series and parallel connection Basics

8/9/2019 series and parallel connection Basics

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AN ELECTRICAL CIRCUIT

The circuit shown below has a power source, fuse,switch, two lamps and wires connecting each into aloop or circle. When the connection is complete,current flows from the positive terminal of thebattery through the wire, the fuse, the switch,another wire, the lamps, a wire and to the negativeterminal of the battery. The route along which theelectricity flows is called an electrical circuit.


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ELECTRICAL CIRCUIT REQUIREMENTS

A complete Electrical Circuit is required in order to makeelectricity practical. Electrons must flow from and return tothe power source.There are three different circuit types, all require the samebasic components:1. Power Source is needed to supply the flow of electrons(electricity).2. Protection Device prevents damage to the circuit in theevent of a short.3. Load Device converts the electricity into work.

4. Control Device allows the user control to turn the circuiton or off 5. Conductors provide an electrical path to and from thepower source.


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B ASIC CIRCUIT CONSTRUCTION

1. Power Source (Battery, A lternator,Generator, etc.)2. Protection Device (Fuse, Fusible Link, orCircuit Breaker)3. Load Device (Lamp, Motor, Winding,Resistor, etc.4. Control (Switch, Relay, or Transistor)5. Conductors ( A Return Path, Wiring toGround)


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LOADS

The illustration below has a horn in place of the lamp. A ny device such as a lamp, horn,wiper motor, or rear window defogger, that

consumes electricity is called a load. In anelectrical circuit, all loads are regarded asresistance. Loads use up voltage and controlthe amount of current flowing in a circuit.

Loads with high resistance cause less currentto flow while those with lower resistanceallow high current rates to flow.


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WH AT IS O H M'S LA W ?

A simple relationship exists between voltage,current, and resistance in electrical circuits.Understanding this relationship is important forfast, accurate electrical problem diagnosis andrepair.


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O H M'S LA W

O hm's Law says: The current in a circuit is directlyproportional to the applied voltage and inverselyproportional to the amount of resistance. Thismeans that if the voltage goes up, the currentflow will go up, and vice versa. A lso, as theresistance goes up, the current goes down, andvice versa. O hm's Law can be put to good use inelectrical troubleshooting. But calculating precise

values for voltage, current, and resistance is notalways practical ... nor, really needed. A morepractical, less time-consuming use of O hm's Lawwould be to simply apply the concepts involved:


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SOURCE VOLTAGE is not affected by either

current or resistance. It is either too low,normal, or too high. If it is too low, current willbe low. If it is normal, current will be high if

resistance is low, or current will be low if resistance is high. If voltage is too high,current will be high.


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CURRENT is affected by either voltage or

resistance. If the voltage is high or theresistance is low, current will be high. If thevoltage is low or the resistance is high, currentwill be low.RESISTANCE is not affected by either voltageor current. It is either too low, okay, or toohigh. If resistance is too low, current will be

high at any voltage. If resistance is too high,current will be low if voltage is okay


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When voltage is applied to an electrical circuit,current flows in the circuit. The following specialrelationship exists among the voltage, currentand resistance within the circuit: the size of the

current that flows in a circuit varies in proportionto the voltage which is applied to the circuit, andin inverse proportion to the resistance throughwhich it must pass. This relationship is called

O hm's law, and can be expressed as follows:E = I R

O H M'S LA W FORMULA


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Voltage = Current x ResistanceE Voltage applied to the circuit, in volts ( V) ICurrent flowing in the circuit, in amperes ( A)R Resistance in the circuit, in ohms

In practical terms " V = I x R" which means"Voltage = Current x Resistance".

1 volt will push one amp through 1 ohm of resistance.


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O H M'S LA W SYM B OL SH ORTCUT


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APPLICATIONS OF O H M'S LA W

As an application of

Ohm's law, anyvoltage V, current I or resistance R in an

electrical circuit can be determinedwithout actually measuring it if the twoothers values are known.

Current = Voltage / Resistance.


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In the following circuit, assume that resistance R is 2 and voltageV that is applied to it is 12 V. Then, current I flowing in the circuit

can be determined as follows:


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This law can also be used to determine thevoltage V that is needed to permit current I to

pass through resistance R:V

= I x R (V

oltage=Current x Resistance).

In the following circuit, assume thatresistance R is 4 ohms. The voltage V that isnecessary to permit a current I of 3 A to passthrough the resistance can be determined as

follows:


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Still another application of the law can be used to determine theresistance R when the voltage V which is applied to the circuit

and current I flowing in the circuit are already known

i i i , i i i i i i . , i i ii i i , i i i i i i . , i i i

In the following circuit, assume that a voltageV of 12 V is applied to the circuit and current Iof 4 A flows in it. Then, the resistance value Rof the resistance or load can be determined asfollows:


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TYPES OF CIRCUITS

Individual electrical circuits normally combine one ormore resistance or load devices. The design of theautomotive electrical circuit will determine which

type of circuit is used. There are three basic types of circuits:

Series Circuit

Parallel CircuitSeries-Parallel Circuit


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SERIES CIRCUITS

A series circuit is the simplest circuit. Theconductors, control and protection devices, loads,and power source are connected with only one

path to ground for current flow. The resistance of each device can be different. The same amountof current will flow through each. The voltageacross each will be different. If the path is broken,

no current flows and no part of the circuit works.Christmas tree lights are a good example; whenone light goes out the entire string stops working.


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A Series Circuit has only one path to ground, soelectrons must go through each component to

get back to ground. A ll loads are placed in series.Therefore:1. A n open in the circuit will disable the entire

circuit.2. The voltage divides (shared) between theloads.3. The current flow is the same throughout thecircuit.4. The resistance of each load can be different.


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The combined resistance R O in this circuit is equal to the sum of individual resistance R1 and R2. In other words: The totalresistance(R O ) is equal to the sum of all resistances (R1 + R2 + R3

+ .......)

Therefore, the strength of current (I) flowing in the circuit

can be found as follows:


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Resistance R0 (a combination of resistances R1 and R2, which areconnected in series in the circuit as illustrated) and current Iflowing in this circuit can be determined as follows:


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VOLTAGE DROP

A voltage drop is the amount of voltage orelectrical pressure that is used or given up aselectrons pass through a resistance (load). A llvoltage will be used up in the circuit. The sumof the voltage drops will equal source voltage.A voltage drop measurement is done bymeasuring the voltage before entering theload and the voltage as it leaves the load. Thedifference between these two voltagereadings is the voltage drop.


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VOLTAGE DROP TOTAL

When more than one load exists in a circuit,the voltage divides and will be shared amongthe loads. The sum of the voltage drops equalsource voltage. The higher the resistance thehigher the voltage drop. Depending on theresistance, each load will have a different

voltage drop.


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0V + 5V + 7V + 0V = 12 V


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VOLTAGE DROP CALCULATION

When current flows in a circuit, the presence of aresistance in that circuit will cause the voltage tofall or drop as it passes through the resistance.

The resultant difference in the voltage on eachside of the resistance is called a voltage drop.When current ( I) flows in the following circuit,voltage drops V1 and V2 across resistances R1

and R2 can be determined as follows from O hm'slaw. (The value of current I is the same for bothR1 and R2 since they are connected in series.)


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The sum of the voltage drops across all resistances is equal to the voltage of thepower source ( V T):


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PARALLEL CIRCUIT

A parallel circuit has more than one path for current flow.The same voltage is applied across each branch. If the loadresistance in each branch is the same, the current in eachbranch will be the same. If the load resistance in eachbranch is different, the current in each branch will bedifferent. If one branch is broken, current will continueflowing to the other branches. In parallel connection, twoor more resistances (R1, R2, etc.) are connected in a circuitas follows, with one end of each resistance connected tothe high (positive) side of the circuit, and one endconnected to the low (negative) side. Full battery voltage isapplied to all resistances within a circuit having a parallelconnection.


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Resistance R0 (a combination of resistances R1 and R2)in a parallel connection can be determined as follows:

From the above, the total current I flowing in this circuit can bedetermined from O hm's law as follows:


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The total current I is also equal to the sum of currents I1 and I2flowing through individual resistances R1 and R2

Since battery voltage V is applied equally to all resistances, the

strength of currents I1 and I2 can be determined from O hm'slaw as follows:


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Resistance R O (a combination of resistancesR1 and R2, which are connected in parallel inthe circuit as shown below), the total current Iflowing in the circuit, and currents I1 and I2flowing through resistances R1 and R2, can bedetermined respectively as follows:


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SERIES PARALLEL CIRCUIT

A series-parallel circuit has some components inseries and others in parallel. The power sourceand control or protection devices are usually inseries; the loads are usually in parallel. The samecurrent flows in the series portion, differentcurrents in the parallel portion. The same voltageis applied to parallel devices, different voltages toseries devices. If the series portion is broken,

current stops flowing in the entire circuit. If aparallel branch is broken, current continuesflowing in the series portion and the remainingbranches.


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The combined resistance R02 in this series-

parallel connection can be determined in thefollowing order:a. Determine combined resistance R01, whichis a combination of resistances R2 and R3connected in parallel.b. Then, determine resistance R02, which is acombination of resistance R1 and combinedresistance R01 connected in series.


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Total current I flowing in the circuit can be determined fromO hm's law as follows:

The voltage applied to R2 and R3 can be found by thefollowing formula:


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series and parallel connection Basics