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Topic: Multiple LEDs Voltage vs Amps (Read 697 times) previous topic - next topic



First thank you very much for you help, the community, and Arduino.  Right now I am working on a project where I would like to run 20-80 RGB LEDs.  For now lets just say 20 rgb LEDs.  Each Led can use 15mA so that would mean I would need 900 mA to run the system.  Now my question when looking for a power supply is what voltage should I get.  I mean what is the advantage for lets say a 12v at 1 Amp vs 9v at 1 Amp.

Again thank you for your help


Sep 16, 2014, 06:10 pm Last Edit: Sep 16, 2014, 06:14 pm by omersiar Reason: 1
W (Watt) = V (Volt) * I (Current)

Basically you will get 12 * 1 = 12 Watt total power capacity with 12V 1A rated power supply and 9W with 9V 1A rated power supply. These watts what your power supply can give not consumed

You will consume
900mA * 12V = 10.8W

900mA * 9V = 8.1W

With 12V you will get brighter LEDs, and you will consume more power
With 9V you will get less brighter LEDs than 12v and consume less power than 12v

I may be wrong, I just give you basic idea.



Sep 16, 2014, 06:22 pm Last Edit: Sep 16, 2014, 06:33 pm by elac Reason: 1
12V @ 1A = 12W
9V @ 1A = 9W......That's the difference. Advantage will be if you are running 3 LEDs colors in series @ 9.XV then the 12V would be the one you want.
Each RGB LED will consume up to 45mA @ a limited 15mA per color X 20 = up to 900mA total draw.
How will you be setting up these LEDs?  All the same color at the same time?
It's all about the skills


really appreciate the help guys. 
I am working on purchasing everything I need but want to make sure I buy the right power supply resistors ect.

I thought the brightness would be based off of the Amps not off the watts.....
I really did not think I needed to worry about watts..

I am running the arduino to a shift register using

then out of the shift register to a TIP120 or TIP122 transistor then to the rgb LEDS.

The LEDS will be always on but different colors.  It will work like a meter.  left side a blue green right side a Red green.
base on something like pressure ect. from another input the "meter" will sift showing more blue green and less red green or less blue green and more red green.

Right now I am just doing the 20 rgb leds but would like to get a supply that will be able to handle the 80 rgb leds

Sorry for my ignorance on the subject.


You might want to do a test first and have different values of resistor for different colours so when they are all full on you get a decent white and not a tint. Most RGB LEDs give off vastly differing levels of brightness for the same current.


Yeah I plan on using different resistors for the different colors.

So which power supply should I get a 12 V power supply or a 9 V?  Also any good places to get the power supply from?


Sep 16, 2014, 08:44 pm Last Edit: Sep 16, 2014, 08:47 pm by _pepe_ Reason: 1

Most of the RGB LEDs are common anode or common cathode, and they cannot be wired in series. So the required power supply voltage for such LEDs is rather low.

If the currents are limitted using resistors, then the right power supply voltage should be about twice the highest direct voltage of the LEDs inside a RGB LED.

For instance if the specs of the RGB LEDs read :
- red: 1.9V@15mA
- green: 3.1V@15mA
- blue: 3.1V@15mA

then a 6V regulated power supply would be enough. Higher voltages would increase power loss.


Cool Thank you all for your responses...
I think I am going to look for a 9V 4Amp power supply.  This will give me room to go up to 80 leds (3.6 Amps)
9V just seems to be more standard then a 6V (though i could be wrong)

Any suggestions where one could get such a thing?
Also anything I should look out for because this is the first time trying to tap into higher power then what is supplied by the arduino?  I have not messed with anything with 9 volts or 4 Amp.


There are bunch of 12V 4 Amps Power supplies, i don't know how about 9v 4Amps. And you should use proper transistors or MOSFETs for high current circuit.


Thank you for responding.

I think a TIP 122 Transistor should be able to handle it correct?


do i need thicker wires or will the standard arduino wires that come in the start kicks work?  Is working with 9v 4amps dangerous?


Sorry with the questions above one last thing.  will i need to get different watt rated resisters?


A resistor rating is only the maximum power it will take. There is no need for anything big in any resistor.

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