50 Watts Inverter Circuit

A 50 watt inverter might look quite trivial, but it can serve some useful purposes to you. When outdoors, this small power house can be used for operating small electronic gadgets, soldering iron, table top radios, incandescent lights, fans etc.

Let’s learn how to build this homemade 50 watt inverter unit, beginning with a brief description regarding the circuit diagram and its functioning:

 

Circuit Description

The circuit may be understood with the following points:

Referring to the figure, transistors T1 and T2 along with the other R1, R2, R3 R4, C1 and C2 together form a simple astable multivibrator (AMV) circuit. A multivibrator circuit basically is composed of two symmetrical half stages, here its formed by the left and the right hand side transistor stages which conduct in tandem or in simple words the left and the right stages conduct alternately in a kind of a perpetual “motion”, generating a continuous flip flop action.

The above action is responsible of creating the required oscillations for our inverter circuit. The frequency of the oscillation is directly proportional to the values of the capacitors or/and the resistors at the base of each transistor.

Lowering the values of the capacitors increases the frequency while increasing the values of the resistors decreases the frequency and vice versa. Here the values are chosen so as to produce a stable frequency of 50 Hz.

Readers, who wish to alter the frequency to 60 Hz, may easily do it by just changing the capacitor values appropriately.

Transistors T2 and T3 are placed at the two output arms of the AMV circuit. These are high gain; high current Darlington paired transistors, used as the output devices for the present configuration.

The frequency from the AMV is fed to the base of T2 and T3 alternately which in turn switch the transformer secondary winding, dumping the entire battery power in the transformer winding.

This results in a fast magnetic induction switching across the transformer windings, resulting the required the mains voltage at the output of the transformer.

Parts Required

You will require the following components for making this 50 watt homemade inverter circuit:

R1, R2 = 100K,

R3, R4 = 330 Ohms,

R5, R6 = 470 Ohms, 2 Watt,
R7, R8 = 22 Ohms, 5 Watt

C1, C2 = 0.22 uF, Ceramic Disc,
D1, D2 = 1N5402 or 1N5408

T1, T2 = 8050,

T3, T4 = BC316,
T5, T6 = 2N3055 (TO-220)

General purpose PCB = cut into the desired size, approximately 5 by 4 inches should suffice.

Battery: 12 volts, Current not less than 10 AH.

Transformer = 9 – 0 – 9 volts, 5 Amps, Output winding may be 220 V or 120 volts as per your country specifications

Sundries: Metallic box, fuse holder, connecting cords, sockets etc

 

Testing and Setting Up the Circuit

After you finish making the above explained inverter circuit, you may do the testing of the unit in the following manner:

Initially do not connect the transformer or battery to the circuit.

Using a small DC power supply power the circuit.

If everything is done rightly, the circuit should start oscillating at the rated frequency of 50 Hz.

You can check this by connecting the prods of a frequency meter across T3’s or T4’s collector and the ground. The positive of the prod should go to the collector of the transistor.

If you don’t own a frequency meter, never mind, you do a rough checking by connecting a headphone pin across the above explained terminals of the circuit. If you hear a loud humming sound, will prove that your circuit is generating the required frequency output.

Now it’s time to integrate the battery and the transformer to the above circuit.

Connect everything as shown in the figure.

Connect a 40 watt incandescent lamp  at the output of the transformer. And switch ON the battery to the circuit.

The bulb will immediately come ON brightly…..your homemade 50 watt inverrer is ready and may be used as desired by for powering many small appliances whenever required.

Breathalyzer circuit using 8051

Alcohol Breathalyzer circuit using 8051 microcontroller (AT89S51).

This article is about a breathalyzer circuit using 8051 microcontroller which outputs the blood alcohol content (BAC) from the breath. The BAC is displayed in percentage on a 3 digit seven segment display. The microcontroller used if AT89S51 which belongs to the 8051 family and the alcohol sensor is MQ135 gas sensor from Futurelec.

MQ135 gas sensor.

MQ135 is a stable and sensitive gas sensor which can detect  ammonia, carbon dioxide, alcohol, smoke, nitrogen dioxide etc. The sensor consists of a tin dioxide sensitive layer inside aluminium oxide micro tubes, measuring electrode and a heating element inside a tubular aluminium casing. The front end of the sensor is covered using a stainless steel net and  the rear side holds the connection terminals.

The ethyl alcohol present in the breath is oxidized into acetic acid while passing over the heating element. This ethyl alcohol falls on the  tin dioxide sensing layer and as a result its resistance decreases. This resistance variation  is converted into a suitable voltage variation using an external load resistor. The typical connection arrangement of an MQ135 alcohol sensor is shown below.

MQ135 alcohol sensor

MQ135 has different resistance values at different temperature and different concentration of gases. The manufacturer recommends to calibrate the sensor at 100ppm of ammonia or 50ppm of alcohol. The recommended value of the load resistor is between 10K to 47K.

Circuit diagram.

Breathalyzer using 8051

The voltage output of the alcohol sensor is converted into a digital format using the ADC0804 (IC1). The Vref/2 pin of the ADC is held at 1.28V using the voltage divider network made of R14 and R15. Vref/2 =1.28V means the step size of the ADC will be 10mV and the output of the ADC will increment by one bit for every 10mV increment in the analog input. Refer the datasheet of ADC0804 for a better grasp. Digital out of the ADC (D0 to D7)  is interfaced to Port1 of the microcontroller. Control signals CS, RD, WR, INTR are obtained from the microcontrollers P3.7, P3.6, P3.5, P3.4 pins respectively. R9 and C1 are associated with the clock circuitry of the ADC0804.

Capacitor C3 connected between Vin+ and Vin- of the ADC0804 filters of noise (if any) in the sensor output. If C3 is not used the digital output of the ADC will not be stable. This filter capacitor will surely induce some lag in the ADC response but it is not very relevant in this entry level application. The microcontroller performs required manipulations on the ADC digital output in order to convert it into BAC % and displays it on the three digit seven segment display. Port0 of the microcontroller is interfaced to the multiplexed three digit seven segment display. The drive signals for the threes digits are obtained from the microcontroller’s P3.0, P3.1, P3.2 pins respectively.

Program.

ORG 00H
MOV P1,#11111111B
MOV P0,#00000000B
MOV P3,#00000000B
MOV DPTR,#LUT
MAIN: MOV R4,#250D
      CLR P3.7
      SETB P3.6
      CLR P3.5
      SETB P3.5
WAIT: JB P3.4,WAIT
      CLR P3.7
      CLR P3.6
      MOV A,P1
      MOV R5,A
      SUBB A,#86
      JC NEXT
      SETB P3.3
      CLR PSW.7
NEXT: MOV A,R5
      SUBB A,#115D
      JNC LABEL
      MOV A,#00000000B
      CLR PSW.7
LABEL: MOV B,#5D
       MUL AB
       MOV B,#8D
       DIV AB
       MOV B,#10D
       DIV AB
       MOV R6,A
       MOV R7,B
DLOOP:SETB P3.0
      MOV P0,#01000000B
      ACALL DELAY
      CLR P3.0
      SETB P3.1
      MOV A,R6
      ACALL DISPLAY
      MOV P0,A
      ACALL DELAY
      CLR P3.1
      SETB P3.2
      MOV A,R7
      ACALL DISPLAY
      MOV P0,A
      ACALL DELAY
      CLR P3.2
      DJNZ R4,DLOOP
      SJMP MAIN
DELAY: MOV R3,#255D
LABEL1: DJNZ R3,LABEL1
        RET
DISPLAY: MOVC A,@A+DPTR
         CPL A
         RET
LUT: DB 3FH
     DB 06H
     DB 5BH
     DB 4FH
     DB 66H
     DB 6DH
     DB 7DH
     DB 07H
     DB 7FH
     DB 6FH
END

Notes.

• The MQ135 gas sensor requires around 5 minutes of preheat before the first use.
• The MQ135 takes few minutes to retrace back to its normal condition after a positive test (alcohol present in the breath).
• If there is no alcohol in the breath  the sensor output will swing back to its normal condition very fast.
• Read these articles Interfacing seven segment display to 8051 microcontroller , Interfacing ADC to 8051 microcontroller  before attempting this project.
• This breathalyzer circuit is just an entry level one and is not suitable for high end applications such as law enforcement or laboratory application.
• The logic for converting the digital output of ADC into BAC percentage was obtained using approximation techniques.

What are the Different Types of LED’s available

This article is a guide for any one who is interested in knowing about the different types of LED’s available in the market. This can be considered as a general informational guide on LED and a buying guide for hobbyists as well.  One important challenge I faced while writing this guide was to incorporate consumer LED’s and professional/hobbyist LED’s into a single article. Let your comments say if I have been successful in this attempt.

Over the years semiconductor technology has advanced to bigger heights. The result is what we see around us in the form of smart gadgets. LED or Light Emitting Devices have also been a part of this revolution as any LED is a semiconductor. Now we have LED’s which give better illumination with low power consumption. These LED’s have better life span too. Certainly these advancements have lived upto influence  the shapes,sizes & even the format of circuit in which an LED can be mounted. So that’s quiet exciting!

Miniature LED’s

These are the one’s you see almost everyday in your life as indicators in mobile phones, television sets and a range of digital devices. They are usually available in market on a predefined,standard size & shape. This is to ensure its compatibility to different circuit boards. Different companies manufacture these LED’s in 5V and 12V ranges. They come in a “ready to fit” mode which can mounted on circuit boards directly. Usually they don’t need support of any additional cooling systems like a heat sink.

High Power LED

These LED’s are the result of advancements in semiconductor technology. As the name hints, these LED’s are known for its high output. They are capable of producing light output with higher luminous intensity. High power LED’s come in different shapes & sizes. A common example of high power LED in daily use is “LED strips” that are used light walls & room interiors. A picture of the same (an LED strip) is shown below. High power LED’s has very high heat dissipation. These LED’s need to mounted along with a cooling system (usually a heat sink).

A note on LED Strips

LED strips are a classic example of high power LED’s put together into a commercial product. In this product, high power LED’s are mounted onto a super flexible circuit board. They usually come with an adhesive sticker on its back that the strip can be pasted on to surfaces like walls or wood. LED strips are used for decorative purposes.

Application Specific LED (AS-LED)

These are LED’s which are manufactured for a particular application in mind. Some examples are digital billboards, public displays, bi color & tri color LED’s. There are many other examples, which I can talk about.  A picture of the LED based digital display is shown below.

A bi color LEDis two diodes mounted on a single frame. It has 2 pins in which one is common. The common can be anode or cathode. A picture of bi color LED is shown below. This LED can produce 2 colors at different times. They are mounted in such a fashion that one diode will turn on for forward bias and the other will turn on for reverse bias.

A tri color LED is similar to bi color LED. It is 2 diodes mounted on a single frame with 3 pins.Another type of LED’s in practical use are RGB (Red, Green, Blue) LED’s.

Electrical Earthing / Grounding

Introduction

Electrical earthing / grounding is one of the most important aspects of any electrical installation. Earthing or Grounding is a technique which is as old as the use of electrical power on a commercial scale. The practice came in to existence in the early days of electricity when the systems in use were all ungrounded and that led to frequent hazardous incidents caused due to electric shocks.
The term Earthing or Grounding simply means connecting the electrical system  equipment to the ground by means of a suitable conductor. Such a ground connection provides a common return path for safe discharge of electricity to the ground.
A properly grounded electrical system serves mainly two purposes:
a) It prevents from the risk of electrical shocks to any human being coming in contact with the system.
b) It protects the connected equipment from any possible damage occurring due to leakage currents or lightening or voltage surges, by providing a safe passage to these currents to ground.
Earthing of an electrical system is achieved by inserting an electrode (plate type / rod type) in to the solid mass of earth and then connecting this electrode to the earth wire coming from the electrical equipment.

Earthing considerations, the basics

While it is easy to understand the definition of Earthing, the topic of Earthing and its application in practice is often the most misunderstood of all. It will therefore be worthwhile to explore some points about the basics of Earthing:

• The concept of Earthing is based on the fundamental assumption that – Earth potential is always considered at “zero”. i.e. Earth irrespective of where it is connected to, is always a zero potential ground mass.
• For the above reason, any electrical equipment or appliance when connected to earth (“earthed”), also turns to a zero potential.
• A good Earthing is one which gives very low resistance to the flow of current to ground.
• Therefore, it is important to see that the earth resistance is kept as low as possible.

Ungrounded System

This type of system is not in practice anymore. However, it will be worthwhile studying it beforehand. In an ungrounded system, the current flows from source to the load and returns back to source and complete the circuit. There is no point in this loop where the system is grounded. Due to absence of a ground connection, there is no way a fault current can pass out of the loop. (See fig below:)

In case in the event of any abnormal fault current, there will be occurrence of first fault by causing insulation failure at some point in the circuit. Due to ungrounded circuit, this fault will remain undetected and may lead to subsequent second fault and a possible short circuit and thus cause a severe hazard to the whole circuit and it will break down.

Neutral Grounded System

The solution to above issue of ungrounded system is provided by a Neutral Grounded system. This system avoids the risk of developing the first fault and eliminates subsequent risk of short circuiting due to second fault in the circuit.
In this type of grounding, one of the poles of the source is connected to the ground mass. This is also called “Neutral”, while the other pole that carries the charge to the load is called a “Phase”. The neutral conductor always carries the return current from the load.

In case in the event of any insulation failure in the phase conductor leading to high fault current, due to availability of a grounded conductor in the neutral line, the excess fault current will pass through to the ground. Through the ground path this current will safely return back to source to complete the circuit. Thus, through the use of grounded Neutral, the risk of equipment damage due to fault current is avoided by providing a safe passage to fault current to the ground.
It should be noted that in this particular type of system, the Neutral is always providing the return current path from load to the source. Hence for the same reason this conductor is always insulated from the ground. Due to this important function, the degree of insulation will also be same as phase conductor.

Grounded At Customer Side

In the previous section we have seen Neutral Grounding done at source side. This type of system although fine, but may not be adequate in practical situations where source is at a significant distance away from the load. In such situations, the fault current arising at fault point and travelling through the Neutral conductor would not be grounded at the nearest grounding point and hence the risk of damage to the electrical circuit would still be present.

A practical solution to this situation is by way of extending this ground reference to the customer location. All the electrical points and equipments at customer installation (that can become potential fault points in the event of failure), are connected to a common reference ground bus at customer side. All the metallic housing of the equipments are connected to this bus.
This type of earthing not only protects against insulation fault, but also protects the metallic body of the equipments from any potential electrical shocks.

Construction of a Transformer

The transformer is quiet simple in construction. As told earlier, it consists of two magnetically linked windings, wound on two separate limbs of iron. It consists of the following basic parts:

1. Core
2. Windings

CORE

Usually the core of a transformer is constructed with a material having high permeability, such as silicon steel laminations, so that the core losses such as eddy current loss and hysteresis losses are reduced. Since the steel sheets have a very high resistivity, so the current losses are greatly reduced.
A transformer core can be constructed in two ways, depending upon the arrangement of the primary and secondary windings. These two ways are:

1. Core Type construction
2. Shell Type Construction

Core type construction

If the windings are wound around the core in such a way that they surround the core ring on its outer edges, then the construction is known as the closed core type construction of the transformer core. In this type, half of the winding is wrapped around each limb of the core, and is enclosed such that no magnetic flux losses can occur and the flux leakages can be minimized.
This type of arrangement proves quiet useful for the flux circulation, such that each limb is covered by the windings and hence the flux circulates through the complete core. But during this circulations, a bit of leakages also occur.

Shell type construction

In shell type construction of the core, the windings pass through the inside of the core ring such that the core forms a shell outside the windings. This arrangement also prevents the flux leakages since both the windings are wrapped around the same center limb.

WINDINGS

Firstly, Arrangements of windings is also an important issue in the construction of a transformer.. The winding connected to the main AC power supply is called the primary winding, while the one connected to the load or some external circuitry is called the secondary winding.
Windings of a transformer are made up of a conducting material to allow the magnetic flux to build up and hence the current can be passes from one winding to another. These windings are wound on two separate limbs of iron to increase the magnetic flux as iron is an efficient conductor and exhibits excellent magnetic properties. These coils are also insulated from each other. Since both these coils are wound on two separate limbs and due to the distance between them, flux leakages also occur which reduce our magnetic flux density and results in a reduced magnetic coupling between the two coil windings.
To avoid this situation, the distance between the two windings is reduced, so that the flux leakages can be minimized and a strong magnetic induction can be created and sustained between the two coils. But this arrangement also does not completely eliminate all the flux problems, since the magnetic losses are still present.
In core type construction, these windings are arranged in a concentric manner on the limbs, while in a shell type core construction, the same windings are arranged in a sandwich like pattern.
Other than these two main parts, Transformer tank and Conservatory tank are also used in transformer construction:

Conservatory tank

Since some type of container is also required to keep the transformer core and windings in and to safely insulate them, so a tank is used to keep the laminating oil, to minimize its deterioration and maintain oil levels. This tank also contains some other important arrangements like a number of important sensors and a gas detecting relay as well, which acts as a gas sensor and rings an alarm if detects the presence of some unwanted gas and immediately secures your external circuitry by disconnecting the transformer.

That’s all for today, in the coming post we will throw some light on the losses of transformer. In transformer as we have seen the primary and secondary coils are magnetically linked hence the conversion of electrical energy into magnetic energy causes few energy losses which we will discuss in detail in the coming lecture.

What is a Transformer?

A Transformer is a device which transfers electric current from one circuit to another, usually by the principal of mutual induction. During this process, the frequency remains constant whereas the voltage can be increased or decreased according to the need.
This transfer of electricity occurs with the help of two coils. One of which is known as the Primary Coil, which is connected to a source of alternating current. The other is known as the Secondary Coil, and it is connected to an external circuit. This constitutes the basic structure of the transformer and is shown below:

Working principle of a transformer

Transformer works on the Principle of Faraday’s Law of Mutual Induction. This principle states that the rate of change of flux is directly proportional to the induced electromagnetic flux.
Similarly, in a transformer, when an alternating current flows through one of the coil, it creates a magnetic field around it, which constantly produces a changing magnetic flux and so, when another coil is brought near it, some of the EMF is also induced in the secondary coil as well. Since the secondary coil forms a closed loop, the EMF produces the current in it as well.
So in short, this mutual induction between the coils is responsible for transferring the electric energy.

These windings are usually made on an iron core to make the magnetic field stronger, and laminated afterwards, so that the flux does not weaken due to air, which is a perfect insulator. But still some power losses are observed such as Eddy Current losses and Hysteresis loss.

Types of transformer

Categorized on the basis of voltage build up, we primarily classify the transformers into two basic categories:

1) Step Up Transformer
2) Step Down Transformer

• STEP UP TRANSFORMER:

If we increase the number of turns in the secondary coil, such that they become greater than the number of turns in the primary coil, the induced voltage can be increased in direct relation. i.e. if the turns in the secondary are ten times the number of turns in the primary, then the induced voltage will also be ten times then the one in the primary.

• STEP DOWN TRANSFORMER:

Similarly, if the number of turns in the primary coil is more than the number of turns in the secondary coil, the voltage induced will be lesser than the original voltage.
This property of Transformer is really useful in transferring electrical energy especially over long distances. To avoid power losses, initially a step down transformer is used and at the receiving end, a step up transformer is used which builds up the voltage on the required level. Such types of Transformers are known as single phase, two windings voltage transformers.

• 3 PHASE TRANSFORMERS:

But two phase, 3 phase or higher phase transformers can also be built up, especially for commercial and industrial purposes, where the load is quiet large, three phases are mostly used. Connections of the transformer in a 3 phase are shown below:

As clear from the figure, a three phase transformer will have three primary coils and three secondary coils. The manner, in which the three windings are connected with each other, can be a delta connection or a Y connection. Both of these are shown below:

If the coils are connected in series, forming a closed loop, then the connection is known as a delta connection, but if the three windings are connected such that all have a common point then a Y-type connection is formed. It has a neutral wire at the common end point. Both of these connections are equivalent and are inter convertible from one form to another.
In the next part of this tutorial, we will have a look on the construction of transformer, which I think is very essential for an electrical engineer to know. I will explain the basics of transformer design like windings etc. and will check how to design a transformer.
So stay tuned and join our newsletter via email so that you get these amazing tutorials rite in your mailbox. Take care.

Electrical engineering

Electrical engineering (sometimes referred to as electrical and electronic engineering) is a professional engineering discipline that deals with the study and application of electricity, electronics and electromagnetism.

The field first became an identifiable occupation in the late nineteenth century with the commercialization of the electric telegraph and electrical power supply.

The field now covers a range of sub-disciplines including those that deal with power, optoelectronic, digital electronics, analog electronics, artificial intelligence, control systems, electronics, signal processing and telecommunications.

Branches of electrical engineering

• Power engineering
• Control engineering
• Electronic engineering
• Microelectronics
• Signal processing
• Telecommunications engineering
• Instrumentation engineering
• Computer engineering