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Designing and Building a LED Fixture

138K views 399 replies 65 participants last post by  AquaDwell 
#1 · (Edited)
This is getting to be an obsession with me! Hours spent on the computer, searching for parts and data, sketching out design layouts, doing calculations, etc. So, I decided to share what I'm doing, hoping that cooler, more experienced heads will speak up where appropriate.

I have a 45 gallon tank, with about a 30 inch by 15 inch footprint, about 20 inches tall, with a PC light fixture mounted about 24 inches above the substrate level. My goal is to replace the PC guts with a LED array that won't break my bank account wide open, and will give me around 50-100 micromols per sq m per sec of PAR at the substrate level.

One approach is to use relatively low output LED's and many of them to get that intensity. Another is to use the fewest number of LED's that will do the job, but using high output units. The first discovery I made is that lower power LED's don't cost 1/10th of what higher power ones cost, so every arrangement I looked at, using many LED's ended up with a higher material cost than using just 3 high output LED's. So, here is the layout I decided to pursue further:


You can get this LED, http://www.luxeonstar.com/endor-reb...ma-p-179.php?zenid=mq7qbu6j6941aoe1im80dot2b2 with a lens to concentrate the light, for about $24 each.

Next I figured out the approximate angle of the cone of light I would need to get good coverage of the substrate with these. It turns out to be about 45 degrees. (The LED emits light in about a 160 degree cone, but the intensity drops pretty fast as you move from the centerline - the lens will partially correct that.)

To verify that this would give me enough light I found this chart to use to convert the LED lumens output to a PAR intensity at the substrate:
From this it looks like a good number to use is 70 lux per micromol per sq m per sec, where one lux is one lumen per meter squared. Since I will have most of the substrate getting light from 2 LED's I used 25 PAR units to calculate from: 25 x 70 = 1750 lumens per sq. meter. And, the area each LED will primarily illuminate is about a 20 inch diameter circle, or .3 meters squared. 0.3 x 1750 = 525 lumens. The LED I chose gives about 435 lumens output at 700 milliamps of current, but can be driven to 1000 mA, so this comes close to what I want.
 
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#82 ·
Small details take a long time! I made some stand-off brackets from sections of the left over aluminum channel, to hold the heat sink in place, and installed the switch which will change the current from 350 to 700 mAmps, plus the socket half of the power line connector.






The heat sink is just laying on the brackets now, while I decide how to get access to screw it to the brackets. I think I will use clip-on nuts on the brackets, with screws going from the outside of the heat sink into those nuts. But, first I have to find the nuts.
 
#84 ·
Yes, that's what I ended up doing. I looked for clip-on nuts, but none that I found could open wide enough for the 1/8" thick aluminum bracket. The brackets are 6061T6 aluminum alloy, which is a very strong, hard aluminum alloy, and they should hold threads very well. Tapping them was harder than usual for aluminum, as a result, but it works well now.

My last two trips to HD ended up with me leaving empty handed, but looking at hardware stimulates my creative juices, so each time I figured out a better way as I searched for what I though I wanted.

Incidentally, I used a combination tap drill thread tap to tap the holes. This is a drill for the first half inch, then becomes a tap for a half inch, followed by a countersink for the last bit. I bought it for another project, so I already had it, and it works extremely well in a cordless drill with speed control.
 
#86 ·
I'm finishing the wood enclosure today and tomorrow, plus probably the next day. It will be oak veneered on the outside and finished with polyurethane. The inside now has two coats of polyurethane, and a strip of aluminum foil glued along the front and back pieces to reflect the stray light down into the tank.

My LEDs left Hong Kong 2 days ago, so given the slowness of aircraft today, I can expect another week before they arrive here.:icon_eek: (I was sure Ford Tri-moters were all out of service now, but....)
 
#91 ·
My wife keeps asking why I need to keep building light fixtures. My answer is that I am getting at least 3 months of pleasure out of this one, learning about LEDs, how to make them work, figuring out circuits for connecting them and for the drivers, designing the heat sink, designing the enclosure and building it, etc. I consider it cheap entertainment. Oh, and it might be a nice light, too.
 
#92 ·
My wife keeps asking why I need to keep building light fixtures. My answer is that I am getting at least 3 months of pleasure out of this one, learning about LEDs, how to make them work, figuring out circuits for connecting them and for the drivers, designing the heat sink, designing the enclosure and building it, etc. I consider it cheap entertainment. Oh, and it might be a nice light, too.
I dont know about cheap entertainment, my DIY projects usually end up costing more than if I had just bought them. However, I totally agree that I would rather spend 3 months learning how to do something and at the end coming away with a new knowledge set and the product as opposed to just buying it and coming away with just the product. Plus I normally get one or two new tools out of it; "Sorry honey I have to buy it there really isnt another way to do this right."
 
#95 ·
This is getting to be an obsession with me! Hours spent on the computer, searching for parts and data, sketching out design layouts, doing calculations, etc. So, I decided to share what I'm doing, hoping that cooler, more experienced heads will speak up where appropriate.
Hoppy? Obsessed with DIY gear? Never! ;)

My current light, running 10 hours a day, is a single 55 watt PC
This LED fixture would use about 33 watts, saving me about 220 watt hours per day, or about 80.3 KW hours per year, at $0.17 per KW hour, saving me $14 per year. My bulb needs replacing about once a year at about $30 each time, with the shipping, for a total annual savings of $44 per year.
It sure seems like turning off your computer (several hundred watts) and looking at your existing tank with existing light would result in much greater energy conservation, and costs nothing out of pocket. Sorry, just had to say it! :)
 
#96 ·
Hoppy? Obsessed with DIY gear? Never! ;)



It sure seems like turning off your computer (several hundred watts) and looking at your existing tank with existing light would result in much greater energy conservation, and costs nothing out of pocket. Sorry, just had to say it! :)
Turning off my computer would make me depressed. If I am depressed I might take to visiting one of the local Indian Casinos and seeking pleasure from hitting jackpots. That would likely result in at least a bit more money down the drain than my projects cause. Then, of course, to help with that enjoyment of pulling slot machine levers, I would need liquid refreshment, and would most likely drive home afterwards, possibly causing a 10 car crash on the freeway, with the resultant lawsuits which again might run to more than my DIY projects cost, not to speak of the cost to society for housing and feeding me for a few years in a secure undisclosed location.

Man! I'm good at this. I gotta keep this somewhere to use on the wife.

Back to business:
http://www.woodcraft.com/depts.aspx?deptid=2122 is where I bought my veneer, at their local store here. I just use ordinary contact cement, since I'm not making furniture intended to last for centuries. The nice sharp corners are a result of planing with a miniature block plane, and using sandpaper. But, the real secret, which I rarely divulge is to take my photos from a great enough distance and at the right angle to hide the mistakes.

More business:
I have been stalled on my DIY driver project after discovering that my soldering skills are not going to allow me to use the pre-made circuit boards that look so nice. Last night it finally occurred to me that I have made several DIY printed circuit boards the old fashioned way, with tape, dots, and etchant. That allow one to space things and provide visible spots for solder. So, I have just finished laying out a circuit board design, and am ready to spend a bit more $$ on that - thus saving numerous lives on the freeway.
 
#98 ·
Cheers!

Those solder pads ARE LITTLE. This star is still managable. IMO, try not to use the Luxeon Rebel stars ever. Those solder pads are half this size. It is a nightmare to solder those.
 
#102 ·
Today I bought the stuff to make a printed circuit board for the drivers - prices are a lot higher for this stuff than the last time I did this, back about 30 years ago. And, of course the tape and little dots are smaller, and harder to work with, but I did get it ready for the ferric chloride treatment to remove all of the excess copper.


Tomorrow, I may make a few more of the lines wider. 700 mA seems like a lot of current for such thin lines.

Since I was spending money today, I also bought a tap drill and #4-40 tap to do the holes. I decided that the time spent threading 48 holes would be less than the time spent groping to put nuts on little screws if I didn't tap the holes. I quit totaling the costs now that a lot of it is duplicated as I change my mind, plus for tools and supplies I can use later.
 
#103 ·
Nice! About 30 yrs ago I did the same thing, built a temperature controller on a self-made circuit board like that. Oh the feeling of accomplishment. :tongue:

If you have the space/room/area, increasing the size of the copper conductors seems like a good idea.

Can't wait to see your original and the new fixture shining at a wall, side by side. :biggrin:
 
#104 ·
Nice! About 30 yrs ago I did the same thing, built a temperature controller on a self-made circuit board like that. Oh the feeling of accomplishment. :tongue:
That feeling is pretty close, in space, to the feeling of frustration when it doesn't work - I have experienced both.
If you have the space/room/area, increasing the size of the copper conductors seems like a good idea.

Can't wait to see your original and the new fixture shining at a wall, side by side. :biggrin:
Well I did increase some of them, but, of course, after I finished the etching process I wished I had widened them more. Oh well, it's only money.

My new and original fixture will never be side by side, and both operating. I only have one tank and I value my marriage much too much to go for another 45 gallon tank.

Back to business: The etching went easily, but eventually I will have to dispose of the used ferric chloride - nasty stuff.

And, with the added room, more appropriate to my eyesight and hand steadiness, the assembly soldering went like a charm.


Next will be installing this into the fixture housing and wiring it up as far as the leads to the LEDs. Then I will probably go back to mechanical things, since I have now figured out how to make one of my cantilever, parallelogram linkage supports with springs to help with the adjustment, and I want to make that for this fixture. That will mean another $15 for springs.
 
#110 ·
Wasserpest's idea about shining the old and new lights on the wall together has made me anxious to get to that point, so I started on mounting the LEDs instead of working on the mounting system for the fixture. I used a acrylic sheet to make a drilling guide to maintain the same spacing for all of the LED mounting holes:



Next will be tapping the holes, and I plan to use my cordless drill to do that. It can have the torque limiter set very low, and will operate very slowly, so it should work. Has anyone tried this?

EDIT: I now have 1/4 of the holes tapped, and the cordless drill makes it much easier than using one of those tap wrenches. With the torque limiter set very low I don't think there is much chance of breaking the tap. But, 36 more holes to go to find out.
 
#111 ·
The #4-40 holes are all tapped now, and the cordless drill method for tapping worked very well. When I started a hole I let the drill clutch slip, backed the tap up a bit, let the clutch slip again, backed it up, and next time just tapped straight through. 48 holes went fast, with the only breaks I took being to ease my back from bending over to do this.

Now the heat sink is installed, the ground wire hooked up, the + and - leads poked up to where they go, and once I get some heat conductive grease I will be ready to install the LEDs.


I suspect the soldering will be a real chore for me, but the solder pads look like they are big enough to make it I Dee ten Tee proof.

EDIT:
An electrical question: Does anyone have an opinion about whether or not the negative lead should also be grounded? The circuit diagram for the driver circuit shows it grounded, but I'm not so sure I think it is desirable to do so.
 
#114 ·
An electrical question: Does anyone have an opinion about whether or not the negative lead should also be grounded? The circuit diagram for the driver circuit shows it grounded, but I'm not so sure I think it is desirable to do so.
Keeping the neg lead grounded will always ensure that your negative potential is 0v. I usually ground all the negatives.
 
#112 ·
This is turning out to be an awesome fixture, Hoppy. I almost took the plunge yesterday and bought some led supplies, because this build is so inspiring. I wound up buying a 70 watt metal halide instead, but I'm also getting some leds to supplement the actinic lighting. Keep up the good work :thumbsup:
 
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