------Question for 609-1112-120F Please Put your question below------
What is the resistance and wattage of resistors to accommodate higher supply voltages?
These panel indicators are designed for specific voltages. 6VDC, 12VDC and 24VDC to provide 15mA to the LED.
We haven’t been provided the Forward Voltage of the LEDs but lets just say the Red Led forward voltage is 2.1V and we are calculating the resistor value for the 12V LED.
12V - 2.1V = 9.9VDC.
9.9V / 0.015A = 660 Ohms resistor would be close to what they have installed.
Quarter Watt resistors would be sufficient.
What is the max current for each of these LED’s as a function of temperature? Is 2.1 VF a reasonable estimate for the 6, 12 and 24 V LED’s?
You’re going to want to shoot for 15mA or 20mA, running higher would decrease the life of the LED.
2.1V Forward Voltage is an estimate and that would be the same for 6, 12 and 24VDC.
I chose 2.1V because when I look at Red LEDs a majority of them have a Forward Voltage of between 1.9V and 2.2VDC.
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Are you forgetting about the internal resistor in the LED that keeps the current at say 15 mA, and then, after calculating the resistor for the elevated voltage, forgetting to subtract out this internal resistor?
In my provided example was how to calculate the included resistor, in the example case, 660 Ohms would be the approximate value of the included resistor.
If you have a 36 Volt source and a 12V LED module for example:
Subtract the forward voltage from the source voltage:
36V - 2.1V = 33.9V
Calculate the total Ohms to achieve 15mA.
33.9V / 0.015A = 2260 Ohms
Subtract the included resistor 660 Ohms from 2260 Ohms
2260 - 660 = 1600 Ohm resistor you would want to add in series to increase the voltage to 36VDC.
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