Barney Garcia
I like the idea of LED light strings that rarely need new bulbs but the flicker drives me crazy! Here's the solution for single strings of LEDs all in series:
Most strings will run well on about 20 mA of DC instead of the AC which makes them flicker and this simple circuit converts the AC to DC and reduces the voltage a bit. The 39 uF capacitor should have a 200 volt or higher rating but the capacitance may be a bit less, perhaps as low as 10 uF. The rectifier diode may be just about any power rectifier that has a sufficient voltage rating. The resistor may be an ordinary carbon composition, 2 watt type or 4, 2.2k, 1/2 watt resistors in parallel. The resistor will get a bit warm. The resistor may be replaced by a 24 volt, 50 mA bulb or three, 18 volt, 1 watt zener diodes:
Any of these will effectively drop the line voltage to about 80 volts and dissipate about 1 watt. (Using the direct rectified line voltage without a series limiter will supply the LEDs with over 50 mA which might shorten their life. Then your back to finding bad bulbs!
By the way, if the string doesn't light, reverse the wires between the LED string and the capacitor, the polarity does matter.
After you cut the wire close to the plug, slide on a length of plastic tubing that will become the housing. I used point-to-point wiring with this zener version and insulated all the exposed metal with liquid tape. The plastic tube housing was then slipped over the circuitry, forming a second insulation layer and protective housing. The ends of the tube may be filled with epoxy or similar compound. I painted the final assembly with green paint to make it less noticable.
B.G.
Article coming soon.
