Correct Voltage for my two LED's

[joey_d1119]

Hey all,
I have 2, 5mm LED's, for my PL original enterprise. I was told that 3 volts is the minimum for one LED. So If I have two 5mm Leds and I have a 9 volt adapter is it enough to light them, and not enough to burn them out?
Thanks,
Joey

[mikew]

You are almost certainly going to have to provide some more information before your question can be answered in full. How much current are they rated for (and how much you want to pass) as well as the voltage drop across the LEDs themselves.

Also, you will almost certainly not be able to hook these up directly to your power supply. You'll need a resistor to limit the current, the size of which will be determined by the current and voltage ratings of your LEDs and how you plan to hook them up.

Mike W.

[joey_d1119]

http://www.lsdiodes.com/5mm/5mmwhite12000.htm

Click on that link.

If both LED's max is 4 volts, will one more volt make a difference? I am going to wire them up very simply, just + to+ and - to -, then connect that to a female plug via wireing which connects to the 9 volt adapter.

[macfrank]

http://www.lsdiodes.com/5mm/5mmwhite12000.htm

Click on that link.

If both LED's max is 4 volts, will one more volt make a difference? I am going to wire them up very simply, just + to+ and - to -, then connect that to a female plug via wireing which connects to the 9 volt adapter.

If you hook up the two white LEDs in series directly to the 9V power supply without a current limiting resistor you'll probably fry them pretty quickly.

The LED series/parallel array wizard says that for your white LEDs and a 9V DC power supply, you'll need an 82 ohm rcurrent limiting resistor. It'll draw a schematic for you, too.

Frank

[joey_d1119]

9 Volt Source
4 diode forward voltage
25 forward current
2 LED's

R= 47 ohms

It says I need a 1/4 watt resistor.

I didnt see an 82 ohm in my answer via the wizard. Did I enter the numbers wrong? If it is 82, will a 78 resistor be acceptable?

Also, If I use a 4.5 volt source it says I need 2 1ohms resistors, but the help section says the calculations are based for operating the LED's at 60% power. So If I use a 4.5 volt source without resistors shouldnt the LED's be fine?

[macfrank]

9 Volt Source
4 diode forward voltage
25 forward current
2 LED's

R= 47 ohms

It says I need a 1/4 watt resistor.

You should always go with the typical values on a device spec sheet, since that's where most of the devices will fall. From the speadsheet you linked, the typical values are:

Forward Voltage: 3.6V
Forward Current: 25ma
2 LEDs

From the wizard:

R= 82ohms with a 9V power supply.

I didnt see an 82 ohm in my answer via the wizard. Did I enter the numbers wrong? If it is 82, will a 78 resistor be acceptable?

That should be fine.

Also, If I use a 4.5 volt source it says I need 2 1ohms resistors, but the help section says the calculations are based for operating the LED's at 60% power. So If I use a 4.5 volt source without resistors shouldnt the LED's be fine?

Using the listed typical LED values and a 4.5V power supply, you'll need two 39 ohm resistors. The resistor (not the LED) power rating has been derated to 60%. You'll probably have an easier time finding an 1/4 watt resistor than a 1/8 watt, so just stick with it.
LEDs need current limiting, unless you're right at their forward voltage. Even then it's always a good design practice to add a resistor, however small. You don't want to accidentally blow out an LED in a finished model.

[TimeScape]

Also, check this out:

http://www.culttvman.com/assets/Model_Lighting_.pdf

I beleive you can also find it here on Starship Modeler.

[Sparky]

That spec sheet said max was 4 volts, so even a little more and that and they are saying it will burn the LED. Running LEDs at max will give you lots of brightness for much less time.

We ran <A HREF="http://www.kc6sye.com/images/images_05_ ... hrudck.jpg" target="_blank">these</A> Whites <A HREF="http://www.kc6sye.com/images/images_05_ ... hrudck.jpg" target="_blank">at 3.25volt</A>