When I dare to use an
A) electric blanket, or a electric frying pan set on "low",
at the same time when there is a
B) UPS computer power supply, or Ham radio power supply
also turned on anywhere in the house, the power supplies hum most
worryingly. One must make a choice: A) food, warmth, or B) fun.

What is the name of this waveform resonance with the current limiters
of A phenomena? Is there some kind of filter I can apply?

wrote in message ...
When I dare to use an
A) electric blanket, or a electric frying pan set on "low",
at the same time when there is a
B) UPS computer power supply, or Ham radio power supply
also turned on anywhere in the house, the power supplies hum most
worryingly. One must make a choice: A) food, warmth, or B) fun.

What is the name of this waveform resonance with the current limiters
of A phenomena? Is there some kind of filter I can apply?

Check for a loose wire somewhere in the circuits that are affected. Check
the voltages at the affected devices to see if they change when the frying
pan is cut on and off.

"RM" == Ralph Mowery writes:

RM Check for a loose wire somewhere in the circuits that are affected. Check
RM the voltages at the affected devices to see if they change when the frying
RM pan is cut on and off.

Thanks but a ham told me (in Chinese) that this is a well known
phenomenon with cheap current limiters, that take a bite out of each
crest of the AC sine wave as their method of limiting. That's why such
appliances cause power supplies in the same house to hum when such
appliances are switched to LOW or MEDIUM, but not HIGH. If only I
could find the English name of this phenomenon, I could look up what
to do about it.

In article , wrote:

"RM" == Ralph Mowery writes:

RM Check for a loose wire somewhere in the circuits that are affected.
Check
RM the voltages at the affected devices to see if they change when the frying
RM pan is cut on and off.

Thanks but a ham told me (in Chinese) that this is a well known
phenomenon with cheap current limiters, that take a bite out of each
crest of the AC sine wave as their method of limiting. That's why such
appliances cause power supplies in the same house to hum when such
appliances are switched to LOW or MEDIUM, but not HIGH. If only I
could find the English name of this phenomenon, I could look up what
to do about it.


You've got a cheezy SCR-based control in the electric blanket. When it
turns on, you get a fast current spike. IR products in your power
wiring turn this into a voltage spike (drop), and since it's a
reasonably fast, sharp edge, it's rich in harmonics.

Now let's look at your power transformers, such as the one in your ham
radio supply, or in the UPS. When they're getting nice clean sine
waves, they hum along merrily (they hum because they don't know the
words).

But when that spike from the SCR wanders in, the windings in the
transformer try to reproduce it, humming now at harmonics of the power
line, and humming a different and more irritating tune.

When the electric blanket is on high, the SCR is essentially turned on
through the entire cycle (or half-cycle depending on topology).
Turning on at close to zero voltage minimizes the switching spike.

Fixes:

Brute force filter at the electric blanket, and/or a snubber on the SCR.

Get an electric blanket that uses a (zero-crossing) triac control.

Heavier, shorter power wiring to the electric blanket, the UPS and ham
radio gear, or both.

Ditch the electric blanket and get a live-in friend!

Before we rebuilt our house, when the fuser heater in the laser printer
in the office kicked on (another cheap SCR switch), the fluorescent
lights in the room would flicker. After rebuilding, and replacing all
the wiring, going from AWG 14 to AWG 10 and 12, that laser printer
didn't make the lights flicker any more. Replacing it with a more
efficient laser printer helped a lot, too.

--
Namaste--

When I dare to use an
A) electric blanket, or a electric frying pan set on "low",
at the same time when there is a
B) UPS computer power supply, or Ham radio power supply
also turned on anywhere in the house, the power supplies hum most
worryingly. One must make a choice: A) food, warmth, or B) fun.

What is the name of this waveform resonance with the current limiters
of A phenomena? Is there some kind of filter I can apply?

That sounds to me as if you're running into a "harmonic currents"
issue. This occurs if you have something connected to the mains which
draws current in a nonlinear fashion (i.e. current drawn is not
linearly related to the instantaneous value of the voltage sinusoid).

In my experience, the commonest cause for this is a device which uses
a triac "chopper" to control the amount of current being used. Such
devices "switch on" partway through each powerline cycle (120 times a
second), so the current jumps from zero to a fairly high value. The
sudden jump creates a load on the line with frequency components at
harmonics of the 60 Hz powerline frequency... hence the name.

The devices you indicate (electric blankets, frying pans), and light
dimmers are notorious culprits.

Some of these devices may draw current in an asymmetrical fashion...
e.g. they might use a half-wave rectifier diode, and thus draw current
on only the positive half of the AC cycle and not on the negative (or
vice versa). "Light bulb saver" discs (little disc-shaped diodes that
go into a light socket before the bulb) do this. In effect, the
asymmetrical load creates a DC offset on the voltage "seen" by other
devices on the same circuit.

All of these "bad loads" can cause transformers in other devices to
start humming or buzzing. Toroidal power transformers are
particularly subject to buzzing if there's an asymmetrical load / DC
offset on the line.

I don't know of any good way of filtering out this sort of problem...
an isolation transformer can help somewhat, sometimes, but it's an
expensive solution and I don't think it's very effective.

If you've got really severe humming/buzzing with something as simple
and low-wattage as an electric blanket, , I'd be a bit concerned
that this might indicate that there's a problem in your house
wiring... overloaded circuits, a bad or loose connection somewhere, or
even a loose or open neutral. The latter is a dangerous situation.
If you should notice lights getting brighter, or appliance motors
speed up, when you turn *on* a light or appliance elsewhere in the
house... then you may have an open neutral and should call the power
company immediately. I've had this happen twice (squirrel chewed
through the neutral wire in our building's drop from the pole
transformer), and PG&E always reacted immediately... their dispatcher
said that they consider a "low voltage / high voltage" situation to
require immediate action.

You might want to have an electrician check out your house wiring.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

a You've got a cheezy SCR-based control in the electric blanket.
Ah, http://en.wikipedia.org/wiki/Silicon...lled_rectifier
a Brute force filter at the electric blanket, and/or a snubber on the SCR.
Ah, http://en.wikipedia.org/wiki/Snubber
a Get an electric blanket that uses a (zero-crossing) triac control.
But its my http://en.wikipedia.org/wiki/Security_blanket
a Heavier, shorter power wiring to the electric blanket, the UPS and ham
a radio gear, or both.
OK, and what is that brute force filter, and do those snubbers come in
AC inline versions that you just plug into requiring no snippers for dumbo me?
a Ditch the electric blanket and get a live-in friend!
Tried that last time.

On Wed, 31 Dec 2008, wrote:

Date: Wed, 31 Dec 2008 21:51:08 +0000 (UTC)
From:
Newsgroups: rec.radio.amateur.equipment
Subject: power supply hums when electric blanket on

When I dare to use an
A) electric blanket, or a electric frying pan set on "low",
at the same time when there is a
B) UPS computer power supply, or Ham radio power supply
also turned on anywhere in the house, the power supplies hum most
worryingly. One must make a choice: A) food, warmth, or B) fun.

What is the name of this waveform resonance with the current limiters
of A phenomena? Is there some kind of filter I can apply?


You can think about so-called power filtering or power conditioning
transformers or voltage stabilizing transformers. They are not cheap
and can get heavy, too, but come in at least three versions: i) low end,
ii) mid range, and iii) fancy-schmanzy high end, all
with various kinds of specifications on max output harmonic content,
voltage regulation plus/minus, etc. Some use
transformer-capacitor-inductor networks, some use an unusual core geometry
to exploit a curiosity in electrodynamics of transformers to get the
effect. But they are all designed to take out spikes, harmonics, and
weirdo waveform problems. Some of these are offered by high-end computer
backup-PS companies since some computer installations experience funny
glitchy-buggy problems from their power lines.

Can't help you with search terms and I know the proper term will give you
magic results (lots of hits on what you want). Good luck, but our modern
world is hooking up all kinds of weirdo electronic crap to the power grid.

For ham radio, you might want to think about a 12 volt deep cycle marine
battery and charger to give you clean power.

"Dave Platt" wrote in message
...
When I dare to use an
A) electric blanket, or a electric frying pan set on "low",
at the same time when there is a
B) UPS computer power supply, or Ham radio power supply
also turned on anywhere in the house, the power supplies hum most
worryingly. One must make a choice: A) food, warmth, or B) fun.

What is the name of this waveform resonance with the current limiters
of A phenomena? Is there some kind of filter I can apply?

That sounds to me as if you're running into a "harmonic currents"
issue. This occurs if you have something connected to the mains which
draws current in a nonlinear fashion (i.e. current drawn is not
linearly related to the instantaneous value of the voltage sinusoid).

In my experience, the commonest cause for this is a device which uses
a triac "chopper" to control the amount of current being used. Such
devices "switch on" partway through each powerline cycle (120 times a
second), so the current jumps from zero to a fairly high value. The
sudden jump creates a load on the line with frequency components at
harmonics of the 60 Hz powerline frequency... hence the name.

The devices you indicate (electric blankets, frying pans), and light
dimmers are notorious culprits.

Some of these devices may draw current in an asymmetrical fashion...
e.g. they might use a half-wave rectifier diode, and thus draw current
on only the positive half of the AC cycle and not on the negative (or
vice versa). "Light bulb saver" discs (little disc-shaped diodes that
go into a light socket before the bulb) do this. In effect, the
asymmetrical load creates a DC offset on the voltage "seen" by other
devices on the same circuit.

All of these "bad loads" can cause transformers in other devices to
start humming or buzzing. Toroidal power transformers are
particularly subject to buzzing if there's an asymmetrical load / DC
offset on the line.

I don't know of any good way of filtering out this sort of problem...
an isolation transformer can help somewhat, sometimes, but it's an
expensive solution and I don't think it's very effective.

If you've got really severe humming/buzzing with something as simple
and low-wattage as an electric blanket, , I'd be a bit concerned
that this might indicate that there's a problem in your house
wiring... overloaded circuits, a bad or loose connection somewhere, or
even a loose or open neutral. The latter is a dangerous situation.
If you should notice lights getting brighter, or appliance motors
speed up, when you turn *on* a light or appliance elsewhere in the
house... then you may have an open neutral and should call the power
company immediately. I've had this happen twice (squirrel chewed
through the neutral wire in our building's drop from the pole
transformer), and PG&E always reacted immediately... their dispatcher
said that they consider a "low voltage / high voltage" situation to
require immediate action.

You might want to have an electrician check out your house wiring.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!


cut the ground off the blanket that will make the hum go away

In article ,
KC8QJP wrote:

cut the ground off the blanket that will make the hum go away

That strikes me as very poor advice, for three reasons:

[1] I've never seen an electric blanket or bed-heating pad here in the
U.S. which *has* a ground prong. They all use two-wire
(hot/neutral) plugs.

[2] If there *is* a ground prong on a device which is used in close
proximity to a human body, it's probably there for a very good
reason (safety). Removing a safety ground from such a device
seems like a really bad idea.

[3] If the reason for the humming is a harmonic-currents problem (as I
suspect) then it has *nothing* to do with the presence or absence
of a ground connection. It's due to irregular current flows on
the hot and neutral wires. Floating the device free from the
safety ground will have not reduce the problem at all.

"Floating" an equipment-chassis ground can sometimes help reduce hum
in audio/video equipment if the hum is due to a ground loop. I don't
believe that ground loops have anything at all to do with the original
poster's buzzing-transformer problem.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

DP [1] I've never seen an electric blanket or bed-heating pad here in
DP the U.S. which *has* a ground prong.
No ground prong on my blanket or frying pan.
Thick house wiring all done by myself, so that can't be the problem
(don't tell Mom about the day I made a loop and all the conduits in
the walls shook.)
Therefore I shall, as a nod to the less privileged who perhaps don't
even have electric power, learn not to eat or sleep while using the
computer or my radio equipment (BM4IFV, not on air anymore, now just
on email). OK, thanks. Bye.