Monday, Jun 28, 2010 at 20:02
Geoff, I guess we had better go back to the theory books eh? I will agree that some diodes have a nominal voltage drop of .6v i.e those rectifiers made of silicon.
Others (made of germanium) have a .2 volt drop. However, there is not an LED made that has anything near those !!! Most LEDs have (depending on colour , and therefore construction) a voltage drop between 3v to even 4.5 volts each. So 100 LEDS would require at least 300volts b4 they even glow. Try it yourself; connect say, 5 LEDs in series and put across 12v. They will not light up. That is why I said 20 LEDs in series. If they are red LEDs they will require 72v to even light up. Actually, white LEDS are mostly made from blue LEDS which require even more volts to work. You can run a red led on a 3v lithium battery with no resistor. It will not blow up !!!
75v DC is not life threatening in most circumstances. I would have no hesitation in grabbing hold of a 75vDC supply because ordinary skin resistance is too high to allow lethal current to flow. Old radios used to run on 90v batteries, and never got a shock from them! 6 car batteries in series ( 75.6v) are capable of melting steel etc, but they certainly won't kill you if you grab hold of it. The resistance of the human skin is just too high.
Ian
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