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Wiring battery fairy lights to usb power

taa800

New Member
I have a set of fairy lights that use 2 2032 batteries to power them. That's a total of 6 volts. I'm trying to wire them so I can plug them into the wall and since usb puts out 5v, I thought that would work. When I wire it up and plug it in, the lights are much brighter than they are with new batteries, and they are slightly warm to the touch. I would have thought with having 1 volt less going through them, they'd be dimmer, not brighter. What am I missing here? Everything I read online talks about voltage and never mentions amperage. Is that something I need to be considering?
Thanks
 

Pommie

Well-Known Member
Most Helpful Member
It could be that the batteries are in parallel or the load causes a voltage drop. Try adding a 1n4001 (diode) in series with the LEDs. If it doesn't work, turn the diode around as they only conduct one way.

Mike.
 

Visitor

Active Member
The current from 2032 batteries is limited, so a USB power supply will supply much more current. You'll need a series resistor to use a USB supply.

Big Clive on YouTube has modified a number of LED strings and fairy light strings to run from USB battery packs. He explains the brightness/battery life tradeoff well and goes over what value of resistors to use. Highly recommended watching.
 

audioguru

Well-Known Member
Most Helpful Member
Measure the "6V" from the two weak little 2032 batteries when the LEDs are lighted. It might be 3V to 4V, not 6V.
Look at an Energizer datasheet for a CR2032 weak little battery cell. It is designed for a load of only 0.19mA which is close to nothing. Fairy lights overload it.
 

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