DIY LEDs - The write-up

[kcress]

If you are having difficulty soldering make sure you have a powerful enough iron. Not hot.. Powerful. For these stars you should be looking at minimum 50W Personally I'd use about 175W or 225W. I would tin nothing and just solder it completely, as fast as possible, the first time - mounted or not.


Generally the remaining rosin is not a problem. In the case of these stars cleaning it off would cause more damage than leaving it there.

 

[hllywd]

I'm curious why you wouldn't tin anything kcress... IMO it makes things so much easier when you can have the iron in one hand and simply the wire in the other, I'm not talented enough any more to hold the iron, wire, and solder at the same time... let alone add a loose LED to the mix!

Sorry, I did use "hot" where I should have used "power". Like I said though I found this 40W Weller locally, and through 48 of my 96 LEDs it seems more than adequate. Now if I was doing this for a living it would be a different story altogether. I remember using much better irons in college, and I agree there's definately a difference.

 

[Jay1982]

Thanks guys for the feedback. Much appriciated. I'm using a 40W iron. I'll go buy a better one tomorrow and I'll do what has been outlined above. I'll try re-doing this star that I pictured. Do I heat it up and pry it off? Or do I just scrap it and use it for testing?

 

[hllywd]

You should be able to melt the solder to remove the wire. No reason it should be trashed I can see.
Tim

 

[kcress]

I'm curious why you wouldn't tin anything kcress...

Hi hllywd.
Pre-tinning has its place but.. The physics of soldering are kind of complex. When you pre-tin you leave a layer of already heated flux on all the various surfaces. This can cause subsequent soldering to be sub-par. Also using the 'heat up the two and just melt them together' method means you get almost no flux action on this second solder-less heating.

If you ever watch the flux action under a microscope you will see the flux push everything foreign away allowing only the two items to be connected with solder. When you use the tack them together method none of this happens.

In most cases for our LED fixtures it's still good enough. But I would rather not. I realize that to do it the right way you need three hands. I have one of those little stands with alligator clips sticking off of it. I just grab the wire with one of them and have it hold the wire to the pad. Then I can show up with the iron and the solder.

Jay1982; You would want to re-heat that joint. You always want a hot solder joint, not a cold solder joint. 'Bulbous' is often a sign of a cold solder joint. The other sign is a dull un-shiny result.

 

[kcress]

GEORGEDOPE; If you want to use that driver with parallel strings, go ahead. Add a 5 Ohm 10Watt resistor in each string. This resistor will help balance the string currents due to the inevitable mismatched string voltages.


Next turn down the voltage limit on the driver until you just detect some dimming. Then turn it back up a wee bit.

Now when one of the three 700mA strings opens the remaining two will theoretically have 1050mA sent thru them. But to have this happen the voltage must rise significantly, except, you just limited that voltage rise with the adjustment. The limitation will keep the current below 1050mA by a significant amount.

The only thing you aren't fully protected from is a shorted LED in one of the strings. The math shows that with those resistors you would probably see one string increase about 50mA and the other two drop by 25mA. Someday I will check that on a build. For piece of mind you can add a 3/4A fast blow fuse to each string.

 

[Jay1982]

Thanks kcress and hllywd! Will do!

 

[CJO]

Originally Posted by der_wille_zur_macht
To help clear it up. The driver you have has TWO ways to adjust the power that the LEDs are running at (actually three, but the third - voltage limiting - doesn't come into play when it's run as a constant current LED driver.)

First, there is the internal trimpot. Think of this as the max. limiter for current provided to the LEDs. The trimpot sets the max current (amps) your LEDs will run at. You adjust this internal pot simply by turning it with a screwdriver and reading the CURRENT (amps, not volts) on the output string, i.e. in series with the LEDs.

Second, there is the external dimming signal, connected to the external wires. This external circuit allows you to dim DOWN from the max current set by the internal pot. You control this function by providing a voltage signal to these wires, between zero and 10 volts. The LEDs aren't actually running at this voltage, it's merely a signal. The driver translates the signal into a percentage of the current set by the internal trimpot.

So, when your external signal source (ALC, whatever) is providing a 10v signal, your LEDs aren't running at 10v, they're running at 100% of the current limit set by the internal pot.

The internal pot is a set and forget kind of thing - you configure it when you install the system, and then you likely won't touch it again. Depending on your plans and which LEDs you're using, typical values might be between 700 and 1000mA.

The procedure Stu suggested above is 100% exactly what I would suggest. Turn the trimpot all the way down (counter clockwise). Wire everything up, with your external control signal set at 100% (i.e. 10v). Put a multimeter set to measure amps in series with the LEDs. (make sure it's well connected, you don't want loose connections!) Plug the whole thing in, and measure the current. Leaving your external signal set to 10v (100%), adjust the internal trimpot upwards until you get the current you want, which will be between 700 - 1000mA for most people. Then, unplug the driver, remove the multimeter from the circuit, close the circuit, and you're ready to go.

Since the drivers are constant current, can't we set the internal pot without having to connect all of the LEDs?

CJ

 

[TheFishMan65]

Yes, if you have something to simulate the LEDs. The pots (at least the ones I see) don't have numbers and some are multi turn. There is no set it here for 700 ma. So you have to measure it as you adjust it. If you don't have a load the current will be 0 amps.

 

[zangmann]

Wired up my first stip of RBs and seem to have run into a Bin issue. It seems that the XREs I received are from several different color bins? It wouldn't be such a big deal and I probably wouldn't have noticed had it not been for the fact that I got several of the same color bins together then a few of completely different bins right next to them. This creates a noticeable change in the blue color in different areas of the tank.

Is there a way to tell prior to affixing the stars to the heatsink which bin/color ithe LED is? I tested each before mounting but the color differences only became noticeable once the whole strip was lit.

My plan was to alter these bins to negate some of the differences, the different colors really show themselves when 2-3 are in the same sequence.

Edit: Is it possible i was sent both Blues and Royal Blues?
I questioned the supplier before ordering and was told all are part #:
CREE XR-E Royal Blue XREROY-L1-0000-00A01

 

[TheFishMan65]

zangman, where did you order from? I don't think you can identify the difference once they are on a star. I think the only way to tell is the original labeling on the box from the company.

 

[zangmann]

I'd rather not say until I speak directly to the supplier, but it was one of the big ones that sell kits.

 

[skippyreef]

Where are you guys putting the drivers ? I am doing the remote thing so I ordered an 18/18/6 Hoffman box.

 

[TheFishMan65]

I don't want a bunch of wires running to the fixture for each bank so mine will go in the fixture. That leaves 24 volts and PWMs. I am contemplating a Arduino in the fixture to get rid of the PWM wires.

 

[CJO]

Yes, if you have something to simulate the LEDs. The pots (at least the ones I see) don't have numbers and some are multi turn. There is no set it here for 700 ma. So you have to measure it as you adjust it. If you don't have a load the current will be 0 amps.

Thanks!
CJ

 

[F35-Joint Strike Fighter]

Just out of topic that does anyone know where I can get a replacement for PFO LED? I have 24" fixture and couple LEDs are bad now. I can do rework easily...

TIA

 

[Jay1982]

I did a quick search of the internet but didn't really find my answer. I bought a multimeter yesterday. When I am wanting to see if I should turn my trimpot on my ELN meanwell down. What setting do I put the multimeter on for the Amps? Is it:
200μ, 2000μ, 20mμ, 200mμ 10A. I personally think its 2000μ but I'm probably wrong, lol.

 

[F35-Joint Strike Fighter]

I did a quick search of the internet but didn't really find my answer. I bought a multimeter yesterday. When I am wanting to see if I should turn my trimpot on my ELN meanwell down. What setting do I put the multimeter on for the Amps? Is it:
200μ, 2000μ, 20mμ, 200mμ 10A. I personally think its 2000μ but I'm probably wrong, lol.

Always set the amp meter at the highest then go lower for acuracy. In this case, set it at 10A but don't forget to hook it up in serie.

 

[Jay1982]

So I continued soldering today and the rosin (yellow gunk) is exploding when I'm trying to soldering. Its splashing on my arms and on the dome of the dice. Why is it doing this?

 

[Jay1982]

Oops, I also noticed that I forgot to thank you G35. Sorry about that! :wavehand: