been stripped down visual checks were done to see whether any damage had been done to the motor that might require replacement, first to be checked was the armature the visual checks that were done were to look for physical damage things like chips and scratches on the armature the insulation and the coil windings around the armature. Overheating this would be seen as discolouration on the metal, burning would be seen as black soot marks around the armature, and poling this is done by  the armature scraping on the pole shoes, srape marks would be visable on both the armature and the pole shoes.

The next test was to test whether there is a short to ground from the commutator segments and the armature core, the reading should be open circuit if there is a reading this would indicate that there is short in the insulation and reduce the performance of the starter motor as the magnetic fields would be affected that are produced from the armature, and the armature core would need to be replaced.

 The next test is a continuity test in which you check for resistance of the commutator, as the commutator connects to the brushes this means resistance must be low or the peformance of the starter will be affected and the armature would have to be replaced. The continuity test was done to check whether the commutator segments had a circuit, and checking the resistance of the segments, if there was resistance this would affect the magnetic field that is produced and thus reduce the performance of the starter motor and the armature would have to be replaced.

Next the commutator diameter was measured using a micrometer if the commutator came up to be to small in diameter this would make a poor connection between the brushes and the commutator this would create resistance and cause sparking if this was the case then the armature would have to be replaced. Then the mica undercut was measured using the micrometer again this is done to make sure that there is enough space to stop any two segments from shorting together and if the mica is not deep enough it can wear out the brushes very quickly.

The next test was to check for armature shaft runout this is done by putting the armature on some "V" blocks and using a gauge on the side read how much deflection there is whilst spinning the shaft around. If there is to much runout this could lead to poling on the pole shoes and the armature core or it could do physical damge by chipping insulation or windings or the core itself if there is to much deflection then the armature shaft needs to be replaced.

Then an alternative test to checking continuity of the commutator segments was done, this test applied 48 volts to the segments giving a much greater load to the windings so that any faults would show under greater load than normal. This test is done by using a 48 volt test light if everything is in good condition the light should glow then using the same machine the armature ground test was done if the test light did not glow then the armature shaft is not grounding.

Then using the 48 Volt test light do the ground test by placing one probe on a commutator segment and the other on the armature core or shaft the light should not glow.



Then using a machine called the growler the the armature core was tested for internal shorting, (internal shorting is when the insulation is damaged on a winding of wire and the current flow misses some of the windings) this is done by turning on the growler machine spinning the armature and holding a hacksaw in over the top of the armature if the hacksaw vibrates during the test this will indicate an internal short this could affect the performance of the starter motor and the armature would need to be repalced.

The next test was to test continuity of field coils this test only counts if the field coils are not grounded, set the multilmeter to ohm's and place the probes on each end of the winding and test the resistance of the field coils if there is to much resistance then the magnetic field would not be as strong and the starter motors performance would be reduced and the field coils would need to be replaced. If the field windings are grounded then place the multimeter probe on the field wire and the black probe on the starter motor body. This is check the resistance of the field wires and for grounding if the field wires are grounded this would give a reading on the multimeter and the field wires would have to be replaced.

Next the length of the brushes was measured this is to check for wear and tear if the brushes are to short this will give bad contact onto the commutator and this would cause sparking and create resistance.Next the insulated brush holder assembly was tested for grounding the reading should come up open cicuit if it doesn't this means that the commutator and armature are not getting the full voltage from the brushes and the performance of the starter motor would be reduced this means that the brush holders would have to be replaced.

Next the starter motor solenoid was tested to check the condition of the pull in and windings, this test is done to check whether there could be resistance within the winding connections or lack of resistance caused by internal shorting this is tested by checking the amp draw  if the pull in winding was shorting the magnetic field could be to strong and the pull in winding could burnout if there is to much resistance then the winding wont produce a strong enough magnetic field to to pull in the plunger in either case the solenoid would have to be replaced. Next the hold in winding was tested to make sure that it could actually hold in the plunger and checked whether the windings could have had to much or to little resistance.causing undesired operation of the plunger if there was to little resistance this could produce a very strong magnetic field and cause the plunger to stayin when it should let go if there is to much resistance the winding might not be able to hold in the plunger and the starter wont go this would mean that the solenoid would have to be replaced.

The last test to be done was to a visual inspection on the pinion gear, bushes, and the clutch, checking the pinion gear for cracks or scratches that could indicate that the pinion gear is engaging the ring gear of the flywheel in a undesirable way causing damage to both the pinion gear and the ring gear, then the bushes are checked for wear and tear and whether the clearance between the housing and the shaft are appropiate then the one way or overrunnig clutch is checked for free movement and its ability lock in place correctly, after all this the starter motor has been thouroughly checked and it is now ready to be put back together.

Once the starter has been put back together it is ready for a no load test in which the readings should be the about the same as they were before the starter motor was stripped this would indicate that the motor has been put back together correctly and all the connections are good.

STARTER MOTOR ON CAR TESTING

The task to be done was to test starter motors on the car, checking for voltage drops, amp draw and testing the overall efficiency of the motor.

The first test do be done when testing starter motors on car, was the check the OCV of the battery to make sure there is no surface charge and that the battery is charged enough to carry out the tests this is done so that readings are as accurate as possible.

 Once this has been established de-activate the ignition or fuel injection system so that the motor will not start then having the multimeter wired up the same test as the OCV start turning over the starter motor and this will give a cranking voltage this voltage must not fall below 9.5 volts or the test will not be able to go any further. As results would be invalid.

 The next test is to check voltage drops along the starter circuit first testing voltage drops from the battery positive to starter solenoid input then across the solenoid and then the earth side of the circuit from starter motor body to battery negative. These tests are performed whilst the starter motor is turning over, in a perfect circuit the voltage drop across these areas would be zero however dirty contacts and corrosion can cause voltage drops across the circuit as voltage must be used to allow current to continue flowing.

The last test to do is to test the current draw from the starter motor this is done using an ampmeter and connecting it to the positve side of the starter solenoid terminal then having someone turn over the starter motor to get a reading off the meter, if the reading is above specification this could indicate resistance along the circuit and the motor may have to be replaced, if the amp draw was below specification, in the real world the starter would not fail but in the case of testing it in the assesment it must be failed.



Alternators off car testing and on car testing

OFF CAR TESTING/BENCH TESTING

The task that had to be done was to strip down an alternator, and test the individual components to make sure that everything is still working on the alternator, then rebuild it again to a condition that it can be put back on a car.

The first thing that must be done is to remove the back cover of the alternator along with the brush holder and voltage regulator then remove the rectifier then the test are ready to be performed on these components.

The first test to test whether there was grounding on the rotor widing this test is done by setting the multimeter to ohm's 2k and putting the red probe on the slip ring and the black probe on the rotor shaft there should be no reading if there is a reading this means there has been a short circuit and the rotor would not produce a magnetic field and the alternator would have no output. The next test was for rotor winding internal resistance this test is done by setting the multimeter to 200 ohm's and by placing the probes on each end of the slip ring. If the test had come up less than two ohm's which is the minimum specification then this would mean there is an internal short or a break in the insulation of the rotor windings and the current will be missing some of the windings. This would mean less windings for the current to pass through and this would produce a weaker magnetic field and the alternator would have a reduced output. If the reading was higher than six ohm's which is the maximum specification this could mean that there corrosion on the winding connections causing higher resistance this higher resistance will reduce current flow and this would mean a weaker magnetic field from the rotor winding and this would mean that the alternator would have reduced output and the battery would get less charge.

The next test was to test the resistance of the stator windings which should be very low if the resistance is above specifications then this would mean that the current being induced into the stator from the rotor would be reduced and this would give the alternator less output. The other test on the stator windings was test whether there was grounding, this test is done using a multimeter setting it to ohm's 2k and then placing the red probe on the common stator winding terminal the terminal that has the most wires and the black probe goes on the alternator body, the reading should come up open circuit if there was a reading on the meter this would indicate that a circuit is being produced and the current being induced into the stator would be grounding on the alternator body rather than going to ground at the battery this will result in less output from the alternator and the stator would need to be replaced.

The next test was to test the voltage drops across the positive diodes of the rectifier, if the readings came up below the specification this would indicate that the diodes are not consuming the power and this could result in a higher output from the alternator, if the reading was higher than specification this would indicate that there are poor or dirty contacts at the diodes which would cause resistance and more voltage would have to be used to allow the current to flow through the diodes and this would give a reduced output from the alternator. The next test was to see whether there was a circuit from the alternator positive output to the diodes this test is done by putting the multimeter on diode test then put the positive probe on the rectifier's positive output and the negative probe on each of the diodes the reading should come up open circuit, if their was a reading this would indicate faulty diodes as they would be allowing current to flow in the wrong direction, if this is the case then the rectifier would need to be replaced. The next test was the negative diodes of the rectifier this test should give the same readings and if the there were readings that were not to specification this would give the same problems as the positive diodes and the rectifier would need to be replaced.

The next component to be tested was the voltage regulator this was tested using a transpo regulator tester, the specifications to test the voltage regulator can be found in the regulator test manual, by checking the model of the regulator, once the regulator has been wired up to the tester correctly the test can begin. This tester tells you how much output it allows the alternator to give, if the reading was above specification this would mean that the battery is being overcharged and this would cause the battery plates to swell and the battery would produce alot of hydrogen, however if the set point (regulating voltage) is not to high above the specification this would not affect modern day batteries as they are designed to take a higher charge. If the reading was below specification this would mean that the regulator is not allowing the alternator to produce its full charge ability and the battery would not be fully charged.

The last test was to measure the length of the brushes to make sure that they were long enough to make good contact with the slip rings, if the brushes were to short ths would cause a poor connection on the slip rings and this would cause a lot of resistance and even sparking this would result in a lower output from the alternator as current cannot flow freely and new brushes would need to be put in.

ALTERNATOR ON CAR TESTING

With on car testing the first thing that was performed was visual check to make sure that the drive belt was in good condition that there were no cracks and that the belt was tensioned to 5mm deflection, then the alternator wiring connections were checked to make sure that the connections were in place and making a good connection. Then the alternator mounts were tested to make sure that the alternator was held securely in place and that the was a good eathing point for the alternator circuit.

The next test was an OCV of the battery to make sure that its charge was above 12.4volts which is 50% charged if it is below this it could affect the results of the test and give incorrect readings. Then the regulating voltage was tested to make sure that the regulator was in good condition this test is done exactly the same as an OVC except the motor is running, the test is done by running the motor at 2000 RPM untill the charge has reached its peak then this would be the regulating voltage, if the reading was above 14.8 volts this would indicate a faulty regulator and the alternator would be over charging the battery and would give the battery a short life span.

Once the regulating voltage is at the maximum then a no load current test can be done, this is done by running the motor at 2000 RPM whilst no accessories are on this means that there is no radio or air conditioning to draw the current and create load on the circuit. To get a reading, use a ampmeter and place it around the alternators positve output cable then you will get a reading. If there is a higher than specification reading this could indicate that the battery is not fully charged and the alternator is still trying to charge the battery or there could be something wrong with the volatge regulator.

The next test was to measure the regulating voltage under load, this is done by hooking up the multimeter as if you are doing an OCV test except now the engine is running at about 2000 RPM and all the accessories are on like the headlights the airconditioning and the radio to create a load on the battery and to test what the output of the alternator if the reading is below specification then the alternator is not producing enough charge and the battery has to supplement this, this could mean that there is something wrong with the voltage regulator. Next the battery was tested to see how much current was drawn from it under load using the ampmeter on the positive lead this test is done with out the motor running. Next using the ampmeter measure the current flow through the alternator positive output the current flow from the alternator should be the same if not higher than the load that is being applied to the battery, this will indicate how much current is being supplied to the battery whilst the battery is under load. 

The last test is to test voltage drops on the positive and negative sides of the charging system this test is performed whilst the motor is running at around 2000 RPM, the positive side is tested by setting the multimeter DCV and placing the red probe on the positive battery post and the black probe on the alternator positive output. The voltage drop should be no more than 0.2 volts, the negative side is tested by placing the positive probe on the alternator body and the black probe on the negative battery post this result should be no higher than 0.2 volts, in a perfect circuit these readings should be zero. If the readings are higher than this, it will mean that voltage is being used up to pass through this part of the circuit and will result in a lower output from the alternator. 



Logic Probe Construction

The task we had to do was to make a component known as a logic probe, this component is a pen sized tester used to test particular points in an electronic circuit, the logic probe is used in finding faults and testing circuits. The logic probe that I made has a main use of dealing with an automotive application and testing electronic circuits on vehicles as the probe is rated to 24v.

This logic probe is a basic one and relatively simple, this description will give a step by step instructions on how it was made.

Step 1: There are two L.E.D's (light emitting diodes) a green one and a red one, and there are two resistors which are rated at 1000 ohm's (1.0kOhm), you then connect one of the resistors to the green l.e.d's long leg which is the positive side, this connection is made by doing a western union twist in which you inter twine the leg of the l.e.d and the resistor by wrapping the legs around each other (it does not matter which end of the resistor you use). It is however different for the red l.e.d you will do the western union twist with the short leg of the red l.e.d which is the negative side. You will then get two wires a red one and a black one around around 1000mm (it does not have to be exact). You will then trim off around 20mm of the insulator on both wires, and wrap the red wire around the free end of the resistor connected to the green l.e.d you will then wrap the back wire around the free end of resistor connected to the red l.e.d (you dont need to do a western union to attach the wires). At this point you will then solder together all the connections that you have made, so you will solder the twist that you made at the resistor and l.e.d and the connection that you made at the resistor and the wire that you wrapped around the resistor. You will then slide some heat shrink up both wires each piece of heat shrink will be around 50mm long, which you will slide up till it touches the l.e.d this should cover all the soldering connections that have been made. Using a heat gun shrink the heat shrink over the soldering connections that you made to create some insulation.

Step 2: You will then get a brass rod around 160mm long with a pointed end, at this point get two pieces of heat shrink one which will be about 60mm long and the other 75mm long, now getting the shorter heat shrink slide it over the pointed end leaving about 10mm from the point then getting the larger piece of heat shrink slide that over the non sharpened end of the brass rod leaving around a 10mm gap in the middle between the two heat shrinks. Then using the heat gun shrink the heat shrink on the brass rod making sure that the pointed end and the middle of the rod is left exposed. Now that there is heat shrink on the rod the part in the middle that was left exposed now must tined with solder, this is done to make it easier when connecting the l.e.d's which will be described later on. Once you have soldered or tined the middle part of the brass rod get the two l.e.d's and wrap the leg that has not got anything on it around the middle of the brass rod when you do this remember to keep the red l.e.d infront of the green one. Both l.e.d's should be standing verticle and in line this is done mostly for aesthetic purposes. Now with the two wires hanging below the brass rod bend them up so that they are in line with brass rod. Then using some wider heat shrink cut two pieces around 20mm long and slip one end up the wires until you reach the l.e.d's and then using the other piece slide that up until you reach the the end of the brass rod, and heat shrink them down, this is done to support the wires and stop them moving around.

Step 3: Now with the two l.e.d's standing up use a hot glue gun on the sides and underneath the l.e.d's to give support and stop them from moving and potentially breaking. Once the l.e.d's have been supported by the glue get some 10mm diameter clear plastic tubing and cut a length around 100mm long, then cut a rectangular grove which needs to fit around the two l.e.d's plus allow another 5-10mm to extend past the l.e.d's. Then slide the tube up the wires and have the cut out groove fit around the l.e.d's make sure that it fits securely and that the grove extends past the led's.

Step 4: This step is about improving the appearance of the logic probe get some 10mm diameter black heat shrink cut a 20mm length, then slide it over the pointed end of the brass rod and have it go over the clear plastic tubing that is extending past the l.e.d's now using the heat gun shrink it over the front of the brass rod.(it will not shrink tightly onto the rod at this point) Now cut a 90mm length of 10mm diameter black heat shrink and slide it over the wires till its hard up against the green l.e.d now use the heat gun to shrink the heat shrink over the back of brass rod with the clear plastic tubing, now cut two lengths of red heat shrink around 20mm long and slide one up the pointed end of the brass rod until it is touching where the clear plastic tubing is but not covering it. Then do the same for the other end, slide the heat shrink over the wires until it reaches the clear plastic tubing but not covering it, then use the gun to shrink the ends of the heat shrink onto the brass rod. Then you need to begin twisting the red and black wires together neatly then use red or black heat shrink every 400-500mm to stop the wires from unravelling, do not twist the last 300mm of wire as this is where the alligator clips will go.

Step 5: Get two alligator clips and remove the plastic covering off of them, an easy way to do this is to clip the alligator clips on to something small like the handle of a small spanner. Then strip the insulation off the end of both wires around 10mm, then twist the exposed wire as tightly as you can and put it through the small hole in the clip and then cut off the excess wire and solder the wire to the alligator clips, once the clips have cooled down slide the plastic back over the clips and you will have a completed logic probe to use in an automotive application.

This will give a circuit which indicates whether your connected to a negative side of a battery or positive, one way of testing this is to put the red wire on the positive battery post and the black black wire on the negative battery terminal. If the circuit has been wired up correctly then both l.e.d's will glow as a circuit has been created through both l.e.d's. Now put the probe or brass rod on the positive terminal and the black wire on to negative or ground and the red l.e.d will glow and the green one will go out, the red l.e.d glows brighter when the probe touches the positive terminal because more current is able to flow through the l.e.d than when both are connected up because there is now less consumers(l.e.d's and resistors) using up the current meaning more current can be provided to the red l.e.d. The green l.e.d goes out because a circuit has been created through only the red l.e.d current cannot flow through the green l.e.d as it is stopped because an l.e.d is like a one way valve current can flow one way but not the other. Now place the red wire on the positive battery terminal and put the probe onto ground this will make the green l.e.d glow and the red one will go out. The resistors that are attached to the l.e.d's reduce current flow as a 12volt battery would provide far to much current to the l.e.d's and burn them out almost immediatly. The resistors reduce the current to allow the l.e.d's to operate under there normal low power rating and the resistors allow for the probe to be used on circuits up to 24 volts, this is why the 1.0kohm resistors were used.

The finished logic probe should now look like the one in the image below.

Batteries

The task that had to be done was on an automotive battery and it was to check the condition of the battery by testing many different parts of the battery and checking the condition of the battery such as corrosion around the terminals and battery posts. This is just one of the basic checks that were done.

We started working on batteries in pairs in the unitec workshops as a practise session before we worked on batteries in cars but the checks are done in exactly the same way, we started by noting down the make of the battery which was a Lucas battery and the battery number which was 46G, we then noted down the cold cranking amperage (CCA) and the type of battery which is convetional.

We then carried out a visual check of the battery this is done by checking things like how tight the terminals are on the batteries positive and negative posts, whether there is any corrosion around the terminals which is seen as a yellowish or blue powder that builds up around the battery posts and can even rust metal on car body work if the battery area has not been well maintained by neutralising the acid, we then described what needs to be done to fix the problems which in the case of our practice session work there was some corrosion on the positive battery post. The way to fix corrosion is by mixing baking soda in warm water, this neutralizes the acid and prevents the acid or corrosion from spreading and effecting other areas of the car body or doing damage to the battery by creating a weaker connection at the terminals and thus creating resistance.

We then checked the electrolyte level this is another visual check in which you remove the battery cell covers on a conventional battery and check how high the level of electrolyted is, electrolyte is a mixture of 34% sulphuric acid and 66% distilled water. The level of the electrolyted should be around 1-2mm above the battery cell in our case all the cells were above the level that they should have been by about 1cm this means that there is weaker solution and could produce less voltage as the electrolye mixture is weaker than what it should be. This can also effect the life of the battery and shorten it.

We then did a open circuit voltage (OCV) test in which we test the voltage level of a battery, this is done by making sure there is nothing switched on that can drain power like a radio or interior light, as these will affect the results, you then get a multimeter set it to direct current voltage (DCV) set the multimeter to 20volts and take a reading by puuting the red probe on the positive battery post and the black probe on the negative battery post you will then get a reading which should around 12.8 volts which is what you get from a fully charged battery. If the voltage is higher than that it is known as surface charge and can be cleared by switching on the headlights of the car for 1 minute or in the case of working in the unitec workshop getting a battery load tester and setting it on 50 amps for 30 seconds to remove the surface charge as there is no other way to remove surface charge in this case. If the battery is below 12.4 volts which is classified as 50%charged then it is to discharged to carry on testing you must slow charge the battery for 10-12 hours at 4 amps and then let it settle for 24 hours.

We then did a hydrometer test which measures the specicfic gravity of the electrolyte in the battery cells, this gives and indication to the condition of each of the cells in the battery. The hydrometer test is done by removing all of the battery cell caps then getting a hydrometer and put the end of it into the electrolyte then gently squeezing the rubber bulb at the other end, now slowly release the rubber bulb and electrolyte will begin to fill the glass chamber at the point that the float inside the chamber is floating you take the reading off the float which has a scale on the side of it. Then note down the number given from the test and the cell being tested. Whilst doing this take note of the colour of the electrolyte it should be clear if it is murky then it shows the cells are disintergrating and the battery will need to be replaced soon. But if it is clear then there is nothing wrong with the cells. After taking down the readings from the hydrometer test minus the highest reading by the lowest reading to get the specific gravity variation a perfect battery should have no variation at all, but the variation is allowed to go up as high as 50 points if it is any higher than that then the battery needs to be replaced. If the specific gravity reading was low in one of the cells which it was in the pracitical session this would indicate that the cell is struggling to retain a charge and the battery would have to be replaced.

We then did a high rate discharge test, in which you get a battery load tester making sure that the loader is fully switched by turning the nob to the off position. Then hook up the tester,positve lead to positive terminal, negative lead to negative terminal. Then turn the tester up to half the the cca's of the battery which our battery was 410cca's so you turn the load tester up to 205 amps and leave it there for 10 seconds, The needle on the load tester should not move off of 205 amps and the voltage of the battery must remain above 9.5volts, The multimeter is hooked up to the battery during the test to get the voltage reading. If the tester cannot maintain 205 amps or the battery does not stay above 9.5 volts this could indicate that the battery is not charged enough to carry on testing or the battery cells are struggling to maintain charge if this is the case then the battery needs to be replaced as its life expectancy would be very short.
Then we measured parasitic draw which was not done in the assesment, this is done by setting the multimeter to milliamps then put the negative probe of the multimeter on the negative post of the battery and put the positive probe on the negative terminal of the battery now holding the negative probe in place lift up the negative terminal and a reading should appear on the mulitimeter this is the parasitic draw caused by other electrical components in the car, below 50 milliamps is an acceptable reading.

We then used a digital battery tester to test the battery this was not done in our assesment either, connect up the digital tester postive lead to positive on battery negative lead to negative on battery this will provide power to the tester and it will switch on, SAE will flash up very quickly on the screen then a number will appear make sure this number matches the CCA's of the battery. Then press test and either pass or fail will appear in our case the battery passed, then press test again and the OCV of the battery will come up then press test again and the tester will give you the calculated cold cranking amperage of the battery and in our case it came up 10 amps less than what the battery specicfied.

These were the steps that we went through to test the condition of the battery and the steps that we had to do in our assesment except for the ones that I mentioned that were not tested which was using the digital battery tester and measuring parasitic draw. In both the practice and the assesment the battery passed the test. And both were in good condition nothing needed to be done to the batteries.