Slight correction: 240VAC is RMS voltage, and has a peak voltage of 240 * sqrt (2) = 340Vpk. Your resistor needs to be 18.8k to limit current to 18 mA, and will dissipate ~6.1W peak or 4.3Wrms. You still need (at least) a 5W resistor, however. Jul 20, 2016 at 0:13. Google Capacitive Dropper Led for the typical setup.
All the calculators in step 2 are just doing some simple math that you can do at home: The formula to calculate resistance in a circuit is: R=V/I or, more relevant to what we're doing: (Source Volts - LED Volts) / (Current / 1000) = Resistance * So if we have a 12v battery powering a 3.5V 25mA LED our formula becomes: (12 - 3.5) / (25 / 1000 Pricing and details on the GTR Lighting Resistors: &utm_source=youtube&utWhen a series LED connection is in question, you will just need to replace the "LED forward voltage" with "total forward voltage" in the formula, by multiplying FV of each LED by the total number of LEDs in the series. Suppose there are 3 LEDs in series then this value becomes 3 x 3.3 = 9.9. LED Current or I refers to the current rating of theHowever, if our voltage was 12V, we would have to rework our calculations to keep the same amount of current flowing through the LED. Our duty cycle would need to drop to 14.167% (1.7V divided by 12V) and our minimum PWM frequency would decrease to 14.285kHz (the inverse of [10us divided by 14.167%]). HOWEVER!, this is cause for concern. In the The ballast resistor can be calculated using the formula: R = V −V LED I = 12− 2 0.03 = 333Ω R = V − V L E D I = 12 − 2 0.03 = 333 Ω. The resistor must have a resistance of 333 Ω. If the precise value is not available, choose the next higher resistance value to keep the current below the LED limits. It is quicker to wire them in your scenario than any other way. As you add LEDs to your parallel array, the voltage requirements stay the same. As you add LEDs to your parallel array, the current requirements increases the amount that each LED requires (5 LEDs @ 20mA = 100mA requirement/draw). 100 Ohm 1/4 watt resistor.