a few questions

[shortstack]

i just ordered 15 cree p4 and 3 cree r2's from DX. i want to use these (not all of them) for a room in my house. im not sure which ac to dc driver i need, or where is the cheapest place to get it. the room is about 20x20 and single story. how many led's should i use for the room? i want it to completely replace the regular fixure. i dont have a problem drilling into the ceilling. i would like to have the leds as possible but i dont want to have to buy like 4 of the drivers.

if someone can give me some insight i would appreciate it. thanks

 

[R33E8]

You can use this driver: http://www.ledsupply.com/xi-led120a0024v10d.php

This driver would need 3 strings of 6 leds on each to run each LED at 350mA(a reasonable current). Make sure the LEDs are heatsinked well to prevent thermal runaways.

 

[shortstack]

how many led would this drive total? 6?

 

[R33E8]

It will drive all 18. You make 3 sets of 6 LEDs in series (I would do 5 Q4's and 1 R2) then connect all of the sets to the driver in parallel.

 

[shortstack]

well i dont wanna use all 18 of them i was thinking maybe half. i would really like for them to be ran at 700mA unless you guys think its too much, i would rather use less leds.

also what about this one? http://www.ledsupply.com/xi-led120a0024v18f.php

 

[blasterman]

700mA is fine - assuming you have them heat-sinked really, really good.

(They call these '3-watt' LEDs for a reason.)

IMHO, I've found little lighting difference in running Crees and Luxeons at full power -vs- 75% of max ratings for fixed lighting use. The extra couple of lumens aren't worth the extra heat and increased stress on the power supply.

 

[shortstack]

thanks for the info. i was thinking of using 3 led and have 3 or 4 "fixtures" i would think this would be bright enough ? i plan on heat sinking them well too. I was thinking either retrofil them in a 4" "canned" lighting or just using a piece of aluminum (like 3" x 4") kinda like this http://members.cox.net/brlux/CPF/Led home lighting/Home lighting new 3.JPG . i was wondering how i figure which driver i need? so the driver puts out 12 volts right? each led needs 3.7volts so i can connect 3 led in series? how do i figure the resistor i need and how to figure the mA for each? i would really appreciate the info. thanks

 

[shortstack]

well i ended up buying 2 Xitanium 350mA and 1 700ma driver, i decided i wanted the led to be driven at around 350mA so there efficient. i wanted to only use one of the 3 driver's if at all possible, also what size resistor will i need? thanks in advanced

 

[superjoe83]

you shouldn't need any resistors if your using a driver made for those LED's

 

[shortstack]

so i just hook them up and go, would i connect them in series or parallel

 

[shortstack]

ok got the drivers in today, look real nice. i would like to use 1, 12w 350mA driver, i have 2 recessed lighting fixtures (cans) ok now someone tell if im wrong. the output on the driver goes to 32.8 vdc (350mA) so each led only uses 3.7 so that means i can wire 8 led's in series and be fine.

I am planning on putting 4 leds in each light fixture and using 2 for the room. i will use 3 cree p4's and 1 cree r2, might switch them all to R2s if the p4's aren't bright enough.