Favourite Photos...

Favourite Photos...
Reading Lines GP35 #3647

Monday, 6 July 2015

Double Head Dwarfs with SMD LED's...

Well after successfully installing the SMD LED into the single head dwarf it was time to move onto the more challenging double head version.

First step was to install the much thinner coated wire, these are around 32AWG.  These wire still have a plastic coating so it is easily removed.  Again I made sure that I pre-fluxed & tinned the SMD pads and wires first to ensure a quick and good bond of the solder.

The next stage was to coat the wired SMD LED with liquid electrical insulation, this is to prevent the SMD pads from shorting out onto the brass case of the Tomar Signals.  The case needed some filing to get the SMD case to fit into position so that light emitted came through the opening evenly.

As can be seen below the Bivar SMD LED fits quite well into the case of the Tomar signal.  The liquid electrical insulation (LEI) also helps to keep the SMD in place and aligned.

Below is the back of the dwarf signal and the LEI holding the the bottom aspect in place.  As can also be seen there are four wires for each LED, one common (black) & three (red) for each colour green, yellow & red.

The stage involved getting the second SMD wired and into the brass case, all of the wiring and both SMD LED's fit into the Tomar case quite well.  The LEI works really well to insulate the electrical connections and hold the SMD LED's in place, for added stability you could also CA them in too instead of relying on the LEI.

After the LEI had cured I powered up the SMD LED's to check there wasn't any shorting from the electrical pads to the brass case, and also to check the colour produced with differing resistors.  The output of these LED's are quite bright and as such could be reduced up to a 1000 ohm value with resistors, this would actually increase the overall LED life too.  

And the final the result...  A Slow Clear (CR1988 Signal Aspects).

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