Modifying LED light to work off car battery

[Bluemobile]

I should know this since I studied Ohm's Law in college but I must've slept through that class because I am drawing a blank.

Anyway, I am trying to modify an LED lamp to work off a car battery and need to modify the circuit to work off 12 volts instead of 4.5.

I took the lamp apart and retraced the circuit. Originally it powered off 3 1.5 volt batteries. This was fed into a 1 ohm resistor which was then fed into 24 leds wired in parallel. By looking at this it appears that each LED is drawing 4.5 volts. What I am not sure about is what current is running through each diode (20mA)?

I don't have specs of the diodes either so I am kinda guessing here. I am assuming they are 4.5 forward voltage and 20mA. This would make sense since they used a 1 ohm resistor. What's the typical resistance of the LEDs?

Here is a diagram of how it was wired up initially.

Could I wire in (a) resistor(s) in parallel with the LEDs to balance the circuit?

Would someone mind explaining to me how to calculate this circuit. Thanks in advance.

 

[CampingLED]

:welcome:

You can try this circuit driving the 24 LEDs. Current to each LED should be 350/24 = approx 15mA. LEDs are current driven and you should not attempt to drive them by Voltage calculations alone.

Alternatively you can play with series and parallel combinations. 3 LEDs with resistors in series with 8 parallel groups. If you want 20mA you need 8 x resistors that should be 120 ohm 1/8 Watts each.

 

[T0RN4D0]

paralel driving, ideal for killing LEDs