[PPRAANet] LED Christmas Trees w/lights DANGER, DANGER

[DickT-W0RAA]

FROM A HAM RADIO REFLECTOR - please pass along

(Note:  it has a bit of technical stuff, but the point is in the warning - 
Tom)

I've got a story to relate that's not strictly ham related (perhaps suitable 
for your other groups), but very important.

We just put up our Christmas tree this afternoon. It is a pre-lit LED tree 
that we purchased from the Christmas Warehouse five years ago. The LEDs on 
this tree continuously change color (each LED appears to have its own 
built-in control circuit), and it's very pretty to watch. However, after the 
tree had been running about 30 minutes I noticed a strong burning odor. It 
smelled like burning plastic, definitely not an odor the tree had emitted in 
the past. The odor got stronger and stronger, and I was about to unplug the 
thing when I saw a billow of white smoke coming from the back of the tree, 
accompanied by a sizzling sound. I quickly unplugged it at that point. The 
lights were still working perfectly, by the way.

So what went wrong? The lighting on the tree has four strands of 
color-changing LED lights. For each strand there is a little rubber "bullet" 
wired in series with the bulbs. When the tree was new we had noticed that 
these "bullets" got rather hot to the touch. The bullet on the lowest string 
of lights was the source of the smoke, and its molded green plastic casing 
was visibly melted and burned black. I cut that "bullet" out, and proceeded 
to the shop to carefully carve away the molded casing to see what was 
inside, and how it had failed.

Inside the "bullet" is a 2k, 1 watt power resistor (quite discolored!) in 
series with a 1N4007 diode. So the bullet serves to half-wave rectify the AC 
to power the LEDs, and limits the current in the circuit. But wait - - if 
you encapsulate a power resistor in plastic, that's not so good for heat 
dissipation. After many hours of operation, the heat will degrade the 
plastic, which dries out and becomes highly flammable. The rectifier diode 
is also fraction of an inch from this very hot resistor, so the effect on 
the diode junction can't be good either!

What can be learned from our experience?

1. Because LED lighting inherently runs a lot cooler than incandescent 
lamps, it's easy to be lulled into a false sense of security when working 
with it. LED lighting is not inherently safe. Treat all holiday lighting 
with the same respect as you would any other lighting source.

2. Inspect lighting and decorations carefully each time you put them up. 
Look for obvious signs of trouble - - cracked or broken wires and 
insulation, burn marks, and so forth. Discard any lighting that's 
questionable.

3. Even LED lighting sets can have components that get very hot, depending 
on how well (or poorly) the set is engineered. The bulbs in our set ran 
perfectly cool, but the little rubber "bullets" sure got hot - - and proved 
to be a real fire hazard. Lighting sets that lack an authentic Underwriters 
Laboratory (UL) mark and listing number may not be a safe choice.

4. Don't leave a Christmas tree on when no one is there to enjoy it. Fires 
can start in seconds, as our experience this afternoon amply demonstrated. 
Make sure that everyone in your home knows the rules for safe operation, and 
knows how to turn the power off. (An extra smoke detector placed near the 
Christmas tree may not be a bad idea either.)

Decorative lighting adds a nice touch of magic to the holidays. Using a 
little extra care around it will make your holidays safer, and very well may 
prevent a tragedy.

Tom Dailey

DAILEY SERVICES LLC
Fire Alarm Sales & Support
Wheat Ridge, CO