Monday, 20 October 2014

AC Adaptor Power Supply – Acrylic Enclosure

This weekend I made an enclosure for my AC Adaptor. The requirements were pretty simple … make an enclosure that has holes for the power switch, potentiometer, input wires, output wires and for the nuts to anchor it to the base.

I also wanted the enclosure to be clear so that the LED power indictor would make the device light up when it was powered … I didn’t want to have to look for a single 5mm LED on a black enclosure, so I decided that it would be a good idea to make it from clear acrylic. It would also add to a 70’s kind of vibe, “Orac” from Blake’s 7.

Another reason that I thought that a clear enclosure would be good was that I had spent some time and effort in making the simple breadboard design uncluttered and “pure”, and I didn’t want to hide the electronics away from the world. It is what it is, and there is a certain aesthetic appeal.

So, with that in mind, I went and (carefully) hacked up some 5mm clear acrylic sheet. I did the rip sawing of the sheet using a jigsaw with a hacksaw blade (24 TPI – teeth per inch). I made a guide from a straight piece of pine that I had lying around and this gave me a piece that was about 10cm x 80cm. I then cut the work piece using a chop saw. I got some chip-out on the cuts with the chop saw because the blade was just a standard timber blade with 3 TPI. I’ll be getting a higher TPI blade for the chop saw when I can afford it.

After cutting the sides, base and lid, I then measured out where the holes should be, and the diameter of the holes. The Potentiometer needed a 6mm hole, the switch needed a 5mm hole and the holes for the wires and nuts were all 3mm.

Then i had to cut another top and another face piece because I had not accounted for the height of the breadboard inside the case (d’oh!). The breadboard sits on 4x12mm threaded nylon standoff spacers … I forgot the 4mm of nut that came through the bottom of the standoff.

I used an general purpose Tarzan’s Grip glue (the kind you use for gluing plastic models together). This kind of glue melts the plastic pieces together and forms a weld. You don’t want to use a cyanoacrylate (superglue) because:

  1. It doesn’t glue the pieces together well enough and
  2. It causes “ghosting” on the plastic … kind of a white smut on the surface that is very difficult to get off.

I then used some acetone to clean up the joints. You need to use some care with acetone in this case because it can also cause some ghosting and because breathing in the fumes is toxic. I dipped a cotton bud into the acetone and then rubbed the joints vigorously.

Then I sanded the edges until I was happy with the surface … I could have sanded more and I could have gone to a higher grit (I only went as high as a 600 grit). I didn’t want the joints to be invisible as I wanted them to catch some of the glow from the LED. This was going to highlight the edges and make them more of a feature.

Here is the end result.

Enclosure 01

With the power turned off … and

Enclosure 02jpg

With the power turned on.

At the moment, the top is just sitting on the enclosure. I want to make some acrylic hinges from some cut-off pieces so that the enclosure is all one piece.

The only real downside to using clear acrylic for the enclosure is that it shows up fingerprints very well … and I don’t want to keep cleaning it.

The next thing that I want to make for this is the bending jig for the heating element so that I can actually use it to bend acrylic. Well … that’s a project for later.

NOTE: After using this circuit with a 12V Adaptor, the potentiometer started smoking, so I would NOT recommend that you use it for anything beyond 9V. For 12V, you would need a higher resistance potentiometer at least.

Further Note: After more investigation, this is entirely the wrong approach for building a variable voltage supply. I’m now going to start looking at building one based on an LM317 transistor.

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