Sorry, but I have a hard time believing that.
If it was "a very common problem", can you offer a cite proving that a
60 hz transformer and 10-50 feet of unshielded wire with 24 vac on it
can cause interference at radio frequencies?
Wouldn't you expect that if that story was true those big pole pig
transformers and all that higher voltage wiring running on the poles on
nearly every street would have caused the radios to melt? <G>
According to the FCC Interference Handbook, defective doorbell
transformers are often a source of interference to TVs and other
household electronics. It may be a neighbor's transformer. I think it
happens when part of the core comes loose and vibrates.
I'm no EE, but I would guess that most of the in-house interference is
back down along the power lines, not through the air. I know that on the
baby shortwave I use to AM-band DX myself to sleep at night, when some
unknown something in my house (or one of the neighbor's houses on the
same pole can) is running, I can't get S**t to come in. But if I unplug
the wall wart and run on batteries it comes in fine, as long as the
unplugged cord is over a foot from the radio. Intermittent as hell, and
Several electric utilities say so. It can also come from microarcs in
transformers on poles. When they get a complaint, they check poles with
an ultrasound detector to pick up noise from an arc.
When a doorbell transformer fails, I imagine it's usually an open
primary. When it first opens, I imagine the vibration of the
transformer could keep the break arcing indefinitely.
There's always something new to learn....
When I asked for a cite I was thinking only of properly operating
I located this FCC cite:
(It's on page 14 of the .pdf document.)
It sayss there's a thermostatic overload inside (some?) doorbell
xformers designed to protect them from overheating and starting a fire
if the doorbell button sticks on - or there's a short in the secondary
The report says that those thermal overloads (which I expect break the
120 volt primary circuit.) cycle off and back on around once every seven
seconds and that the inductive spark at its contacts can propogate
through house wiring and cause flashes of interference on a tv or
"static clicks" in radios.
Who woulda thunk it?
I wonder how long that cycling mode would continue before those thermal
overload contacts got burned enough to stop connecting and leave an open
That's the second time I've made a mistake this year...Thank G_d it's
almost December. <G>
Interference from a neighbors transformer is rampant in that when people
realize it uses 3 bucks of electricity a year to run they buy a couple
of hundred feet of copper cable and conduit (so it's code compliant) and
illegaly trench it to the neighbors power.
On Fri, 21 Nov 2008 01:14:34 -0600, The Daring Dufas
You didn't ask Jeff personally. Had you done so, it would have been an
email, instead you asked a general question on Usenet, and someone was
nice enough to reply with good information. And, yes, we know what
your name is: "Asshole".
Dang! Nobody seemed to get the little dig at Jeff.
What you will find are 6, 8, 10, 12, 16 and 24 volts
AC. Some really old stuff will be DC dry cell powered
but only if the owner wants to keep it original for
nostalgic or antique collecting purposes. Most of the
doorbell transformers I install have triple taps for
8, 16 and 24 volts. Many doorbells will need a 10 volt
transformer and if you need 24 volts to ring your ding
dong you're either deaf or have a seriously complicated
system. I have setup some serious systems for industrial
and commercial buildings by making use of the very loud
and fun to play with devices manufactured by Edwards
Signaling which now belongs to GE. My personal favorite:
I had a friend who was having problems with
Bulgarians stealing the copper and aluminum
out of his small apartment complex. I took
a motion sensing floodlight and an Edwards
120 volt square fire horn which we installed
at the rear of the apartments. One night he
was awakened by the wonderfully loud obnoxious
sound of that horn accompanied by some equally
loud screams and cursing in the local Bulgarian
dialect. The next morning he found a lot of blood,
bits of dark flesh and torn black clothing on
the barbed wire fence. For some reason his losses
to the vandalizing thieves abated.
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