# Bournville Radio Sailing and Model Boat Club

# Using Light Emitting Diodes (LED's)

Light Emitting Diodes (LED’s) are a marvelous solution for lighting up model boats. Unlike traditional grain of wheat bulbs they generate virtually no heat so are safe to use in plastic and balsa models.

LED’s are polarity sensitive and need a specific voltage and current flow to operate so we need to ensure we set them up correctly.

In general Red LED’s operate at 2 volts where as White, Blue & Green LED’s operate at around 3 volts. All LED’s need a constant current flowing and for most small LEDS this will be a maximum current of 20mA (0.02A).

Two and three volt supplies are not common in most models so we need to include a resistor to limit the current flow and reduce the voltage to the LED.

In example 1 I have a 12v battery and I want to install a red LED.

Red LED’s need 2volts and a maximum of 20mA.

To work out the resistor value we can use the formula

In our example we have a 12volt battery – 2volts of the led = 10 volts to be dropped over the resistor with a current of 0.02Amps flowing.

Our formula to work out the resistor value looks like this

500 Ohms is not a preferred resistor value so we would use the next available higher value = 510 Ohms which will give us a current flow of 19mA. This is calculated by dividing our 10volts by the resistor value of 510 ohms.

We now need to ensure the resistor wattage is rated high enough for the current flowing. To do this we multiply our 10volts by the current 0.019Amps = 0.19watts so a 0.6watt rated resistor will do the job.

If your battery voltage is high enough the follow configuration is also possible. We add the led voltages together and subtract this from the battery voltage.

Our formula for this example is

200 Ohms is a preferred value so we are good to.

One final thought. LED’s can be very bright and look a bit unrealistic when running at their full current rating. To solve this run the LEDs as a lower current by using a higher value resistance.

Bournville Radio Sailing and Model Boat Club