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jaharr01:
I ordered these 10 PCS 3W RGB Color High Power LED Light Emitter 4 pins with 20mm Star Base
http://www.ebay.com/itm/161057070124?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649

I haven't messed with RGB LEDS before so I have a question. If I use 5 of these it says the maximum voltage is 3.6 per LED I used an LED calculator
DC Forward Voltage (VF): Red: 2.0-2.5Vdc, Green: 3.2-3.6Vdc, Blue: 3.2-3.6Vdc,
DC Forward Current (IF): Red: 400MA/ Green: 350MA/ Blue: 350MA

Solution 2: 1 x 5 array uses 5 LEDs exactly
+12V                   R = 22 ohms
                R = 22 ohms
                R = 22 ohms
                R = 22 ohms
                R = 22 ohms



The wizard says: In solution 2:
•   each 22 ohm resistor dissipates 3520 mW
•   the wizard thinks the power dissipated in your resistors is a concern 
•   together, all resistors dissipate 17600 mW
•   together, the diodes dissipate 7200 mW
•   total power dissipated by the array is 24800 mW
•   the array draws current of 2000 mA from the source.

Is this correct,should this work OK?
Jay
PL1:
Have you considered using a 5v power supply?

12v - 3.6v = 8.4v drop across the resistor -- 70% of the total energy is wasted/dissipated as heat. (8.4v/12v)
  5v - 3.6v = 1.4v drop across the resistor -- 28% of the total energy is wasted/dissipated as heat. (1.4v/5v)

Using a 5v supply will result in about 16.66% (1.4v/8.4v) of the heat dissipation/power waste required for a 12v circuit -- assuming that you choose resistors that allow the same amount of current to pass.

Also, each channel (red, green, and blue) will need a resistor that keeps it within the voltages you mention in your OP.
3.6v applied to the red channel = very bright for a while followed by a "magic smoke" leak.   :angry:

For 5 RGB LEDs, you need to calculate for 15 channels (5 red, 5 green, and 5 blue), each channel will need a current-limiting resistor that brings the voltage down to a safe level for that color in the LED.


Scott
jaharr01:
Yes I can,I can use a switchable power supply. It also has 5V. Will they be less bright at 5v?
jaharr01:
They are flashers on my pinball build so they need to be bright
PL1:

--- Quote from: jaharr01 on July 05, 2014, 02:34:07 pm ---They are flashers on my pinball build so they need to be bright

--- End quote ---
Bright = good.

Overdriven = bad.

Having a larger current-limiting resistor will not make your LEDs brighter.

Picture drinking from a drinking fountain (regular 20-30mA LEDs) vs. chugging from a beer mug (your 350mA+ RGB LEDs) vs. drinking from a fully-open firehose. (your LEDs connected to 5v or 12v *without* current-limiting resistors)

You can't keep up with the firehose, it will overwhelm you unless you put a pressure/flow reducer (current-limiting resistor) inline with the hose.


Scott
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