DC Power Supply for LEDS...


goscrewyourselves

I'm the one
Looking for recommendations for a suitable DC Power Supply for running my LED Lighting.

My Lighting will consist of around 40 X 3 mm LEDS in all when completed. With that many LEDS, would I be better off using 2 power supplies with 20 LEDS on each?

All recommendations will be appreciated, thanks.
 
Thanks Suzie. I do have an old AC/DC Power Supply and tried it last night. I connected the LED (with 1.5K resistor) to the DC side and nothing happened. I then connected it to the AC side and it worked fine? I was led to believe that LEDS operated on DC though.
 
Hmm, I double checked the wiring instructions and saw that the "long" lead (on the LED) was the power lead to which the resistor should be attached. I only have one LED for the house I just built.

whiteinvertedconewiringsheet_zps1735caa7.jpg


If that should work on the DC side of the Power Supply, then I must have messed up so will change the wires and resistor around and see if that works.

Thanks Suzie.
 
It helps to know the voltage of the led's before calculating resistor value

The flat side of the LED is called the cathode. It hooks up to the negative side.
The Anode side is round and also has the longer lead. It connects to the positive.
 
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The voltage is shown in the above diagram, 3.2 - 3.4 volts. What was recommended by the company and shipped with the LEDS was 470 ohm resistors (1/2 watt)
 
You make it sound so easy ... thanks.

While I think of it though, If an LED at full brightness/power has an X amount of brightness to it, how much will that X amount of brightness be reduced by adding resistors?

For example, if an LED produces 100 brightness without a resistor, would adding a 200 ohm resistor reduce that brightness by 200? Does that make sense? I guess what I am trying to say is how do I know what size resistor to use to reduce the brightness by 50%, for arguments sake, or is that a trial and error thing?
 
Tony, there is a formula to figure the resistor size for a LED.

Source voltage - LED voltage/ LED amperage.

example; (12 volts - 1.5 volts) or 10.5 volts/.01 amps

10.5/.01= 1050 ohms

To make the LED dimmer use a lower voltage for the LED.

12-.75/.01
11.25/.01 = 11.25 ohms.

EDIT: You need to check the amps for the LED. I don't remember what amps is standard.
Either .01 or .1
 
If you are using a higher voltage power supply, you can significantly reduce your current consumption by wiring LEDs in series. For example, with a 12 volt power supply you can power three of your white LEDs in series(3.4v * 3 = 10.2v, which is less than 12v). In the example posted, you have 3.4v leds running at 18 ma.: (12-3.4)/470=0.018. With 40 LEDs, that would be 0.72 amps. If you group them in threes, they would only draw 0.25 amps(13 groups of three drawing 18 ma, + one more individual drawing 18 ma). Each group of three would get one resistor, and it would have to be adjusted to the desired current draw(for 18 ma, 12-(3.4x3)/0.018=100ohms ).

18 ma is probably way brighter than what you want, I was just using these numbers to demonstrate. Regardless, whatever brightness you run the LEDs at, you can significantly reduce your load if your voltage is high enough to run them in series groups.
 
Thanks guys but apparently I am doing some thing very very wrong. I have added TWO 1500 ohm resistors to the one LED and cannot see any difference in the brightness or intensity of the light what so ever.

I tried using one of the recommended resistors (470 ohm) on another LED for comparison. The single 470 ohm light looks no different to the light with 3000 ohm of resistance attached to it, in terms of brightness etc.

What in heck am I doing wrong????
 
Thanks Suzie and your right, the way I am going I'll have resistors for everything by the end of this month. Nice to know that I just have good LED's and that it is not necessarily me who has messed up for a change :)
 
White LEDs can have a pretty broad range to them from dim to full brightness, especially the current high efficient type. I used to use the common 1000 ohm resistor for my headlights, but I'm now finding 2000 to 3000 ohms works just as well and still plenty bright.

When I've used white LEDs for class lights, I use a 47,000 ohm resistor which gives them a nice "glow" - don't want the class lights as bright as the headlights !

Mark.
 
Mark,

Darn and I thought going up to 3000 ohm was pretty high. What you describe, brightness wise, sounds like what I am after, more of a nice glow than a bright light.

Looks as though I should be aiming for at least 40,000 ohm. So now I have to buy 20K and 10K resistors and maybe some 30K and 40K resistors as well.
 
At 47,000 ohms, they are "on", but that's about it. Don't expect them to cast ANY light at that setting. For general lighting, 2000 to 5000 ohms with the efficient white LEDs is good. These yellow LEDs being used for "garden lights" have a 10,000 ohm resistor. They don't really cast any light, but you can see they are on - kinda like the real thing ....

749157a8e058810a18adb50a02a9368d3b2d69b.JPG

Mark.
 
Thanks Mark. I wish I could get a picture of what my lighting looks like so you guys could see how bright they are with 2 X 1500 ohm resistors attached. I just received 20 X 20K and 20 X 30K resistors today, so I will try one of them and see what happens.

I know someone mentioned it could be a trial and error thing until I get the look that I like. Not truly understanding the "power or effectiveness" of the resistor makes it a bit more trial and error for me, thankfully, resistors are cheap! I also get the impression the building the light is in and its color plays apart as well.
 
Well, I just replaced the 2 X 1500 ohm resistors with one 20K resistor and that seems to have done the job, bright enough for it to be obvious but not so bright that it blinds you.

I think the 20K resistors will work well for me in my buildings, while 30K or 40K will work for any ambient lighting. I might change out the white LEDS for yellow ones though and see how much of a difference that makes.

Thanks everyone for your in puts, they have been greatly helpful and encouraging. I'll try to get some decent "night shots" so you can see the results and provide your thoughts.
 
Good to see some getting some edumication here.
A lot of the info people recommend is based on the older style, less efficient LED's.
They've come a long way technology wise. Scenes like Marks were only possible with Bulbs just a few years ago.
 



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