Improving the
Roco TEE RGP DMU (6)

Original page created on 24/10/2015; updated on 30/06/2020.

Trailer

Trailer board and tail lamp circuit

Wiring of the trailer

This wiring will be simpler than the motor car, because the plastic chassis has more uniform surfaces. To connect the front to the back, I use pieces of self-adhesive copper tape. Obviously, they must be isolated when passing on the ballast. I do not trust the layer of glue for this isolation. Electrician tape, here blue, is therefore first stuck to the ballast. On both ends of this one, the plastic chassis is isolated, thermally this time, where the soldering will be made, by pieces of 0.8 mm thick non-copper plated board with a point of cyanoacrylate or Uhu Strong & Safe.

Note that there are only three wires concerned, because the green wire is directly connected to the light strip.

On the left, the copper ribbons are connected to the wires coming from the coupling. On the right, they are connected to the tail lamp power supply.

Browse the image with the mouse to get a more detailed view.

Electrical coupling

To say it right away: it would surely be much easier and quicker to install a commercial four-pole electrical coupling. It has the advantage, by its symmetry, to allow coupling to each side of the same vehicle (which would not have an extraordinary interest here). But, given its size, I’m not sure it can work without stopping somewhere.

And here is mine, seen from below:

1. “Strong” hook on trailer side
2. Soldering is on the other side
3. “Weak” hook on motor car side
4. Soldering is on this side, directly on the connector pins
5. The tongue is thinned on the wire passing zone and has a “strong” hook

This coupling, of the rigid bar type, is made of 0.8 mm thick epoxy. It consists of two parts:

• the bar strictly speaking, the role of which is both mechanical and electrical, provided with a 1.27 mm pitch male connector, and whose tails are such that one is more easily disconnected than the other by a simple traction on the coupling. This bar is intended to remain hooked to the trailer;
• a tongue-shaped plug with a single dovetail, and provided with a female connector. This part is intended to remain attached to the motor car.

The most difficult to achieve is the tormented shape of the dovetails. Even if you have a digital milling machine, which is not my case, you will have to file the re-entrant angles, which must be sharp.

Then, soldering the wires (at 1.27 mm pitch) will seem a bed of roses.

A small advantage of this solution is that the space between the motor car and the trailer is reduced by 1 mm (because I decide!), compared to a standard coupling: the space between the two NEM housings, normally 15 mm, is here of 14, this without hampering the elongation.

With regard to the installation into NEM boxes, whose minimum internal height is 1.7 mm according to NEM 362, it is necessary to consider that the total thickness will be composed:

Notes

Note: based on the above model, I studied an electric coupling using professional components. See the article.

Latest tips

I forgot to mention it, even if it goes without saying: the light guides of the lamps have to be removed, but their ends must be cut and put back in their housing.

When removing an axle from the motor car, for example, to change a tyre, be sure to disassemble the brake linkages — which should not therefore be glued — as they may be damaged by the protruding hub of the wheels.

References of the components used

For LEDs, the supplier is the LED-Megashop shop on ebay. Prices vary according to quantity.

• LED for light strips: PLCC white LED 2800 K / 1200 mcd ref. 3528
• LEDs for lamps: PLCC BICOLOR LED 2700 to 3500 K / 1200 mcd ref. 142
• LED for frontal upper light: format 1206 white LED 3500 K / 500 mcd ref. 111

The bicolour LEDs, which are given for a colour temperature of 2700 to 3500 K, are, at least for mine, closer to 2700. Used alone, this would not be a problem. But in comparison with the frontal headlight at 3500 K, the difference is visible! I have more or less solved this problem by inserting for the latter a yellow filter cut out of a notebook protector.

For CMS resistors, I found a distributor in Poland whose prices are practically half lower than the lowest I found in France (€0.76 per 100 pieces of the same value, price 2015). Only small problem: the approximate translation of the site in English. This is Transfer Multisort Elektronik (TME). There is a very interesting feature on this site, which I would like to find elsewhere, especially when you have to order many articles: it is the possibility of sending them directly an Excel file, or a text file with separator, respecting of course some constraints on the columns order and contents.

The 1.27 mm pitch connectors are purchased from Conrad.

• Ten point female connector ref. 741198-62
• 25 point male connector ref. 741104-62. The picture is wrong, but it is the right component.

Last minute. Warning, warning!

According to the LED-Megashop shop, the bicolour LEDs proposed have their two diodes (red and white) oriented to the same direction. However, when I bought them in 2013, they were in the opposite direction, with the same reference. The tail lamp circuit of the trailer is valid only for the head-to-tail type!