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LED Signal Lamps
L.E.D. Light Emitting Diode is a Excellent choice, for they have NO FILAMENT and will last indefinetely if the Voltage is correct and the Anode and Cathode isn't shorted. They may have a Dropping Resistor to ensure the voltage is where it should be. Automotive voltage will usually vary from 10 to 16 volts D.C. in this case the more expensive ones may also include a Voltage Regulator to keep the voltage constant. Ever wonder why you paid so much more for a Cell Phone cig adapter or Cam Corder Cig Adapter? They require constant voltage and not Variable voltage.
All L.E.D.s I worked with were less than 3vdc and I have not seen the ones in question, they very well may make 12vdc ones now.
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LED Signal Lamps
Murf
It is recommended to use a Higher Voltage Power supply for LEDs. You are correct about the Transformer, Voltage Regulators which look like SCRs are used to keep the circuit voltage constant a Capactitors my be used to keep the drops from affecting the circuit. Permanent drops such as a bad alternator could cause your LEDs to operate below spec and make them unstable in performance. You may operate a 3 volt LED on a 12 volt power supply and what you would need to know is what to use for a Dropping Resistor's Ohms. The LED will Drop 3 volts of the 12 volts and you will need to dissipate the remaining 9 volts and to do so you will use a dropping resistor. What this means is this, it isn't altering the Voltage for the ramining circuit but rather for the calculatiing of the dropping resistor, so Take your 12 volts or Automotive with a good Alternator run at 13.8 volts (no draw or drain) and subtract the 3 volts of the LED that leaves 10.8 volts now devide that by the current of the LED which different voltage LEDs have different current ratings based on color etc. Let's use 25ma for reference. 10.8 devide by .025 equals 432 so you will need a 432 ohm dropping resistor to be sure the LED circuit sees 13.8 volts. What I do not remember is if that is Kilo Ohms or just ohms, been too long.
P.S. it has been 12 years since I left Tandy and done any real work with them. I have no doubt things have changed, I have noted LED Flashlites and not too long ago you would not be able to afford one, that was true with the Calculator as well. Demand in electronics brings Prices DOWN, unlike other market areas.
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