Increasing voltage from 4.5 (actual 4.9) to 12 volts;

What resistor should I add on to the current setup?

Two sets of white LED (each removed from flashlight) run in parallel to the 3-AA battery source. The neg or current connection is the spring (or resistor) that came with the flashligt. I would like to use a 12 volt rechargable lead acid battery.?

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seandogue7 years ago
Power the leds using a 5V PWM stepdown regulator from the 12V source. Apply a small value resistor to strip the excess voltage.
lemonie7 years ago

This is your silly answer:
Hack your battery down to ~10V by removing a cell, run them in series with a suitable resistor (zero.gx)

gmxx7 years ago
It depends also on the current the LEDs need. You need to measure it. You're going to waste more than half the energy you use for the LEDs in heat in the resistor. Steve
davis1019 (author) 7 years ago
each set has 4 LEDs