I have a set of mini holiday LED lights that were originally powered by 3 AA batteries, but the battery holder broke. I thought it would be great to power them with a USB cable instead, so I soldered a USB connection directly onto the LED string and tested it with a 5V wall adapter. While it worked, I noticed the chip on the board is getting too hot and melting the hot glue I used to secure it. That's not ideal for decorating around the house! I've heard mixed opinions on whether I need a resistor when doing this, as batteries start at about 5V and drop to 4.5V over time. Has anyone successfully made this conversion? Is there a way to bypass the original circuit board or connect the LEDs directly to a USB power source without damaging them?
3 Answers
The chip heating up isn't always a bad sign; electronics can get warm. Just make sure it has airflow—hot glue might be trapping heat. Most LED strings have resistors built in for battery use, so bypassing the board could complicate things. Without seeing your setup, it's tough to say definitively, but proceed with caution!
I switched my battery-powered lights to USB by using diodes; they protect the LEDs and drop the voltage slightly. One diode typically drops about half a volt, which worked perfectly for my setup!
To get a better handle on this, measure the current and voltage with the LEDs connected to the batteries, then use a high wattage resistor to drop the 5V down if necessary. It's a solid way to ensure you’re not overloading them.
That’s a clever idea! I might try that; how many diodes did you end up using for your string?