LED Series Christmas Lights

Tue Dec 27, 2011 7:07 am   

I recently was given two strings of LED blue/white Christmas lights.
The bulbes are in series, with 35 lights in each string. There are
also a couple of lumps in the series lines. They appear to be just
resistors, not diodes, as I measure the same value (~500 ohms) with
either polarity of my multimeter. My guess is that the resistors are
there just to decrease the current so that the LEDs are not running
overrrated. I am thinking of putting/rewiring the two strings
directly in series and then reducing the series resistors until I get
the same overall brightness of the new 70-light string. Has anyone
done any experimenting like this?

Tue Dec 27, 2011 7:54 am   

"hrhofmann_at_att.net" wrote:


Leave it alone. The forward voltage drop on white or blue LEDs is
higher than red or green, so that's why they chose 35 LEDs per string.
If you get too close to the actual line voltage and use lower
resistance, any spike will cause a high current surge through the
string. If you aren't capable and willing to design and build a
constant current boost supply, you are wasting your time.


--
You can't have a sense of humor, if you have no sense.

Tue Dec 27, 2011 10:58 pm   

hrhofmann_at_att.net <hrhofmann_at_att.net> wrote:

my guess is the string won't even light up with 70 LEDs in series. Messing
with that resistor will probably make the thing an even bigger fire hazard
than it is now. If you really want a long string of lights, just add an
extra wire the length of the first one to power the second and have the
use a common return line. Old zip lamp cord or speaker wire works nice for
stuff like this.

Wed Dec 28, 2011 3:30 am   

On Dec 27, 12:54 am, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:

Good point about surge limiting, altho I am not sure if LEDs are any
more susceptible than tungsten filament lamps.

Wed Dec 28, 2011 3:30 am   

On Dec 27, 2:58 pm, Cydrome Leader <prese...@MUNGEpanix.com> wrote:

The separate sets have an outlet at the far end, so easy to put
together. My posting was just curiosity.

Back in 1944, when I was only 8 years old, my grandmother took me to
Macy's in New York City to buy me a Christmas present. She was
horrifed that the only present I wanted was a string of Christmas
lights so I could play with the bulbs and wires. First inkling I was
destined to become an electgrical engineer.

Fast forward to 1957, when I graduated from college with a EE degree
and got a job at Bell Laboratories. I had a dream job designing
switching system interconnect circuits, but also enjoyed playing with
Christmas lights.

Really fast forward to 2011, I still enjoy playing with Christmas
lights.

Wed Dec 28, 2011 4:49 am   

On Tue, 27 Dec 2011 17:49:09 -0800 (PST), "hrhofmann_at_att.net"
<hrhofmann_at_att.net> wrote:


My first indication of the same affliction was shoving my fingers into
the wall outlet. I assume the resultant shock didn't cause any
lasting harm, but I'm not sure. My logic was that anything that
powerful was worth learning. It's been downhill since then.


When I graduated from college in approximately 1971, aerospace and the
space program had just collapsed. I ended up with a job installing
radios in cement mixers. No flashing lights or electrocution devices
at the time.


It's almost 2012 and I'm going broke fixing electronics and giving
away free advice on Usenet. So, I'm slowly switching back to fixing
sewing machines. (I was my fathers ace mechanic when he owned a
factory in the L.A. garment district). No flashing lights, but plenty
opportunity to do damage.

I do like Christmas lights, but they only last until the squirrels are
done chewing on the wires.


--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl_at_cruzio.com
# http://www.LearnByDestroying.com AE6KS

Wed Dec 28, 2011 7:10 am   

"hrhofmann_at_att.net" wrote:


Tungsten has a time constant, and the resistance goes up as the
voltage increases. LEDs are current operated at a lot more constant
voltage. A few volt rise in the power line rasies the current flow.
Harmonics and spikes on the power line will cause higher peak current
flow in the LEDs. It would be like operating a Zener very close to it's
knee voltage with only a very low resistance to limit the current.


--
You can't have a sense of humor, if you have no sense.

Wed Dec 28, 2011 9:55 am   

On Dec 27, 10:10 pm, "Michael A. Terrell" <mike.terr...@earthlink.net>
wrote:

The variation in atom size in III-V semiconductors creates more
defects than a homogeneous semiconductor like silicon would have,
because of the strained lattice. High currents will propagate those
defects, creating areas where the steady-state current will bypass the
p-n junctions (so-called dark current, because it doesn't produce
light). So the useful life of the LED string would be unnecessarily
reduced.

Wed Dec 28, 2011 11:49 am   

"Jeff Liebermann" <jeffl_at_cruzio.com> wrote in message
news:ku3lf7tm101k0niv2q6oiojgo71dqtp0p0_at_4ax.com...


"Done", as in "thoroughly cooked"?

It would break your mother's heart if she knew you liked Christmas lights.

Wed Dec 28, 2011 6:17 pm   

On Wed, 28 Dec 2011 02:49:44 -0800, "William Sommerwerck"
<grizzledgeezer_at_comcast.net> wrote:


I use solar powered LED lights. Besides using less power, it's more
ecologically correct by not electrocuting the squirrels. I leave the
lights in place all year to light up the stairs and balcony, leaving
plenty of opportunities for the squirrels to ruin my day. One string
has perhaps 10 splices. The squirrels are cute, but they're rather
destructive.


Nope. Hannukah is the Festival of Lights. The story of Esther
specifies using oil lamps, which is proscribed in the local fire code.
So, we use electric lights. As long as the lights looked something
like a menorah, my parents were satisfied. However, they drew the
line with the Hannukah bush. I wanted to also celebrate Christmas,
but when they told me that Hannukah was 8 days, and that I was suppose
to get one present per day, I decided I could live without Christmas.
Unfortunately, the added presents were fairly tacky:
<http://en.wikipedia.org/wiki/Hanukkah_gelt>
Lesson learned: Next time, get it in writing.

Hannukah also created another area of contention over playing the
dreidel.
<http://en.wikipedia.org/wiki/Dreidel>
Basically, it was gambling, which my parents tended to discourage but
tolerated because it taught useful skills (math, statistics,
probability, bookkeeping, loans, etc). Us kids were soon bored with
the dreidel, and switched to playing craps with dice. It was many
years before I could understand why the dreidel was acceptable, but
the dice were not.

At some point, when I was about 15, I morphed into a very junior
Beatnick.
<http://en.wikipedia.org/wiki/Beatnick>
Glorified poverty and a minimalist lifestyle meant that I was required
to discard all the trappings of affluence, reject all modern
conveniences, drop out of society, avoid clean clothes, and read
poetry, thus somehow demonstrating that I was a non-conformist. My
parents interpreted that as a rebellion, which they celebrated by
cutting off my allowance, demanding that I wash the dishes, and
refusing to supply the ritualistic gifts on the usual occassions. This
made life intolerable, so I ran away from home. I eventually
returned, somewhat wiser, just in time for Hannukah. After receiving
the requisit lecture, I was welcomed with a peace offering gift, which
I gratefully accepted, thus ending my life as a non-conformist. The
lights of Hannukah will always remind me of my first major screwup.

Happy Holidaze.

--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Wed Dec 28, 2011 7:12 pm   

On Dec 28, 5:49 am, "William Sommerwerck" <grizzledgee...@comcast.net>
wrote:

When I was 13 I reasoned that if you got a whole bunch of extension
cords and plugged them into various different outlets in the house,
then wired them all in series you could achieve infinite
possibilities. That was only topped by the 120.0 V to 6.0 volt step
down transformer I tried to wind on the metal frame of my bed. The
schematic showed 8 turns on the primary and 2 on the secondary.
Couldn't figure out why I lit up he room.....Lenny

Wed Dec 28, 2011 7:29 pm   

Jeff Liebermann wrote:

My son asked me, as a joke, if I could buy him a 5 trillion dollar Zibabwean
bill from eBay. I thought he was serious, so in the grand tradition of
Chanuka Gelt, he got 5 trillion dollars yesterday. :-)

It's made quite a splash in the humor section of redit.

Geoff.


--
Geoffrey S. Mendelson, N3OWJ/4X1GM
My high blood pressure medicine reduces my midichlorian count.

Wed Dec 28, 2011 8:31 pm   

Jeff Liebermann wrote:

The solution has been know for eons.
That is the proper seeds in birdfeeders
and the proper vegetable extract applied to other things:
http://google.com/search?q=Hobanero-video
Those little dudes will leave skid marks getting away.

Thu Dec 29, 2011 4:38 am   

On Wed, 28 Dec 2011 17:29:03 +0000 (UTC), "Geoffrey S. Mendelson"
<gsm_at_mendelson.com> wrote:


A what? Digging....
<http://www.ebay.com/itm/270863837896>
<http://www.ebay.com/itm/250943869930>
Plenty of others. Great idea for Hannukah. I wish you had mentioned
it a few weeks ago so I could have used it on the spoiled brats.

My father used Hannukah gelt to introduce me to how money works. I
think I was 6 years old at the time. He gave me an old silver dollar,
and informed me that it was worth more than a dollar. Huh? This was
new to me. Explanations were useless, but I kept the dollar well
hidden, looking occasionally to see if it would grow. By about 10
years old, I was the only kid in skool with a (co-signed) bank
account. I was buying stock when I was 16. The lessons were
invaluable.

There are lots of lessons that should be applied or demonstrated
early. That includes how to repair things. My father was always
fixing things around the house or delivered by friends. Repaired
presents were common. I just assumed that he enjoyed fixing things.
Later, I found out that he only repaired things because we were
sufficiently broke to not be able to afford new items. However, it
was too late. By then, I was fixing (well, attempting to fix) things
and was hooked.

These days, repair work has changed. In the bad old days, it was
assumed that most items worth repairing were of decent quality. These
days, I can't just repair things. I have to re-engineer the design
and try to improve on what I consider to be crappy design and shoddy
construction. In the past, products were usually designed to be
maintained. These days, they're designed to be non-repairable.
Actually, it's not repair as much as it is remanufacture. In some
product areas, it's impossible to buy quality at any price.

Ok. That's my holiday rant.

--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Thu Dec 29, 2011 4:44 am   

On Wed, 28 Dec 2011 10:31:03 -0800 (PST), JeffM <jeffm__at_email.com>
wrote:


<http://en.wikipedia.org/wiki/Habanero_chili>
Interesting idea, but I don't think it will work in the deep dark
forest. Chili peppers require a warm climate, dry acidic soil, and
plenty of sun. Where I live, only the acidic soil is available. Also,
I don't think it will be practical installing chili planters along the
hand rails and roof edge, where the Christmas lamps live.



--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558