Plz help to make a circuit

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Dear Salam
i have LED of 3V 1Watt and i want to connect them with 12v 7Ah battery
i have connected 4 LED in series to over come 12v and how much risistance is needed for this circuit?????????????
 

you can calculate the value of resistor by,

R = (Supply voltage - (sum of Drop across each LED))/current
supply voltage = 12v
In your case, you have 4 led's in series. for eg. if your led drop is 2V. total drop = 2+2+2+2 => 8V . and how much current do you want to allow to led, if it is 10mA.

R = (12-8)/10mA => 400 Ohm.


Best wishes.
 
Better us 3 in series not four as battery voltage drops to 10.5. LED should glow bright at that level too. Are you sure they are exactly of 3V? These range between 2.8-4.2. 3.3V-3.6V being most common. Current limit is 350mA for 1W LED. Set it with a ampere meter if you don't want to calculate. If your heat sink is poor then limit is 250mA. Start with 3 LEDs in series with 10 ohm two watts resistance.
 
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