Railway Electrics and Electronics

So to the electrical and electronic systems for my model railway.

Since I don't have the money for a computer controlled DCC system, I decided to use the tried and trusted methods for wiring up and controlling the layout ... with a few differences.

First and foremost I needed to convert the AC mains current to a usable DC supply. Rather than buy or build one I rummaged through the workshop and came up with an old HP power supply. This either came from an old printer or a laptop, but I remembered picking it up at a car boot sale for less than a fiver. It's output is 18V DC at 3 Amps. More than enough for such a small layout.

The image below shows the PSU installed under the station baseboard.


When using non DCC control for a layout there are a number of systems that need wiring. Firstly you need to be able to vary the output to the tracks in order to control the speed of the locos. Secondly you need to be able to isolate various track sections so that only the locomotive you are using starts to move. Any other locos on the track need to be kept stationary.

If, as in my case, you are using point motors to operate the points, these need a separate control system. I wanted push button operation for mine.

Finally there is the possibility of adding lighting and electronic signals, but I chose not to have these on such a simple layout.

When using non DCC, it is nice to have a good looking control panel, so after designing all the electrical systems on paper I set about making a control panel.

Below is a sheet of anodised aluminium I had left over from a customer job. I bought these on e-bay, just search for 'Aluminium Sheet'. A 2mm thick piece should cost no more than a few pounds.

I next drew out a 'mimic board' which follows the track plan. This allows switches and buttons to be placed in an ordered and easy to follow pattern. I then drew on sections for the various controls. Below you can see the panel part way through construction. I have drilled all the holes and mounted the isolating switches and point motor push buttons. Again these buttons and switches can all be bought on e-bay for pennies.

The next image shows the back of the panel. All these connections will have to be wired up.

Below is the final panel front. Controls have had Dymo clear labels added along with mountings for the LED indicators. The point motor indicator panel is at the bottom left, the speed, direction and inertia panel is at the bottom right and the mimic board covers the top portion of the panel. 'Maes Ifor' ( Ivor's Field), is the name I chose for my fictitious South Wales area station.

Next I built a sloping box from leftovers of the MDF used for the corner section and glued / screwed the panel to the side of the station area. This can be seen below.

The point motors are operated by two solenoid magnets which, when energised pull a bar from side to side. This in turn operates the switch on the points changing their direction. The problem with this is that if the solenoids are directly energised from the PSU the coils may not have enough 'kick' to overcome the spring on the points, and energising them for more than a few seconds will burn out the coils.

In order to get around this problem a 'capacitor discharge unit is used to store up power from the PSU and then release it in a short, powerful burst when the button is pressed. With careful design, the circuit for this can also be used to ensure that once the charge has been sent to the point motor, if the button is held down inadvertently, no further charge reaches the coils until the button is released and the capacitor re-charged.

I set about designing and building the circuit. It is a very simple circuit and quite a few examples are available on the net. I simply used components 'reclaimed' from old devices. The capacitors were reclaimed from an old TV and the power transistor was from a huge number I had left over from another job. Almost any NPN power transistor would do. For example you could substitute a 3055 MOSFET from an old amplifier instead. I will publish all the circuit diagrams that I devised for the layout in another post.

Above is the capacitor discharge unit. The two blue cylinders are the capacitors, and the other minor components on the board for the protection and control circuitry. They are all glued to the base of an old battery box.

Box cover on ......

And finally installed onto the underside of the station baseboard.

Next came the wiring for the tracks. The wires were carried through holes in the baseboard and then through tie wraps to the controller box. Below shows the start of the wiring loom. I used red and black for the fixed feeds and brown and blue for the switched feeds (isolating sections).

The image below shows the wiring loom completed. the white wires are multi-core (six core alarm cable), that I had in the workshop. these will operate the point motors that require three cables each.

You can see the main PSU and the CDU under the board. The huge mass of coiled wires laying on the top of the baseboard will all have to be terminated in the control box! At this stage it is a good idea to ensure that all the cable ends have been clearly labeled.

The next thing to do is to design, build and test a controller. I wanted one that had the option of simulated inertia and braking for more realistic operation. When I checked the prices to buy one of these units I found that they were in excess of £75.00! Some were over a hundred. I thought I could do better for about a fiver!

I also wanted a switchable option for PWM control. This is a method of 'pulsing' the power to give better slow speed control. None of the manufacturers sold a controller that offered the range of features that I wanted, so ultimately I had no choice but to construct my own.

Till next time .......