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Generators

Difference between AC and DC generator in 7 important points


Difference between AC and DC generator

When we talk about types of Dc generators we pointed to the difference between AC and DC generator, but before we deepen in that we should know that both AC and DC generators convert mechanical power into electrical power to produce electric current and both depend on their work on Faraday’s law of electromagnetic induction.

At this article, we will focus on 7 important points that clarify the difference between AC and DC generator.

The first difference between AC and DC generator According to design:

In contrast; Ac generator produces alternating current this current flows through a fixed coil and a moving magnet, the north, and south poles of the magnet make the current flow in opposite directions and here it produced.

Of course, Ac generator also has armature coil and commutators and here they rotate in a simultaneous manner.

The brushes are of carbon and they receive the current flows through the slip rings; the armature and the outside circuit are connected through only one brush.

For DC generator

As we illustrate before; Dc generator produces direct current (the current doesn’t change its direction) and this current flows through a coil rotates in a fixed field, and we attach the ends of the coil to a commutator which balances the charges flows into the generator.

It also has a commutator (slip rings) and armature coil and the current produced depends on the connection between the armature and the external circuit.

And of course we need a help to connect the commutator to the output circuit and that happens with the help of brushes.

The Second difference ” Armature” :

In Ac generator it’s constant it’s always the rotor.

In Dc generator, the armature may be the stator or the rotor.

 

The third difference “Commutator” :

Ac generator works with brushes and slip rings and it doesn’t contain commutator.

Difference between Ac and DC generator

Dc generator works with one commutator additional to the brushes and slip rings.

 

The Fourth Difference “Produced Voltage” :

Ac generator produced a very high voltage which varies in amplitude and time, and it has a normal 60 or sometimes 50 HZ.

Produced voltage of AC generator

 

DC generator produces a relatively low voltage which is constant in amplitude and time, the output frequency equals zero.

Produced voltage of DC generator

The fifth difference “Usage” :

Ac generators used  for power generation in office and  home to power small and electrical appliances like:

  • Vacuum cleaners.
  • Food Mixers.
  • Dishwashers.
  • Refrigerators.
  • Juicers.
  • And electrical fixtures.

That’s because AC generation and transportation across long distances is very easy.

Dc generator is used to power very large electric motors such used for:

  • Subway systems.
  • Also, it can be used with battery charge banks for mobile and off-grid uses.
  • Also in the flashlight.
  • Hybrid and electric vehicles.
  • Flat-screen TVs.

That’s because DC generator provides reliable and efficient energy supply in this usage.

The Sixth difference “advantages” :

Ac generator has the advantages of:
  • We can easily increase and decrease the AC current produced by transformers.
  • The energy losses in transmission are less than in DC generator.
  • It’s simple and cheap in construction costs.
  • The transformers also facilitate the distribution of the Ac voltage produced.

Dc generator has many advantages such as:

  • It has a simple design and construction.
  • It’s ideal for running big motors and big appliances which require direct current to provide power.
  • It’s able to charge batteries directly.
  • It reduces fluctuations described for some steady state applications by smoothing the output voltage by the regular arrangement of coils around the armature.

The seventh difference “disadvantages” :

As all other electric machines,  Ac generator has the disadvantages of:

  • They are high in cost.
  • High energy losses during transmission.
  • The output current produced  is 10 times more dangerous than the DC current

Unfortunately, DC generator has some disadvantages as:

  • Dc generator can’t be applied to a transformer so it’s difficult to distribute it.
  • There would be a voltage drop over long distances.
  • Dc generator has low efficiency because there are copper losses, eddy current losses, hysteresis losses and mechanical losses.
  • The construction is complex as it has a commutator and slip ring.

The waste of energy due to sparking occurred in air gaps.

Finally, to be fair we must tell you that Ac generators have the massive majority as we illustrated Dc generator brushes need periodic replacement at variance Ac generators need lower maintenance.

 


Electrical Engineer