Measure twice, cut once redux

It’s an old adage, and one that I, along with most others, have learnt the hard way.  Well, I just had another practical lesson that has cost me probably seven hours of work.  A couple of years ago we built a hardwood deck, and are very pleased with it, except for the decklights which all failed (see here).

Useless deck lights

The failure was due to what I think is dreadful design on the part of Micromark. The unit has a lid that is spot-welded to the main can, but water can get drawn inside by capillary action. And, the glass is not sealed to the lid, but has a rubber washer. I’m not sure what was the actual route in, but when the water is in there is no way for it to get out. Quite apart from the visual issue, the water also caused the LEDs to fail, as you can see in the discolouration in the photo below.  Just in case anyone else is searching on the internet to find out if others have hit this issue with these poorly designed lights, these are Micromark Twilight 66 units.

Failed decklight closeup

So, my thought was to simply buy a new set of lights, with a design that was actually waterproof.  No dice – there was nothing that had the same 32mm hole diameter.  So, my backup plan was to buy more of the same poor design, and waterproof the seams myself.  But, when I searched for 32mm units, I found that they seem to have been withdrawn.  I could get 20mm, 42mm or 66m … but not 32mm.  So, back to square one.

I had the old units, so I thought I could re-use those with new LED drivers.  It felt like it would be good to get a little more functionality, so I knocked up circuit that allowed two independent sets of LEDS to be controlled down just two wires, including voltage regulation to ensure even brightness – test set-up shown below with both sets on full brightness.

Test decklight replacement circuit

I put this in one of the old cans, as a lash-up just to try it out in the dark (you can see the silly little spot welds below) :-

Test decklight replacement

The result was …. useless.  It turned out that the distribution block for the lights was more than a simple splitter, but actually has some regulation built in … so it wasn’t possible to get AC to the lights without rewiring, and it is far from easy to re-wire since I can’t now get under the deck without taking all the deck boards off.  So, in a moment of irritation, I loked online to see if I could find the instructions.  As I looked at them, I found was the dimensions of the light variants,and this is where I get the measure twice moment.

The lights I have, that go through a 32mm hole, are not 32mm lights. They are 42mm lights.  The 32mm lights that are no longer available have 20mm holes.  I had assumed that the 32mm hole mean that these were 32mm units, and simply never checked.  The 42mm lights are still available, so the seven or so hours I had spent was wasted – I’ve bought a new set of lights, and sealed them properly using gap filling glue around the glass-metal boundary and the edges of the spot-selded seam.  Fingers crossed that these survive longer!

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