Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Transformer output current question

  1. Oct 24, 2012 #1
    hello, i'm super noob. My understanding is not yet clear.

    it sounds like folks here are describing current as something that's output by the transformer, but i thought current does not exist until there's a load.

    so my question is, how big of a load can it handle (not sure what 'big' really means, but anyway....) ... i thought that was the OP's question.

    for example, i have a 12 volt battery rated at 5 amp-hours. if i step it down to 6 volts, would the secondary winding have a 'rating' of greater than 5 amp-hours?

    or rather, will i increase the effective amp-hours of the battery by stepping down its voltage? or, will the battery be able to drive a more demanding load? or, will i be able to draw more instantaneous current?

  2. jcsd
  3. Oct 25, 2012 #2
    Re: When transformers decrease voltage, do they increase the current?

    Good morning Johny radio and welcome to Physics Forums.

    You should not add on to old threads like this, you should start a new one of your own.
    It is perfectly legitimate to start with a small quote from an old one and ask for an explanation of something you don't understand.

    Transformers are usually four terminal devices.
    More complicated transformers do exist.
    That is they have two pairs of terminals called the input pair (also called the primary) and the output pair (also called the secondary).

    It is very important to realise that they are AC devices and do not work on DC so your query about connecting batteries does not form a valid connection method.

    The input and output terminals are usually electrically isolated from each other.
    The transformer has no source of (electrical) energy of its own.

    So yes, you are correct, nothing happens unless we connect the terminals to circuits.

    The primary termianls are connected across a source of alternating voltage.
    Current then flows in the primary circuit and creates a voltage between the secondary terminals by magnetic action.

    The ratio of the secondary voltage to the primary is a characteristic property of the transformer. So the secondary voltage is n times the primary.

    n can be equal to one, greater than one or less than one.

    At this point there is no secondary circuit, but if we now connect a load across the secondary terminals current will flow.
    In real world transformers the secondary voltage will drop slightly when 'on load' like this.

    This current is determined by dividing the secondary voltage by the load resistance.
  4. Oct 25, 2012 #3


    User Avatar

    Staff: Mentor

    << Posts moved to a new thread >>
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook