On Wed, 18 Jul 2007 17:20:33 +0100, "Norman"
wrote:


"Charles" wrote in message
...

"Norman" wrote in message
o.uk...
I have used LED's many times before but never in series.

I need to run as many LED's as possible from a 12v supply. Is there a
formula for series LED connections ?

Multiply the drop across one LED by the number in series (e.g., 2 V x 6 =
12 V) up to the limit of the supply. However, it is better to leave a
couple of volts for a series resistor. So, you could connect 5 in series
with a 100 ohm resistor. Even better, use a constant current supply with
a compliance voltage range large enough to forward bias all of the diodes.


Cheers for the help. I have not been ignoring you, my PC decided to clean up
my news massages and I cant get them back.
Reading your suggestion I am guessing that the 100 ohm resistor is enough to
lose 2 volts.
eg. if my final voltage is 14 volts, I can get away with 6 leds and a 100
ohm res ?

Also guessing I needs to know if the leds want 2v or 1.6 / 1.8v ?


Short of looking at the specifications for your particular LED, let's
say 1.6 volts. Feeding 14 volts would require (guesstimate) about 200
ohms.