Discussion in 'General Electronics Chat' started by xpn, Aug 25, 2009.

  1. xpn

    Thread Starter New Member

    Aug 25, 2009
    Hi All,

    I'm very new to this electronics stuff and hope that someone can help me. I've searched the forums but I don't think I know quite how to phrase my question to get some results so I apologize if this is a common question.

    While im learning 'electronics' I like to visualize the theory behind what I am doing. Now, I came across transformers in which voltage is stepped up/down by a ratio of turns between the primary and secondary coils. Now... upon reading a few electronics tutorials, the common explanation of what is happening is as follows:-

    As voltage is increased from primary to secondary coils, current is decreased by the same ratio.

    As voltage is decreased from primary to secondary coils, current is increased by the same ratio.

    Now this is the bit that I can't understand. In my early learning, I was taught that voltage is the potential difference, or force that allowed current to flow (I hope I got that right).

    So.. if this is the case, how can less force (voltage) lead to an increase in current (flow) ?

    If you haven't guessed im visualizing flowing water to try and understand the flow of electrons.

    Any help will be appreciated.
  2. KL7AJ

    Senior Member

    Nov 4, 2008

    Because the RESISTANCE is less. It takes less effort to cause the current to flow
  3. davebee

    Well-Known Member

    Oct 22, 2008
    Those simple phrases are hiding a lot of physics that are going on behind the scenes
    of the transformer, and are describing transformer action in a rather casual manner.

    Looking with a little more detail -

    Apply some voltage to the primary coil. Current starts to flow in the primary. A magnetic field builds around the primary coil. That magnetic field induces current flow in the secondary coil.

    The secondary current flow unbalances the charges in the secondary, producing a voltage across the secondary leads.

    If the secondary has the same number of turns as the primary then it produces the same voltage as was applied to the primary.

    If the secondary has twice the turns, then the magnetic field generated by the primary current acts on twice as many turns, and the voltage induced in each turn adds, resulting in double the voltage at the leads of the secondary.

    Each primary turn acts on twice as many secondary turns, so it only takes half the current in the secondary to couple magnetically with the primary magnetic field, so the current capacity of the secondary is half that of the primary.

    My point is that in this case, where the secondary voltage is twice the primary, that is what the explanation is referring to by the phrase "as the voltage is increased" leads to the current decreasing.

    Maybe a better way to describe transformer action is to note that the turns ratio of
    the primary to the secondary produces a similar voltage ratio from primary to secondary, and the secondary current will decrease by the same ratio. The result is that power in, which can be calculated as volts times amps, will equal the power out.
  4. GetDeviceInfo

    Senior Member

    Jun 7, 2009
    the transformer is a type of power converter.

    flowing water;

    high pressure, low flowing water drives a positive displacement motor which then drives a centrifugal pump via a speed increase gear train. The centrifugal pump now pumps a high volume of water at a lower pressure. The mechanics convert torque into speed via the gearbox.
    The transformer converts voltage to current via mutual inductance.