[Shop-talk] Wiring a string of LED lights

[David Scheidt]

On Sun, Oct 3, 2010 at 11:08 AM, Scott Hall <scott.hall at comcast.net> wrote:
> B I'd like to use a string of LED lights I found at a box store as a closet
> light. B Basically, I've run the string around the inside of the door so
when
> you open the door a plunger switch turns on the lights. B With the overhead
> light you could just see the top shelf, with the sting of lights, you'll at
> least be able to see (the front of, at least) all the shelves.
>
> I'm fine with all of if except the light string is wired with a 120v plug
> and has a fuse integral to it. B I know I could just wire in an outlet and
> box, but that seems cludgy and, well...just too easy.
>
> So I was going to snip the cord, see if I could disassemble the plug and
> then wire the fuse inline.
>
> And then it occurred to me that those are probably either not LEDs like I
> thought (I'm pretty sure they are), or they might not be 120v LEDs and that
> plug might have more than just a fuse in it.
>
> That's the point at which I decided to ask here.
>
> Any advice? B These are the 'lights in a vinyl rope' jobby. B It's got a
cap
> at the end that allows you to connect additional strings, I think. B Came
> from Lowe's or Home Depot and you can get them in various colors.


The ones I've looked at (which were all christmas lights, but the
principle is the same for all of the things I've seen) have between 25
and 50 leds (30 or 35 is most common; longer strings consist of
multiple strands in (electrical, if not physical) parallel)  hooked up
in series, to produce suitable forward voltage, and a resistor to
limit the current to non-led exploding values.  There are a pair of
wires that run the whole length of the strand, to provide 120 volts to
the plug on the end.

If you've got substantially fewer LEDs, you may have a more
complicated circuit.

You probably could cut the plug off, but I wouldn't.  The quality of
these things is not good, and they fail long before the diodes wear
out.  Much easier to unplug and replace than unwire and replace.

--
David Scheidt
dmscheidt at gmail.com