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Chad

Chad's LED fixture

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I need to know more about your circuit to provide you w/ a diagram with a || LED circuit. But I personally like || circuits better than a circuit in series due to the non-dependance on the rest of the circuit. There are considerations that you have to make though, such as the increase in power consumption by the circuit.

 

So from what I gather, the PWM is providing a wave signal to the CCDs which trigger them to output voltage to the LED circuit, which will increase and decrease with the signal. The output voltage from the CCDs to the LED circuit will be 24V. That seems awfully high when the datasheet on the XR-E LEDs states the forward voltage is 3.3v @ 350mA or 3.7v @ 1A or pulsed at 1kHz @ 3.9v & 1A. Am I missing something or is there some other way you are controlling the output voltage from the CCDs?

 

Also, how are you mounting the LEDs to the heatsinks? thermal tape, thermal compound? Over time, gravity usually wins so do you have some other way of holding them in place? A pilot hole w/ a couple of self tapping screws per LED should be more than enough. Also, I am not sure if you plan on removing the packaging paper from the heatsinks, but in a couple of spots it appears that the LEDs are on top it. I would avoid leaving any of the paper on the heatsinks between the LED and the heatsink. That is just going to create a thermal barrier. Also, it's a good idea to clean the heatsink w/ alcohol where you will be attaching the LED w/ the compound. fwiw: I like Arctic Silver thermal compound.

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Guest thefishman65

OK, you have me confused.

 

First CCD - charge coupled device - don't use them here what are you referring too? I assume you mean CAT.

 

The PWM causes the voltage to be applied longer or shorter the voltage does not change (other than start/stop issues). The CATs supply what ever voltage is needed to reach the desired current. We typically run 6 LED so for 1 amp the drop would be 6 * 3.7 or 22.2 volts. The CATs need 0.5 over to work so ideally the power supply in this case would output 22.7 volts. Any other is wasted as heat by the CATs.

 

For heat transfer I personally use screws and thermal compound. Some folks use thermal epoxy and some berquist(I think) tape. Think of it as double sided tape would good thermal transfer properties.

 

Does this help any?

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Kinda getting a little off the topic of Chad's DIY LED light fixture build....

 

If we get much deeper into the design of the CAT LED Driver board, it might be good to start a new thread specific to the subject that we could easily find later on.

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There are other significant considerations with running strings in parallel, namely wiring complexity and load balancing.

 

The main power supply for the build is a 200W 24 Vdc power supply that is somewhat adjustable on the output voltage... I ought be be able to get 22 volts out of it (which is my theoretical target)... I will measure drops on the strings and set it for the ckts, though. The CAT4101 chips do not regulate outlet voltage, just maintain a constant current for a given voltage.

 

Also, gravity isn't something that I need to worry about. The optics and leds are sandwiched between the fixture bottom and the heat sinks. I did use thermal paste and screws, though.

 

 

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A little bit of progress today... 7.5 hours of running wires and soldering. Still not doing powered checks, but soon.

 

Part way into the tedious process of wiring.

6712432155_8eee0afdd6_b.jpg

 

Wiring done. Soldering started. After I finished soldering, I scrubbed everything with alcohol, then checked every LED for continuity, grounds, and verified it was wired correctly. After I bolt down the heat sinks, getting back to make a repair and trouble shoot will be more difficult.

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Heat sinks in place:

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Close up of sinks in place, still need to be bolted down. When I put the terminals in, the wires will be cleaned up pretty nicely.

6712435447_0074dd9620_b.jpg

 

Slowly, but surely, it is coming together!

 

Next up: Finish bolting the heat sinks down, wire the strings to the drivers, and do powered checks.

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Wow, I have been busy which means that I haven't spent a whole lot of time working on this... However, I did make some progress worth an update (IMO, it's my thread anyway!)

 

 

I spent a bunch of time polishing up my edges and making the fixture look much better. For those interested, I wet sanded with 600 grit, then 1200 grit, then buffed with my power drill using Ultra Cut and Ultra Finishing compounds. The finish is almost mirrored, especially on small surfaces. Larger surfaces have a little bit of distortion, but the overall effect was well worth it - look at the reflection on the top surface :)

 

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Once the fixture was all polished up, I got back to wiring. In this picture my driver just need to be connected to the power supplies and the strings.

 

6912484017_0e95bcfecf_b.jpg

 

One of the things that I enjoyed about doing this project is that I can jump from thing to thing when one gets frustrating. In this picture, I have pretty much finished up all of the non-controller wiring, but have not cleaned it up yet (I still want to be able to very easily access everything until after I do energized checks). I also started polishing up the perforated stainless steel using some Mother's mag polish and some buffing wheels... these went from raw machined SS to quite shiny... It looks nice

 

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A close-up of the shininess (doesn't come through terribly well, but I think you get the idea):

 

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Test fitting the trim pieces

 

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And installed (and dirty!! I'll clean it up really nicely when it is complete).

 

6912486729_12040108df_b.jpg

 

Well, that's that for now. I expect I am going to remain really busy for the next couple of months, but as I get some work done I will update.

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BTW, Im kind of amazed at the number of views this thread has!

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why didn't you use flat topped screws instead of button head? not that I'm complaining- it looks nice and I think you should let me demo it for you on the 500...

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Once I decided that I should screw the perforated SS on, I knew the screws would be visible, so I decided to make them obvious and (hopefully) a little decorative in the industrial sense...

 

Not sure how well that worked out... maybe I will leave that up to y'all... What do you guys think?

 

Once I get this beast done... it is decidedly going over MY tank :)

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LOL, I think it's been two months since I did anything more than clear the mail off of it since it is still on my dining room table and in the same condition as the last couple of pics! rolleyes.gif

 

I decided I would make the final push to get my master's degree this semester (I've only been working on it since 2005... so it was time), with two classes and defending my thesis, my normal project time has been really eaten up by coding and homework. That all ends soon, though, and I will get back into it. I was thinking about it, I really don't have much left. A little wiring, assembly of the controller, and in-place tweaking on the code. Probably only 2-4 days of actually working on it.

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It lives.

 

7378_4587222405452_880672899_n.jpg

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Wow....I wasn't sure if you we're going to get this thing finish this year....

 

LOL, neither was I

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