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LEGO → System → Trains → 12V
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7864 Transformer / Speed Controller 12V is a Trains set released in 1980. It contains a single 12V transformer.

The speed regulator can be used for powering 12 volt and 4.5 volt trains by turning the control switch over. In the flipped over position, the switch will not rotate all the way, limiting the output to approximately 4.5 volts.

It includes one 0-12V socket used for powering the train lines, one 12V socket for the many switches that can be added so that points, signals or crossing barriers can be controlled, and one 13V socket.

On the bottom of the unit is a 'Bühler' logo and the input and output voltages table.

Other Features

The transformer incorporates two safety features:

  • A short circuit cut-out which severs power to the regulated output whenever the wires are crossed, or connected to a track layout that is inherently short circuited.
  • An overload cut-out which will pulse the regulated output should the motor draw too much power. This condition can occur if too many trains are operating on the same track - or if a non-LEGO motor is connected to the transformer.


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