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DIY LED Pendant Light

27K views 164 replies 32 participants last post by  Hoppy 
#1 ·
There are some good reasons for using pendant lights. When a light fixture sits right on top of the tank, the PAR near the top of the tank is always much higher than that near the substrate. So, even if you use a light which gives you very low light at the substrate, up near the top of the tank you have far higher light intensity, making it more difficult to avoid algae problems. When the light is located a foot or more above the top of the tank, the difference in PAR between the substrate and near top of the tank is far less.

Lights hanging high above the tank make in-tank maintenance much easier, and more likely to be done. And, when you are doing it you can easily see what you are doing. Also, pendant lights can look very good.

A major disadvantage of high hanging lights is the spillover light, and the glare. Those can be minimized or even avoided if a well designed pendant light is used.

My low light 65 gallon tank has a LED light sitting right on top, with the PAR at the substrate around 25 PAR, which is definitely low light, but the light shining on the Hamburger Mattenfilter, which extends up above the water surface, is high light, and, I have BBA growing on the filter foam, which has gradually migrated to the whole filter foam surface, making it easy for it to also migrate to the plants.

I want to try using 2 pendant lights, each centered over an 18" square of the 18 x 36 foot print of the tank, with the lights hanging 12 - 18" above the tank. Because I enjoy working with LEDs, I'm building my own lights, based on 10 watt LEDs from Ebay.

To minimize spillover and glare, the LEDs will be mounted inside cylindrical "cans" 4 inches in diameter and 6 inches long. I want the lights to be sturdy, not at all fragile, and I want to add low power red and blue LEDs to improve the color rendition of the cool white 10 watt LEDs.


I found some heatsinks made for 10 watt LEDs on Ebay:


For the "cans" I started out expecting to use 4" aluminum ducts, made for clothes dryer installations. But, then I found some 4" aluminum tube, with .085" wall thickness, on Ebay at a good price, so I chose to use that.

I bought a 12" long piece, and cut it into 4 smaller pieces, using a hacksaw:


I cut two 1/8" long rings, to use as retainers for the heatsink ends, then cut the remaining tube in half, to end up with about 5 7/8" long "cans".

I cut 17/32" pieces out of each of the 1/8" rings to make them fit inside the 4" tubes snugly.


After filing the ends of the rings and tubes to smooth them a bit, I used Loctite to glue the rings inside the ends of the tubes. They are now very tightly attached to the tubes. The heat sinks will fit against the rings, so the heatsink will support the tubes, with the "cans" hanging.

However, the heatsink mounting lugs, 4 places on each of them, are too big to fit into the cans, so I used a hacksaw and file to trim them back to fit into the tubes.


The heatsinks now fit in the tubes, and form the top of each "can".


Each heatsink will have a 10 watt cool white LED mounted in the center, with a blue and a red LED mounted on the sides of the 10 watt one. To expand the mounting surface to accept 3 LEDs, I attached a 1/8" x 1" x 2 1/2" piece of aluminum bar to the heatsink LED mounting surfaces.


The 10 watt LED will be held in place with 2 flathead screws, and the blue and red ones will be cemented in place.

Next will be to get a 10 foot piece of 1/2" electrical conduit, and make 2 hangers from it. To bend the conduit I found a used conduit bender on Ebay for about $12, so I bought it, figuring on relisting it on Ebay when I finish with it.
 
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#37 ·
do you have the name of the emitters you will be using? and the efficiency. seems odd to go through a build without getting very efficient emitters. also do you have the color temp of the emitters. i am hoping to get at least one of my cannons up and running tomorrow. i will have one 30 watt bxra bridgelux 4k , 2 cree xml 7k, 2 different reds, 2 royal blues, 2 cool blues, and one violet and green. the 3 watters will all be run on different drivers so i can see what they do to the appearance of the light. using just the 4k 30 watt emmiter it gave 34 parr 36 inches below the light using a 60 degree optic. i also need to trim and bend and rivet my reflectors which i will be repurposing the pieces i had cut out of light tube aluminum to make diy MH reflectors. i will be trying for a 10 degree out angle on all 4 sides and making it square. sorry for the hijack but following with great interest.
 
#38 · (Edited)
You can get loads of information on LEDs, when you use Cree LEDs, and a lot of information for other name brands, but the really cheap ones on Ebay come with a color temperature and lumen rating, and that's about all. The ones I ordered have these specs:
LED Emitter: 30W
Color: Cool White
Output Lumens: 2500-3500LM
DC Forward Voltage (VF): DC 33-35V
DC Forward Currect (IF): 1050MA
Color Temp: 2850-3050K(Cool White)
Beam Angle: 140 degrees
LifeSpan Time: > 50,000 hours

I suspect the color temperature isn't correct, but I won't know until I see them lit up. The driver, which comes with the LED, has these specs:
Driving power: 30w
Model: 10series 3 in parallel
Input Voltage: 85V~265V
Output Voltage: 33-35V
Current:1050mA
Efficiency > 88%
Power Factor >0.98
Operating Temperature: -20~80
Size (L * W * H): 85mm * 26mm * 21mm

The major spec. that attracted me for this combination of LED and driver is:
$5.72 with free shipping

Theoretically I don't need that high a lumen output, so I am thinking of using a parallel resistor to "waste" some of the 1050 mA current, running the LED at a lower current so the heat from it is much less. I would probably shoot for about 700-800 mAmps. At 800 mAmp, I would need a 140 ohm resistor, able to dissipate about 10 watts, in order to bypass about 250 mAmps of the 1050 mAmps driver output. I could get a 25 watt 300 ohm pot from Ebay for about $10, and that would work as a dimmer by bypassing current. If the LED failed the pot would be subjected to 1050 mAmp, about 100 watts until the LED driver failed - a very short time. (Needs more thought!)
 
#45 ·
I sent you a PM with the Ebay item I bought. It is definitely listed as both LED and driver.
Theoretically a 20 watt LED will not provide the PAR I want at the distance I want the light to be. If I do this right I will be able to dim the 30 watt LED a little, and be able to dial it in to the PAR I want. Obviously I need to do some more thinking before using the idea of bypassing some of the current through a potentiometer. There is a way to do this safely, but I haven't thought it through yet.

I like this projekt. Good job.

Some spontanious thoughts:

* Why not incorporate the thick aluminium tubing in the heatsink solution? Thats a lot of cooling potential just sitting there so close to the led.

* As you have discovered, 10w "cheap led" is way to weak for anything but nano.
I originally planned for the aluminum can to be part of the heatsink, but I wasn't able to find a circular heatsink that I could easily modify so it would make good thermal contact with the can. Those that are a big enough diameter require a lathe to machine the OD down to match the ID of the can. And, smaller ones have a too small OD to match any available tubing size. That's when I decided to just rely on the can to act as a chimney to enhance the air flow through the heatsink.
…..so wait, are you using any optics with these LEDs or are you trying to use the can as the optic?
The can is the optic. It collimates the wide beam of light from the LED into a much narrower beam.
Could you send to me too Hoppy. thanks

Jefff
Now that I am switching to a higher wattage LED/driver my parts list is changed. I will wait until I find out if this will work at all, and until I have made any other changes that are needed, before I send out another list of parts.
 
#41 ·
I like this projekt. Good job.

Some spontanious thoughts:

* Why not incorporate the thick aluminium tubing in the heatsink solution? Thats a lot of cooling potential just sitting there so close to the led.

* As you have discovered, 10w "cheap led" is way to weak for anything but nano.
 
#46 ·


This should work, unless it constantly blows fuses on start-up, or unless the surge when a LED fails damages the parts before the fuse blows. It isn't as cheap as I expected though. I will look at dimmable drivers again.

Note: the 550 mA current through the resistors and fuse is when the LED is dimmed the most, down to 500 mA current.
 
#47 ·
Re-thinking a bypass current dimmer design, I don't need continuous adjustment of the LED current, just an option to reduce the current a bit to ease the cooling requirement. So, here is my next idea:


The possible problem I see is the total power required, which is 36 watts and the driver is a 30 watt driver.
 
#48 ·
I managed to measure the PAR from my 10 watt LED without the can. Here is the photo, from before, with the LED 20 inches from the PAR meter:

and the photo I just took, without the can, with the LED 20 inches from the PAR meter:


You can see the PAR dropped from 21 to 13 at that distance, so the can increased the PAR by 62%. Without the can the PAR drops from 13 to 10 outside of a 12 inch circle.
 
#52 ·
It certainly looks like it can be done, but I haven't received the LED or driver yet, so I can't tell if it is made the same way. It probably is, except this driver is already equipped with the DC supply set for 33-36 volts output.
 
#50 ·
Hi Hoppy,
I got two ideas for you
(a) Heatsink- if you use a box shape, you can easily attach the heatsink to the side of box. For circular beam, just allow a circular(or even hexagonal) opening at end.

(b) For dimming- why dont you use the light filters you used for your PAR meter? may be have a dial like thing that you can over lap with two half filtered discs, and dial these discs like volume tuner to arrange intensity. Just felt resistor stuff a bit complicated. And this ll look bit special too.

Cheers!
 
#53 ·
As I noted before, I don't have a box shaped aluminum tube, but I do have the circular one, so that's what I have to work with for now.

I don't want to dim the output, just reduce the power, to reduce the heat output to the heatsink. And, that may not even be necessary. I'm sort of zeroing in on how to mount a fan on this, without it looking bad or not being effective. It is still a work in progress.

I have thought a lot about adjusting the color temperature using the light filters, but that always involves losing a lot of light too. It would work, but require a higher wattage LED.
 
#55 ·
Someone else who didn't pay attention to detail and thought that aluminum tube was giving you a 10x increase in PAR :)

but, neat project, and the pic (021/120 par ;)...) with the pendant looks pretty nice. simple design, clean, effective, just overall looks good.
 
#56 ·
If you wanted a fan, you can drop the heatsink down an inch or so. Then secure it with screws or dowels inside. Then put the fan on top (doesn't even have to be a fast flowing fan). Then to mount the light create a cross that will fit within the can and hang it from there on top of the fan.

Doing it this way will hide everything.
 
#57 ·
This is how I plan to assemble the new, thicker heatsink, the fan, and the can. The can has the stop "hoop" in the top. The heatsink will have the mounting ears trimmed back so it just fits in the can. The top half of the heatsink will have the fins trimmed back so that part extends above the top of the can, with the bottom part hitting the stop in the can. The fan will sit on top of the heatsink, with the mounting lugs at the top held to the stubs of the mounting lugs on the heatsink with twisted wire in 4 places. The assembly to be hung from a loop of the same wire from a pair of the mounting lugs of the fan. The electric wires will snake into the can through the fins on the heatsink. For now I will omit the red LED - until I see how hot the heatsink gets from just the 30 watt LED. The LED will be screwed to a piece of 1/4" thick aluminum plate which will be held with one countersunk screw to the hub of the heatsink which is only an inch in diameter. (With use of heat conducting grease, of course)

The reason the heatsink will be partly above the top of the fan is to get more area for air flow through the heatsink fins, and to raise the LED to the location where I had the 10 watt one. It won't look as good as it did, but I think I can make it look ok - probably paint the fan housing white to match the aluminum tube can.

The fans I have ordered from Ebay at $10 apiece - $$$ keep adding up!
 
#60 · (Edited)
I will mass produce them when bananas grow in Antarctica.:icon_mrgr

I received the 30 watt LEDs and drivers yesterday. The LEDs are huge, compared to 3 watt star mounted LEDs - about 2 inches square with the mounts. The Drivers are just a DC voltage supply with a voltage regulator set up as a current regulator. I can't identify which of the tiny resistors soldered on the bottom of the circuit board are the current setting resistors, nor can I tell what resistance they have. And, this requires a magnifying glass for me to even pick them out. I doubt that I will try to remove a resistor to drop the current - I do think there are 3 parallel resistors that do that job.

The voltage regulator terminals are the 3 closely spaced solder dots on the top left side of the photo. But, I can't trace the connections well enough to identify the current setting resistors.
 
#61 ·
Hoppy-

Can you see a part # on U1? That may be the driver IC and more could be learned if the chip is identifiable?
 
#67 ·
Hoppy-

The two resistors marked 1R20 should be the current sense resistors that your looking for. They appear to be made in the metric "1206" package and should ohm out at 1.2 ohms each. If they happen to be wired in parallel with each other, I'd say de-solder one of them and try out the driver again.Removing one resistor should essentially cut the current reaching the CS pin in half and reduce the driver's output considerably.
 
#68 ·
I will try the drivers as they are first, and if they are usable that way I won't bother with trying to reduce the current. I'm pretty sure it is beyond my ability to desolder one of those resisters, or re-solder it back. Maybe I could have done that 20 years ago, but not now.
 
#70 ·
The efficiency isn't a concern of mine. I will be delighted if it works, provides the PAR I want, and doesn't spill light all over the room. For the best efficiency you would always use LEDs sitting right at the top of the tank, and that isn't the goal here.
 
#72 ·
Brief diversion from your build to ask a couple questions.

Do you think you would get the same light dispersion if you were to go with a number of smaller LEDs instead of a single 20-30W LED? I'm bouncing the idea of fabricating a light in much the same way, but using a punched Aluminium plate to hold 7 LEDs mounted on a star pcb's. I'm hoping that by having the aluminium plate make good contact with with the walls of the fixture the whole fixture will form an effective heatsink with a chimney effect to promote airflow.

Here's a screenshot of what I was thinking:



Ok, back on topic.

How do you plan on mounting the pendant with the fan on top like that?
 
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