Coach Lighting
Colin Verry
Pictures by the author
Over the years OVER THE YEARS I have constructed twelve Ian Kirk coaches of LMS and LNER types. I followed in my father’s footsteps and chose to fit metal bogies rather than those in kit. I toyed with illumination, but after several attempts with rechargeable batteries, I gave up.
Having reached an age when climbing under a three-foot high outdoor baseboard to install the necessary wiring to run satisfactorily with DC operation is no longer easy, I decided to change to DCC. Suddenly the opportunity to have illumination relatively simply was open to me.
Having lost Maplins, I now purchase my electronic supplies from Rapid Online, obviously you may have your own chosen source. I use a Truopto 3mm warm white LED, maximum forward current 15mA. The electronics involved is relatively simple and I recommend the MERG publication Electronics for Model Railways. It’s free to download. The appropriate section is Chapter 13, Train Lighting, in particular page 15.
The circuit utilises an LM317 device, which can be configured as a constant current source. The beauty of this is that you can connect the LEDs in series without worrying about balancing resistors. Since the same current flows through each LED, all the LEDs in the chain should have identical characteristics. (Do not mix 5mA LEDs with 30mA LEDs.)
The maximum number of LEDs in the chain depends on three factors:
- The DCC voltage from your command station.
- The voltage drop in the LM317. The output can be expected to be 3V lower than its input voltage.
- The forward voltage drop of the LEDs used. Different coloured LEDs usually have different voltage levels before they illuminate (white LEDs are usually 3V)
The current you choose to feed to the LEDs need not be their maximum rated current. For example, my 30mA LEDs illuminate quite brightly at 10mA.
The circuit is simple to assemble on a small piece of strip-board, which will easily fit into the coach lavatory compartment and be invisible from the outside.
The benefit of this type of controller is that you can limit the current consumed and not overstretch your DCC system. I have limited the source to an output of 10mA and they all light very well. I decided on one per compartment, seven in total. The regulated output voltage is approximately 13.5 VDC, so I have four in series and three more in series in parallel as shown.
These are mounted on strip-board four copper strips wide by the length of the coach bulkheads and the lamps centred on each compartment, copper strip upwards, and lamps pushed through the board to point down.
Guard Coach Interior
side view
All this functioned well when stationary and then I arrived at the problem of current collection. I tried several iterations of plunger types, even simple phosphorbronze wipers. I was disappointed with them all, even though I had used the largest capacitor 4700 μF, there was always a noticeable flickering.
I rethought my approach completely. Ian Kirk’s coaches are plastic which is an excellent insulator. I chose metal bogies to add weight and these had fully insulated wheels, but if I converted these to one side uninsulated the other conducting, then it would be a simple matter to collect current from the track.
I already had wheels, but if you are starting from scratch you can purchase 3ft 7in wheels, one side insulated and the other uninsulated from Roxey Mouldings and others.
I decided that conversion was my best option. I gently pulled off one wheel from the axle and removed the plastic bush. Then using my fly press (pillar drill) I inserted a short length of ⅛in outside diameter copper tubing and trued it up on both sides with files and wet-and-dry paper, to simulate the plastic bush. I opened up the side of the tube facing the body of the axle and with a taper reamer and a 2.5mm washer behind the wheel, pressed it back onto the shaft with my press. The washer recreates the flange on the plastic bush and brings the wheel spacing back to design.
Pivot assembly below
and mounted pivot (right)
My bogies were from Wayoh and they utilise a No 16 flat-head rivet to provide flexibility between the bogie frame and the support plate. Poor connections are a pain and can often lead to failure, so I modified one side and replaced the rivet with a ¹∕16in outside diameter tube into which I inserted a length of extra flexible lead and soldered this into the side frame. This required a little fettling of the whitemetal side overlays but it guarantees a good connection when screwed to the pivot nut.
I am satisfied now; even outdoors the lights remain on and do not flicker. Was it worth 18 months, I am not sure, but when I start on my next batch I will know exactly what to do. I hope that this will be of interest to other members.
