# Running electric blanket on DC?

E

#### Eric R Snow

Jan 1, 1970
0
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

D

#### Don Kelly

Jan 1, 1970
0
Eric R Snow said:
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

T

#### Tim Williams

Jan 1, 1970
0
Eric R Snow said:
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.

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

Tim

A

#### amdx

Jan 1, 1970
0
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

B

#### Bob Masta

Jan 1, 1970
0
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

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

R

#### Rudolf Zeitschek

Jan 1, 1970
0
Don said:
--------

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.

E

#### Eric R Snow

Jan 1, 1970
0
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

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

K

#### Kim Clay

Jan 1, 1970
0
Be a hero & convert it

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

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

W

#### William J. Beaty

Jan 1, 1970
0
Eric R Snow said:
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_name=CTLG&product_id=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=,44-533,&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 [email protected] UW Chem Dept, Bagley Hall RM74 [email protected] Box 351700, Seattle, WA 98195-1700 ph206-543-6195 http//staff.washington.edu/wbeaty/ S #### Steve Evans Jan 1, 1970 0 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. Good idea! wimmin will buy anything. it's not a good idea to convert hte blanket to dc, anyway. All the time its running on AC, there's an even distribuion of blood cells in your body. If you change to DC, all you blood cells will either get drawn to your head or your feet depending on which way around the polarity is. ;-) S #### steamer Jan 1, 1970 0 --Getcher self a couple of warm doggies; works wonders, heh. R #### Rich Grise Jan 1, 1970 0 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 E #### Eric R Snow Jan 1, 1970 0 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

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

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
[email protected] UW Chem Dept, Bagley Hall RM74
[email protected] 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

E

#### Eric R Snow

Jan 1, 1970
0
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

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