From: peter2@hipson.net   
      
   On Wed, 18 Jul 2007 17:20:33 +0100, "Norman"   
    wrote:   
      
   >   
   >"Charles"  wrote in message   
   >news:2cadnVWCkP_zyRDbnZ2dnUVZ_u-unZ2d@comcast.com...   
   >>   
   >> "Norman"  wrote in message   
   >> news:a4cji.129081$hj5.101518@fe2.news.blueyonder.co.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.   
      
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