Cree Star and problem

[1-3-2-4]

not sure what's up.. I just mounted two royal blue Cree XR-E's on a alimum bar with mounting screws.. So I wried in series and the LED's wont come on at all I'm using a buckpuck to drive them at 700mA

 

[moderator007]

What was the voltage you applied to the driver? Best I can tell 2 royal blue XR-E's will have a 6.4v vf in series. The driver needs 2v over the total leds vf. Needs more than 8.4v to drive at 700ma. Best I can tell. Is your polarity correct?

 

[1-3-2-4]

I was doing 13V then moved to 19V.. maybe I got the wiring wrong? it goes pos-neg from the driver and then pos from the first star to neg to the next? Don't I need to wire back from the last star?

 

[moderator007]

I was doing 13V then moved to 19V.. maybe I got the wiring wrong? it goes pos-neg from the driver and then pos from the first star to neg to the next? Don't I need to wire back from the last star?

Should go negative from driver to negative of first led. Then positive of first led to negative of second led. Then second led positive to driver positive.
Looking at their product overview PDF. Its probably most efficient at around 10v with 2 leds.

 

[1-3-2-4]

odd.. I did that and it wont turn on both LED's at all.

 

[1-3-2-4]

The stars or maybe the screws must be conducting on the bar because just touching my soldering iron anyplace on the bar causes the first LED connected to the buck to glow faint.

Ahh never mind got it finally

 

[1-3-2-4]

Wow I really gotta mix some white in here.. I wonder if I could put one more star... I did not know royal blue was going to be a bit Uv'ish.. I have a stack of green papers that turn a bright green and all my LED's with yellow dies all glow under the the XR-E

 

[CKOD]

Wow I really gotta mix some white in here.. I wonder if I could put one more star... I did not know royal blue was going to be a bit Uv'ish.. I have a stack of green papers that turn a bright green and all my LED's with yellow dies all glow under the the XR-E

Thats because underneath the yellow phosphor led, is a royal blue die.

 

[1-3-2-4]

then that makes sense

One question on my buck I'm using a photocell aka LDR to dim the LED's.. however they don't dim that easy.. like turning on the light in the kitchen they still pretty much stay on.. However if I hit the LDR with my LED flashlight from maybe 15 ft away I can see the LED's dim.

 

[Th232]

One question on my buck I'm using a photocell aka LDR to dim the LED's.. however they don't dim that easy.. like turning on the light in the kitchen they still pretty much stay on.. However if I hit the LDR with my LED flashlight from maybe 15 ft away I can see the LED's dim.

Fun fact: bright lighting in a house may not be that bright.

http://en.wikipedia.org/wiki/Lux

 

[1-3-2-4]

At this point I don't think the LED's would ever turn off.. sun does come in the window in the day but unless it's hitting the LDR it's never going to be bright enough.. I think I'm about to order this larger LDR to see if it helps since these are so small.