I found a really good site called Jacobs Online which is American - http://jacobs-online.biz/ .
They have articles which explain the best bits to buy – http://jacobsonline.biz/understanding_transformers.htm – the transformer is the key and wiring diagrams for your transformer - http://jacobs-online.biz/power_supply_design.htm . I imported mine from the States at a huge importation cost. I am sure one could buy the same thing cheaper in the UK. It is quite technical, but you basically have to vary the voltage from about 12 to 24 volts – you could use a train set transformer, but mine was disposed of when I was about 14 – many years ago!!!
This an extract from the site which shows the various transformers that are available
This is a graph to show the relative wire sizes and lengths which you can use.
You need variable voltage because for a 0.5 metre wire you probably need about 12volts whereas about 24 volts is needed for a 1.5 metre wire. You basically use a conventional light dimmer, a small pygmy light, a mains switch, a box to put the bits in, and three lengths of wire with plugs and sockets. I bolted the transformer to the base of the box, to keep it steady and in position. The diagram from the Jacobs online site speaks for itself:-
It is American, so for 110v read 240v. Don’t buy a dimmer from Jacobs as it is 110v and will not work on our system. I decided to put all my bits in a nice metal project box.
I used standard audio wire, and some thin earth wire.
I had a quite a task sourcing things but these were my bits. Most were found on Ebay
Transformer – I chose the one suggested by Jacobs Online which would produce a variable current of between 12 and 24 volts
Switch – standard -
Dimmer – don’t order the type that does not activate until it is generating 40watts – most home light dimmers do this. There is a type that activates immediately – you want the type which is used to power overhead ceiling fans. Detach the small cartridge to put into your component box
Project Box – 20 x 20 x 8cm metal box to house all the bits – see photo above
Banana Jacks, Crocodile Clips, & and Sockets eg.
Mains Lead & Socket (I got 5 metre as you can never has too much cable)
Inline Fuseholder and Fuse.
Pygmy Light and Holder – I had trouble finding something suitable but found a light on the Toolstation website which is ideal. The one I bought had an sprung on/off push switch, which I removed
The idea is that the light shows you at a glance if the dimmer push on/off switch is activated, and how many volts are being pushed through the transformer. I have tried it, and it seems to work well.