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Homework Help: A question about transformers

  1. Dec 26, 2013 #1
    1. The problem statement, all variables and given/known data
    Hey there! I have simple problem:
    To start a spark in a car ignition system, voltages of 5-17kV are required. A transformer with winding ratio 1:100 is used with a 12V battery, so we get a 1200V voltage. How are higher voltages achieved in such systems?
  2. jcsd
  3. Dec 26, 2013 #2


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    Staff: Mentor

    The transformer turns ratio gives the voltage ratio only for sinewaves, i.e., AC of appropriate frequency. The coil in a car is designed to operate differently. It is supplied with interrupted DC and the high voltage output is defined by the more general induction characteristic

    [itex]voltage = k. di/dt [/itex]

    The faster the points interrupt the primary current, the greater is di/dt, hence a greater voltage pulse goes to the spark plug.

    http://imageshack.us/scaled/landing/109/holly1756.gif [Broken]
    Last edited by a moderator: May 6, 2017
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