Multiple LED lighting and resistor values

[Orion_dab]

I am building various trek model ships. I went to different electronic stores and bought different color led's 3mm and 5mm in size.

To start, I bought a roll of 360 ohm resistors to use with each led.

My cct are run in parallel to the power supply--9V battery or 9V plugin.

I have noticed, that when combining certain leds in parallel with other color leds, one will not work.

After some research I found out that every color led has its own unique forward voltage drop.

Some of my led's are just the clear bulb (but will illuminate different colors), other leds are just colored (red/green ect).

Has anyone come across this issue and what was your solution?
Using different value resistiors for each color/size led?

[Ziz]

It's a standard lighting issue. All LEDs have slightly different power needs because of the different colors and sizes.

Plan out your lighting on paper. What I've done in the past is make a copy of the instruction sheet and just draw on that. Makes it easier to see how and where the lighting needs to go and how you can route the wiring before you start modifying the kit.

Once you've got all that worked out, list out all your LEDs and the voltage/amperage each one wants. You'll need different size resistors for each power range. There is a little wiggle room though, so don't freak if one wants 2.2v and another wants 2.3v - they're effectively the same.

Work out all your math first. That will save you a lot of troubleshooting headaches later on.

[Bellerophon]

A breadboard and voltmeter are very useful, too. If you don't know what resistor value an LED needs, plug it into the breadboard with a resistor in series, with your supply voltage applied. Since LEDs typically operate with about 20 ma of current, use a resistor that won't pass more than say 10 ma: with a 9 v battery, you'd need about a 1k resistor. You see for yourself how bright the LED is and you can measure the voltage across the resistor, then the current I=V/R. This will give you a good idea how low of a resistor you can get away with without burning out the LED.

Many LEDs died to bring me this information.

[galaxy_jason]

You are trying to run multiple LED's in parrallel off the same current limit resistor. Never do this. You need a seperate resistor to each, or you can run a few in series.

http://electronics.stackexchange.com/qu ... allel-leds

[Tchail]

I have a spreadsheet where I (try) to keep track of the voltage and amperage of my LED purchases.

From my experience, white/green/blue LEDs typically require 3v, while red LEDs use 2.2v.

And most LEDs typically require 20 mA of current.

Hope this helps,

-Tchail

[Orion_dab]

My 9V battery blew open so I am running a current limiting resistor along with individual resistors in the cct. It seems to be working well now.

My model has various different LED's from different manufactures, different sizes and even uses strip lighting.

For my next model I will purchase all LEDs from the same manufacturer and use a slightly lower resistor for the LEDS that use a higher forward voltage (white/green/blue).

I will also use a plug in power supply because I use a lot of LEDS in parallel and dont want to overcurrent a standard 9V battery.

[Grumpy Popeye]

another thing you can do is just get white LEDs and tint them with clear red/green/blue ect.. that way you can save the headache of working with different voltages.

also, this site has a handy calculator to help with figuring out resistor values

http://led.linear1.org/led.wiz