Monday, 27 August 2018

Enlightenment for Hartmut

There's something very romantic about a lighted passenger train passing through the night. Mysterious voyagers on their way to mysterious destinations, seen briefly as they cross the night-silent countryside.

It looks good on the garden railway too, a train chugging along in the dark garden. You can imagine yourself standing on a hillside, the rural tortillard trundling through the night, taking a few sleepy farmers home from the market. So it has been my goal since the beginning to have all the passenger trains illuminated.

Two of them I did a while back, but the third was still waiting. The engine is the LGB Saxon IV K 0-4-4-0 Mallett, which we christened Hartmut - alongside his bigger brother Helmut, the big 0-6-6-0 Mallet (2085D) of uncertain prototype. He has an authentic train of three coaches from the Royal Saxon Railway.

The first two trains are Thomas, with his coaches Annie and Clarabel, and Marcel with his two French coaches. In Thomas's case, it was partly driven by necessity. He has completely rigid wheels, with no vertical freedom of movement. He would constantly get stuck because often only one wheel is in contact with the rail on one side. Between dirty track and intentional dead sections - for example, on points - that can just never work. The solution was to adapt one of the coaches to collect power too, and run a cable to the engine. While I was at it, it seemed simple enough to add lighting as well.

So Thomas, and each of his coaches, have 4-pin JST connectors to form a link throughout the train. The first coach has LGB pickups on both axles, and metal wheels. In the roof are a couple of 6V grain of wheat bulbs in series, from Micromark.

Inside Thomas is a buck converter from eBay that reduces the 18V track power to something suitable to drive the lights. In real life there were just a couple of oil lamps, lit at dusk by the guard, very different from the bright fluorescent lamps in modern trains. You wouldn't be able to read, you'd just about be able to make out your neighbours' features - should you want to. Running the nominal 12V light chain on 9V gives just the right dim, yellowish gloom. The lights are controlled by the DCC decoder in the engine, meaning you have to remember to turn them on.

When I first installed the lights in Marcel's train, I didn't bother with the power pickup in the coaches, since he is an LGB engine with pick-up skates and some vertical flexibility to the wheels. But even so he sometimes has trouble especially on the siding pointwork. When I restored him to operation after his lengthy service as a guinea pig for my intelligent locomotive experiments, I added power pickup to the first of his coaches. Apart from that, the setup is identical to Thomas.

One thing I realised is that there's no point in being able to control the lights. During the day, and even quite a long way into twilight, they are invisible, so it's harmless to have them on. And at night, you always want them on. That means there's no need to connect to the locomotive, which simplifies things a lot. Instead I fitted power pickups on the first coach. This also meant I could use smaller 2-pin JST connectors, which are easier to connect between the coaches and less likely to get in the way of the couplings.

The grain of wheat bulbs work well enough but they are a pain to install. On the web I saw some LED light strips for LGB coaches, so I bought three of them. In fact they are just short segments of readily-available LED ribbon, with six LEDs, together with some connectors and a big (8200µF) capacitor for each one, so they don't flicker on dirty track. It would have been a lot cheaper and just as simple to have bought a 6-foot length of ribbon.

To finish the job needed a little eBay buck converter hidden on the floor of the coach, to turn the track power into something suitable for the LEDs. It turned out that 9V was just right for them, too. I used one of the 8200µF capacitors, so dirty track has no effect. The lights stay on for about 10 seconds even when the track power is turned off completely.

The little circuit board with (left to right) the big reservoir
capacitor, the voltage reduction board, and the
bridge rectifier.
In real life all trains carried - and still do - a red tail lamp. This is very important because it makes it easy to see whether part of the train has gone missing. The signalmen had to watch each train carefully to be sure the light was still there, day or night. If not, it was time to send an urgent message - a bell code of 4-5 in UK practice - to the previous signal box, so another train wasn't cleared to run into whatever was left behind. It has been on my list for a while to add a tail lamp to the long goods train, so I thought Hartmut's train should have one too.

The under-body wiring, with the wheels on the left side
removed.
In my box of LGB bits and pieces I found an LGB tail lamp. It's designed to clip on to a vehicle, and fits perfectly onto the veranda of Hartmut's coach. Whether that is the prototypically correct position, I have no idea. I searched for a picture of the tail end of an old-fashioned German passenger train, but to no avail. Goods trains evidently carried two tail lamps, one on each side as high as possible. The lamp comes with a bulb in a huge brass holder, that would be very conspicuous. I replaced it with a red LED, the wiring concealed behind the veranda. The wiring hides a 2K2 resistor which reduces the LED's brightness, though having watched the train at night, I think a higher value (lower current, less light) would have been better.

The LED strip installed in the roof, secured in place with two
little bridges of Sugru.
One unexpected problem I ran into is that the LED strips kept falling off the roof. They have double-sided sticky tape on the back, but it clearly wasn't up to the job. I added a layer of double-sided sticky foam, and then made little bridges of Sugru to be doubly sure. If you haven't used it, Sugru is wonderful stuff. It's a bit like epoxy putty, but much simpler to use since it doesn't have to be mixed. You open up a little foil envelope, take out a piece the size of the end of your thumb, and mould it to whatever shape you need. It is set reasonably hard after a few hours, and completely after 24 hours or so. And it lasts for ever. The first thing I ever used it for was to hold a heavy soap rack in place in the shower. After several years it is as strong as ever. I used quite a bit more to hold wires in place, especially underneath the carriages.

I put Hartmut and his train back together, keen to see them trundling around in the twilight. But I was disappointed. The lights came on, but Hartmut showed no signs of mobility. On the bench I discovered that his Zimo DCC decoder, which he has had since I first got him nearly 20 years ago, had died. Luckily I had a spare, but on that one the light outputs seem to be non-functional. Since Hartmut only ever goes in one direction, I just hot-wired the front lights to be on all the time. Running at night, I noticed that the interior light in the cab is way too bright, so that will need a resistor added somewhere.

After all that, Hartmut and his train are lit up like the others. They look very good and slightly mysterious as he chuffs slowly round the layout in the dark.

Hartmut and his train by twilight

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