The resistors used are based on the amount of current needed to light the LED's and based on the voltage supply desired. It will take a large number of batteries to generate enough current (1 amp or more) and last a long time without going dead in this case.
The resistors will give off heat .. however, at 12 volts.. with a 3.4v drop across a single LED with 25mA of current.. you would need to pick our a resistor of the appropriate Ohms .. so we know there is a voltage drop of 3.4 volts across the LED.. which means we will have a voltage drop of 8.6 volts across the resistor.. no matter what resistor rating we choose.. so, if we need .25mA current.. this means 8.6v / .025 = ~ 350 Ohms.. If you can find that value..It just needs to be with 20 - 30 points of the calculated value..
The wattage, ie size of the resistor to get can be calculated as 8.6v * .025 = .215 Watts.. So, you might think about getting 1/2 watt resistors if you are using a 12 volt power supply..
Again, the formula is Voltage - LED forward Voltage / LED current = Resistor size in Ohm's. Wattage is Voltage * current ..
THe foward voltage drop required across the LED can vary between 1.4 volts and up.. just look at the specs on the LED package.. Also, the amount of current to light it up can vary too.. The best approximation to make.. is get the current with in, say 5 mA of MAX current and you should be ok.. you'll know it wasn't good if you let the smoke out
I typically use 18,000 mcd @ 30 degree viewing angle.. about 3.4 volt forward voltage at 25mA.. ( About 5mm in size) You can shave the plastic down to a point for tight fitting spaces..
The resistors will give off heat .. however, at 12 volts.. with a 3.4v drop across a single LED with 25mA of current.. you would need to pick our a resistor of the appropriate Ohms .. so we know there is a voltage drop of 3.4 volts across the LED.. which means we will have a voltage drop of 8.6 volts across the resistor.. no matter what resistor rating we choose.. so, if we need .25mA current.. this means 8.6v / .025 = ~ 350 Ohms.. If you can find that value..It just needs to be with 20 - 30 points of the calculated value..
The wattage, ie size of the resistor to get can be calculated as 8.6v * .025 = .215 Watts.. So, you might think about getting 1/2 watt resistors if you are using a 12 volt power supply..
Again, the formula is Voltage - LED forward Voltage / LED current = Resistor size in Ohm's. Wattage is Voltage * current ..
THe foward voltage drop required across the LED can vary between 1.4 volts and up.. just look at the specs on the LED package.. Also, the amount of current to light it up can vary too.. The best approximation to make.. is get the current with in, say 5 mA of MAX current and you should be ok.. you'll know it wasn't good if you let the smoke out
I typically use 18,000 mcd @ 30 degree viewing angle.. about 3.4 volt forward voltage at 25mA.. ( About 5mm in size) You can shave the plastic down to a point for tight fitting spaces..
see my other builds at:
http://www.skunkwurkzmodels.com
http://www.skunkwurkzmodels.com