# LED Module arrays

Discussion in 'General Electronics Chat' started by blkburban, Apr 13, 2009.

1. ### blkburban Thread Starter New Member

Apr 10, 2009
3
0
Hi,
I am pretty mechanicly inclined but not very elecrontic savvy, here is my project and questions regarding said project.

I want to set up a board with 18 white 10mm and 12 blue 10mm LED's.
I want to be able to have them modular so that i can run anywhere from
2 to 10 boards, from the same power supply.

Question 1 12V or 24V?
Question 2 How Many Amps?
Question 3 What type of heat am I talking about dissapating and will a fan be sufficient or will i need heat sinks as well?
Question 4 How do I calc my Resistors for each series since the bulbs have different forward voltages, do I average them out?

Specs
WHITE
DC Forward Voltage: Typical: 3.4 V Max: 3.8V DC Forward Current:20mA
BLUE
DC Forward Voltage: Typical: 3.0 V Max: 3.8V DC Forward Current:20mA

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2. ### Audioguru New Member

Dec 20, 2007
9,411
896
Each string of LEDs is typically 19.2V and could be as high as 22.8V plus a couple of volts for the current-limiting resistor.
Do you think it can be powered from only 12V?

How many Amps is determined by how many strings you will have. 20mA for each string.
The heat will be typically 24V x 20mA= 0.48W for each string.

If the LEDs total 19.2V then the current-limiting resistor will have 24v - 19.2V= 4.8V across it. Then the resistor value is 4.8V/20mA= 240 ohms.
If the LEDs are at their max voltage of 3.8V each then a 240 ohm resistor limits the current to only 5mA.
You might need to measure and sort the LEDs.

3. ### blkburban Thread Starter New Member

Apr 10, 2009
3
0
Sorry for the 12V I was thinking of strings of 3.

What is the formula for converting the wattage heat to temp, or how would I go about figuring out if air cooling is enough VS. a fan?

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
283
Power is Voltage times Current: P = EI.

Mar 24, 2008
20,772
2,540
6. ### thatoneguy AAC Fanatic!

Feb 19, 2009
6,357
718
This is a help once you understand the concepts/reasons:
LED series parallel array wizard

It will display possible combinations given the Supply Voltage, LED Current, and LED Voltage. Don't rely on it for solving all problems, as it only calculates "basic" LED chains with resistors.

I'd strongly recommend fully understanding the information by others above, and in the the link by Bill before using the wizard. When you know how and why things are connected the way they are, it is much easier to make it work and/or repair.

7. ### blkburban Thread Starter New Member

Apr 10, 2009
3
0
Thanks For all the help guys,
after a crash through all the introductory pages here and trudging through my MENTAL RESISTANCE to learning mathmatic computations my wife was none to happy I was up till 3am when the lightbulb finally went on so to speak.
once again THANKS FOR THE HELP