LED setup

[Wreckless_Process]

ok i am going to be running 8 LEDs

theres 4 sockets i am goign to be using from a 12v DC system

so 2 leds per socket.

these are hte resistors they offer:
http://www.lsdiodes.com/shop/index.php?main_page=product_info&cPath=10&products_id=68
these are the LED ill be using in this setup:
http://www.lsdiodes.com/shop/index.php?main_page=product_info&products_id=17

how would i set that up?

also i was told for some otehr LEDs im buying that i would need 390ohm resisters per LED for a single led setup

they dont offer 390. would i get the next rating up in ohms or down?
heres the next up:430ohm
down:360ohm

 

[Stuey83]

It says they do offer 390 ohms. If they don't have it, go to a slightly higher value. Don't forget that the resistor values are only approximate. In other words, if you have two resistors labelled 390 ohms, they can be anywhere betwen 370 ohm and 410 ohm. Typically a value is accurate to within 5% of its designation. Some are superaccurate, but you'll have to pay extra and it's only necessary in some specialized applications.

I'm not sure what you mean by how to set the LEDs up. You connect the resistor in series (in-line) with the LED, which is connected in proper polarization to the powersource. Your several LEDs should be connected in parallel.

 

[Mohonri]

You'll be setting up the LEDs something like this:

12V(PSU) --->resistor--->LED--->GND(PSU)
or like this:
12V(PSU) --->resistor--->LED--->LED--->GND(PSU)

You'll use a smaller resistor for the second case. In order to calculate the size of the resistor, you can simply use a resistor calculator like this one or this one (better).

 

[Wreckless_Process]

well i noticed for my second situation it actually is rated for 330 but it reccommended 390 so im guna go 360 i hope that will work

 

[Mohonri]

I would recommend going with the 390--there won't be any noticable difference in brightness, and you'll extend the life of your LEDs significantly.

 

[Wreckless_Process]

they are out of 390. if they dont have them when my paypal finishes registering my new credit card. will 360 be ok?

 

[Stuey83]

Then you might want to go the next step above 390. It's not a big deal if you go with 360. if your LEDs burn out, buy some more.

 

[Wreckless_Process]

the leds only requre 330. the next 10% is 390 but they are out so im thinking 360 would be fine

 

[Stuey83]

Where are you getting these numbers from? V = IR. Those LEDs have a typical current of 30mA. R = V/I --> R = 400 ohms. If you hook up more than 1 in series, use a lower valued resistor.

 

[Wreckless_Process]

i dont htink u kno what im talkign about.

http://metku.net/index.html?sect=view&n=1&path=mods/ledcalc/index_eng

both the 5mm and 3mm led both are 2.1 forward and 30ma and im running a 12v system

so for 1 LED it would be 330ohms, next 10% would be 390ohms

for 2 leds(most i would possibly be running)

@ 2.1 forward, 30 ma, on a 12v would be 260ohms, next 10% would be 270ohms


the 360 would be for the single led setup cuz they are out of 390, and if 330 would work, and 390 would work, why wouldnt 360.

 

[n00btard]

which is brighter, multiple LEDs connected in series or parallel? I always get mixed up on that...

 

[Mohonri]

In theory, it should be the same. However, in general, it's better to put LEDs in series with each other. That way, every LED has the same current flowing through it, and therefore the same brightness. You *can* put resistor + LED strings in parallel with each other, but it's better not to put the LEDs themselves in series, because differences in manufacturing will give them slightly different forward voltages, and if they all are hooked to the same source voltage, they will have varying currents->varying brightness.

In other words:
Good:

12V-->resistor-->LED(s)-->GND
12V-->resistor-->LED(s)-->GND
12V-->resistor-->LED(s)-->GND

Bad:

               +>LED-->GND
12V-->resistor-->LED-->GND
               +>LED-->GND

 

[Stuey83]

i dont htink u kno what im talkign about.

*DOH*, you're right, I forgot about the forwarding voltage. I'm still in physics 2 tutoring mode, sry.

I second Mohonri's configuration suggestion!