Calling out to Weezard for LED advice

Weezard, you're a true renaissance man. What a lovely haiku. Mine was rather bleak by comparison. :(

Not sure I get "Tomorrow" unless it's this one:
"Creeps in this petty pace from day to day
To the last syllable of recorded time"

I got impatient and ordered the LEDs just now. 2 blues and 5 reds. And at only .80 each I took a chance on a couple finger guards.

I'd like to squeeze 5 reds on the light but the power supplies I'm looking at seem best to drive 4. (Did I mention that 100-15? :D :D :D )

So, maybe I'll use red #5 in the next build.

Also found some PMD controllers at Quickar. There's one for $10 that looks like something I saw on your lamp, prolly that blue controller that you jumpered around after it fried. Those might be useful, unless they're failure-prone. :angelsmiley:

The thermal glue arrived, too. The 92mm fans do line up (to miss) the fins. I am thinking now about cramming 6 reds in a domino-6 pattern and centering the blues in the middle. Weezard, is that "too much light" in a small area?

[attachment=o213587]

[attachment=o213588]

I could fit 4 fans on this thing......

[attachment=o213589]

Is that too much light?

Now, that's just crazy talk.:D

I like the 6 n 2 setup.
You can go from 3:1 R:B to 6:1 with the flip of a switch.
Though a dimmer would give the control that you want.
I like the centered blue array as well.
Blue triggers phototropism and we want the terminal bud to seek the center of the light.
2 fans should be jus' fine.
Depends on how hard you drive the leds.

Once they are mounted on the sink, you can light 'em up with the variable supply, and see how a passive sink handles the heat.
If it stays under 40 degrees C. you don't really need a fan.
Between 40 and 50 C. in the first hour?
Add a thermal switch in series with the fan to conserve power.
Over 50 degrees in a the first hour of burnin?
Hardwire both fans.

On that PWM.
Prolly the same one that I fried.
Can't blame the device though.
I pushed my luck with a fraction of a volt over the max rating.:o

(Li'l tiny Zards make big dumb mistakes alla time)

Nobody's prefect
Weeze

The server just got overloaded, or so it claimed, and ate my post! Gotta start saving work as I go, maybe.
Anyway, the first heatsink is all drilled and tapped. Ordered (4) 92mm fans.

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I like the 6 n 2 setup.

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Me, too! 6 it is! :D

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You can go from 3:1 R:B to 6:1 with the flip of a switch.

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I need some help here. If I just switch a blue LED out of the circuit won't the driver attempt to deliver the current (that was split between the blues) to the single blue?

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If it stays under 40 degrees C. you don't really need a fan.
Between 40 and 50 C. in the first hour?
Add a thermal switch in series with the fan to conserve power.
Over 50 degrees in a the first hour of burnin?
Hardwire both fans

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Thank you so much. I needed that info badly. Is there a way to get an accurate enough reading without buying an IR thermometer? And, do you have a part# or description of the thermal switch I might need?

Thought of another possible layout. [attachment=o213685] Thoughts? LED's should be here Thursday! :D:D:D Thanks for all your help. This is fun! :thumbsup:

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Originally Posted by DreadedHermie

The server just got overloaded, or so it claimed, and ate my post! Gotta start saving work as I go, maybe.
Anyway, the first heatsink is all drilled and tapped. Ordered (4) 92mm fans.


Me, too! 6 it is! :D

I need some help here. If I just switch a blue LED out of the circuit won't the driver attempt to deliver the current (that was split between the blues) to the single blue?

Sorry, works fine with C.V. forgot we were dealing with C.C. here.:o
You are correct, switching one out would make the supply increase the voltage to try to keep the current constant.
Once you exceed Vf.max, poof! All bus' up!
All da magic smoke gets loose an' he no work now.:rastasmoke:


Thank you so much. I needed that info badly. Is there a way to get an accurate enough reading without buying an IR thermometer? And, do you have a part# or description of the thermal switch I might need?

Candy thermometer will work and an educated fingertip will serve you well during burn-in.

As for thermal switch. I just hit E-bay and typed "thermal switch" into the search engine.
They are cheap and plentiful.
Won't hurt to hardwire the fans until you know if you actually have need of the switches.
They are easy enough to add later.

Thought of another possible layout. [attachment=o213685] Thoughts? LED's should be here Thursday! :D:D:D Thanks for all your help. This is fun! :thumbsup:

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My pleasure!
It was on my way.:D

Aloha
Weeze

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Sorry, works fine with C.V. forgot we were dealing with C.C. here.
You are correct, switching one out would make the supply increase the voltage to try to keep the current constant.

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I think those Mean Well's I want are CV and CC, if that makes any difference.

Let's say I have 13V @ 4800 mA going to 4 blue LEDs in parallel. Each blue is drawing ~1200mA, yes? Now, I switch one blue out of the circuit. Do the remaining 3 blues divide the 4800mA if the voltage remains at 13V?
That's the part I'm not sure about. Maybe a safe way to check it would be "backwards," like setting things safely for one LED and switching a second one INTO the circuit, and seeing what the driver does in response?? :stoned:

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Originally Posted by DreadedHermie

I think those Mean Well's I want are CV and CC, if that makes any difference.

Let's say I have 13V @ 4800 mA going to 4 blue LEDs in parallel. Each blue is drawing ~1200mA, yes? Now, I switch one blue out of the circuit. Do the remaining 3 blues divide the 4800mA if the voltage remains at 13V?

No.
If the voltage remains constant, each led will still draw 1.2 A. for a total of 3.6A.

I = E/R
If we change R. and keep I. constant, E. must change.
If E. is held constant and we change R., then I. must change.
etc.
It's the LAW. :D

That's the part I'm not sure about. Maybe a safe way to check it would be "backwards," like setting things safely for one LED and switching a second one INTO the circuit, and seeing what the driver does in response?? :stoned:

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Once you've tested and recorded Vf. and I. for each individual LED, you will know if one will try to "hog" the current.
(A led with significantly lower Vf. will draw more current than it's neighbor.)
That's why we never try to run paralleled leds at or near I. max.
With luck, all your emitters will be within .01 V. and it will not be an issue.
So, bring them up one at a time to 1.2A and record the Vf.
We can then make minor adjustments as needed.:cool:

Gotta run.
zooooom.
W.

Finally. I'm making some jigs by cementing 2 washers together, so I can epoxy the LEDs to the heatsink without putting pressure directly on the lens. :)

I'm gonna glue first, then wire. Weezard, is 20 guage stranded wire enough to supply each individual LED?

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Originally Posted by DreadedHermie

Finally. I'm making some jigs by cementing 2 washers together, so I can epoxy the LEDs to the heatsink without putting pressure directly on the lens. :)

I'm gonna glue first, then wire. Weezard, is 20 guage stranded wire enough to supply each individual LED?

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I would not do that!

Actually, I did just that.:o
But, I won't do it again.
Solder before you mount ,or buy a honkin big soldering iron.:D

The heatsink steals the heat and soldering then becomes a chore.

20 guage stranded will do jus' fine for short runs.
For long runs, I'd use 16 gauge stranded.

The PCB is so flexible, can't I just lift up the solder pad end and slip something between the pad and the heatsink while I solder? I've only just now attached one LED and only cemented pad behind the emitters, not the entire body of the device.

Seemed easier than having the thing squirm around while I try to attach the wires, then fighting the wires while I try to glue the LEDs down(?)