01-29-2011, 02:15 PM
Two basic things about LEDs: One, they ALWAYS need resistors.
Two: the resistors may already be on the decoder (check the instructions), if not, then for the various shades of 'white' LEDs you pretty much can;t go wrong with a 1K resistor. For EACH LED. There's all sorts of crazy calculations you do if you really want to, but every commonly avaialble white LED I've seen (outside of specialty ones you cna get from the fancy electronics suppliers - like those super-power ones used for floodlights and stuff) has almost exactly the same voltage drop and current limit, and when plugged into the formulas the result is ALWAYS around 1K
Ok, there's a third point - the current rating for an LED is the MAXIMUM it can take without greatly shortening the life. How much shorter depends on hw far you exceed the limit. So should you bothe to go through the calculations, do NOT plug in the current rating from the LED spec sheet, that will leave you with zero headroom or, if you use just basic 10% tolerance resistors, actually over the limit.
--Randy
Two: the resistors may already be on the decoder (check the instructions), if not, then for the various shades of 'white' LEDs you pretty much can;t go wrong with a 1K resistor. For EACH LED. There's all sorts of crazy calculations you do if you really want to, but every commonly avaialble white LED I've seen (outside of specialty ones you cna get from the fancy electronics suppliers - like those super-power ones used for floodlights and stuff) has almost exactly the same voltage drop and current limit, and when plugged into the formulas the result is ALWAYS around 1K
Ok, there's a third point - the current rating for an LED is the MAXIMUM it can take without greatly shortening the life. How much shorter depends on hw far you exceed the limit. So should you bothe to go through the calculations, do NOT plug in the current rating from the LED spec sheet, that will leave you with zero headroom or, if you use just basic 10% tolerance resistors, actually over the limit.
--Randy
Modeling the Reading Railroad of the 1950's in HO
Visit my web site to see layout progress and other information:
http://www.readingeastpenn.com
Visit my web site to see layout progress and other information:
http://www.readingeastpenn.com