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Battery eliminator Physics Project

Battery Eliminator is a device used to convert high voltage alternating current into low voltage direct current. A circuit arrangement is employed with which 220 volt alternating current is converted into 4 volt direct current. Since with the help of this appliance, the use of the battery is eliminated, therefore it is known as a battery eliminator. It consists of following parts :


Transformer :

                   Transformer device used to convert small alternating current at high voltage into low voltage alternating current or low voltage alternating current into high voltage alternating current. In our project step-down transformer is used.

Rectifier :

                   Rectifier device used to convert alternating current into direct current. Rectifier have two types.

          (i) Half wave rectifier

          (ii) Full wave rectifier.

                   In our project full wave rectifier is used which converts a full wave of alternating current into full wave of direct current.

Transformer

Transformer :

The transformer is a device used for converting a low alternating voltage to a high alternating voltage or a high alternating voltage into a low alternating voltage.



Principle :

                   It is based on the principle of mutual induction that is if a varying current is set-up in a circuit induced e.m.f. is produced in the neighbouring circuit. The varying current in a circuit produce varying magnetic flux which induces e.m.f. in the neighbouring circuit.

Step-down Transformer :

                   In our project step-down transformer is used :

                   This transformer converts high voltage at alternating current into low voltage alternating current. In step-down transformer the number of turns in primary coil remains large as compare to secondary coil.

Construction :

                   The transformer consists of two coils. They are insulated with each other by insulated material and wound on a common core. For operation at low frequency, we may have a soft iron. The soft iron core is insulating by joining thin iron strips coated with varnish to insulate them to reduce energy losses by eddy currents.

                   The input circuit is called primary. And the output circuit is called secondary.

Theory :

                   Suppose, the number of turns in the primary coil is NP and that in the secondary coil is NS.

                   The resistance of the coil is assumed to be zero. Let dq/dt be the rate of change of flux in each turn of the primary coil. If Ep be the e.m.f. in the primary circuit then.

                             EP  =  NP                                         (1)

                   We suppose that there is no loss of flux between the primary and secondary coils. Then, the induced e.m.f. in the secondary coil will be :

                             ES  =  NS                                         (2)

                   From equations (i) and (ii), we find :

                            

                   Ns/Np = K is called transformer ratio or turn ratio.

                   For step up transformer    K  >  1

                   For step down transformer  K < 1

                   That is for step-up transformer NS > NP, therefore  ES>EP.

                   For the step down transformer NS < NP therefore ES < EP.

Efficiency :  The efficiency of the transformer is given by :

                                     

                   If Ip and Is be the currents in the primary and secondary circuits.

                                     

                   For ideal transformer      = 1 = 100%.

                   Therefore ESIS = EPIP

or

                  

                   Therefore, for step up, transformer current in the secondary is less than in the primary (IS < IP). And in a step down transformer we have IS >  IP.

Energy Losses in Transformer :

                   In practice, the output energy of a transformer is always less than the input energy, because energy losses occur due to a number of reasons as explained below.

1.      Loss of Magnetic Flux : 

        The coupling between the coils is seldom perfect. So, whole of the magnetic flux produced by the primary coil is not linked up with the secondary coil.

2.    Iron Loss :

        In actual iron cores inspite of lamination, eddy currents are produced. The magnitude of eddy current may, however be small. And a part of energy is lost as the heat produced in the iron core.

3.    Copper Loss :

        In practice, the coils of the transformer possess resistance. So a part of the energy is lost due to the heat produced in the resistance of the coil.

4.    Hysteresis Loss :

        The alternating current in the coil tapes the iron core through complete cycle of magnetisation. So energy is lost due to hysteresis.

5.    Magneto restriction :

        The alternating current in the transformer may be set its parts in to vibrations and sound may be produced. It is called humming. Thus, a part of energy may be lost due to humming.

Rectifier

Rectifier :

                   The rectifier is an electronic device used to convert alternating current to direct current.

                   The P.N. Junction as Full Wave Rectifier.

Full Wave Rectifier :

                   It is a device used to convert full wave of alternating currents into full wave of direct current.

Principle

                   It is based on the principle that a crystal diode conduct only in forward bias and then an output current flows in the circuit. When D1 is forward biased, the D2 is reverse biased and vice-versa. The diode D1 and D2 send current through the load resistance in the same direction during both halves of the time period. This cause full wave rectification of the input power.

Construction

                   The full wave rectifier consists of two P-N junctions diodes connected to secondary part of the transformer. When input A.C. is applied across the primary coil (P) of a transformer. One terminal of the secondary coil (S) of the transformer is connected to the positive terminal of the junction diode D2. In the secondary part of the transformer a load resistance R1 is connected. The output is drawn across the two terminals of the load resistance.

Working

                   In case of a crystal diode as full-wave rectifier the two diodes D1 and D2 are used in such a way that during 0 to II crystal diode D1 becomes forward-bias and on output current I, flows similarly during next half cycle II and 2II crystal diode D2 becomes forward bias and on output current I2 flows in the circuit in this way a crystal diode converts full wave of alternating current into a full wave of direct current.

Efficiency of Full Wave Rectifier :

                   The efficiency of the full wave rectifier may be 80%.

working

                   Working of a Battery Eliminator : A battery eliminator consist of mainly three working parts, transformer, Rectifier, Filter circuit. In our project report step down transformer is used. This transformer converts high voltage alternating current into low voltage alternating current. This low voltage alternating current passes from rectifier which converts alternating current into direct current. In our project full wave rectifier is used. In full wave rectifier two diodes D1 and D2 are used in such a way that during 0 to II crystal diode D1 becomes forward - bias and an output current I, flow in circuit. Similarly during next half cycle II and 2II crystal diode D2 becomes forward bias and an output I2 flows in the circuit. In this way a crystal diode converts full wave of alternating current into a full wave of direct current. The direct current which we get from rectifier output circuit is fluctuating direct current. In order to make it pure direct current filter circuit are used. In our project capacitor is used as a filter circuit. It is an electrolytic capacitor of capacity 16V, 1000 microfarad. The output now available is 4 volt direct current and it may be suitably connected with the transistor.

 





 





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