[Shop-talk] xmas lights, shunts, and magic

[David Scheidt]

On Sun, Dec 5, 2010 at 3:37 PM, David C. <cavanadd at frontier.com> wrote:
> Ok, I'll be the first to admit that I'm not up on Christmas lights and
> decorations. B My primary response to the holidays, and Christmas in
> particular, is to ignore them/it to the fullest extent possible. B I
haven't
> bought Christmas lights in probably 25 years. B Given that, I was under the
> impression that:
> 1. B Pretty much all Christmas lights these days are LED; and
> 2. B Series wired Christmas lights went out sometime around the middle of
the
> first Eisenhower administration. B Shunts? Seems like a solution looking
for
> a problem.

Heh.  All LED lights are series wired.  (Someone, somewhere, probably
makes a very, very expensive set where that's not true.  But it's true
of anything you're going to get at a mass market store.)  They've got
between 20 and 40 diodes wired in series,  plus a current limiting
resistor.  If there are more bulbs than that, it's because there are
two (or more) strands wired in parallel. Some of the nicer ones
apparently have a reverse voltage  diode, but none of the ones I've
taken apart have had one.  They've got shunts, too.  not because LEDs
burn out, but because they get stepped on or hit with hammers.


--
David Scheidt
dmscheidt at gmail.com