Electric Blanket EM Field - When it's turned off

Electromagnetic Compatibility, TVI, BCI, etc Interference Issues

Electric Blanket EM Field - When it's turned off

Postby VK2XTC » Sat Aug 06, 2016 2:22 pm

Hi,

This is an odd post but hoping some one may know.

I purchased the kids electric blankets this winter and find that when plugged in and turned off, they generate approx. 100 volt AC field.

My child sits on the bed, with sheets ,blankets etc, insulating her from the Electric blanket. The blanket is plugged it , but switched off at the controller.
I hand one lead of the multimeter to her, I hold the other, shoes off standing on a wooden floor.

The multimeter read 100 volts AC.
Physically unplug the blanket from the wall, drops back to millivolts .

Tried different power points thinking the Power Point may be wired incorrectly. (Active neutral reversed)
Tried a different electric blanket, same brand, Homemaker (Target Brand) and slightly different voltage but same result. Approx. 100 Volts AC

This has to be bad for the kids ( 7 & 10 year olds) sleeping in an EM Field, if is was turned on I would understand , but it's while it's turned off.

So, can anyone point me to some regulations as to if this is permitted.

Suggestions , comment welcome.



Brian
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Re: Electric Blanket EM Field - When it's turned off

Postby VK3JUG » Mon Aug 08, 2016 8:27 am

Just a thought have you checked the Neutral to Earth connection and or the the actual house Earth is intact?.
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Re: Electric Blanket EM Field - When it's turned off

Postby VK5TM » Mon Aug 08, 2016 11:01 am

These are the standards electric blankets need to comply with:

Class specification:
AS/NZS 60335.1 and
AS/NZS 60335.2.17:2004+A1-2 (until 26 October
2015) or
AS/NZS 60335.2.17:2012.

That information came out of this - http://www.fairtrading.nsw.gov.au/pdfs/Businesses/Explanatory_notes_and_declaring_order.pdf
Which in turn is at the bottom of this page - http://www.fairtrading.nsw.gov.au/ftw/Businesses/Product_safety/Electrical_articles/Safe_electrical_goods.page
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Re: Electric Blanket EM Field - When it's turned off

Postby ZL2WHO » Mon Aug 08, 2016 11:53 am

Hi Brian.
My guess is that the switch on the controller is controlling a scr of triac or whatever. If the controller off position and be reconfigured to interrupt the phase then no field should be present when switched off.
Even with this field present as there is no current flowing then no emf will be generated so my take on it is safe. When heating it might be a different story.
Iv used an electric blanket every now and then and its never affected me affected me.. :crazy:
I worked in a switch yard many years ago and with one probe in the dirt and the other at varying heights one could see the voltage going up to about 600v when it was raised above ones head.
Did i mention its never affected me.. ?

The house earth steak ( mmmmm steak ) wont do a hell of a lot. NZ and Aus have a MEN system which is Multi Earth Neutral. Its the collection of all the earth stakes on all houses in the area that do the grounding not just one.

73
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Re: Electric Blanket EM Field - When it's turned off

Postby VK4BXI » Mon Aug 08, 2016 1:29 pm

Hi Brian,
This is the edge of an area where there aren't really any "ex..perts" around who can be definitive on what's good or bad. what you are measuring is capacitive current at 50 Hz. If you try to do the same with an old AVO mark 8 with a low impedance you will measure only a couple of volts (if that !). Try the same around the house with a DVM and you will get stray volts all over the place. Indeed this is one of the banes of modern DVM's they show "ghost" volts with nothing apparently connected.

50Hz magnetic fields are another story altogether !
A friends 8 year old Daughter had serious mal fits for a long period of time. It turned out that due to the poor way the house was wired there was a 50 Hz magnetic field in her bedroom that averaged some 25~50 milli-teslas over her bed. The recommended value by the WHO is no more than 2 milli-teslas.
A long story ..short. We had the wiring fixed by a "good" electrician. From that day on,from an average of a couple of fits a week, to none. Its not conclusive and the little girl may have been super sensitive to the fields but I'm starting to believe there could be more to "sick building" syndrome than just bad air-conditioning.

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Re: Electric Blanket EM Field - When it's turned off

Postby VK2XTC » Mon Aug 08, 2016 6:50 pm

Thanks for all who responded.

To confirm, the field is there with the unit turned off, not just when operating.
I'd be ok with it in that form, and it would make sense to induce a field when the unit is turned on. I'd just run it for a while to warm up the bed put the kids in , kiss them goodnight and turn off the power.

However it's all the time, even when it's turned off. And that I'm not happy with.

My wife first noticed it when you went to kiss the oldest one good night. You could feel a slight tingle on your lips.
I can touch her face and feel an ever so light static type charge from her. This is while fully insulated from the blanket, sitting on top of the bed.It's an EM field of some form.

Now, we are all hams and have all been a bit too close to large RF fields over the years. From light static tingles to full on RF burns that turn your skin white similar to freezer burns.
And I suspect if we could work it out we would probably be able to prove the old saying that hams tend to have more girls than boys.

But this is a little bit more serious than shocking the odd magpie sitting on the yagi.

I'll chase the electrical earth of the house and get an electrician to check the house and the power points.
I'll chase the manufacture (Homemaker) sold via Kmart and consider it a design fault with the unit switched incorrectly.

I also sent an email to Choice to see what testing they have done. It seems they tested them for softness, and warmth. But not really looked at EM Fields.
I also compared to the one on my bed, no field that I can detect, on or off.

Has something to do with a Cheap Design switching PSU made in China.



Again , thanks for the responses.


Brian

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Re: Electric Blanket EM Field - When it's turned off

Postby VK5TM » Mon Aug 08, 2016 8:20 pm

Going back to 2012, Homemaker blankets were on a recall notice, not because of what you are experiencing though.

See notice here: http://www.productsafety.gov.au/recall/kmart-homemaker-electric-blanket-re-announced-pra2011-12679

In fact, if you go through the recall lists, quite a lot of electric blankets have recall notices against them.

We have a king size water bed which has two seperate waterbeds in the one frame and we have a similar situation when one of the two heaters turns on while the other is off re the tingling sensation.
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Re: Electric Blanket EM Field - When it's turned off

Postby VK2JDS » Tue Aug 09, 2016 8:39 am

I dont like the sound of the problem you have identified Brian. We never use them here.
Older types used a transformer with a switch setting which tap was applied to the coil in the blanket.
These days as has been suggested if the unit is connected to the mains and employs a scr to chop the mains up to vary the heating current then they are very noisy, and that noise will affect your multimeter for sure. And likely inducing those spikes into your children.... i would be interested to know if its actually got some sort of isolation from directly applied chopped mains. The electric blankets at morwell when i was at Gippstech had only a small 3 position controller and there was no way they could have fitted a transformer to provide isolation inside it.
Perhaps you could do some tests with an android phone and an application called androsensor or similar and look at the magnetic field readings.

Lastly , as an alternative bed heater there is always the good old hot water bottle, or better still is a dc type of heater mat commonly available from pet supply places.
Its run from a 12volt supply and the model designed for large dogs should do a bed ok. We have one here for the old dog and it provides a gentle warmth directly from battery or plugpack. Just a thought.
73 from the bush. Dave vk2jds
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Re: Electric Blanket EM Field - When it's turned off

Postby VK3BSF » Tue Aug 09, 2016 8:51 am

Get that electric blanket off your bed and junk it before a calamaty strikes..forget about testing.. safety is more important ..there shud be NO volts present if switched off correctly..a qualified electrican is your best bet to check on earth-neutral connections.
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Re: Electric Blanket EM Field - When it's turned off

Postby VK4GJW » Tue Aug 09, 2016 9:49 am

Easy fix, dont use electricity, use water! A tad more expensive, but hey, NO EMF fields at all! :D

http://www.chilitechnology.com.au/shop/ ... rm-winter/
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Re: Electric Blanket EM Field - When it's turned off

Postby VK2MUS » Tue Aug 09, 2016 9:55 pm

I fully support what VK3BSF said - get it off the kids beds as fast as possible
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Re: Electric Blanket EM Field - When it's turned off

Postby VK3ZAZ » Wed Aug 10, 2016 5:14 pm

http://articles.mercola.com/sites/articles/archive/2009/02/24/is-your-electric-blanket-safe.aspx

It concludes that the existing standards for public safety are completely inadequate to protect your health.
The report includes studies showing evidence that electromagnetic fields can:
•Affect gene and protein expression (Transcriptomic and Proteomic Research)
•Have genotoxic effects – RFR and ELF DNA damage
•Induce stress response (Stress Proteins)
•Affect immune function
•Affect neurology and behavior
•Cause childhood cancers (Leukemia)
•Impact melatonin production; Alzheimer's disease; breast cancer
•Promote breast cancer (Melatonin links in laboratory and cell studies)



My wife got a three wire pacemaker last year and is monitored via a sentinel unit connected to Melbourne
and the one thing that went was the electric blanket which caused interference to the pickup loop,
so we cuddle up and keep each other warm with a water bottle for assistance.
cheers
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