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.