Battery Pack

3 cell rechargeable battery packs: Not recommended to use this low a voltage with white LEDs. Its operating voltage is too close to battery voltage. One solid color LED and a series resistor (white 82 ohm or yellow 130 ohm) or x-mass tree bulb can work. However, current will change rapidly with voltage as the batteries discharge.

4 cell rechargeable battery packs: First choice is one series connected white LED and a series connected resistor (white 160 ohm or yellow 220 ohm) or x-mass tree bulbs (6 W-20) current limiter. LM317 current limiter circuit doesn't work because voltage is too low. The rechargeable cells could be Ni-mh or Ni-cad. Typical circuit follows.

8 cell rechargeable battery packs: First choice is two series connected white LEDs and a LM-317 (using R=82 ohm) current limiting circuit. Second choice is a resistor (320 ohm) or x-mass tree bulb (6 W-20) current limiter. The rechargeable cells could be Ni-mh or Ni-cad. If two sets of 2 series LEDs are connected in parallel then use a LM-317 (with R= 41 ohm).

12 Volt lead-acid batteries: First choice for two parallel of three series connected white LEDs is to use a LM-317 with 62 ohm current limiting circuit. Second choice is a resistor (130 ohms) or x-mass tree bulb (3 series W-20) current limiter. First choice for seven parallel of three series connected white LEDs is to use a LM-317 with 15 ohm current limiting circuit. Second choice is a resistor (40 ohms) or x-mass tree bulb (4 series W-35) current limiter. 5 yellow LEDs is about equivalent to 3 white LEDs in terms of voltage drop thus the same driver circuit should work.

Offered by Mike.