How do I wire 4 LEDs (3.5v), a small pc fan (12v), using a switch and 2 9V batteries or 3 if needed?
What i did was, using 4 wires (since there are two leds on each side of the helmet) i connected the LEDs together by connecting the positive sides to each other and the negative sides together then i connected the positive wires to the positive wire of the fan and those wires to the negative wire of the switch. Then i connected both positive battery wires to the positive wire on the switch, and then connected all the negative wires from the LEDs and the fan and the battery together. I hit the switch and the white lights turned blue and dimed to nothing all almost instantly. the fan worked and still works but the LEDs died... so is the math/voltage wrong or what am i missing. i thought i would need and additional battery to make it 27v vs 26v but if 18 overloaded then IDK wtf to do.