Testing an Electric Blanket

[n cook]

I appreciate all those who have given constructive suggestions. For
the record, my wife has Multiple Sclerosis one symptom of which is poor
blood circulation. She is always "cold" even in the summer. More
blankets, which only keep body heat in, don't help. What is needed is
a heat source other than her body. Hence the electric blanket. She
still complains it isn't warm enough and I have no idea how to test if
it is working properly merely from a heating perspective. It feels
warm but not hot. I assume, without taking the thing apart, that there
are a bunch of resistive elements wired in parallel. Thus some could
be open and the blanket still heat.

The other concern is safety since, unfortunately, another of her
symptoms is incontinence.

The blankets we have are perhaps 20 years old. They still seem to work,
but do not get very warm. On the other hand, I don't recall how warm
they are supposed to get. I am sure they are regulated so that you
don't inadvertently burn yourself from a high setting. I would have
just gone out and bought a new one if money weren't an issue.

In searching the web, I noticed many Electric Utilities offer "safety
tests" for electric blankets, so there must be some protocol. I was
just hoping someone here knew it although it is hardly "electronics".

Another article I found suggested that they "used to be unsafe" but
newer standards have been adopted which make them safe.

Leaving out the "tin foil hat" concern about electromagnetic fields, I
assume the main risks are shock and fire. My presumption was that the
UL certification covered those and the ones I have carry UL
certification.

I suppose the best thing to do is to just buy a new one. And yet,
without understanding the failure modes of the old ones, there still
remains in my mind a safety concern.

One thing you might consider is a heavy duty "space-blanket" sold in outdoor
pursuit shops, not the thin emergency types as used at the end of marathons
but the mesh reinforced ones. It, of course, does not pre-heat the bed but
does reflect your own body heat back to you during the night which is
probably the main concern.

 

[n cook]

I appreciate all those who have given constructive suggestions. For
the record, my wife has Multiple Sclerosis one symptom of which is poor
blood circulation. She is always "cold" even in the summer. More
blankets, which only keep body heat in, don't help. What is needed is
a heat source other than her body. Hence the electric blanket. She
still complains it isn't warm enough and I have no idea how to test if
it is working properly merely from a heating perspective. It feels
warm but not hot. I assume, without taking the thing apart, that there
are a bunch of resistive elements wired in parallel. Thus some could
be open and the blanket still heat.

The other concern is safety since, unfortunately, another of her
symptoms is incontinence.

The blankets we have are perhaps 20 years old. They still seem to work,
but do not get very warm. On the other hand, I don't recall how warm
they are supposed to get. I am sure they are regulated so that you
don't inadvertently burn yourself from a high setting. I would have
just gone out and bought a new one if money weren't an issue.

In searching the web, I noticed many Electric Utilities offer "safety
tests" for electric blankets, so there must be some protocol. I was
just hoping someone here knew it although it is hardly "electronics".

Another article I found suggested that they "used to be unsafe" but
newer standards have been adopted which make them safe.

Leaving out the "tin foil hat" concern about electromagnetic fields, I
assume the main risks are shock and fire. My presumption was that the
UL certification covered those and the ones I have carry UL
certification.

I suppose the best thing to do is to just buy a new one. And yet,
without understanding the failure modes of the old ones, there still
remains in my mind a safety concern.

My recommendation would be a mixture of low tec and high tec and no electric
blanket.
A conventional hot water bottle to pre-heat the bed and an underblanket of
reinforced mylar space blanket.

 

[T Shadow]

I appreciate all those who have given constructive suggestions. For

the record, my wife has Multiple Sclerosis one symptom of which is poor
blood circulation. She is always "cold" even in the summer. More
blankets, which only keep body heat in, don't help. What is needed is
a heat source other than her body. Hence the electric blanket. She
still complains it isn't warm enough and I have no idea how to test if
it is working properly merely from a heating perspective. It feels
warm but not hot. I assume, without taking the thing apart, that there
are a bunch of resistive elements wired in parallel. Thus some could
be open and the blanket still heat.

The other concern is safety since, unfortunately, another of her
symptoms is incontinence.

The blankets we have are perhaps 20 years old. They still seem to work,
but do not get very warm. On the other hand, I don't recall how warm
they are supposed to get. I am sure they are regulated so that you
don't inadvertently burn yourself from a high setting. I would have
just gone out and bought a new one if money weren't an issue.

In searching the web, I noticed many Electric Utilities offer "safety
tests" for electric blankets, so there must be some protocol. I was
just hoping someone here knew it although it is hardly "electronics".

Another article I found suggested that they "used to be unsafe" but
newer standards have been adopted which make them safe.

Leaving out the "tin foil hat" concern about electromagnetic fields, I
assume the main risks are shock and fire. My presumption was that the
UL certification covered those and the ones I have carry UL
certification.

I suppose the best thing to do is to just buy a new one. And yet,
without understanding the failure modes of the old ones, there still
remains in my mind a safety concern.

Most electric blankets build up resistance over time. I've only had one
last(put out full heat) more than 5 years. Most just out of warranty. The
one I have now says it doesn't do that and is a little past that age. It's
still working fine. Would have to look the brand name up. Hadn't heard of it
before purchase. IIRC it has Mills in the name.

 

[Michael A. Terrell]

I appreciate all those who have given constructive suggestions. For
the record, my wife has Multiple Sclerosis one symptom of which is poor
blood circulation. She is always "cold" even in the summer. More
blankets, which only keep body heat in, don't help. What is needed is
a heat source other than her body. Hence the electric blanket. She
still complains it isn't warm enough and I have no idea how to test if
it is working properly merely from a heating perspective. It feels
warm but not hot. I assume, without taking the thing apart, that there
are a bunch of resistive elements wired in parallel. Thus some could
be open and the blanket still heat.

The other concern is safety since, unfortunately, another of her
symptoms is incontinence.

The blankets we have are perhaps 20 years old. They still seem to work,
but do not get very warm. On the other hand, I don't recall how warm
they are supposed to get. I am sure they are regulated so that you
don't inadvertently burn yourself from a high setting. I would have
just gone out and bought a new one if money weren't an issue.

In searching the web, I noticed many Electric Utilities offer "safety
tests" for electric blankets, so there must be some protocol. I was
just hoping someone here knew it although it is hardly "electronics".

Another article I found suggested that they "used to be unsafe" but
newer standards have been adopted which make them safe.

Leaving out the "tin foil hat" concern about electromagnetic fields, I
assume the main risks are shock and fire. My presumption was that the
UL certification covered those and the ones I have carry UL
certification.

I suppose the best thing to do is to just buy a new one. And yet,
without understanding the failure modes of the old ones, there still
remains in my mind a safety concern.

Use an AC ammeter to check the current draw, and compare it to the
specifications on the controller.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Fred McKenzie]

I appreciate all those who have given constructive suggestions. For
the record, my wife has Multiple Sclerosis one symptom of which is poor
blood circulation. She is always "cold" even in the summer. More
blankets, which only keep body heat in, don't help. What is needed is
a heat source other than her body. Hence the electric blanket. She
still complains it isn't warm enough and I have no idea how to test if
it is working properly merely from a heating perspective. It feels
warm but not hot. I assume, without taking the thing apart, that there
are a bunch of resistive elements wired in parallel. Thus some could
be open and the blanket still heat.

Nelson-

Of even more concern than fire and shock, is that a temperature she likes
may actually be too hot and cause harm.

You should ask a doctor about this. We "do gooders" may be giving you
advice that would roast your wife!

The hot water bottle(s) sounds like a good idea. If she were sufficiently
comfortable to fall asleep, would she remain asleep after it cooled?

Fred

 

[Nelson]

Nelson-

Of even more concern than fire and shock, is that a temperature she likes
may actually be too hot and cause harm.

You should ask a doctor about this. We "do gooders" may be giving you
advice that would roast your wife!

The hot water bottle(s) sounds like a good idea. If she were sufficiently
comfortable to fall asleep, would she remain asleep after it cooled?

Fred

I assume by "cause harm" you are referring to possible burns. I don't
know about that but you reminded me of an interesting point which I
hadn't considered and that is that MS patients are frequently
negatively affected by heat... they get noticibly weaker (Uhthoff's
Phenomenon).

I think I am going to try the "Space Blanket"/Hot Water Bottle
combination. I appreciate all the helpful suggestions and the group's
patience with this "Off Topic" subject.

 

[Franc Zabkar]

Even more fires are started by clothing draped over fires which this is
equivalent to - highly dangerous. Restricted air supply leads to excessive
heat build up.

I lift the blanket and warm the bed with the heater while holding both
in my hands. Sorry if I implied otherwise. I find that one minute is
more than enough.

- Franc Zabkar

 

[n cook]

I assume by "cause harm" you are referring to possible burns. I don't
know about that but you reminded me of an interesting point which I
hadn't considered and that is that MS patients are frequently
negatively affected by heat... they get noticibly weaker (Uhthoff's
Phenomenon).

I think I am going to try the "Space Blanket"/Hot Water Bottle
combination. I appreciate all the helpful suggestions and the group's
patience with this "Off Topic" subject.

If anyone needs convincing about space blanket effectiveness, borrow one or
buy a cheap thin emergency one and try this. Cover your hand with a pillow
case or T shirt or something to avoid direct skin contact (then has opposite
effect of conducting heat out) and place inside a folded section of the
blanket - a few seconds and your hand will begin feeling warmer.
Such an effect and a blanket top and bottom would probably be too effective

 

[ian field]

Use an AC ammeter to check the current draw, and compare it to the
specifications on the controller.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Most electric blankets use diodes in the power selector switch - this might
confuse an AC ammeter!

 

[Michael A. Terrell]

Most electric blankets use diodes in the power selector switch - this might
confuse an AC ammeter!

I've never seen diodes in any I've worked on. They just had a
mechanical thermostat that switched the element on and off.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[ian field]

I've never seen diodes in any I've worked on. They just had a
mechanical thermostat that switched the element on and off.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Were they made in the 30's?

 

[Michael A. Terrell]

Were they made in the 30's?

No, in the '70s and '80s, here in the US.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[ian field]

No, in the '70s and '80s, here in the US.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

I suppose there's some merit to using a simmerstat since ambient temp
influences on time and therefore heating level, but the constant clicking
does tend to keep some people awake!

All the modern ones I've seen used very thin element wire, and presumably a
large PTC for self regulation with switch selected diodes for power control.
The last one I opened the switch unit had a lot of diodes the element was
sort of co-axial, the centre wire was thinner than a human hair and the
second element was spiral wound thicker wire round the inner insulation, I
think the switch se;selected various combinations of one, other or both
elements with or without series diodes to give about 5 different power
levels.

 

[Paul Hovnanian P.E.]

Not really electronics, I know, but I'm hoping some one can throw me a
pointer. I'd like to test for both safety and shorts/opens/too much
resistance. The only thing I could find on the web is safety testing
by electric utilities.

Any DIY help would be appreciated.

Put a GFCI receptacle in where you plug this blanket in.

 

[Bill Jeffrey]

Put a GFCI receptacle in where you plug this blanket in.

I'm not sure a GFI would do any good. All electric blankets I have ever
seen are two-wire devices, and there is no ground in or around the
blanket. No ground = no ground fault = happy GFI.

I did see a blanket fail once, out in the middle of the blanket (i.e.,
not near the connector). I THINK the failure mechanism was a heating
wire that had been flexed enough that it was ready to break - but hadn't
quite broken yet. The fracturing wire got thinner, which increased the
resistance at that point, which overheated the wire at the incipient
break, which caused a hot spot that was hot enough to scorch the blanket
material (the material does not support flame, by the way).

This was NOT a short circuit. The heating wires are well separated, and
anchored in place quite well.

Bill

 

[Dave D]

I'm not sure a GFI would do any good.

Of course it would, provided the victim had a path to ground, ie through the
bed itself..

All electric blankets I have ever seen are two-wire devices, and there is
no ground in or around the blanket. No ground = no ground fault = happy
GFI.

I can't speak for the rest of the world, but AIUI here in the UK such safety
devices work by detecting an inconsistency between live current and neutral
current, which would indicate some current is flowing to earth, either
through a human being or other fault condition. It works just as well for
two wire as three wire devices, and in fact the device doesn't care or know
one way or the other.

Dave

 

[mc]

I can't speak for the rest of the world, but AIUI here in the UK such

safety devices work by detecting an inconsistency between live current and
neutral current, which would indicate some current is flowing to earth,
either through a human being or other fault condition. It works just as
well for two wire as three wire devices, and in fact the device doesn't
care or know one way or the other.

Right, but still not much of a help with an electric blanket, since there is
unlikely to be another path to ground. The hazards are: (1) a fire, or (2)
person in bed making electrical contact with the heating element at 2 points
that are at substantially different voltages.

 

[Bob]

You might try a heating mattress pad instead. If you cannot afford
one, send me a response & I'll have one shipped to you free of charge.

 

[James Sweet]

Slim but possible, but that's perhaps not their primary danger.




You would perhaps have a different attitude if you'd been in a house where
an electric blanket burst into flames and set the bed alight. Half an hour
later and my parents would have been under it and asleep. Lucky I was in the
house at the time- they didn't smell the burning at all but I did and we
managed to put it out quickly.

Dave

Well I have a smoke alarm on the ceiling over my bed, as everyone
should. The blanket provides comfort that I'm willing to take a small
risk to enjoy.

 

[James Sweet]

Most electric blankets build up resistance over time. I've only had one
last(put out full heat) more than 5 years. Most just out of warranty. The
one I have now says it doesn't do that and is a little past that age. It's
still working fine. Would have to look the brand name up. Hadn't heard of it
before purchase. IIRC it has Mills in the name.

Maybe they're just not built like they used to be. My grandma has one
that's at least 40 years old, it's on the bed in a spare room now and
when I've stayed there I still never turn it up past 3 or so, set it to
5 or 6 and I'm sweating, it goes all the way up to 10.