LED mount - economical solution required

backboiler

I'm looking to put some LEDs along the top of a new wall I'm building outside the back of the house and would like to see if anyone on here has any innovative ideas on how to mount them in the wall.
Ideally the idea would be cheap, say no more expensive than the typical plastic LED mounts available - of the order of €0.10 to €0.20 per diode. I will use 47 LEDs in total and would hope to do them all in a few hours so take that into account. The electrical side of things is not a problem, I'm just looking for advice on the mechanical fixing of the LEDs into the bricks.

As things stand I have standard size bricks (215 x 102.5 x 65 mm) with a sinlge 6.5 mm hole drilled all the way through each. These can be enlarged if required, I suppose. The LEDs are your usual 5 mm (T1-3/4) type. The requirement is to make them mechanically secure and since these will be outside weatherproofing is important. They'll be located approx. 45 mm under the 55 mm-deep nosing of a step or projecting wall cap so shouldn't have any direct rain. It would be an advantage if I could get at them in case of trouble but that's not essential.

So there you are. Any ideas? I have a few but would be interested to see what other minds come up with so I'll not pollute the pool yet.
If anything's unclear, please let me know and I'll expand.

mathew

could you use some sort of filler or putty to fill the hole around the LED? Its a bit permanent I know, but its cheap, easy and durable..

backboiler

mathew wrote: »

could you use some sort of filler or putty to fill the hole around the LED? Its a bit permanent I know, but its cheap, easy and durable..

I'd still be a bit worried about moisture coming through from the top or through the brick. Maybe...

mathew

backboiler wrote: »

I'd still be a bit worried about moisture coming through from the top or through the brick. Maybe...

Moisture shouldn't be too much of a problem at the LED.. Only at the battery or power source.. Not entirely sure on your set up tho.. So i could be wrong...

backboiler

Have a look at the later pictures in this thread (posts 34 and 39).
http://www.boards.ie/vbulletin/showthread.php?t=2055284636
You'll see that the every top brick has a hole for an LED. That's the plan. What's not done yet is the top edge of the wall, which will be a paving plag overhanging the edge so offering protection from direct rain but there'll still be some finding its way through the material, picking up some nice component-lead-corroding minerals on its way, no doubt.

The power will come from a mains-powered 12 V supply located either in the house or in a shed so it'll be dry. Plan is to use 0.75 mm2 twin core flex behind the wall. LEDs have Vf of 3.4 V so they'll be arranged in 16 parallel groups of 3 (well 15 x 3 + 1 x 2), at 20 mA per group, total of about 320 mA at the near end tailing off to 20 mA at the far end.

Turbulent Bill

To be honest, I'd go for LEDs that come complete with a weatherproof housing, cable retention etc. - I'm sure something like this exists. The holders you showed in your first post are only really for PCB or internal applications, and there's a high chance of moisture ingress. You could try to seal or cover the mounting, but in that case it would be easier just to get the off-the-shelf parts. These would also be much simpler to replace if a single unit fails.

You should also do a test-run at night with a single LED in a simple circuit to check that the light intensity and viewing angle are what you want before installing them all. These can vary considerably for different LED types, so you could end up with a barely-visible glow or an AC/DC lightshow...

Great job on the brickwork by the way, looks very well.

spideog7

backboiler wrote: »

The LEDs are your usual 5 mm (T1-3/4) type.

backboiler wrote: »

LEDs have Vf of 3.4 V so they'll be arranged in 16 parallel groups of 3 (well 15 x 3 + 1 x 2), at 20 mA per group

Are you sure the forward voltage for these LEDs is 3.4v? It sounds very high for standard LEDs, normally they are around 1.7 or 1.8. Unless you're using high brightness such as some of the CREE products, but then you're talking about spotlights with a running current between 300mA to 1A.

Another thing worth checking is the viewing angle, most standard LEDs are only really visible from the front ~10 or 15 degrees because the plastic casing they are in has a lens incorporated into the front of it. I know you really only have less than 180 degrees anyway but it's worth noting.

Another suggestion would be to make sure all the circuitry is in the house/shed then you can always upgrade that again too, like putting in a current driver instead of resistors, this would allow you to dim the light when there was nobody in the garden, by dropping the current back a little. Then just heatshrink over your wire to LED conection which might help protect against moisture.

Just some thoughts, I think it'll look good though, so long as you get the ideal LED.

Regards

mr potato head

LED Chrismas lights for outdoor use?

backboiler

@spideog7,
Yeah, white LEDs - just blue ones with some yellow gunk on top - so they have a high Vf. The 2θ½ value for them is 25° as you say but it's enough to give the decorative point light source I'm interested in. The curves of the wall will help in this regard too.
I've thought of having the option of future proofing in case I want some disco action in the future but decided against it mainly because of all the additional wire it'd need. There's no way to efficiently connect 47 LEDs over a 15 metre line (or is there...?). For now I'm happy enough to have the limited control of maybe adding a voltage regulator to be able to dim them slightly if required.

@TurBill,
The enclosed LEDs would be the best solution no doubt but I'm looking to keep costs down and when you start talking waterproofing the price shoots up rapidly. Here's an example for about €4.50 each. You're dead right about the plastic ones and TBH at this stage I don't know why I mentioned them.
I've checked the brightness and it seems a bit over bright in a dark room at night but haven't tried it in the real location. Good thinking. As I mentioned above, I can tune down the supply voltage if I have to. 320 mA is easy enough to regulate.

Oh and earlier I forgot to say a thanks to mathew for the suggestions.

My original plan involved putting 1.6 mm (internal diameter) heatshrink around the LED lead solder joints, then 6.4 mm heatshrink around the wide ende of the LED back to the end of the leads and fill with some kind of sealant before shrinking, then seal the whole lot again with another layer of 6.4 mm heatshrink, bring the overall diameter of the assembly to just over 6.5 mm - the diameter of the holes. I've done one without the sealant part and it seems a nice snug fit. I'll need to see if I can put some more sealant in to stop the lamp getting pushed too far back as well.

Any better ideas from anyone?

backboiler

mr potato head wrote: »

LED Chrismas lights for outdoor use?

You know what, why didn't I think of that earlier? :rolleyes: They're probably not as bright as I'd have liked but would have done the job. Could pick them up for half nothing as well.
Ah well, my 50 LEDs are here so I'll use them but good idea. Thanks.

spideog7

Clearly you have thought this through

Yea white LEDs do generally have a higher Vf alright, should have thought of that. Wiring would be the only problem with controlling them centrally, you'd have to have 16 wires running out, one to each parallel group.

Best of luck with mounting them, take some pics when it's done.

stylers

use glue lined heatshrink (> 8 mm unshrunk dia) with one of the leads insulated with sleeving or 3mm heatshrink - time consuming but possibly the only way to make them entirely waterproof.. you'll only need short bits and its not terribly expensive in lengths from RS or farnell..