DIY LEDs - The write-up

[ReefEnabler]

Grim that reminds me:

Anybody recall a member by the name of Pdelcast? A while back he made his own PCB strips out of aluminum. Apparently he had access to a machine called a "pick and place" machine or something that placed the Cree dies onto his PCB strips and reflow soldered them.

Anyways, he hasn't logged in for over a year so I don't think we will get answers out of him. But does anybody else have tips for making a strip like this?? Are there companies you could hand a diagram and a bunch of Dies and have them make the PCBs and attach dies to the strips like that?? Would be as easy as a T5 retro kit after that's done.

I'd love to go all-LED on my tank, but if I went to that scale, I'd want to use more sophisticated methods than star soldering.

 

[der_wille_zur_macht]

Are there companies you could hand a diagram and a bunch of Dies and have them make the PCBs and attach dies to the strips like that??

Yes, but on anything lower than a very large mass-production scale it's going to be outrageously expensive unless you somehow have free access to the machines (at work? No one's going to have this sort of production facility in their garage!) If you can find my DIY driver thread, we talked about it in there a few weeks ago.

 

[DFason]

Do you think this heatsink will be fine with two 40mm fans over top?

6 XR-E RB at 1000ma
6 XP-G CW at 700ma

-Dave

 

[der_wille_zur_macht]

What length did you specify?

 

[DFason]

8.5 or 9". I was going with 1.25" spacing between each emitter.

-Dave

 

[akindbro4u]

Do you have a multimeter that can detect duty cycle or frequency? Or at least voltage?

I'd start by reading the voltage coming off the LM317. Make sure it's 10v. Then I'd test the output (where the DIM connections are supposed to be). Make sure you're getting something reasonable.

FWIW that circuit is "backwards" compared to what I'm used to for a 555 so I'm having trouble deciding how to troubleshoot it.

Did you solder the IC in place or use a socket?

Think I figured it out. 555 requires dc correct? I just noticed my wall wart was 12v ac.

 

[adova]

I just received my LED's and heatsinks and have a couple of questions:

I am planning on screwing these into the heatsinks, but it appears that no matter which of the cutout indentations that I would choose whould have the screw head touching a positive or negative contact point when tightened.

Secondly, what guage / type wire are you using between LEDs?

Thanks,

Shawn

 

[stugray]

"have the screw head touching a positive or negative contact point when tightened."

I use nylon screws & washers.

"Secondly, what guage / type wire are you using between LEDs?"

I use 18 ga. solid core, pretinned, but others have used 20 ga. stranded.

Stu

 

[stugray]

Reefenabler,

"I'd want to use more sophisticated methods than star soldering. "

I recall someone asking a few pages back if there were any MCPCB ( Metal-Core PCB ) houses out there. Now you know why ;-)

I never heard back how MUCH more it is than a normal PCB house.....Or WHO does it.

I have also considered running my Vias using copper tape over kapton and soldering to that, but it is not less trouble but more work than wires.

Stu

 

[rcgates]

Think I figured it out. 555 requires dc correct? I just noticed my wall wart was 12v ac.

Sorry I can't help with the circuit, but your wall wart is 12V dc output with AC input.

I don't know of a country that uses 12V AC power, 110 or 220 is the usual.

 

[stugray]

"Sorry I can't help with the circuit, but your wall wart is 12V dc output with AC input. "

I have a 24-28 VAC wallwart laying around somewhere.

Furnaces & doorbells still use 28 VAC in the U.S.

You probably have two of them screwed to the wall in your furnace room.

But youre right, 12VAC is rare.

Stu

 

[der_wille_zur_macht]

Think I figured it out. 555 requires dc correct? I just noticed my wall wart was 12v ac.

Yes, absolutely, you need to give it DC. I wonder if that voltage regulator's any good now.

8.5 or 9". I was going with 1.25" spacing between each emitter.

-Dave

That strikes me as acceptable as long as you can ensure the fans are always working, but buying one and trying it is absolutely the best bet!

I don't know of a country that uses 12V AC power, 110 or 220 is the usual.

Speaking in terms of what's coming out of the wall you're correct, but it's totally possible that his wall wart is producing 12v AC on it's output. I have plenty of AC wall warts in my parts drawer. Not as common as DC units perhaps but they're out there for sure.

 

[akindbro4u]

it figures the one i grab is ac. don't know if the reg is any good. dosen't really matter there cheap enough. that will teach me to look better at what I grab from the parts drawer,

 

[kcress]

If you can't read what is on the label you MUST measure it with a voltmeter. Measure for AC and DC.


Stu; I said back there somewhere. The smallest run of metal clad starts well above $1,000. The process is entirely different from normal boards.

 

[TheFishMan65]

I don't know the difference in the heat exchange of a aluminum board verses this copper. Anyone know how well 6 oz copper boards would work compared to aluminum? However, I think I read that CREE must be mounted to a heatsink.

Search for XLamp Thermal Management:

Cree does not recommend operating XLAMP without a heat sink

[EDIT]
Another good note:

In the most cases, power LEDs will be mounted on metal-core printed circuit boards (MCPCB), which will be attached to a heatsink.

Yes they said "In the most cases"

 

[der_wille_zur_macht]

You may have seen this (is it where your quotes came from?) but here's Cree's guide to thermal management for xlamp LEDs:

http://www.cree.com/products/pdf/XLampThermalManagement.pdf

I understand the attraction of putting everything right onto a board instead of MCPCBs that are then screwed to a heatsink, but thinking in terms of full lifespan, it's going to be a lot easier to replace an LED mounted on a star screwed to a heatsink than to deal with an LED that's directly surface-mount soldered to a huge PCB with a ton of other LEDs. It would pretty much mean the whole unit would be trash, from an average hobbyists' perspective - there's no way joe blow is going to swap out a SMT HP LED.

 

[The Grim Reefer]

Is there any advantage to using the stars over the round boards?

 

[Santoki]

A perfect example of this would be the Solaris units. I recently had the opportunity to peak inside one as I gasped at the shear proprietary complexity of it all. 5 emitters mounted per board. There was no easy way to replace a single LED. Even removing the optics seemed to be a potential challenge.
The boards were then mounted to a tiny strip of aluminum surface (≈1cm wide), which then extended down to some thin flimsy heat-sinking part. Not a very good scalable or serviceable design if you ask me....
-R

 

[der_wille_zur_macht]

Is there any advantage to using the stars over the round boards?

The only thing I can imagine is that the "star" shapes are vastly more popular, which means potential replacements down the road are more likely. If you buy a one-off shape from a vendor, you're betting on that shape being available in 6 or 8 years if/when you need to replace an LED - that is, vs. having to rework your design to accommodate a star at that point, which admittedly wouldn't be a big deal.

It would be interesting to know if there's any difference in heat transfer between the two - i.e. does a big star have a lower thermal coefficient because it's slightly more massive than a smaller circle? Or does it not make a difference if they're both bolted to a huge heatsink?

 

[The Grim Reefer]

The only thing I can imagine is that the "star" shapes are vastly more popular, which means potential replacements down the road are more likely. If you buy a one-off shape from a vendor, you're betting on that shape being available in 6 or 8 years if/when you need to replace an LED - that is, vs. having to rework your design to accommodate a star at that point, which admittedly wouldn't be a big deal.

It would be interesting to know if there's any difference in heat transfer between the two - i.e. does a big star have a lower thermal coefficient because it's slightly more massive than a smaller circle? Or does it not make a difference if they're both bolted to a huge heatsink?

The star does have a whole lot more exposed side area but I have no clue if that is as important as contact area with the heat sink. Got to be some reason they came up with that design.