Electric blankets, Gratuitous complexity??

On Fri, 09 Nov 2012 20:22:06 -0500, "Steve W." <csr684@NOTyahoo.com>
wrote:

>Jamie wrote:
>> Vic Smith wrote:
>> 
>>> On Fri, 9 Nov 2012 19:01:11 -0500, "Existential Angst"
>>> <fitcat@optonline.net> wrote:
>>>
>>>
>>>> And the reason quickly became clear:  some electronics don't work with 
>>>> modified (read: shit) sine wave power.
>>>
>>> Well-known inverter - and cheap generator - gotcha.
>>> I mentioned it in one of these "inverter" posts regarding furnace
>>> control boards.  Too bad you missed that.
>>> Only way to avoid the gotcha is to pay up for pure sine wave.
>> 
>>   Or, just put a small transformer on the affected device.
>> 
>> Jamie
>> 
>
>OR stick a small battery back-up like you use on a computer. They smooth 
>the AC and filter it as well.
 The small standby UPS does no wave shaping when allowing the load to
run on "line " voltage - and most are, at best, modified sine wave
output.

On Sat, 10 Nov 2012 11:19:15 +1100, Sylvia Else
<sylvia@not.at.this.address> wrote:

>On 10/11/2012 11:01 AM, Existential Angst wrote:
>> OK.....
>>
>> And the reason quickly became clear:  some electronics don't work with
>> modified (read: shit) sine wave power.
>> But, what electronics are in a g-d electric blanket???
>>
>> So I take apart the three-heat controller, and lo and behold, the goddamm
>> thing looks like the motherboard of a small PC....    holy shit....   for a
>> $25 blankeypoo????
>
>It's probably a triac style dimmer circuit - likely the cheapest way of 
>making a three-heat electric blanket these days. It would indeed fail to 
>work with a modified sine-wave.
>
>Sylvia.

Maybe he can find a "vintage" electric blanket. on ebay or a thrift
store, pr criaigs list, or an "estate sale" (which iiuc is a big yard
sale when the parents or grandparents die.   Mine certainly has no
electronics in it, just a thermostat that reads the air temperature,
not the blanket temp.   I don't use mine every year -- probably only 5
or 10 --, but it's over 30 years old and working fine.   I think his
modern style might be only 10 years old, or less. 

I don't know what the new ones look like but my non-electronic
controller has a clear plastic dial with numbers from 1 to 10, and a
light underneath the dial that illuminates the number.  If I try to
use over 1.5 it's too hot in a bedroom that is 65^F. .   Iff I take
the metal back off the plastic case, it's clear how little is inside
of it.  No circuit board. 

Really older blankets might have a problem with low frequency
radiation.  I'm not sure if that was ever decided to be dangerous
(causing cancer iirc after many years?) , but they changed the wiring
arrangement anyhow so that for every wiire going one direction,
there's a nearby wire going the other direction, to neutalize the
raidation.    AFAIK that works. and it's probably present in any
blanket less than 20 or 15 years old. 

On Fri, 09 Nov 2012 20:01:00 -0600, "Lloyd E. Sponenburgh"
<lloydspinsidemindspring.com> wrote:

>Sylvia Else <sylvia@not.at.this.address> fired this volley in 
>news:ag5mgpF21h6U1@mid.individual.net:
>
>> Such circuits typically prevent current from flowing at all within a 
>> half cycle, until a point is reached where the remainder of the half 
>> cycle would deliver an amount of energy that would, if delivered over 
>> the entire half cycle, represent the desired power. Once triggered, the 
>> triac conducts until current drops below some smallish threshold.
>> 
>> A circuit designed to do that with a sine-wave is going to be somewhat 
>> thrown by an input that is a modified sine-wave.
>> 
>
>I'm fully aware of how SCR and Triac (or generically, Thyristor) 
>"dimmers" function, and how to build them (from scratch, without any 
>supplied schematic).
>
>I'm also aware that a "modified sine wave" or "simulated sine wave" would 
>satisfy the needs of most of that type of circuit, with the exception 
>that the initial triggering and the the subsequent "near zero"-crossing 
>cutoff might occur late and early, respectively, from where they ought.
>
>Such circuits don't work nicely on square waves, primarily because they 
>don't have time to properly turn off.  There's usually some capacitance 
>in the gate circuit (sometimes driven by a diac) that prevents a very 
>rapid change from full voltage through zero to the opposite polarity  
>from lasting long enough below the quench voltage for the device to turn 
>off.
>
>Such _can_ be the case with a simulated sine wave, where the voltage 
>might go from (say) +10V-0--10V on a square edge.  But most inverter 
>companies realized a long (long) time ago that doing it that way causes 
>problems, so they switched (pun) to a waveform that stays at zero long 
>enough for such devices to turn off properly.
>
>Only a really old, or really cheap Chinese inverter would not have that 
>feature.  For all I know, he has both AND a cheap Chinese blanket that 
>didn't take into consideration the problems it might see on old Chinese 
>inverters.
>
>But it's not the case that simulated sine wave inverters universally 
>cause problems with thyristor switches.
>
>LLoyd
  What he NEEDS is a 12 volt blankie.  My baby brother has been a long
distance trucker across north america, from Alaska to Florida - and
has 12 volt mattress warmer and 12 volt electric blanket for YEARS.

Lost 'em both when he rolled the truck last year. Bust his neck too,
but he's back on the road - doing mostly short haul flatland driving
hauling crude - less than 2 years after the crash.

On Fri, 9 Nov 2012 17:53:22 -0800 (PST), Mark <makolber@yahoo.com>
wrote:

>
>
>If you don't mind wrecking the controller, you could wire the heater
>directly to the plug and use it on high...

As I say above, in my experience high would be intolerably hot and
even half temp, 5 out of 10 would be too hot to take,   I've never
used more than 2, but even in a truck cab with no other heat, I doubt
anything more than 3 would be tolerable.   He could test that in
advance by using an extension cord from the house and sleeping in the
truck  with the blanket at half-temp. 

>  or wire in a switch with a
>diode and have full and 1/2. That would also defeat the timer
>function. Also beware this also might disable the overheat safety
>feature.  I'd include a thermal fuse if I was going to do that.  It's
>no fun waking up on fire.

Really?  

JK 

micky wrote:
> 
> Really older blankets might have a problem with low frequency
> radiation.  


   Very doubtful, considering that one cycle is 5000000 meters long. 
That's 5,000 Kilometers or about 3106 miles.  How big is that blanket?

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message 
news:LYKdnWLgX8cYWgDNnZ2dnUVZ_rmdnZ2d@earthlink.com...
>
> micky wrote:
>>
>> Really older blankets might have a problem with low frequency
>> radiation.
>
>
>   Very doubtful, considering that one cycle is 5000000 meters long.
> That's 5,000 Kilometers or about 3106 miles.  How big is that blanket?

Well, if it has a poorly designed triac controller, it may radiate RFI. 

"tm" <No_one_home@white-house.gov> fired this volley in news:k7khim$at3$1
@dont-email.me:

> Well, if it has a poorly designed triac controller, it may radiate RFI. 

Even well-designed ones do on the turn-on.  Only a lot of down-line 
choking and shielding will get it down to reasonable levels.

But it's not likely that the RFI emitted from a 1/2-amp controller would 
emit enough to be harmful to tissue.  Could screw up your pacemaker, I 
guess...

Lloyd

tm wrote:
> 
> "Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
> news:LYKdnWLgX8cYWgDNnZ2dnUVZ_rmdnZ2d@earthlink.com...
> >
> > micky wrote:
> >>
> >> Really older blankets might have a problem with low frequency
> >> radiation.
> >
> >
> >   Very doubtful, considering that one cycle is 5000000 meters long.
> > That's 5,000 Kilometers or about 3106 miles.  How big is that blanket?
> 
> Well, if it has a poorly designed triac controller, it may radiate RFI.


   Which wouldn't be low frequency.

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message 
news:tvadnRooF-HbUADNnZ2dnUVZ_oqdnZ2d@earthlink.com...
>
> tm wrote:
>>
>> "Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
>> news:LYKdnWLgX8cYWgDNnZ2dnUVZ_rmdnZ2d@earthlink.com...
>> >
>> > micky wrote:
>> >>
>> >> Really older blankets might have a problem with low frequency
>> >> radiation.
>> >
>> >
>> >   Very doubtful, considering that one cycle is 5000000 meters long.
>> > That's 5,000 Kilometers or about 3106 miles.  How big is that blanket?
>>
>> Well, if it has a poorly designed triac controller, it may radiate RFI.
>
>
>   Which wouldn't be low frequency.

Wouldn't that depend on your definition of "low frequency"? My AM radio is 
low frequency :) 

On Fri, 09 Nov 2012 22:18:39 -0500, "Michael A. Terrell"
<mike.terrell@earthlink.net> wrote:

>
>micky wrote:
>> 
>> Really older blankets might have a problem with low frequency
>> radiation.  
>
>
>   Very doubtful, considering that one cycle is 5000000 meters long. 
>That's 5,000 Kilometers or about 3106 miles.  How big is that blanket?

Are you saying unless something is 3000 miles ong, it can't radiate
low frequency?.  I don't think so.   And if that were the case, then a
radio transmitter broadcasting at 600 KHz would require an antenna
that was a third of a mile long. 

The question is not whether it can radiate, but whether the low
frequency is harmful.    This was the controversy that also centered
around power lines, often just past the backyard of people's homes.
But you do remind me that most of the opinion, or maybe the consensus
arfter a few years, was that that was not harmful.    By then electric
blankets had already been rediesigned, since they were much easier to
redesign than power lines. .    But yes, they're no longer thought to
be  a risk, I think.  I'd forgotten.