Running electric blanket on DC?

[Eric R Snow]

Greetings All,
I know this is silly but here it goes:
My wife and I keep our bedroom un-heated so it gets cold in the
winter. An electric blanket warms the bed before we get in. My wife
would like to keep it on all night instead of using all the extra
covers but is concerned that the "electrical magnetic field" emanating
from the blanket will give us cancer or something. I mentioned that
it's low frequency AC that people are all worried about and we are
subjected to it all day from wires in the walls etc so why worry about
the blanket? I know it's closer so any effect AC might have would be
greater from the blanket but sheesh! Then, I foolishly said that if
the blanket were run on DC we wouldn't need to worry. Now she wants me
to fix the blanket to run on DC. I took apart the control and it seems
like the heat control is just a bi-metal switch and the light is a
little neon bulb. Is there any reason why it couldn't be run on DC? I
envision a full wave rectifier and a capacitor. And it looks like
there is enough room in the control for these extra parts. Is there
anything inside the blanket itself that precludes Dc operation?
Thanks,
Eric R Snow,
Machinist, electonics hobbiest

 

[Don Kelly]

"Eric R Snow" <etpm@whidbey.com> wrote in message
news:rvgvq0hgrsmpr61bnb14sm25o4clg6adhb@4ax.com...

Greetings All,
I know this is silly but here it goes:
My wife and I keep our bedroom un-heated so it gets cold in the
winter. An electric blanket warms the bed before we get in. My wife
would like to keep it on all night instead of using all the extra
covers but is concerned that the "electrical magnetic field" emanating
from the blanket will give us cancer or something. I mentioned that
it's low frequency AC that people are all worried about and we are
subjected to it all day from wires in the walls etc so why worry about
the blanket? I know it's closer so any effect AC might have would be
greater from the blanket but sheesh! Then, I foolishly said that if
the blanket were run on DC we wouldn't need to worry. Now she wants me
to fix the blanket to run on DC. I took apart the control and it seems
like the heat control is just a bi-metal switch and the light is a
little neon bulb. Is there any reason why it couldn't be run on DC? I
envision a full wave rectifier and a capacitor. And it looks like
there is enough room in the control for these extra parts. Is there
anything inside the blanket itself that precludes Dc operation?
Thanks,
Eric R Snow,
Machinist, electonics hobbiest
--------

It could be done but I wouldnt recommend it. The thermostat switch would
likely fail quickly and start a fire as it is much harder to interrupt DC.
What you would be doing is trading an insignificant (if present) hazard for
a much greater one. Much safer to leave it alone.

I suggest that you direct your wife to John Moulder's site.
http://www.mcw.edu/gcrc/cop.html
and to stop worrying. Either that or get a good down duvet.
Also :
http://www.cnn.com/interactive/health/0210/interactive.medical.myths/2003/content.0205.html

--
Don Kelly
dhky@peeshaw.ca
remove the urine to answer

 

[amdx]

Meh. Take it apart, look like you're doing something, >then put it back
together as it was. As long as she >knows you did something, but not

exactly what, she'll >buy it. Tim

Perception is reality!

Mike

 

[Bob Masta]

On Thu, 02 Dec 2004 17:56:49 -0800, Eric R Snow <etpm@whidbey.com>
wrote:

Greetings All,
I know this is silly but here it goes:
My wife and I keep our bedroom un-heated so it gets cold in the
winter. An electric blanket warms the bed before we get in. My wife
would like to keep it on all night instead of using all the extra
covers but is concerned that the "electrical magnetic field" emanating
from the blanket will give us cancer or something. I mentioned that
it's low frequency AC that people are all worried about and we are
subjected to it all day from wires in the walls etc so why worry about
the blanket? I know it's closer so any effect AC might have would be
greater from the blanket but sheesh! Then, I foolishly said that if
the blanket were run on DC we wouldn't need to worry. Now she wants me
to fix the blanket to run on DC. I took apart the control and it seems
like the heat control is just a bi-metal switch and the light is a
little neon bulb. Is there any reason why it couldn't be run on DC? I
envision a full wave rectifier and a capacitor. And it looks like
there is enough room in the control for these extra parts. Is there
anything inside the blanket itself that precludes Dc operation?
Thanks,
Eric R Snow,
Machinist, electonics hobbiest

I recall reading some years ago that in response to the
alleged problem, manufacturers were rearranging
the heating wire routing inside the blanket to
largely cancel the fields. I believe the new wiring
is just one big "hairpin" that is then routed around
the blanket. There is no loop to be inside of.

I might add that the original studies on the "problem"
were of ridiculously poor quality, both on statistical
and logical grounds. They probably would have
never gone anywhere except that a reporter wrote
up a big scare-mongering story in the New Yorker,
and suddenly eveybody figured this was a real
problem. Things like this can easily happen in
a scientifically illiterate society.

Just my 2 cents' worth!



Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com

 

[Rudolf Zeitschek]

Don Kelly schrieb:

"Eric R Snow" <etpm@whidbey.com> wrote in message
I envision a full wave rectifier and a capacitor. And it looks like
there is enough room in the control for these extra parts. Is there
anything inside the blanket itself that precludes Dc operation?
Thanks,
Eric R Snow,

--------

It could be done but I wouldnt recommend it. The thermostat switch would
likely fail quickly and start a fire as it is much harder to interrupt DC.
What you would be doing is trading an insignificant (if present) hazard for
a much greater one. Much safer to leave it alone.

I agree and would like to mention a further problem:
If you just rectify (without filtering by a condenser) you get the same
heat, but you still have a lot of alternating current (and field).
If you filter to get pure DC, you need a very large condenser and ir
will give the peak voltage (165v for 117V AC) and the blanket will
overheat.....
Greetings R.Z.

 

[Eric R Snow]

On Fri, 03 Dec 2004 13:29:30 GMT, NoSpam@daqarta.com (Bob Masta)
wrote:

On Thu, 02 Dec 2004 17:56:49 -0800, Eric R Snow <etpm@whidbey.com
wrote:

Greetings All,
I know this is silly but here it goes:
My wife and I keep our bedroom un-heated so it gets cold in the
winter. An electric blanket warms the bed before we get in. My wife
would like to keep it on all night instead of using all the extra
covers but is concerned that the "electrical magnetic field" emanating
from the blanket will give us cancer or something. I mentioned that
it's low frequency AC that people are all worried about and we are
subjected to it all day from wires in the walls etc so why worry about
the blanket? I know it's closer so any effect AC might have would be
greater from the blanket but sheesh! Then, I foolishly said that if
the blanket were run on DC we wouldn't need to worry. Now she wants me
to fix the blanket to run on DC. I took apart the control and it seems
like the heat control is just a bi-metal switch and the light is a
little neon bulb. Is there any reason why it couldn't be run on DC? I
envision a full wave rectifier and a capacitor. And it looks like
there is enough room in the control for these extra parts. Is there
anything inside the blanket itself that precludes Dc operation?
Thanks,
Eric R Snow,
Machinist, electonics hobbiest

I recall reading some years ago that in response to the
alleged problem, manufacturers were rearranging
the heating wire routing inside the blanket to
largely cancel the fields. I believe the new wiring
is just one big "hairpin" that is then routed around
the blanket. There is no loop to be inside of.

I might add that the original studies on the "problem"
were of ridiculously poor quality, both on statistical
and logical grounds. They probably would have
never gone anywhere except that a reporter wrote
up a big scare-mongering story in the New Yorker,
and suddenly eveybody figured this was a real
problem. Things like this can easily happen in
a scientifically illiterate society.

Just my 2 cents' worth!



Bob Masta
dqatechATdaqartaDOTcom

D A Q A R T A
Data AcQuisition And Real-Time Analysis
www.daqarta.com
Yeah, I know the study was crap. But my wife prefers to believe the

hype.
Cheers,
Eric R Snow

 

[Kim Clay]

My wife and I keep our bedroom un-heated so it gets cold in the
winter. An electric blanket warms the bed before we get in. My wife
would like to keep it on all night instead of using all the extra
covers but is concerned that the "electrical magnetic field" emanating
from the blanket will give us cancer or something. I mentioned that
it's low frequency AC that people are all worried about and we are
subjected to it all day from wires in the walls etc so why worry about
the blanket? I know it's closer so any effect AC might have would be
greater from the blanket but sheesh! Then, I foolishly said that if
the blanket were run on DC we wouldn't need to worry. Now she wants me
to fix the blanket to run on DC.

Be a hero & convert it

I took apart the control and it seems
like the heat control is just a bi-metal switch and the light is a
little neon bulb. Is there any reason why it couldn't be run on DC? I
envision a full wave rectifier and a capacitor.

Just a FWB (no cap) & its DC - _definitely_ not AC anymore!

And it looks like
there is enough room in the control for these extra parts. Is there
anything inside the blanket itself that precludes Dc operation?
Thanks,
Eric R Snow,
Machinist, electonics hobbiest

Valid data snipped...

Yeah, I know the study was crap. But my wife prefers to believe the
hype.
Cheers,
Eric R Snow

She wants you to convert it to run on DC? Put your full wave bridge in
the circuit. Presto - its DC - Yes its unfiltered DC but it _is not_ AC
anymore! I don't know of any studies that have shown low levels of
pulsating DC causing any problems

Thermostat shouldn't be stressed because of the pulsating nature of the
current - heat output should be the same - the neon light may be
somewhat dimmer (only if FWB is between AC cord & controller) because
just one side is flashing - that will prove its running on DC.

Depending on how much room there is in the control box & the wiring
arrangement, the preferred place for the bridge would be where the
actual heater connects to the controller - the thermostat & neon would
still be conducting AC but the heating element is running on DC. If that
is difficult (maybe because of the small wires?) -
Second best (but still very acceptable) would be at the AC input (cord)
side.

Please think "Safety" when working with AC mains.

Everyone comes out a winner

Kim

 

[William J. Beaty]

Eric R Snow <etpm@whidbey.com> wrote in message news:<rvgvq0hgrsmpr61bnb14sm25o4clg6adhb@4ax.com>...

Greetings All,
I know this is silly but here it goes:
My wife and I keep our bedroom un-heated so it gets cold in the
winter. An electric blanket warms the bed before we get in. My wife
would like to keep it on all night instead of using all the extra
covers but is concerned that the "electrical magnetic field" emanating
from the blanket will give us cancer or something.

Does the blanket generate a strong EM field? WHy not find out?

If you hook a coil to the input of an audio amp, then listen to
the amplified output using headphones, you can easily hear the 60Hz
magnetism detected by the coil. For instance, wave the coil around
an AC wall clock motor, or around an old-style (non-electronic)
fluorescent light ballast. BUZZZZZZ! Once you can detect strong
AC magnetic fields, wave your coil around the electric blanket and
see if it's stronger than, say, standing under a fluorescent ceiling
light.

Here's a great little $12 amp. All hobbyists should have one
of these (I have several. They have lots of uses.) :

Mini audio amplifier w/speaker, 9V
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=277-1008


That, a couple of mini-jacks, and a telephone pickup coil, and
you're ready to scan the environment for those lethal 60Hz hums.


Telephone pickup coil
http://www.radioshack.com/basket.asp?sku=%2C44%2D533%2C&iGo=


When I did this years ago at home, I discovered that the whole
house was full of 60Hz b-fields. It was wired with old-style
knob-and-tube wireing, where all of the conductors are several
feet apart, rather than being twisted together inside a steel pipe.



((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty@chem.washington.edu UW Chem Dept, Bagley Hall RM74
billb@eskimo.com Box 351700, Seattle, WA 98195-1700
ph206-543-6195 http//staff.washington.edu/wbeaty/

 

[Rich Grise]

On Fri, 03 Dec 2004 22:42:23 +0100, Rudolf Zeitschek wrote:

Don Kelly schrieb:
"Eric R Snow" <etpm@whidbey.com> wrote in message
I envision a full wave rectifier and a capacitor. And it looks like
there is enough room in the control for these extra parts. Is there
anything inside the blanket itself that precludes Dc operation?
Thanks,
Eric R Snow,

--------

It could be done but I wouldnt recommend it. The thermostat switch would
likely fail quickly and start a fire as it is much harder to interrupt DC.
What you would be doing is trading an insignificant (if present) hazard for
a much greater one. Much safer to leave it alone.

I agree and would like to mention a further problem:
If you just rectify (without filtering by a condenser) you get the same
heat, but you still have a lot of alternating current (and field).
If you filter to get pure DC, you need a very large condenser and ir
will give the peak voltage (165v for 117V AC) and the blanket will
overheat.....

I'd be worried about any modification to an electric blanket. How does the
thermostat actually sense the temperature of the blanket? Isn't the
resistance of the element itself the sensor? If so, then any messing with
it will upset its operation.

I agree with that other poster - leave the AC, because a DC magnetic field
will cause your blood to pool. ;-) Tell the wife you did some research and
found out that AC is actually beneficial! We're engineers, we ought to
know!

Good Luck!
Rich

 

[Eric R Snow]

On 3 Dec 2004 17:42:27 -0800, billb@eskimo.com (William J. Beaty)
wrote:

Eric R Snow <etpm@whidbey.com> wrote in message news:<rvgvq0hgrsmpr61bnb14sm25o4clg6adhb@4ax.com>...
Greetings All,
I know this is silly but here it goes:
My wife and I keep our bedroom un-heated so it gets cold in the
winter. An electric blanket warms the bed before we get in. My wife
would like to keep it on all night instead of using all the extra
covers but is concerned that the "electrical magnetic field" emanating
from the blanket will give us cancer or something.

Does the blanket generate a strong EM field? WHy not find out?

If you hook a coil to the input of an audio amp, then listen to
the amplified output using headphones, you can easily hear the 60Hz
magnetism detected by the coil. For instance, wave the coil around
an AC wall clock motor, or around an old-style (non-electronic)
fluorescent light ballast. BUZZZZZZ! Once you can detect strong
AC magnetic fields, wave your coil around the electric blanket and
see if it's stronger than, say, standing under a fluorescent ceiling
light.

Here's a great little $12 amp. All hobbyists should have one
of these (I have several. They have lots of uses.) :

Mini audio amplifier w/speaker, 9V
http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&product%5Fid=277-1008


That, a couple of mini-jacks, and a telephone pickup coil, and
you're ready to scan the environment for those lethal 60Hz hums.


Telephone pickup coil
http://www.radioshack.com/basket.asp?sku=%2C44%2D533%2C&iGo=


When I did this years ago at home, I discovered that the whole
house was full of 60Hz b-fields. It was wired with old-style
knob-and-tube wireing, where all of the conductors are several
feet apart, rather than being twisted together inside a steel pipe.



((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
beaty@chem.washington.edu UW Chem Dept, Bagley Hall RM74
billb@eskimo.com Box 351700, Seattle, WA 98195-1700
ph206-543-6195 http//staff.washington.edu/wbeaty/
Greetings William,

Thanks for the link to the amp and the ideas to use it. I can already
think of other uses for it.
Eric R Snow

 

[Eric R Snow]

On Tue, 07 Dec 2004 20:20:29 GMT, Rich Grise <rich@example.net> wrote:

On Fri, 03 Dec 2004 22:42:23 +0100, Rudolf Zeitschek wrote:

Don Kelly schrieb:
"Eric R Snow" <etpm@whidbey.com> wrote in message
I envision a full wave rectifier and a capacitor. And it looks like
there is enough room in the control for these extra parts. Is there
anything inside the blanket itself that precludes Dc operation?
Thanks,
Eric R Snow,

--------

It could be done but I wouldnt recommend it. The thermostat switch would
likely fail quickly and start a fire as it is much harder to interrupt DC.
What you would be doing is trading an insignificant (if present) hazard for
a much greater one. Much safer to leave it alone.

I agree and would like to mention a further problem:
If you just rectify (without filtering by a condenser) you get the same
heat, but you still have a lot of alternating current (and field).
If you filter to get pure DC, you need a very large condenser and ir
will give the peak voltage (165v for 117V AC) and the blanket will
overheat.....

I'd be worried about any modification to an electric blanket. How does the
thermostat actually sense the temperature of the blanket? Isn't the
resistance of the element itself the sensor? If so, then any messing with
it will upset its operation.

I agree with that other poster - leave the AC, because a DC magnetic field
will cause your blood to pool. ;-) Tell the wife you did some research and
found out that AC is actually beneficial! We're engineers, we ought to
know!

Good Luck!
Rich

Perfect answer Rich! I'll just say that the engineers on line have

conducted a study and found that ac is actually good for you as it
keeps the blood evenly distributed.
Eric