DIY SMD LED Pendant Light - Page 3 - The Planted Tank Forum

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post #31 of 253 (permalink) Old 02-07-2014, 07:31 PM
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Promising?

Is it that blue in real life? The picture makes it look more suited for a reef tank
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post #32 of 253 (permalink) Old 02-07-2014, 08:33 PM Thread Starter
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It is definitely not warm white! The color is bluer than 6700K bulbs or even, perhaps, 10000K bulbs. I will be adding two strips of much lower power red LEDs and two of much lower power green LEDs, so that's going to affect the final color quite a bit. It you look at a spectral distribution chart for some typical 5050 SMD LEDs the blue peak is considerably wider and higher than for Cree cool white LEDs. It would probably be best to combine these with at least 1/3 warm white LED strips, plus perhaps a few red lower power LED strips.

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post #33 of 253 (permalink) Old 02-07-2014, 10:43 PM Thread Starter
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More strangeness! The double sided tape is now coming loose from the back of the LEDs, not the aluminum. I think the next step has to be getting a roll of the tape GitMoe recommended. Right now I have to wonder how anyone ever makes this stuff stay where it is installed.

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post #34 of 253 (permalink) Old 02-08-2014, 12:34 AM
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What is the spacing between diodes on the strips? From you photo it looks like it might be 6 per 10 cm segment. By the wildest of coincidences, a chunk of egg crate that I picked up some time ago has 6 squares per 10 cm.

If you could work out how to use egg crate to capture the LED strips against the heat sinks, you could use thermal paste rather than adhesive tape and solve a bunch of problems.
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post #35 of 253 (permalink) Old 02-08-2014, 01:14 AM Thread Starter
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The LEDs are 1.67 cm apart, 300 on a 500 cm strip of tape. But, in the other direction the spacing varies because the strips are not equally spaced. The red and green ones have a different tape width. I have 12 strips in about 6 3/8 inches, which works out to about 1.3 cm average LED spacing. That is a good idea to work on though.

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post #36 of 253 (permalink) Old 02-08-2014, 02:52 AM
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are these supposed to be water proof LEDs?
if not you might want to try those next time, theyre encased in a clear resin which would prevent the LED from separating hopefully
sounds like they used cheap tape for the LEDs

what seller did you get them from on ebay?
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post #37 of 253 (permalink) Old 02-08-2014, 03:36 AM
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More strangeness! The double sided tape is now coming loose from the back of the LEDs, not the aluminum. I think the next step has to be getting a roll of the tape GitMoe recommended. Right now I have to wonder how anyone ever makes this stuff stay where it is installed.
You're no joking, but . . .
if the tape detaches on the side of the LEDs, then one drop of (waterproof ) super glue will fix that.

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post #38 of 253 (permalink) Old 02-08-2014, 05:10 AM Thread Starter
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You're no joking, but . . .
if the tape detaches on the side of the LEDs, then one drop of (waterproof ) super glue will fix that.
No, I wasn't joking, but as the day moved along, only the first strip is a problem. That one was stuck on 3 times before I got it "right". But, the real reason for the separation of the adhesive tape from the LED tape is that I stuck on the LED tape without waiting long enough for the primer to dry enough. The residual solvent in the primer is what made it come loose. Both the small test piece of aluminum and the first strip on the heatsink came loose that way. The remaining strips were installed a couple of hours or so later, after the primer dried more thoroughly. Dumb mistake!!

I plan to buy some of the double sided tape and reinstall that first strip with it tomorrow. It looks like the final 10 strip light will work as I want it to, based on extrapolating the PAR data I have now.

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post #39 of 253 (permalink) Old 02-08-2014, 05:13 AM Thread Starter
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are these supposed to be water proof LEDs?
if not you might want to try those next time, theyre encased in a clear resin which would prevent the LED from separating hopefully
sounds like they used cheap tape for the LEDs

what seller did you get them from on ebay?
No, they aren't the waterproof ones. And, it isn't the LEDs that are separating, since they are soldered in place, it is the doublesided adhesive tape that is separating from the LED tape. Of course the sellers of these tapes provide absolutely no instructions or cautions about how to install them. So, dummies like I feel now, have to learn the hard way.

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post #40 of 253 (permalink) Old 02-08-2014, 05:39 AM
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Progress... I'm still super excited to see how this works out. I can almost guarantee that tape will stick...

Sent from my SM-N900V using Tapatalk
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post #41 of 253 (permalink) Old 02-08-2014, 06:04 AM
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No, they aren't the waterproof ones. And, it isn't the LEDs that are separating, since they are soldered in place, it is the doublesided adhesive tape that is separating from the LED tape. Of course the sellers of these tapes provide absolutely no instructions or cautions about how to install them. So, dummies like I feel now, have to learn the hard way.
if i can get hold of my led supplier this weekend I will try and find out if I can get the LED rolls without any sticky tape on them, then we can use whatever method we want to stick them on including thermal epoxy like Arctic Silver Thermal Adhesive or something similar....

He still hasnt replied back with prices
I might just have to go over to his house soon
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post #42 of 253 (permalink) Old 02-08-2014, 05:43 PM
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thermal epoxy like Arctic Silver Thermal Adhesive or something similar....
Given the surface area involved for all these strips, wouldn't the cost of Arctic Silver be excessive?

And given the low power density and low thermal conductivity of the strips themselves, wouldn't the performance of Arctic Silver essentially be wasted?

(Not that I find Arctic Silver all that special anyway. I once misplaced all my thermal compounds in the wee morning hours, and needed to attach a CPU heatsink immediately, so I improvised and used axle grease. Worked fine and ran it that way for a year, then went back and replaced it with AS paste. Expected a temperature drop in doing so, but instead the CPU temp went up by 3°F!)
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post #43 of 253 (permalink) Old 02-08-2014, 06:32 PM Thread Starter
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Progress... I'm still super excited to see how this works out. I can almost guarantee that tape will stick...

Sent from my SM-N900V using Tapatalk
I checked that tape out, and found it is one of the foam plastic backed tapes, with the foam about a mm thick. That doesn't seem acceptable, due to the heat insulating effect of the foam plastic. So, I bought ordinary Scotch "Permanent Double Sided Tape" which is very thin. I used it for 3 rows, the first one, that had come completely unstuck, and for two rows where the LED tape adhesive seemed very non-tacky. It looks like it will work fine.

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post #44 of 253 (permalink) Old 02-08-2014, 09:48 PM Thread Starter
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All 8 strips of the cool white LED tape are installed, and tested. They all light up fine, but the PAR is not linear vs the number of strips, which it should be. Instead of getting 2X the PAR with 8 strips that I get with 4 strips, I only get 1.45X. That means I am short of PAR at the distance where I want to use this. A possible reason is that the current is less with all 8 strips than it was with 4 strips. I have read that the best way to hook up a long strip of LEDs like this is to apply the power at both ends of the strip - connect the + voltage to the + terminal at both ends, and the same with the - voltage. That will be the next test. It will improve the output if it is resistance of the long wires in the tape that is reducing the current.

The data:
At 20" distance - 40 PAR
At 23" distance - 31 PAR
At 25" distance - 26 PAR
At 35" distance - 14 PAR

EDIT:
I added wires to the other end of the strips, so the power is fed from both ends of the combined strip. It did raise the PAR substantially!

The data:
At 20" distance - 47 PAR
At 23" distance - 37 PAR
At 35 1/2" distance - 18 PAR

The increase in PAR with more strips still isn't quite linear, but it is a lot closer to being linear. And, this is still lower than I want it at 34" distance, where I want to use it. I could lower the distance to 32", and would get about 25 PAR, which is close enough to my goal of 30 PAR. Possibly that will be increased a bit by the 2 red and 2 green strips, which are the next test to do.

Hoppy

Last edited by Hoppy; 02-08-2014 at 10:35 PM. Reason: Add data
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post #45 of 253 (permalink) Old 02-08-2014, 11:59 PM
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Those are some promising numbers. So if I was looking to hit 70 PAR I'd need 24 strips of the same length? And probably dual power supplies? I think at that point it might be more economical to just get a Ray2. But it could be fun to build something...
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