Sunday, 24 January 2010

Working Lights


After a successful outing to the Beds and Bucks 009 Open Day it was time to finish off the lights. I had worked out the best combination of lights and resistor, in this case 2 lights with one 220 ohm resistor should give good life expectancy on the bulbs without too much heat loss dissipation from the resistor. You can manage without a resistor but it does help limit the current should something go wrong one day in the future.

Underneath the layout all wires go to terminal pads. These are simply made from copper clad board that has been sawn into strips and then had grooves added. The pads are flooded with solder whilst on the bench and as many as needed are glued to the underside of the board. To glue the pads I used glue sticks from electric glue guns but melted with the soldering iron - it was out ready.

The wires were all soldered on and then came the moment of truth - power was applied. All worked well for about 5 seconds before pairs of bulbs started flickering. What had I done! Power off quickly. This is where the resistor should have helped to limit the current. After much head scratching I realised that I had used liquid flux when soldering the wires and resistors to the pads. Not all the flux had evaporated so I ended up with liquid lying over the pads and starting to conduct in interesting ways. Dried it all off and it works fine.

In a moment of serendipity Phil Parker has an article this month in Hornby Magazine about soldering. It's a good read and after a brief email exchange I discovered that he would not typically use separate flux in electrical wiring. My belt and braces approach brought it all on myself!

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