Designing and Building a LED Fixture

[Hoppy]

Originally Posted by CardBoardBoxProcessor

so what exactly is needed? a DC converter.. then some resistor? and then just string them all together?

What is needed is:
A DC supply with a voltage just a little above the voltage drop across each LED times the number you have in series.
A LED driver which is an electronic device that holds a constant electric current through it so it powers that group of series connected LEDs at a constant current even when the voltage drop across them changes, as it does. That current, for Cree LEDs has to be 350 mA for the longest life, but not the maximum light output, 700 mA for the best combination of life and light output, or 1000 mA to get the maximum light output, but with reduced LED life.
A heatsink, to dissipate the heat generated by the junction of the LED, which would otherwise cause a quick failure of the LED.
A fan or fans, to cool the heatsink, and, if needed, a 12 VDC supply for the fan or fans.
Finally, a fat bank account or the ingenuity to build your own driver circuits and make your own heatsink.

The primary skills needed are the ability to solder very small connections quickly so you don't overheat the LED while soldering the wires to it, and enough mechanical skill to mount all of those LEDs on the heatsink, and assemble all of the electric parts into a fixture.

[Hoppy]

I'm ready to get my Master Electrician badge now! After lots of careful study, calculations, research into the basic theory behind LEDs, I was able to solve my latest problem - the all-dead LED problem. Just to test all of you, when you turn on an electrical device and it don't work, what is the primary probable cause? Think carefully - this is a trick question.

Do you give up? Well, today needed to work on something else in the garage, so I had to move the LED fixture out of the way first. So I picked up the "power Bricks", the DC supplies, and started to look for a good place to keep them, when I saw a short electrical cord laying on the floor. My Master Electrician skills then came into play. I went over my mental check list of short electrical cords, and checked off all of the possibilities - of which there was one. That is the cord that connects the 48 volt DC supply to the extension cord. Yep, it fell out.

So, it was time to test my analytical skills. I plugged it back in, plugged it into the extension cord, said "let there be light" and was immediately blinded again!

To avoid another of these complex electrical problems that seem to dog me, I ran and got the PAR meter - ok, I don't do much running now, but I got it in any case - and took some measurements. Another triumph for the Master Electrician. At about 20 inches from the light I got 50-70 micromols, just as I was shooting for!

The light is pretty uniform, hitting 70 only at what appears to be directly above a LED, but it could just be my unsteady hand trying to hold a constant distance as I moved the sensor around. In any case my design does give about what I wanted, at the height I wanted it, in air. With water in the picture I suspect the intensity will be a little more, due to the focusing effect of the air to water interface. I feel good again!

[CL]

That's good to hear, Hoppy. lol, it was unplugged

[Hoppy]

I started work on the linkage to support the fixture above the tank today. It should only take a couple of days to make that. Once that part is completed and installed on the fixture, I can replace my AHS light fixture and get some in-tank measurements of PAR. But, to do that I need to redo the aquascaping in the tank to get room to make the measurements. That isn't a problem, since I'm ready to do that anyway.

[sunfire99]

Any updates Hoppy?

[Hoppy]

Here is how it stands right this minute:



Tomorrow I plan to visit a local Grainger store for springs to assist it holding up the 8 pound weight of the fixture. Then, assuming that works out as my calculations say it will, I will clean up and heavily prune my tank, first because it badly needs it, and second, so I can get some PAR measurements that mean something.

There is a light at the end of the tunnel!

[CL]

Originally Posted by Hoppy

Here is how it stands right this minute:



Tomorrow I plan to visit a local Grainger store for springs to assist it holding up the 8 pound weight of the fixture. Then, assuming that works out as my calculations say it will, I will clean up and heavily prune my tank, first because it badly needs it, and second, so I can get some PAR measurements that mean something.

There is a light at the end of the tunnel!

I'm glad to see the hinge system again! It's also good to see that oyu are using the spring idea
Great DIY!

[eyebeatbadgers]

Very informative thread Hoppy, well done. How close (or not close) did you get to your budget?

[Hoppy]

Originally Posted by eyebeatbadgers

Very informative thread Hoppy, well done. How close (or not close) did you get to your budget?

Look!! Over there!! Isn't that Elvis Presley?

OK, no, it isn't Elvis.

Well, I was shooting for $150 budget, but I made enough mistakes and false starts, especially on the constant current device, that I ran over that. The last I figured it out, I was at around $170 for just the light fixture part, not the hood. With the hood it looks like it will be closer to $200-$225. Every time I did something it took a trip to HD to buy nickel and dime stuff, which today costs $5-$10. Yesterday I bought 3 little packages of screws, washers, and nuts, and it came to almost $5. I needed some adhesive to laminate two strips of 1/8" x 3/4" aluminum together, and that came to about $5. Do things like that enough times and you are spending real money. But a major addition was buying stuff for the printed circuit board. Because I used a local electronic hobby supply place, forgetting about Frys, those parts ended up costing about $20. Part of DIY is SIY (spend it yourself).

As I keep telling my wife, I have had about 2 months of solid, great entertainment from this project, and will enjoy it for many more months, all for around $200. If we decide to take in the Sacramento Jazz Festival this weekend it will cost us about $100 just for one day of enjoyment. So, it has to be viewed in perspective. (I have a degree in rationalizing, and that helps too!)

[airborne_r6]

Did you ever solve the problem of the 3 LEDs that were apparently burned out?

[Hoppy]

Originally Posted by airborne_r6

Did you ever solve the problem of the 3 LEDs that were apparently burned out?

No, those three still don't light up. I have been thinking about it, and the only things I can think of are to buy 3 more, or to solder wire to my multimeter probes, and then to the solder pads on the LEDs to see what the voltage drop across them is. But, once I found that I have plenty of light without them, I have not had an incentive to do much about them.

One option I just thought of is to have my wife plug the light in as I hold the probes on the solder pads, and keep my eyes averted so I'm not blinded as I watch the multimeter reading. I may actually try that.

[Minsc]

Really dark sunglasses, perhaps?

I'm looking forward to the PAR comparisons!

[Hoppy]

I finally got the balancing springs attached. It works, but those springs really have a load on them. It took two bloody knuckles to get the aluminum end pieces on the springs, too. This might be too dangerous to have suspended at eye level over the tank - if a spring breaks, a piece could be ejected into someone's face. I need to think about this some more, but, in any case, the light fixture is ready to install now. (After I do some heavy pruning and cleaning of the tank.)

[Regloh]

Very nice work! I like it.
It looks like you have access to a machine shop or something similar

I wouldn't be too concerned with the springs as those are extension springs. They should only collapse to one side if they break at one end. You could try "hiding" them inside a tube shaped housing of sorts, but that becomes impossible to assemble.
I would leave it the way it is. I had a desk lamp once that looked very similar.

I am looking forward to the light readings as well...

[Hoppy]

Originally Posted by Regloh

Very nice work! I like it.
It looks like you have access to a machine shop or something similar

I wouldn't be too concerned with the springs as those are extension springs. They should only collapse to one side if they break at one end. You could try "hiding" them inside a tube shaped housing of sorts, but that becomes impossible to assemble.
I would leave it the way it is. I had a desk lamp once that looked very similar.

I am looking forward to the light readings as well...

My "machine shop" is a hacksaw, two files, some silicon carbide paper, and a couple of hand drills. Aluminum isn't at all hard to work with, even when hardened to T6 as this stuff is. It seems "gummy" when you hacksaw it, and I found that my power "demolition" saw is much harder to use on it than a simple old hacksaw. It also polishes very nicely with silicon carbide papers.

I'm getting over my fear of those springs. The struggle to get the aluminum extensions on got to me for awhile. (Man should have evolved with three arms, not two.)