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LED Project

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chrisab508

New Member
Hey Guys,
I understand that LED projects are popular, and that you get a lot of questions regarding them so I apologize if what I'm asking has been covered.
I am making an LED sign (essentially a neon sign but made with LEDs). My plan is to make the outline of a christmas tree with green LEDs, and some "christmas lights" inside the tree with red LEDs. I have a fairly large perf board because I wanted to make it pretty large. My question to you guys is how do you think I should power it? Given the size I'm looking for, I could be using quite a few LEDs, so I'm guessing a simple battery (e.g. 9v) will not be sufficient. I could do the calculations, however, I feel that someone here has probably tackled this situation previously.
I also have a similar question. I will probably be operating somewhere in the range of 100 LEDs (perhaps more), so I would imagine that I do not want to wire them all in series, or all in parallel (which would be a mess), would you guys recommend splitting them into lines of 10? 20? n?


EDIT: I can get a DC power adapter pretty easily. A 12v, 500mA is easiest for me to get (won't have to order it online), however, a quick ebay search shows me that I can get a 12v 2A power adapter as well. Thoughts?


Thank you in advance, any help is appreciated.

- Chris
 
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codywookman

New Member
Are you set on using batteries or will you be able to plug this tree in? If you can plug it in you might try a converter to switch to DC and drop your voltage to the LED specs.
 

chrisab508

New Member
To be perfectly honest, I originally thought I would be making something small which is why I had a battery in mind. Given the nature of this tree project (and its magnitude) I think that going with a small 12v power adapter would be best. Also, as this is a gift for my mother, a 12v power adapter would mean that--barring any component failures--she wouldn't have to replace anything to keep it running!
 

audioguru

Well-Known Member
Most Helpful Member
Modern bright green LEDs are about 3.5V each. Then you can connect three in series and in series with a current-limiting resistor and use 12VDC to power them.

Red LEDs are about 2V each and 5 can be connected in series and in series with a current-limiting resistor and powered from 12VDC.

Each string uses 10mA to 25mA at 12V.
You do the simple arithmatic to calculate how much total current you need.
 

chrisab508

New Member
One more question, do you guys know if it's ok for me to use an unregulated 12v DC power supply? Or would I need a regulated one?

- Chris
 

audioguru

Well-Known Member
Most Helpful Member
With an unregulated supply, the LEDs will be a little brighter when the voltage is high and a little dimmer when the voltage is low.
 

chrisab508

New Member
Audioguru,
In your experience will that make a noticeable difference in the overall display of the LED sign?

- Chris
 

audioguru

Well-Known Member
Most Helpful Member
Audioguru,
In your experience will that make a noticeable difference in the overall display of the LED sign?

- Chris
You do not show where you are in the world.
If you are in a 3rd-world country where the electricity voltage varies all over the place then the brightness of the LEDs will noticeably change.

If you live in a civilized country where the electricity voltage is always the same then you won't see any dimming.

If you start with a fully charged battery and turn off the LEDs before the battery is too dead then you won't notice the dimming.
 

chrisab508

New Member
Sorry to bring up an old thread, but I have another question. Say my project has roughly 70 green LEDs, all with voltage drop 3.5v, and 20mA. This site (LED series parallel array wizard) gives me a specific array with dimensions and resistor values depending on my my input values (# of LEDs, forward bias, current, and voltage source). Based on this site's estimated power use I don't want to go with a battery because it won't last very long. I can buy a cheap 24vdc, 1A power supply. My question is, with my above numbers and a 24v voltage source, the calculator says that my array will draw 240mA from the source. If my dc power supply is a 1A power supply, will I have to use different resistor values than those given in the array calculator to avoid blowing out my LEDs?

Thank you in advance,

- Chris
 

mneary

New Member
The 1A power supply has 1A available. The LED circuit will only take what it needs, provided you have calculated the resistors correctly for 24V.
 

mbarazeen

Member
you can put all your leds in series and use the mains even to power it up directly, if your insualtion is good not to make any helth hazard. calculate the number of LEDs in series and the value of resitor to be connetced in series, based of the voltage you are working on.
 

audioguru

Well-Known Member
Most Helpful Member
you can put all your leds in series and use the mains even to power it up directly.
No.
He is in California where the mains is only 120V.
Maybe he can use 35 LEDs in series and the other 35 LEDs with reverse polarity.
 

chrisab508

New Member
No.
He is in California where the mains is only 120V.
Maybe he can use 35 LEDs in series and the other 35 LEDs with reverse polarity.

Actually I'm in Illinois haha, I also wouldn't really want to wire them into the mains, I don't really have a problem wiring them into an array and using a DC power supply. Thanks for all the help though!
 
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