Hi,
I have a few of these:
http://www.phenoptix.com/index.php/5mm-rgb-led-common-anode.html
And would like to know what the max voltage I can pump into them would be? I asked the store but didn't get a reply.
thanks.
The forward voltage of a diode (LEDs are just diodes) depends on the nature of the diode (here the colour of the LED), the temperature and the current.
You control an LED by current rather than voltage, since otherwise the brightness is very sensitive to temperature, device variation etc. Typical rough forward voltages for LEDs are about 1.7V for red, 3.2V for green/blue/white. You normally add a series resistor (for each colour) that sets a sensible current level.
So for the red LED, if you want 10mA from a 5V supply then the voltage across the current limiting resistor is 5-1.7 = 3.3V, so a 330ohm resistor will set 10mA. For green/blue 5-3.2 = 1.8 so 180ohm would be appropriate. Connect the common anode to +5V and the individual cathodes via the relevant resistor to 0V (or an Arduino pin).
You do not pump voltage into them, you have voltage over them so they can light up.
This can be typically from about 1,7 volt to 3,5 volt depending on the color.
An general purpose led uses 20mA to fully light up.
You need a data sheet for the led to know it's specifications.
A search engine is your friend.