I need to adapt one of these 60 LED string-lights to be powered through a wall plug. These are micro LEDs all wired in parallel; sadly, I couldn't find specs for this kind of LED. The string's power supply holds 6 AA batteries (3 parallel-wired-pairs in series) so I know it requires a 4.5V supply, but I have no idea about the current.
Also, I have a similar LED string light with 100 LEDs (this one powered with a AC/DC power adapter) that no longer works. The adapter outputs 4.5V / 1A. So I want to ask:
-What specs should I look for in the power supply/wall wart?
-Can I use the power adapter from the broken string to power this smaller one?
-Is it a good solution to just hook the LEDs up to a wall wart with the correct specs or does this circuit need more components to work and for the LEDs not to burn out?
Thank you!
Best Answer
The way these strings work is multiple leds in parallel depending on a single series resistor and/or the the battery Equivalent Series Resistance. Some simpler strings also depend on the Forward Voltage of the LEDs being higher than the battery pack voltage. A 3.3V @ 20mA led will only pull 15 or so milliamps at 3V.
In this case, there is likely a resistor or diode between the battery pack and the led string. Since these have timers, there is probably a mosfet or transistor and an IC internal to the case.
Simplest case, a 4V power supply should be used. Otherwise a 4.5V should be fine. Open the case to confirm there is a resistor or something.
As for current, measure the led string with fresh batteries using a multimeter. This will confirm how much current is being pulled.
As for the broken plug in one, what exactly broke? The string? You can solder, crimp or twist it back together, by removing the clear coat insulation. If it's the power supply, then you can't re purpose it. Check with a multimeter.