7864 Transformer / Speed Controller 12V

7864 Transformer / Speed Controller 12V is a Trains set released in 1980. It contains a single 12V transformer.
It was manufactured in Germany on behalf of Lego by Bühler Motor (whose logo appears on the base of the unit.
It includes one regulated 0-12V socket used for powering the train lines and one constant output 12V socket which can be used for connecting either lighting bricks, or for remote control switches used for signals, points, level crossings and de-couplers. There is also a constant output 13V socket but this is blanked off and is not normally used.
The regulated socket is normally used for powering 12 volt trains, but if the knob is flipped over, it cannot turn all the way around limiting the output to approximately 4.5 volts. The transformer can then be used to power TECHNIC motors 870 and 8700 
The set also contains elements to build a lever type control which fits onto the top of the speed regulating knob.
On the bottom of the unit is an 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.
== Gallery ==
CH_catalog_train_12V_p2_lr.jpg|Leaflet about the 12V to 9V transition presenting the 12V sets still available in Switzerland between 1991 and 1993, including this set.
7864-2.jpg
== External links ==
Category:Trains
Category:12V
Category:Trains Accessories
Category:7000 sets
Category:1980 sets