DIY LEDs - The write-up

[skippyreef]

what does it mean if you touch the positive of the LED and the Negaetive probe to the heat sink and the LED comes on?

 

[der_wille_zur_macht]

If you're touching one pad of the LED with one of your multimeter probes, and touching the heatsink with the other probe, and there is a conductive path (resistance reading on the meter, tone from the meter, light in the LED) it means there's a short somewhere from the desired conductive path (LEDs and wiring) to the heatsink.

 

[der_wille_zur_macht]

Grim, looks good!

 

[NCNBilly]

what does it mean if you touch the positive of the LED and the Negaetive probe to the heat sink and the LED comes on?

You don't have continuity in the circuit. Trace all leads back to the driver, somewhere you are connected to the heat sink rather than the pad.

 

[wld1783]

Grim, looks good!

+1

Like the idea of tossing in a couple of warm white.

Bill

 

[akindbro4u]

what epoxy should I use to attached the lens holder to the stars for my xpgs?

 

[skippyreef]

ok guys,

I redid it and still nothing. I am getting output from the driver DC side per the Multi meter but nothing happens when I connect to the LEDS. again driver is a LPC 35-700 on 12 Cree XRE.

 

[skippyreef]

could it be a bad driver?????

when I touch the + probe to a negative and then to the black to a negative the next led over it lights and the same in reverse.

 

[der_wille_zur_macht]

am getting output from the driver DC side per the Multi meter but nothing happens when I connect to the LEDS.

Exactly what output are you "getting" and how are you measuring it? Is anything connected (LEDs) to the driver when you take this measurement?

 

[stugray]

"could it be a bad driver?????"

No, as mentioned above: you have the solder joints on more than one star shorted to the heatsink.

If NONE of the LEDs come on but you still have current, then the first LED + is shorted to the HS and the last LED - is shorted.

Chances are that a LOT of them are shorted.

You need cleaner solder joints so that none of the solder touches the aluminum of the star.

Stu

 

[skippyreef]

My ELN 60-48D will drive it but the lpc 35-700 wont.

 

[Jay1982]

some of your solder joints look like "balls" instead of "flows". It looks like the pad on the star didn't get heated up enough to make the sold flow on the pad. This could lead to easy detach from what is called a "cold" joint.

Are you doing your soldering while the star is on the heat sink? Not the best way to try, the heatsink will pull heat away from making a good solder joint.

This is how I was going to do it when I started the project. So do you solder the stars on a workbench and wire the whole string and when you are done stick everything on the heatsink?

 

[der_wille_zur_macht]

This is how I was going to do it when I started the project. So do you solder the stars on a workbench and wire the whole string and when you are done stick everything on the heatsink?

Most people probably do something like this:

1) Identify and tin the pads you'll be using with the stars on the bench.

2) Secure the stars to the heatsink

3) Solder the wires between the pads

Soldering on the bench is really awkward because then you have to lift and transfer the whole spider-web to the heatsink and secure the stars. If you want to do it this way, I'd try to make some sort of template that holds the stars in an approximate alignment while soldering - flat, in the correct positions, etc. Then check before/after the move to the heatsink to be sure nothing broke or shorted out.

 

[Jay1982]

Thanks DWZM, how long will it take before the soldered pads on the stars cool down?

 

[rcgates]

This is how I was going to do it when I started the project. So do you solder the stars on a workbench and wire the whole string and when you are done stick everything on the heatsink?

To ensure line up and the hassle of picking up the string of soldered LEDs, I solder on the heatsink...sort-of

I place a non-metal, non-meltable, "shim" under the star, do the solder work and then move to the next.

This raises the star you are working on away from the heatsink and stops some of the "heat" you are soldering with from being pulled away by the heatsink.

 

[skippyreef]

here they are on with the 60-48 ELN

 

[skippyreef]

with the lenses

 

[Jay1982]

To ensure line up and the hassle of picking up the string of soldered LEDs, I solder on the heatsink...sort-of

I place a non-metal, non-meltable, "shim" under the star, do the solder work and then move to the next.

This raises the star you are working on away from the heatsink and stops some of the "heat" you are soldering with from being pulled away by the heatsink.

Awesome, thanks man. What material is the "shim" that you use just out of curiosity?

 

[rcgates]

Awesome, thanks man. What material is the "shim" that you use just out of curiosity?

I usually have some unused circuit boards or such laying around, easy to get at Radio Shack.

 

[skippyreef]

wired second string and same thing. LPC 35-700 will not light it but they come right on with the ELN 60-48