LED's

[Jurasikfrank]

I know no on has been posting in here for a while but still, I thought I'd share a little something. Some of you probably already know about this:
If you have a source 12 volts and planning on lighting 14 LEDs (about 3.3v 20ma each) here's what you can do to reduce the resistance value and draw less current.
EX. 1

In this example, you have 4 times 3 LEDs in series hooked up to 120 ohm resistors and 1 time 2 LEDs hooked up to a 270 ohm resistor. LEDs when connected in series will add up their voltage (3.3v X 3 = 9.9v the 120 ohm resistor dissipates the remaining 3.1v). However, the current will be distributed differently. Each lines of this circuit will see the 12v but the whole circuit will draw only 100 ma (5 lines at about 20ma each).



EX. 2

In this second example, you have 7 times 2 LEDs in series hooked up to 270 ohm resistors. Again, the 7 lines of this circuit will see the 12v but the whole circuit will draw only 140ma (7 lines at about 20ma each).

Here's a link to where I calculate my arrays and where I found these breathtaking images :
http://led.linear1.org

Hope this helps someone.
Remember, less current = less heat... not that we deal with extreme temperatures
Cheers

 

[Jurasikfrank]

BTW, feel free to move this in a different/more appropriate topic.

 

[hooterville75]

Wow, great post dude. I can only hope that someday Ill be able to be experienced enough to try to play with this type of stuff. Being new to the hobby this post is all a bunch of diagram mumble jumble to me but Im going to sit down and try to figure some of this out ha ha ha. I love watching you and Grendels talk about this stuff. You both really know your stuff in regards to lighting. Very good informative post though to those that know what there doing when it comes to lighting. Best of luck to you with this project. Please do post photos of the end result.

 

[Grendels]

And the real easy way is to just use 3V for your power supply, like 2 AA batteries. Then the white, blue and Green LED's don't need resistors. If you need another color, just paint the white LED's with a transparent color of paint.

The only down side to what Jurasikfrank is posting is that if one of the LED"s or the resistor shorts out, then the whole parallel branch will quit working.

If you have ever used the old style Christmas lights where if one bulb went out, the whole string shuts down, then you have experienced the joy of parallel wiring.

With the life time of LED's it really shouldn't be a problem. Just let your circuit proof, by running it for a while before you seal it up in a model. Burnouts will happen pretty early in the life of the circuit.

 

[Jurasikfrank]

Just let your circuit proof, by running it for a while before you seal it up in a model. Burnouts will happen pretty early in the life of the circuit.

Yup, should have mentionned that.
Thanks Grendel.

Also, let me give a dirty little secret : Using a 12v power source, if you wire up 4 white LEDs together (3.3v X 4 = 13.2) you'll be short 1.2v from uptimal brightness but that might bring the brighness down "to scale". See ? wow, you just saved yourself 0,09$ worth of resistors !! You owe me... bing time ;D ;D ;D
Obviously, this kind of work would need to be tested before by an astro physysist under tight supervision... or by a certified addicted modelist in a semi-ascepticized environnement also know as a mancave ;D

Cheers

 

[Elm City Hobbies]

Yeah the weak part of those circuits normally isn't the LEDs, but the resistors.....and how well the circuit is put together.

Glad I passed soldiering class when I was in Electronics! LOL