12V was a voltage standard for LEGO Trains sets from 1969 until 1991 and complemented the older battery powered 4.5V standard. The power of the 12V system came from a mains powered DC Transformer delivered by add-on center conductor rails. TECHNIC also offered a 12V motor in the form of 880 12 Volt Motor which ran from 1977 to 1982.
In order to reach the newer 12V standard, the older – but still co-existing – 4.5V Trains system could be upgraded by using different 12V Trains accessories.
1st Generation (1969-1979) - the "Blue Era"[]
The first train sets numbered 720 (1969) and up operated on 12-volt electrified rails. They were powered from a 12V mains transformer. Automated points were also available, which were operated remotely from the transformer via buttons on the points themselves - differing from the remote operation of the later "Grey System".
This system was only offered in Continental European markets - it was never sold in the United Kingdom which only had the manual or 4.5V versions of the 'blue era' trainsets which were sold right up until 1980.
2nd Generation (1980-1991) - the "Grey Era"[]
In 1980, the Trains theme was completely renewed, with sets in the 77xx and 78xx numbering series. The builds were adapted to the Minifigure, which had been introduced in 1978, with buildings that were intended to integrate with the new Legoland Town theme. The colour of the tracks was changed from blue to grey, although the mouldings were changed to allow the tracks and sleepers to be snapped together, and the 12-volt transformer changed to support utility functions in a more streamlined style with control switches that docked alongside the transformer, following the design style of increasingly streamlined model train controls of the time. The utility functions now included remotely controlled points, signals, level crossings and de-couplers. The models gained a much more realistic appearance, including some with much longer carriage/wagon bodies and swivel bogies. The rolling stock bases were now again assembled from train-specific wheels and coupler and a greatly increased number of universal pieces. As with the previous generation, the electrical parts such as the train motor and the mains transformer unit (7864) were manufactured by Bühler on behalf of Lego. The transformer unit was also compatible with Technic motors, both 4.5V and 12V.
Upgrading a battery-operated train to a 12-volt electric train required changes to the train to fit the smaller, redesigned 12-volt motor underneath. The fixed wheels of the new 12-volt motor were black, finalizing the color scheme that had developed in the blue-track era, where 12-volt locomotives started to be distinguished by black wheels.
The 1980 train catalog and ideas book (7777) enticed Lego fans with night-time dioramas featuring lamp posts and lights inside the trains. Even though light bricks of the same size were available in both 12-volt and 4.5-volt guise, the train headlight/taillight (using unique prisms and holder bricks) and lamppost sets were normally only available with the expensive 12-volt light bricks included. Making these theoretically universal features available only as 12-volt items served to further elevate the 12-volt system away from the more limited 4.5-volt system.
Notable train sets include the 7740 Inter-City Passenger Train Set and 7750 Steam Engine with Tender, particularly the latter for its large wheel pieces which were not found in any other set. 7750 and the 7727 Goods Train also featured a red version of the 12V motor module that also has become a very rare and sought after component. Owners with a worn out red motor had no option but to replace it with a standard black one (7865) or break open the sealed unit and transplant the components.
No new sets for the 12-volt system were introduced after 1986, although the full range remained on sale leading up to its eventual replacement in 1991. Lego continued to supply accessories (but not complete sets) for the 12V system via its mail order service until 1993.
No further 12V sets were released after 1986, and the 12V powered trains were replaced by 9V trains in 1991. Spare parts and accessories for the 12V system (but not complete sets) remained on sale via LEGO mail order service until 1993.
Leaflet explaining the transition from 12V to 9V made in 1993 (in French)
12V Powered Sets[]
Trains[]
| Image | # | Set | Number of pieces | Minifigures | Price | Release |
|---|---|---|---|---|---|---|
 | 722 | 12V Electric Train with 2 Wagons | 151 | 1970 | ||
 | 723 | Diesel Locomotive | 95 | 1970 | ||
 | 724 | 12v Diesel Locomotive with Crane Wagon and Tipper Wagon | 155 | 1972 | ||
 | 725 | Freight Train Set | 425 | 2 LEGOLAND Minifigures | 1974 | |
 | 726 | Western Train | 287 | LEGOLAND Minifigure (x2) | 1976 | |
 | 727 | Locomotive | 134 | 1977 | ||
 | 7725 | Electric Passenger Train Set | 485 | 1 | 1981 | |
 | 7727 | Freight Steam Train Set | 570 | 2 | 1983 | |
 | 7730 | Electric Goods Train Set | 512 | 2 | 1980 | |
 | 7735 | Freight Train Set | 509 | 2 | 1985 | |
 | 7740 | Inter-City Passenger Train Set | 786 | 10 | 1980 | |
 | 7745 | High-Speed City Express Passenger Train Set | 736 | 10 | 1985 | |
 | 7750 | Steam Engine with Tender | 263 | 2 | 1980 | |
 | 7755 | Diesel Heavy Shunting Locomotive | 164 | 1 | 1983 | |
 | 7760 | Diesel Shunter Locomotive | 150 | 2 | $29.99 | 1980 |
Trains Accessories[]
Service Packs[]
| Image | # | Set | Number of pieces | Minifigures | Price | Release |
|---|---|---|---|---|---|---|
 | 11 | Locomotive Traction Tires | 8 | 1977 | ||
 | 12 | Wheel Bearings for Locomotives | 2 | 1977 | ||
 | 19 | Locomotive Piston Assemblies | 6 | 1977 | ||
| 1111 | Rubber Rims for Locomotive Wheels | 8 | 1977 | ||
| 1112 | Train Sliding Wheel Blocks | 2 | 1977 | ||
 | 1119 | Locomotive Piston Assemblies | 6 | 1977 | ||
| 1138 | Replacement Rubber Wheel Treads for Trains | 8 | 1981 | ||
 | 5069 | 2 Lighting Bricks 12 V | 2 | 1987 | ||
 | 5073 | Light Transmitting Elements | 7 | 1987 | ||
 | 5082 | Flashlight Unit 12 V | 1 | 1989 | ||
 | 5084 | Lighting Bricks 12 V for Signals | 1 | 1989 | ||
 | 5086 | Replacement 12V Motor | 1 | 1993 |
