I want to install some led lights behind my gauges in my car to change the color. Regular incandescent bulbs do not offer the color I want. I want to purchase some leds and resistors from radio shack and do it custom because I will have better control over where the lighting goes. I am a little rusty on Ohm's law and need some help.
I have read on some forums that they used 20000 mcd led bulbs and said they used a 1/4 watt resistor. I need the ohm rating. If it is a 12 volt system in my car, what resistor should I use. The system goes up to a little over 14 volts when the car is running.
The instrument cluster has a 7.5 amp fuse in it for the lighting. I have not tested actual amps with the incandescent bulbs in it. I have leds in there now, and I have not tested amps. The resistors are built in to the leds I have now, so I cannot separate the two and test them separately.
I know mcd and Mcd refer to the brightness of the bulb. I just need to know is there any other rating for leds to figure out what resistor to use?Making a 12 volt led circuit?The applied voltage (14 max) minus the forward voltage of the LED (varies with LED colour), divided by the LED current (typically 20 mA) gives the value of the resistor required. The resistor voltage multiplied by the current gives the power dissipate; the resistor power rating must be more than this.Making a 12 volt led circuit?No you can have as many LED's as you want as long as your power supply can deliver the current. For example if your LED needs 20mA of current, then you size your resistor with that. And Let's say your power supply can deliver 200mA, then you can have upto 10 LED's in the system.
