120V led power supply. What do you recommend?

[Lumencraft (Matt)]

Hi everyone,



My cousin would like to have an LED hanging lamp above her table. I have put one together but I would like to have a safe reliable power supply.



The lamp uses 4 XRE emitters. I can wire them s p or any combination. I have tested the heat sinking and 600ma per seems to be about right.



Any help is appreciated.

 

[jonathandowers]

Any updates on the build?

 

[CKOD]

I havent used it but http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=945-1375-ND certainly looks interesting, Digikey had quite a few stocked constant current LED drivers with AC input, on their product index, its under power supplies, external, LED constant current.

 

[Lumencraft (Matt)]

Any updates on the build?

LOL I forgot all about this thread.

Yes I did build this lamp, I dont have any pics but it went quite well. I took an old stained glass hanging lamp and made a copper/aluminum heat sink and wired the emitters in series. I used a standard UL rated power supply that was about 15V 400 ma if I recall. Since the output voltage was higher than the combined vf of my leds I had to use a resistor to set the current, and I also fused the whole system. Its been handing in their kitchen for about a month or two now.

I have found that just about any UL rated power supply (like phone chargers and power cords from other electronics) can be used if you make sure to use a resistor to limit the current so it does not exceed the what the supply is rated for.

 

[RCantor]

Hi! I'm looking in to something similar. How do you calculate and wire the resistance? Thanks.

 

[FlexfireLEDs]

us too! haha thanks

Hi! I'm looking in to something similar. How do you calculate and wire the resistance? Thanks.

 

[AnAppleSnail]

Hi! I'm looking in to something similar. How do you calculate and wire the resistance? Thanks.

Two options:
Find the average forward voltage of your LEDs at the chosen drive level and figure things out:
*Vsupply - Vled - Vresistor = 0
Vled = Vforward @ I
Vresistor = I * R


OR

Make this circuit: Simple CC circuit

I used the CC circuit in my reading lamp. A cell phone charger supplies up to 350 mA at 5V, and the LM317 acts as a switching regulator giving either 1 or 100 mA. Note that you connect LED (+) to Vadj, not Vout. I suggest testing this before installing to ensure correct current. This does remove guesswork about your forward voltages, and adds a $2 part from The RatShack (Radio Shack).

The LM317 wants a bit of voltage headroom, so using a phone power supply would be just short of giving 600 mA to 4 LEDs, which produces about as much useful light as a 13W fluorescent. I have one XR-E in my reading lamp at 350 mA and it's plenty for reading.