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Difference between AC and DC Generator

Generator is a device which generates power or energy. As we know that the energy can neither be created nor be destroyed and hence the generator can transform the energy from one form to another and hence in turn produces energy in the desired form. The electric generator generates electricity by transforming mechanical energy to the electric energy. Some of the different types of electric generators are as follows:
  • Water turbine
  • Internal combustion engine
  • Wind turbine
The water turbine converts the mechanical energy produced by waterfall to the electric energy. The falling water imparts the potential energy to the turbine and rotates it. Due to this rotation the electric energy is produced.

Wind turbine converts the mechanical energy produced by the wind to the electric energy. The free flowing wind has potential energy which is imparted to the turbine which rotates it and hence the transferred mechanical power is converted to the electric energy.

The generators are also categorically divided into two types with respect to the type of current produced by them;
  • DC Generators
  • AC Generators
DC generator:

It is a machine which uses the principle of Faraday's Laws of Electromagnetic Induction. When a conductor cuts a magnetic field, a magnetic field of varying nature is generated. This varying magnetic field generates a current to flow in the current whose direction is opposite to that of the varying field and hence in turn it opposes the vary creator of itself. In this generator the coil or conductor is rotated in the field to produce current.


AC Generator:

It is similar to that of the DC generator which uses varying magnetic field to produce the current. In actual scenario either a conductor is rotated in the varying magnetic field or a varying magnetic field is created around a stationary conductor. In this generator the magnet is moved while the conductor is fixed to produce the current.

Difference between the AC and DC generator:
  • In the AC generators the current changes its direction in each rotation and hence the average current output is zero. In the DC generators the current never changes direction and is always in the one direction and hence the average current output is equal to the magnitude of current produced by it.
  • An AC generator may be easily converted to the DC generator by using a bridge rectifier in the output to rectify the AC to produce DC.
  • DC generator uses half ring collector to output the current while the AC generator uses two ring brushes to conduct the current output.
  • The DC generator can also be made by using two diode at the output of the AC generator so that in each cycle one of the two diodes conducts and the current is outputted. The DC so produced is pulsating DC.
  • In AC generators the coil is fixed while the magnet is movable while in DC generators the coil rotates in the fixed magnetic field.

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From Yahoo Answers

Question:

Answers:^^ what he said. An AC generator (often called an alternator) generates alternating current, a DC generator produces direct current.

Question:both these generators convert mechanical energy into electrical energy...agreed. but how? because in both the generators armature rotates but how dc generator provides unidirectional current? what is the mechanism. please help

Answers:It is quite simple ya. Armature rotates in both the cases. In first half rotation the induced current would flow from one end of the armature say end A to the other B within the coil. So at B heap of charges and at A a pit as charges have been dug out. Just for understanding purpose I give such an analogy. Certainly in the next half rotation, A will be getting heap and B will be the pit. OK. Because the rising end will always become pit and falling side will always get heap. It depends on the direction of the magnetic field also. So I've not gone to that much details. Now in case of AC generator, two slip rings each one connected to each end of the armature ie A and B. Suppose R1 is connected to A and R2 to B. Also there are brushes B1 always in contact with R1 and brush B2 with ring R2. So in the first half rotation, Current ie charges from heap B flow through B2 to A the pit through B1. Hence in the external circuit current flows from B2 to B1 via the load connected. Say L is the load, then current has flown through B2 L B1. Now in the next half rotation because of interchanging of the heap and pit right from B to A and A to B respectively, now current flows from A ie B1 to B ie B2. So current through B1 L B2. As far as the external circuit is concerned, the current flows in opposite directions in one full rotation. Hence because of altering direction of current flow it is named as Alternating Current. Simply AC. But in case of DC, we have to use our intelligence a little bit. What we have to do is the brushes connected would be in such a way that B1 is always having heap and B2 is always a pit. Then current will always flow from B1 to B2. Hence unidirectional. Hence DC. How can we achieve this? Simple ya. Instead two slip rings, we have to use only one ring but that has to be split into. This split ring as it rotates touch the brushes alternatively. That the one rises up would always be in contact with one half of the ring and so with one brush and the other going down would be in contact ever with the other brush. As rising is always have a pit and falling always get heap, the brush B2 will always be a pit and B1 be a heap. So current always flow from B1 to B2. But any way this unidirectional current will have varying magnitude and we call it by the name pulsating dc. So using filters we can make it as a steady dc. In some cases, as our friends have pointed out, just an ac generator giving out ac current and it may get rectified and filtered to have steady dc.

Question:the best website which is much helpful for the electrical engineer.

Answers:ac generators are better than dc generators. AC can provide three phase current which most of the heavy equipments require.

Question:like do the dc gnerators, commutators produce direct currents. or like does Ac gnerators commutators produce alternating current e.t.c.??

Answers:DC generator would have a rectifier built in to convert the AC to DC.

From Youtube

generators DC and AC :Simple video about different between Dynamo (DC generator) and Alternator (AC generator). I think this animation can be useful for education of basic about electricity. YOU CAN DOWNLOAD AND SAVE THIS VIDEO FOR EDUCATIONAL OR OTHER NON-COMMERCIAL USE.

Dc Generator :Check us out at www.tutorvista.com Simple direct current (DC) generators contain an armature (or rotor), a commutator, brushes, and a field winding. The interactive tutorial presented below examines the operation of a simple DC or direct current generator. Translate the slider back and forth to adjust the frequency of the current. Note that the voltage amplitude increases with frequency. A variety of sources can supply mechanical energy to the DC generator to turn its armatures in order for its coils to cut through the lines of force in a magnetic field. These sources include steam, wind, a waterfall, or even an electric motor. In a direct current generator, the commutator's job is to change the alternating current (AC), which flows into its armature, into direct current. To put it another way, commutators keep the current flowing in one direction instead of back and forth. They accomplish this task by keeping the polarity of the brushes stationed on the outside of the generator positive. The commutator is made up of copper segments, with a pair (of segments) for every armature coil being insulated from all the others. The stationary brushes, which are graphite connectors on the generator, form contact with opposite parts of the commutator. As the armature coil turns, it cuts across the magnetic field, and current is induced. At the first half turn of the armature coil (clockwise direction), the contacts between communicator and brushes are reversed. The first brush now ...