Welding Transformer Current Control Core Adjusting Method

Welding Transformer Current Control Core Adjusting Method

Introduction:- There are various types of welding transformers available. Single phase light duty for small fabrication work to large size for industrial work. Single phase transformer are light in weight and generally rated for 200 A welding current. There are few tapping in secondary winding for different current like 100, 125, 150 etc. These transformers work at 230 volt single phase supply.
Four heavy duty use transformers of higher rating comes in different sizes. These transformers input supply voltage is two phase 400 volt. Output current rating is 300 to 600 Amps. There are three points  on output side Common, Low and High. Common is connected to ground and welding lead is connected to low for up to 300 amps current and high for 300 to 600 Amps current. Open circuit out put voltage of welding transformer is nearly 90 volt while during welding it reduces to 50-60 volts. The primary and secondary winding uses strip conductor for winding. Primary winding have tapping for connection to 380 volt or 415 volt by jumper strip setting.

Current adjustment system:- When supply is given to primary winding it produces an alternating flux in the core. The secondary winding which is also wound on the same core linkage with the flux produces by primary winding. So voltage is induced in secondary winding and hence the welding current while welding. So to control the current we have to control the flux linkage to the secondary winding.

For that a by pass magnetic path is provided for flux with the help of adjustable magnetic core as shown in diagram. This core by passes the magnetic flux so flux linkage with secondary winding reduces which controls output current.this adjustable magnetic core slide up down in between the main core with the help of a current controlling handle.
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Resistance Capacitance and Inductance in series and parallel

Resistance Capacitance and Inductance in series and parallel

Resistance in series

When resistances are connected in series the current flowing through all resistance is same  suppose current is I amp
The voltage drop in R1 is    V1 = IR1
The voltage drop in R2 is    V2 = IR2
The voltage drop in R3 is    V3 = IR3

The total voltage  in circuit V = IR
Total voltage V = V1 ÷ V2 ÷ V3
Or  IR = IR1 ÷ IR2÷ IR3
Cancelling out I from both side then we get

R = R1 ÷ R2 ÷ R3

For example if two resistance of 5 ohms and 8 ohms are in series there equivalent resistance is equal to 5 ÷ 8 = 13 ohms.

Resistance in parallel

As shown in circuit three resistances R1, R2 and R3 are connected in parallel the equivalent resistance can be found as below.

Voltage across each resistance is same as V volt

Total current I = I1 ÷ I2 ÷ I3
By ohms law  I1 = V/R1,     I2 = V/R2    and     I3 = V/R3
Summing up all three current total current
I = I1 + I2 + I3
Or
V/Req  = V/R1 ÷ V/R2÷ V/R3

Cancelling  V in both side we get

1/Req = 1/R1 ÷ 1/R2 ÷ 1/R3

For example two resistance of 4 and 12 ohms are connected in parallel there equivalent resistance is

1/R = 1/4 ÷ 1/12 = (3÷1)/12 = 4/12 = 1/3 ohms

There fore R  = 3 ohms

Capacitance in series

Similarly in capacitance if three capacitance are connected in series as shown in figure the equivalent capacitance  can be find as below

If the capacitors are connected in series the charge on each capacitor is equal to total charge Q.
voltage across each  capacitors is given by

V1 = Q/C1,   V2 = Q/C2    and   V3 = Q/C3

Total voltage V = Q/Ceq

Total voltage V = V1 + V2 + V3

Or   Q/Ceq = Q/C1 + Q/C2 + Q/C3

Cancelling  Q in both side we get

Or     1/Ceq = 1/C1  ÷  1/C2  ÷ 1/C3

Capacitance in parallel

If three capacitance are connected in parallel as shown in figure the equivalent capacitance is given by

In Parallel voltage across each capacitor is equal to applied voltage V
Charge on capacitor is

Q1 = VC1,   Q2  = VC2     and   Q3 = VC3
Total charge Q = Q1 + Q2  + Q3   eq --(1)
Putting value of  Q1,  Q2,  and Q3  in eq (1) we get
VC = VC1 + VC2 + VC3

Cancelling out V on both side we get

Ceq = C1 ÷ C2 ÷ C3

Inductance in Series

For inductance if three inductance are  connected in series (not mutually linked) the equivalent inductance is equals to

L = L1 ÷ L2 ÷ L3

Inductance in Parallel

If three inductance are connected in parallel the equivalent inductance is given by

1/L  = 1/L1 ÷  1/L2  ÷ 1/L3

Simple ac circuit

If a resistance is connected to dc supply of voltage V the current I  through resistance R is given by ohm's law

I= V/R amp

But in case of  capacitance and inductance the term capacitive reactance and inductive reactance is used.

Capacitive reactance is equals to 1/2πfC.

Inductive reactance is equals to 2πfL.

Where f is the frequency of ac supply. These formulas are used for ac supply  of any frequency. For dc voltage calculations are done differently.

If a resistance, capacitance and inductance are connected in series then their effective resistance to flow  of  current is known as Impedance Z of the circuit. Z is given by formula

Now for ac circuit if voltage is Vrms, Impedance is Z then current is given by

Irms = Vrms/Z

The term RMS is generally not written but  it  is always there. All readings given by meters are RMS values.

Use of Transistor as Amplifier

Use of transistor as amplifier

Transistor is used in common emitter configuration to get higher gain. Supply voltage can be use as per transistor rating. Transistors maximum collector voltage, collector current, current gain are given in transistor's datasheet. Common emitter ciucuit emitter is connected to negative side of supply (NPN transistor). Collector is connected to positive side through a load resistance. To calculate load resistance value operating value of collector current is decided on the basis of transistor rating. Suppose a transistor has collector current 200 ma we can set operating value in range of 100 ma. The current can very from 70 to 130 ma when signal is applied. Value of load resistance is equal to supply voltage Vcc, minus collector voltage Vc,  divide by collector current ((Vcc - Vc) / Ic). Base is given biasing voltage from positive side of supply. For this base current is calculated by formula collector current Ic/current gain (alfa). Now base biasing resistance is equal to supply voltage/base current. These are rough calculations for easy to work. In this way dc biasing is over. We can check collector voltage, collector and base current by giving supply to the circuit. Now we can give input signal to base through a capacitor of 0.1 MFD and get amplified output from collector with a capacitor of 0.1 MFD. These values can be find in other practical circuit also. This is a single stage amplifier circuit. To get more amplification it needs to use three or for stage. For more power  final power output stage is used.

In emitter circuit emitter by pass capacitor and resistor are used to improve quality of signal by providing negative feedback.

In audio power amplifier stage two transistors are used in push pull configuration.

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Transistor basics as amplifier oscillator and switch

Use of transistor as amplifier

To use a transistor as an amplifier it is used in common emitter configuration. The operating collector current is set nearly half the max collector current with the help of collector load resistance and base biasing resistance. transistor never go in saturation or cutoff value of collector current. Some short of negative feedback is also given by providing emitter resistance and emitter by pass capacitor. This negative feed back improve the quality of signal amplified.

Use of transistor as oscillator

A transistor connected in common emitter configuration just like an amplifier circuit can be converted to a oscillator just by providing a positive feedback from output circuit to input circuit. In common emitter circuit the output wave form is always 180° out of phase with input wave form. if some part of output is fed back to input in additive phase  then it becomes oscillator. below is diagram of resistance capacitance phase shift oscillator.

Use of transistor as switch 

A transistor can be used as a switch to control small current load. Relay can  be controlled by a transistor to control heavy loads. In switch mode transistor is biased to either cutoff current (for switch off) or to saturation current (for switch on).Set reset flip flop can be used with transistor to get latching property.

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DC Motor direction control by two relay H bridge

DC Motor direction control

Small size permanent magnet  dc motor have two armature winding terminal for connection. Normally they are connected to positive and negative of dc supply and motor start in one direction. To change the direction it needs to interchange both wire. This is manual way of changing direction. To control motor with push button or joy stick it requires to use two relays contacts in H bridge configuration. Further we can use solid state IC based H bridge for controlling dc motor. It can also be interfaced with micro controller.

In H bridge configuration we use two relays R1 and R2 which have minimum of two change over contacts. Change over contact have three point ie 1 Common 2 NO contact and  3 NC contact normally it is shown on body of relay which terminal no is connected to which point. All relays have two point normally marked as a and b for coil connection. Relay comes in different ac and dc coil voltage. Relay may also have different no of contacts with different current and voltage rating. The voltage and current rating is to be selected as per load requrement. Coil voltage is selected as per control circuit voltage. Here we will use 12 volt coil. Conection of 12 v supply and motor is as shown in diagram.

Positive of battery is connected to NO contacts of relay R1 and relay R2. Negative of battery is connected to NC contact of relay R1 and relay R2. Motor positive is connected to common of relay R1. Negative of motor is connected to common of relay R2. These four contacts and motor in the circuit form a shape of english later H thats why it is known as H bridge configuration. We use two push button to give supply to relay R1 and R2. When push button 1 is pressed relay R1 picks up. Hence positive supply goes to positive of motor through NO contact of relay R1 and negative supply goes to nagative of motor with NC contact of  relay R2 and motor start running in forward direction. Similarly when push button 2 is pressed relay R2 picks up. Hence positive supply goes to negative terminal of motor through NO contact of relay R2 and negative supply goes to positive terminal of motor throgh NC contact of relay R1 and motor start running in reverse direction. Motor remains stopped when button are not pressed.

The circuit given below can also be used if you have set of 2 NO contact in relay. This circuit can be used for double the voltage than circuit given above..

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Domestic use of motors

Domestic use of motors

Introduction:-

Small size dc motors, brush less dc motors and steeper motor are used in various equipment. In computer and laptop small size brush less dc motor is used for running CPU and power supply cooling fan. In cd drive and dvd drive small size brush less dc motor is used for disc rotation.Small size dc motor is used for disc trey movement system. A small steeper motor is used for precise movement of lens system. In printer brush less dc motor and steeper motor are used for roller and printer head movement. Steeper motor are used in three d printer as well. Record players of old time uses single phase shaded pole motor of very small size. Three/four speeds were achieved by using stepped pulley. tape recorder were using small 6 volt dc motor.

small dc motor

brush less dc motor

steeper motor

Single phase motors

Single phase motor of different types and speeds are used in different appliances. A small 4 pole 1450 rpm capacitor motor is used in a table fan. Some small fan like cabin fan uses single phase shaded pole motor . Shaded pole motors not required capacitor. Simple tullu pump motor used in coolers are small shaded pole motor. The main fan motor used in coolers are kit fan motor normally 150 watt triple speed motor.It has three speed winding run at high medium and low speed with the help of speed changing switch. in addition to this exhaust fans are also used. These motors are of 1450 rpm 4 pole motor or 950 rpm 6 pole motor. 6 pole 950 rpm motor has less operating sound as compared to 4 pole 1450 rpm motor. Exhaust fans are size wise come in 12, 15, 18, 24 inches. but normally 18 inches are used in window coolers. Washing machine also use single phase capacitor motor one for drum rotation and other for dryer rotation. Speed control and timers are used for different washing cycles. In automatic machine micro controller, digital display and key pad are provided to operate machine in different washing mode. Ceiling fan motor is also split phase capacitor motor. in this outer body work as rotor. fan blade or fixed on outer body. the motor is generally 14 pole or 12 pole. 48 inches fan runs at 470 rpm whereas 56 inches runs at 390 rpm.
AC:- In air conditioner three motors are used. first one is heavy compressor motor sealed within compressor unit. It is capacitor motor.It run compressor to compress refrigerant vapor. Second one is condenser cooling fan motor. It is also capacitor motor approximately of 250 watt 1450 rpm. Some AC uses double speed motor in condenser cooling fan. These two motors are fixed in out door unit in split ac. where as fixed in outer side area of window ac. Third motor is blower fan motor 3 speed motor. It is simple capacitor motor with three or four speed winding as the design of AC. In window ac there is only one motor for condenser cooling fan and blower fan. This motor has double ended shaft. Motor is fixed in center. Condenser cooling fan is fixed on outer side shaft end whereas the blower fan is fixed on inner side shaft end. Here the speed of condenser fan is also changes with blower speed setting. Some cooler also have single motor with double ended shaft one side for fan and other side for pump.
Mixer grinder/ sewing machine/ hand drill machine uses single phase universal motor (ac dc series motor) it run at 5000 to 6000 rpm as per design of motor and load condition.This motor is 2 pole ac dc series motor. It has 2 pole field winding with three speed tapping, a armature and 2 carbon brushes. Armature winding trough carbon brushes, field winding, thermal cut-off and speed selector switch all are connected in series.

kit fan motor for  cooler

shaded pole motor                                                                 exhaust fan motor

radio receiver block diagram

Radio receiver working explanation with block diagram
Radio, Transistor or Television works on the same principle. First we will see working of radio in this post. In radio broadcasting station voice is converted in to audio signal with the help of microphone. The output signal from microphone is in the order of millivolt, so audio signal is amplified with the help of audio amplifier. All radio station works at different frequencies allotted to them. A oscillator circuit is used to  generate radio frequency voltage  known as carrier frequency . The amplified audio signal is then mixed with carrier frequency to produce modulated radio frequency. This process is known as amplitude modulation. This modulated radio frequency are then amplified in RF power amplifier and given to antenna which propagates the radio frequency to space surrounding earth.
The Radio used the opposite of this process. A block diagram of radio is given below

First RF signal is received with the help of Arial/antenna. Then this signal is amplified in RF amplifier stage. A local oscillator is used to generate high frequency signal. Then in mixer stage both RF signal and local oscillator signal is mixed to produce intermediate frequency signal (IF). IF signal is amplified in IF amplifier stage. This IF signal is sent to demodulator stage which converts IF signal to audio signal. This audio signal is sent to audio amplifier stage through volume control. Final amplified signal is sent to speaker which convert audio signal to sound.This is all in short. To catch a particular frequency from Arial a coil in parallel with capacitor is used known as parallel tuned circuit. The property of tuned circuit is that they produce highest impedance for resonant frequency. This property  makes them suitable to use in radio frequency selection circuit. Similar tuned circuit is used in local oscillator to produce selected radio frequency. The local oscillator coil frequency is 455 kHz more than radio frequency from antenna coil. when two frequencies mixed in mixer stage they produces their difference frequency 455 kHz as IF frequency. The capacitor connected in parallel with antenna coil and oscillator coil are variable gang capacitor. When adjusted by spindle both capacitor value changes simultaneously. This makes possible that both antenna coil frequency and oscillator coil frequency changes simultaneously and their difference remain constant 455 kHz IF frequency. This makes possible to change different station by changing the capacitor value. While changing band both antenna and oscillator coils are changed with the help of band switch. When coils changed frequency band is also changed and radio can be tuned for other band stations. For each band it need two coil one antenna coil and one oscillator coil. The number of coils is twice the number of bands.

Speed control of DC motor

The main function of a motor is to drive a load at required speed. Any mechanical load has its specific speed torque charecteristics. Motor has to supply more torque than load requirement to produce fast accelaration. When motor torque equals to load torque, speed of load and motor stabilised. DC motor has advantage of full range of speed control from 0 to max speed with full load torque at all speed. The rated rpm of DC motor is known as base speed of motor.Basically speed of motor is directly proportional to applied voltage to armature circuit and inversely proportional to field current. These principles are used as a basis for speed control. Various methos of speed control is as follows:-
1. Armature voltage control:- In this method supply given to armature is controlled from 0 to rated armature voltage by mean a mg set or with the help of thyristor converters. ward leonard method uses a mg set. small motor can also  be control with auto transformer with bridge rectifier. With this method we can control speed up to rated speed. After that speed can be further increased and  controlled by field control method.Ward leonard method is shown in fig in which motor m2 armature is connected with armature of generator G. voltage is controlled with field winding of generator.

2. Field control method:- In this system series field regulator is used for the control of field current. As field current reduces  motor speed increases and vice versa.Field diverter resistances are also used.

Classification of amplifier A B C

Classification of amplifier

1 Classification on the basis of operating point:- The amplifiers are classified on the basis of operating point selection. The amplifier are classified as class:-

Class A - In this full wave form of input signal is amplified. in this the output is of high quality but efficiency is very less.

Class AB - In this 'less than full but more than half ' wave form of input signal is amplified. in this the output is of quality and efficiency is between class A and class B amplifier.

Class B - In this half wave of input cycle is amplified. Two transistors are used in push pull or darlington pair configuration. its efficiency is better than class A amplifier.

Class C - In this less than 180 degree of input waveform is amplified. It has very high efficiency and used in tuned radio frequency amplification circuits.

2 Classification on the basis of uses:-

1 Audio amplifier- Used for audio frequency amplification. Audio frequency ranges from 20 Hz to 20 kHz.

2.IF amplifier - Used for intermediate frequency (455 kHz) amplification in radios. .

3 RF amplifier - Used for amplification of radio frequencies. It ranges from 500 kHz to 30 MHz for radio broadcasting.

4 Video amplifier- Suitable for video frequency amplification.

5. Many other uses requires differently designed amplifier. Mobile communication and satellite TV system work at very high frequency in the range of GHz. so each system need a specific amplification requirement.

Transistor types and configuration

Transistor types and configuration 

Types of transistor:- there are two types of transistors

1 PNP transistor:- inward arrow direction on emitter  lead.
2 NPN transistor:- outward arrow direction on emitter  lead.

Transistors has three lead known as base emitter and collector. There are two junction in a transistor, first is base emitter junction and second is base collector junction. As there are three point in a transistor, one lead is made common for input and output, in this way transistor can be connected in three ways. First as a common base circuit, second as common collector circuit and third as common emitter circuit.
Common base circuit is used for impedance matching it has gain slightly less than one. Low input and high output impedance.
 

Common collector circuit is used as a buffer stage also known as emitter follower circuit, its gain is slightly more than one.

The common emitter circuit is used for amplification purpose its gain is very high in the range of 100-500 as per design. In any transistor circuit base emitter junction is always given a forward bias and base collector junction is given reversed bias. So for PNP transistor emitter is connected to positive side, collector is connected to negative side trough a load resistance, and base is given a negative biasing voltage with respect to emitter. This make the dc biasing circuit completed. now signal voltage is applied to base through a coupling capacitor and out put is taken from collector circuit with a capacitor. capacitor is used to pass ac signal but to block dc voltage from different stage.

Similarly in NPN transistor biasing is done. the emitter is connected to negative side, collector is connected to positive side through load resistance and base is given a positive biasing voltage with respect to emitter. A single transistor makes a single stage amplifier whose gain is less so multi stage amplification is used to achieve high gain and high power amplification.

D C Motor Armature Constructional Details

D C Motor Armature Constructional Details

D C Motor armature is consist of armature core, winding, commutator and shaft etc. The core is made  up of  silicon steel laminations of 0.35 to 0.5 mm thickness.These laminations are stacked and pressed in hydraulic press and riveted to make armature core. There are slots on the periphery of armature core to hold armature winding coils. No of slots (N) are generally 12, 24, 36 fully divisible by number of poles (P). Number of poles are always in multiple of 2, like 4, 6, 8 etc. Number of coils are equal to half the number of slots in simplex winding, each slot holds only one coil side. Number of coils are equal to the number of slots in duplex winding here each slot holds two coil sides. Each coils has two coils side with number of turns T.

Armature winding:-

Lap winding:- lap winding is used for high current low voltage machines. The number of parallel path (A) is equals to number of poles. Example welding generator.

Wave winding:- Wave winding is used for high voltage  low current  machines. The number of parallel path (A) is equals to 2. D C Motor voltage is generally limited 400 volt due to commutator size becomes large.

Commutator:- the commutator is made of copper segments fixed on periphery of insulating material bush. number of segments are equals to number of coils in armature.
Shaft:- Armature core with winding and commutator are rigidly fixed on the shaft. Two bearings are also fixed on both side of shaft to provide free rotation of armature within field poles of motor.