Do I Need a Resistor for my LED Bulb?

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)
baripada,odisha,India

There are two values that you need to specify in a match between an LED bulb and a battery:   the wattage, W_bulb and the operating voltage, V_bulb .   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 I_bulb = W_bulb/V_bulb.  Now you need the value of the resistor necessary to drop the battery voltage to the correct value, V₀.   So  R = ( V_battery - V_bulb)/I_bulb .

LeeH

 

 

(published on 03/29/2017)