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Q & A: Do I need a resistor for my LED bulb?

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Most recent answer: 03/29/2017
I have 9watt LED electronic bulb.I want to run it with a 12 volt battey. How much resistor should I use.
- Kuber (age 23)

There are two values that you need to specify in a match between an LED bulb and a battery:   the wattage, Wbulb and the operating voltage, Vbulb .   In your example you give the wattage but not the operating voltage so the problem is ill-posed.   For a 9 Watt, 12 Volt LED you don't need any resistor, but for a 9 Watt, 6 Volt you do.  Both types of lamps exist on the market.    To find the value of the resister you need the current required to safely run the bulb Ibulb = Wbulb/Vbulb.  Now you need the value of the resistor necessary to drop the battery voltage to the correct value, V0.   So  R = ( Vbattery - Vbulb)/Ibulb .




(published on 03/29/2017)

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