Wayne Boatwright wrote:
On Fri 26 Dec 2008 01:48:54a, E Z Peaces told us...

Jim Beaver wrote:
"Wayne Boatwright" wrote in message
5.247...
On Thu 25 Dec 2008 04:53:05p, E Z Peaces told us...

Jim Beaver wrote:
"E Z Peaces" wrote in message
.. .
Jim Beaver wrote:
I've got my Christmas tree set up in my living room. A couple of
strings of lights (not those mini-lights, but the finger-tip size
bulbs). Here's the problem:

When I turn on the lights, a loud hum arises from the timer for my
yard sprinklers. This timer is mounted on the outside wall of the
living room. Obviously it's on the same circuit, as the hum comes
and
goes when the Christmas tree lights are turned on or off.

The hum is loud. Probably loud enough indoors to wake a light
sleeper from a nap if it suddenly came on. It's even louder, of
course, outdoors near the timer.

The power cords, plugs, and receptacles all seem cool. So I'm
wondering: does this sound like an overloading problem, or more
likely some sort of simple harmonic vibration? Am I in danger of
fire, if everything I can get to seems cool?

I don't know anything much about electrical testing or I'd use a
tester on it somehow. But I don't really know what to look for.

Anyone NOT doing something more interesting on Christmas Eve who
wants to advise me here?

And with that in mind, happy holidays to all here. Thanks.

Jim Beaver
I haven't been able to imagine how the lights could affect voltage
or
current in the timer.

Are there valves near the timer? Sometimes a solenoid valve can hum
loudly.
I discovered this morning that the hum doesn't happen in the daytime.
Which leads me, genius that I am, to conclude that it's not the
sprinkler timer but the low-voltage outdoor lighting system timer. I
have no idea whether this affects matters much in terms of safety,
etc.
Jim Beaver
My idea light is flashing! Does an electric eye turn on the outdoor
lights? Maybe the eye is exposed to one of the outdoor lights as well
as light from your tree in the window, and together they hit it with
enough light to shut it off. That brings the light below the
threshold
and it turns back on. The frequency of the hum would depend on how
long
it took the outdoor filament to heat white hot.

Maybe I've missed something here, but why belabor this situation? Just
plug the lights into a socket that's on a totally different circuit.

All this effort for a temporary lighting situation seems like a huge
waste
of time and effort, or do you just enjoy puzzles?
Hate puzzles. Just trying to avoid running a twenty-foot extension cord
to the nearest receptacle not on this circuit. Christmas is dangerous
enough without decking cables down and across my halls. Also, I find a
house without extension cords running across major thoroughfares to be
more elegant than one with such obstacles.

Jim Beaver
How do the outdoor lights come on? If it's not a timer or a manual
switch, it must be a light sensor.

Incandescent Christmas lights don't generate frequencies, and
"frequencies" shouldn't make a transformer hum. Incandescent Christmas
lights generate light, and light can make a light sensor turn lights off
and on. If you hear a hum, it's probably too fast to see flickering.
The solution would be to shield the sensor from artificial light.


There are too many unanswered questions for me. First, not all Christmas
tree lights are incandescent; some are LEDs. Second, if the outdoor lights
are powered by a transformer and triggered by a light sensor, it seems
unlikely that an indoor Christmas tree could interfere with its function.
If the outdoor lights are interfering, then it would happen irrespective of
the Christmas tree.


The original post seemed to answer your questions about the tree lights.
People like to put Christmas trees in front windows.

Outdoor lighting systems often have a sensor on the timer. Typically,
the sensor turns it on at dusk and the timer turns it off.

Instructions warn the homeowner that ambient light can make the system
cycle. Yard lights are often aimed at the house and sensor, so the
sensor's threshold may be adjustable.

If plugging in the tree lights makes the outdoor system noisy, I think
ambient light from the tree raises the level at the sensor above the
shut-off threshold. The light could come straight from the tree, or it
could reflect off something outside. When the sensor switches the
outdoor lights off, that may reduce the light on the sensor, which would
then switch the lights back on. The flicker of the outdoor lights may
not be conspicuous.

I think the racket comes from relay chatter. If the timer is designed
for 300 watts of 12V lights, a relay would have to work with a 200A
starting surge. I think a relay that big could be heard indoors.