INSTRUCTIONS AND PROPHECIES OF THE Blessed MOTHER ALIPIA GOLOSEEVSKY, Kyiv...
There is nothing easier for an electrician than to connect a lamp. But if you have to assemble a chandelier or sconce with several shades, the question often arises: “What is the best way to connect?” To understand the difference between serial and parallel connection of light bulbs, let's remember the 8th grade physics course. Let's agree in advance that we will consider lighting in 220 V AC networks as an example, this information is also valid for other voltages and currents.
serial connection
The same current flows through a circuit of series-connected elements. The voltage on the elements, as well as the released power, is distributed according to its own resistances. In this case, the current is equal to the quotient of voltage and resistance, i.e.:
Where Rtotal is the sum of the resistances of all elements of a series-connected circuit.
The more resistance, the less current.
Connecting consumers in series
To connect two or more light sources in series, you need to connect the ends of the cartridges together as shown in the picture, i.e. the extreme cartridges will have one free wire each, to which we supply the phase (P or L) with zero (N), and the middle cartridges are connected to each other with one wire.
Through a lamp of 100 W, at a voltage of 220 V, a current flows slightly less than 0.5 A. If you connect two according to this scheme, the current will drop by half. The lamps will shine at half incandescence. The power consumption will not add up, but decrease to 55 (approximately) on both. And so on: the more lamps, the lower the current and the brightness of each individual.
Advantage:
- the resource of incandescent lamps increases;
Flaws:
- if one burns out, the rest do not burn;
- if you use devices of different power, those that are larger will practically not glow, those that are smaller will glow normally;
- all elements must be of the same power;
- it is impossible to include energy-saving lamps (LED and compact fluorescent lamps) in a luminaire with such a connection.
This connection is great in situations where you need to create a soft light, for example, for a wall lamp. This is how LEDs are connected in garlands. A huge minus is that when one link burns out, the others do not shine either.
Parallel connection
In circuits connected in parallel, the full voltage of the power source is applied to each of the elements. In this case, the current flowing through each of the branches depends only on its resistance. The wires from each cartridge are interconnected at both ends.
Advantages:
- if one lamp burns out, the rest will continue to perform their functions;
- each of the circuits shines at full heat, regardless of its power, because full voltage is applied to each;
- three, four or more wires (zero and right amount phases to the switch) and turn on the required number of lamps or a group;
- energy-saving light bulbs are working.
There are no disadvantages.
To turn on the light in groups, assemble such a circuit either in the lamp housing or in the junction box.
Each of the lamps is turned on by its own switch, in this case there are three of them, and two are turned on.
Laws of series and parallel connection of conductors
For serial connection It is important to consider that the current through all the lamps is the same. This means that the more elements in the circuit, the less ampere flows through it. The voltage on each lamp is equal to the product of the current and its resistance (Ohm's law). By increasing the number of elements, you will lower the voltage on each of them.
In a parallel circuit, each branch takes on the amount of current it needs, and the voltage is applied that which produces the power source (e.g. household power supply)
mixed connection
Another name for this circuit is a series-parallel circuit. In the branches of a parallel circuit, several consumers are connected in series, for example, incandescent, halogen or LED. Such a scheme is often used on LED matrices. This method provides some advantages:
- connection of individual groups of light bulbs on a chandelier (for example, 6-horn);
- if the lamp burns out, only one group will not burn, only one series circuit will fail, the rest, standing in parallel, will shine;
- group lamps in series with the same power, and parallel circuits - different, if necessary.
The disadvantages are the same as those inherent in serial circuits.
Connection diagrams for other types of lamps
To correctly connect other types lighting fixtures, you must first find out their principle of operation and familiarize yourself with the connection diagram. Each type of lamp requires certain conditions for operation. The process of heating a spiral is not at all intended to emit light. In the field of high power and area, they were noticeably replaced by gas-discharge devices.
Fluorescent lamps
In addition to incandescent lamps, both halogen and fluorescent tubular lamps (LL) are often used. The latter are common in administrative buildings, boxes for car painting, garages, production and commercial premises. A little less often they are used at home, for example, in the kitchen to illuminate the work area.
LL cannot be connected directly to a 220 V network, high voltage is needed for ignition, therefore a special circuit is used:
- choke, starter, capacitor (optional);
- electronic ballast.
The first scheme is used less and less, it is characterized by lower efficiency, hum of the throttle and flickering of the light flux, which is often not noticeable to the eye. The connection of the electronic ballast is often depicted on the case.
Either one lamp is connected or two in series, depending on the situation and what is available, also with an electronic ballast.
A capacitor between phase and zero is needed to compensate for the reactive power of the inductor and reduce the phase shift, the circuit will start without it.
Pay attention to how the lamps are connected, the same rules cannot be used in lighting with fluorescent light as when working with incandescent lamps. The situation is similar with DRL and DNAT lamps, but they are rarely found in everyday life, more often in industrial workshops and street lamps.
Halogen light sources
This type is often used in spotlights on hanging and stretch ceilings. Suitable for lighting places with high humidity, since they are produced for operation in circuits with low voltage, for example, 12 volts.
A 50 Hz mains transformer is used for power, but the dimensions are large and over time it starts to buzz. An electronic transformer is better suited for this, it receives 220 V with a frequency of 50 Hz, and leaves 12 V AC with a frequency of several tens of kHz. The rest of the connection is similar to incandescent lamps.
Conclusion
Correctly assemble circuits in fixtures. Do not connect energy-saving lamps in series and follow the scheme for switching on fluorescent and halogen lamps. Energy-saving lamps “do not like” low voltage and will burn out quickly, while a fluorescent lamp may not light up at all.
Wago terminal blocks or clamps are suitable for connecting lighting, especially if the wiring is aluminum and the wires at the lamp are copper. The main thing is to follow the safety rules when working with electrical appliances.
One of the pillars on which many concepts in electronics are based is the concept of series and parallel connection of conductors. It is simply necessary to know the main differences between these types of connection. Without this, it is impossible to understand and read a single diagram.
Basic principles
Electric current moves along the conductor from the source to the consumer (load). Most often, a copper cable is selected as a conductor. This is due to the requirement that is placed on the conductor: it must easily release electrons.
Regardless of the connection method, electricity moves from plus to minus. It is in this direction that the potential decreases. It is worth remembering that the wire through which the current flows also has resistance. But its value is very small. That is why they are neglected. Conductor resistance is assumed to be zero. In the event that the conductor has resistance, it is customary to call it a resistor.
Parallel connection
AT this case the elements included in the chain are interconnected by two nodes. They have no connections with other nodes. Sections of the chain with such a connection are called branches. The parallel connection diagram is shown in the figure below.
Speaking in a more understandable language, then in this case all the conductors are connected at one end in one node, and the other - in the second. This leads to the fact that the electric current is divided into all elements. This increases the conductivity of the entire circuit.
When connecting conductors to a circuit in this way, the voltage of each of them will be the same. But the current strength of the entire circuit will be determined as the sum of the currents flowing through all the elements. Taking into account Ohm's law, by simple mathematical calculations, an interesting pattern is obtained: the reciprocal of the total resistance of the entire circuit is defined as the sum of the reciprocals of the resistances of each individual element. Only elements connected in parallel are taken into account.
Serial connection
In this case, all elements of the chain are connected in such a way that they do not form a single node. This connection method has one significant drawback. It lies in the fact that if one of the conductors fails, all subsequent elements will not be able to work. A striking example of such a situation is an ordinary garland. If one of the bulbs in it burns out, then the whole garland stops working.
The series connection of elements is different in that the current strength in all conductors is equal. As for the voltage of the circuit, it is equal to the sum of the voltages of the individual elements.
In this circuit, the conductors are included in the circuit in turn. And this means that the resistance of the entire circuit will be the sum of the individual resistances characteristic of each element. That is, the total resistance of the circuit is equal to the sum of the resistances of all conductors. The same dependence can also be derived mathematically using Ohm's law.
mixed schemes
There are situations when on the same circuit you can see both serial and parallel connection of elements. In this case, we speak of a mixed connection. The calculation of such schemes is carried out separately for each of the group of conductors.
So, to determine the total resistance, it is necessary to add the resistance of the elements connected in parallel and the resistance of the elements connected in series. In this case, the serial connection is dominant. That is, it is calculated in the first place. And only after that, the resistance of elements with parallel connection is determined.
Connecting LEDs
Knowing the basics of the two types of connecting elements in a circuit, you can understand the principle of creating circuits for various electrical appliances. Consider an example. largely depends on the voltage of the current source.
With a low mains voltage (up to 5 V), the LEDs are connected in series. In this case, a pass-through capacitor and linear resistors will help to reduce the level of electromagnetic interference. The conductivity of the LEDs is increased through the use of system modulators.
With a mains voltage of 12 V, both serial and parallel mains connections can be used. In the case of serial connection, switching power supplies are used. If a circuit of three LEDs is assembled, then an amplifier can be dispensed with. But if the circuit will include large quantity elements, then an amplifier is needed.
In the second case, that is, with a parallel connection, it is necessary to use two open resistors and an amplifier (with throughput above 3 A). Moreover, the first resistor is installed in front of the amplifier, and the second - after.
At high voltage networks (220 V) resort to serial connection. In this case, operational amplifiers and step-down power supplies are additionally used.
The lesson deals with the parallel connection of conductors. A diagram of such a connection is shown, an expression is shown for calculating the current strength in such a circuit. The concept of equivalent resistance is also introduced, its value is found for the case parallel connection.
Conductor connections are different. They can be parallel, sequential or mixed. In this lesson, we will consider the parallel connection of conductors and the concept of equivalent resistance.
A parallel connection of conductors is a connection in which the beginnings and ends of the conductors are connected together. In the diagram, such a connection is indicated as follows (Fig. 1):
Rice. 1. Parallel connection of three resistors
The figure shows three resistors (a device based on the resistance of the conductor) with resistances R1, R2, R3. As you can see, the beginnings of these conductors are connected at point A, the ends at point B, and they are located parallel to each other. Also, the circuit can have a larger number of parallel-connected conductors.
Now consider the following diagram(Fig. 2):
Rice. 2. Scheme for studying the current strength with parallel connection of conductors
We took two lamps (1a, 1b) as circuit elements. They also have their own resistance, so we can consider them on a par with resistors. These two lamps are connected in parallel, they are connected at points A and B. Each lamp has its own ammeter connected: A 1 and A 2, respectively. There is also an ammeter A 3, which measures the current strength in the entire circuit. The circuit also includes a power source (3) and a key (4).
By closing the key, we will monitor the readings of the ammeters. Ammeter A 1 will show a current equal to I 1 in lamp 1a, ammeter A 2 - a current equal to I 2 in lamp 1b. As for the ammeter A 3, it will show the current strength equal to the sum of the currents in each individual circuit taken, connected in parallel: I \u003d I 1 + I 2. That is, if you add the readings of the ammeters A 1 and A 2, then we get the readings of the ammeter A 3.
It is worth paying attention that if one of the lamps burns out, the second will continue to work. In this case, all the current will pass through this second lamp. It is very comfortable. So, for example, electrical appliances in our homes are connected to the circuit in parallel. And if one of them fails, the rest remain in working condition.
Rice. 3. Scheme for finding the equivalent resistance in parallel connection
On the diagram of Fig. 3, we left one ammeter (2), but added a voltmeter (5) to the electrical circuit to measure voltage. Points A and B are common for both the first (1a) and the second lamp (1b), which means that the voltmeter measures the voltage on each of these lamps (U 1 and U 2) and in the entire circuit (U). Then U = U 1 = U 2 .
Equivalent resistance is the resistance that can replace all the elements included in a given circuit. Let's see what it will be equal to in a parallel connection. From Ohm's law, we can get that:
In this formula, R is the equivalent resistance, R 1 and R 2 are the resistance of each light bulb, U \u003d U 1 \u003d U 2 is the voltage that the voltmeter (5) shows. In doing so, we use the fact that the sum of the currents in each individual circuit is equal to the total current strength (I \u003d I 1 + I 2). From here you can get the formula for the equivalent resistance:
If there are more elements connected in parallel in the circuit, then there will be more terms. Then you have to remember how to work with simple fractions.
It should be noted that with a parallel connection, the equivalent resistance will be quite small. Accordingly, the current strength will be large enough. This should be taken into account when plugging into sockets. a large number electrical appliances. After all, then the current strength will increase, which can lead to overheating of the wires and fires.
In the next lesson, we will look at another type of conductor connection - serial.
Bibliography
- Gendenstein L.E., Kaidalov A.B., Kozhevnikov V.B. Physics 8 / Ed. Orlova V.A., Roizena I.I. - M.: Mnemosyne.
- Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
- Fadeeva A.A., Zasov A.V., Kiselev D.F. Physics 8. - M.: Enlightenment.
- Physics().
- supertask().
- Internet portal Nado5.ru ().
Homework
- Page 114-117: Questions 1-6. Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
- Can more than three conductors be connected in parallel?
- What happens if one of the two lamps that are connected in parallel burns out?
- If another conductor is connected in parallel to any circuit, will its equivalent resistance always decrease?
Series, parallel and mixed connection of resistors. A significant number of receivers included in the electrical circuit (electric lamps, electric heaters, etc.) can be considered as some elements that have a certain resistance. This circumstance gives us the opportunity, when compiling and studying electrical circuits replace specific receivers with resistors with specific resistances. There are the following methods resistor connections(receivers of electrical energy): serial, parallel and mixed.
Series connection of resistors.
When connected in series several resistors, the end of the first resistor is connected to the beginning of the second, the end of the second - to the beginning of the third, etc. With this connection, a
the same current I.
Serial connection of receivers explains fig. 25 a.
.Replacing the lamps with resistors with resistances R1, R2 and R3, we obtain the circuit shown in fig. 25, b.
If we assume that Ro = 0 in the source, then for three series-connected resistors, according to the second Kirchhoff law, we can write:
E \u003d IR 1 + IR 2 + IR 3 \u003d I (R 1 + R 2 + R 3) \u003d IR eq (19)
where R eq =R1 + R2 + R3.
Therefore, the equivalent resistance of a series circuit is equal to the sum of the resistances of all series-connected resistors. Since the voltages in individual sections of the circuit according to Ohm's law: U 1 =IR 1; U 2 \u003d IR 2, U 3 \u003d IR h and in this case E \u003d U, then for the circuit under consideration
U = U 1 + U 2 + U 3 (20)
Therefore, the voltage U at the source terminals is equal to the sum of the voltages across each of the resistors connected in series.
From these formulas it also follows that the voltages are distributed between series-connected resistors in proportion to their resistances:
U 1: U 2: U 3 = R 1: R 2: R 3 (21)
i.e., the greater the resistance of any receiver in a series circuit, the greater the voltage applied to it.
If several, for example n, resistors with the same resistance R1 are connected in series, the equivalent resistance of the circuit Rec will be n times greater than the resistance R1, i.e. Rec = nR1. The voltage U1 across each resistor in this case is n times less than the total voltage U:
When receivers are connected in series, a change in the resistance of one of them immediately entails a change in voltage on the other receivers connected to it. When turned off or disconnected electrical circuit in one of the receivers and in the other receivers, the current stops. Therefore, serial connection of receivers is rarely used - only when the voltage of the electrical energy source is greater than the rated voltage for which the consumer is designed. For example, the voltage in the electrical network from which the subway cars are powered is 825 V, while the nominal voltage of the electric lamps used in these cars is 55 V. Therefore, in subway cars, electric lamps are switched on in series with 15 lamps in each circuit.
Parallel connection of resistors. When connected in parallel several receivers, they are switched on between two points of the electrical circuit, forming parallel branches (Fig. 26, a). Replacing
lamp resistors with resistances R1, R2, R3, we get the circuit shown in fig. 26, b.
When connected in parallel, the same voltage U is applied to all resistors. Therefore, according to Ohm's law:
I 1 =U/R 1 ; I 2 =U/R 2 ; I 3 \u003d U / R 3.
The current in the unbranched part of the circuit according to the first Kirchhoff law I \u003d I 1 +I 2 +I 3, or
I \u003d U / R 1 + U / R 2 + U / R 3 \u003d U (1 / R 1 + 1 / R 2 + 1 / R 3) \u003d U / R eq (23)
Therefore, the equivalent resistance of the circuit under consideration when three resistors are connected in parallel is determined by the formula
1/R eq = 1/R1 + 1/R2 + 1/R3 (24)
Introducing into formula (24) instead of the values 1/R eq, 1/R 1 , 1/R 2 and 1/R 3 the corresponding conductivity G eq, G 1 , G 2 and G 3 , we get: the equivalent conductance of a parallel circuit is equal to the sum of the conductances of the resistors connected in parallel:
G eq = G 1 + G 2 + G 3 (25)
Thus, with an increase in the number of resistors connected in parallel, the resulting conductivity of the electrical circuit increases, and the resulting resistance decreases.
It follows from the above formulas that the currents are distributed between the parallel branches in inverse proportion to their electrical resistances or in direct proportion to their conductivities. For example, with three branches
I 1: I 2: I 3 = 1/R 1: 1/R 2: 1/R 3 = G 1 + G 2 + G 3 (26)
In this regard, there is a complete analogy between the distribution of currents in individual branches and the distribution of water flows through pipes.
The above formulas make it possible to determine the equivalent circuit resistance for various specific cases. For example, with two resistors connected in parallel, the resulting circuit resistance
R eq \u003d R 1 R 2 / (R 1 + R 2)
with three resistors connected in parallel
R eq \u003d R 1 R 2 R 3 / (R 1 R 2 + R 2 R 3 + R 1 R 3)
When several, for example, n, resistors with the same resistance R1 are connected in parallel, the resulting resistance of the circuit Rek will be n times less than the resistance R1, i.e.
R eq = R1 / n(27)
The current I1 passing through each branch, in this case, will be n times less than the total current:
I1 = I / n (28)
When receivers are connected in parallel, they are all under the same voltage, and the mode of operation of each of them does not depend on the others. This means that the current flowing through any of the receivers will not significantly affect the other receivers. With any shutdown or failure of any receiver, the remaining receivers remain on.
chennymi. Therefore, a parallel connection has significant advantages over a serial connection, as a result of which it has become the most widespread. In particular, electric lamps and motors designed to operate at a certain (rated) voltage are always connected in parallel.
On DC electric locomotives and some diesel locomotives, traction motors in the process of speed control must be switched on for different voltages, so they switch from serial to parallel connection during acceleration.
Mixed connection of resistors. mixed connection a connection is called in which part of the resistors is connected in series, and part in parallel. For example, in the diagram of Fig. 27, but there are two resistors connected in series with resistances R1 and R2, a resistor with resistance R3 is connected in parallel with them, and a resistor with resistance R4 is connected in series with a group of resistors with resistances R1, R2 and R3.
The equivalent resistance of a circuit in a mixed connection is usually determined by the conversion method, in which a complex circuit is converted into a simple one in successive stages. For example, for the circuit in Fig. 27, and first determine the equivalent resistance R12 of series-connected resistors with resistances R1 and R2: R12 = R1 + R2. In this case, the scheme of Fig. 27, but is replaced by the equivalent circuit of fig. 27, b. Then, the equivalent resistance R123 of the resistors connected in parallel and R3 is determined by the formula
R 123 \u003d R 12 R 3 / (R 12 + R 3) \u003d (R 1 + R 2) R 3 / (R 1 + R 2 + R 3).
In this case, the scheme of Fig. 27, b is replaced by the equivalent circuit of fig. 27, c. After that, the equivalent resistance of the entire circuit is found by summing the resistance R123 and the resistance R4 connected in series with it:
R eq = R 123 + R 4 = (R 1 + R 2) R 3 / (R 1 + R 2 + R 3) + R 4
Series, parallel and mixed connections are widely used to change the resistance of starting rheostats during start-up e. p.s. direct current.
conductor resistance. Parallel and series connection of conductors.
Electrical resistance- a physical quantity that characterizes the properties of the conductor to prevent the passage of electric current and is equal to the ratio of the voltage at the ends of the conductor to the strength of the current flowing through it. Resistance for AC circuits and for alternating electromagnetic fields is described in terms of impedance and wave resistance. Resistance (resistor) is also called a radio component designed to be introduced into electrical circuits of active resistance.
Resistance (often denoted by the letter R or r) is considered, within certain limits, a constant value for a given conductor; it can be calculated as
R- resistance;
U- electric potential difference (voltage) at the ends of the conductor;
I- the strength of the current flowing between the ends of the conductor under the action of a potential difference.
When connected in series conductors (Fig. 1.9.1) the current strength in all conductors is the same:
According to Ohm's law, voltage U 1 and U 2 on conductors are equal
When connected in series, the total resistance of the circuit is equal to the sum of the resistances of the individual conductors.
This result is valid for any number of series-connected conductors.
When connected in parallel (Fig. 1.9.2) voltage U 1 and U 2 on both conductors are the same:
This result follows from the fact that at the branching points of the currents (nodes A and B) charges cannot accumulate in the DC circuit. For example, to node A in time Δ t leaking charge IΔ t, and the charge flows away from the node in the same time I 1 Δ t + I 2Δ t. Consequently, I = I 1 + I 2 .
Writing based on Ohm's law
With a parallel connection of conductors, the reciprocal of the total resistance of the circuit is equal to the sum of the reciprocals of the resistances of the parallel-connected conductors.
This result is valid for any number of conductors connected in parallel.
Formulas for series and parallel connection of conductors allow in many cases to calculate the resistance of a complex circuit consisting of many resistors. On fig. 1.9.3 gives an example of such a complex circuit and indicates the sequence of calculations.
It should be noted that not all complex circuits consisting of conductors with different resistances can be calculated using formulas for series and parallel connection. On fig. 1.9.4 shows an example of an electrical circuit that cannot be calculated using the above method.
