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'[EE]:: 12 VAC exposed on domestic appliances.'
2015\05\05@234518 by RussellMc

face picon face
Questions:

1. Would you expect the arrangement described below in a domestic appliance
(Say a halogen bulb based desk lamp).

2. Would you expect it to meet regulatory standards?
(Bonus - what standards does or doesn't it meet. )

3. Is it safe?

4. Would you have such in your home?

5. Do you know f you have one?

*Appliance:*

Domestic market appliance.
12 VAC 2A+ iron core transformer
Assume transformer meets requlatory requirements for isolation etc  - ie
there are no short to mains or similar issues.
This is about the low voltage aspects.

12VAC accessible on extremely easily accessible largish area [tm] contacts.
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2015\05\06@002306 by Denny Esterline

picon face
Google image search "telescopic desk lamp", about six of the first dozen
have the light supported on a pair of telescopic antennas.
To keep from having "unsightly wires" they use the antenna sticks as the
conductors. So, yeah, 12V on parts that are more or less meant to be
touched while live.

Not my favorite bit of kit...


-Denny
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2015\05\06@003756 by Ryan O'Connor

picon face
I just repaired a designer lamp of that style. It had about 13VAC
running down the exposed arms. I did wonder about the safety of the
design, but thought it must be just low enough to be "safe".

On 6 May 2015 at 16:23, Denny Esterline <spam_OUTdesterlineTakeThisOuTspamgmail.com> wrote:
{Quote hidden}

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2015\05\06@004536 by James Cameron

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face
On Wed, May 06, 2015 at 03:44:36PM +1200, RussellMc wrote:
> 1. Would you expect the arrangement described below in a domestic
> appliance (Say a halogen bulb based desk lamp).

No, I didn't expect it before I saw it.

> 2. Would you expect it to meet regulatory standards?
> (Bonus - what standards does or doesn't it meet. )

No.  Bonus declined.  ;-)

> 3. Is it safe?

It's perfectly safe, it won't be harmed.

But combine it with humans and it becomes unsafe.

> 4. Would you have such in your home?

Yes.

> 5. Do you know f you have one?

I've several.  They match your description.  On two of them I've
ripped out the halogen bulb and reflector and fitted an MR16 LED.
Ugly, but works.

I'm thinking of wrapping the conductors in polyimide tape, having had
no luck in finding an insulating tape using the same adhesive out here.

-- James Cameron
http://quozl.linux.org.au/
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2015\05\06@012416 by James Cameron

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face
I've had two fail during use.  The airflow design is inadequate
for hot outback conditions.  The plastic supporting the telescopic
arms grows brittle from the heat, and breaks when the arms are next
moved.

-- James Cameron
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2015\05\06@025412 by RussellMc

face picon face
On 6 May 2015 at 16:23, Denny Esterline <.....desterlineKILLspamspam@spam@gmail.com> wrote:

> Google image search "telescopic desk lamp", about six of the first dozen
> have the light supported on a pair of telescopic antennas.
> To keep from having "unsightly wires" they use the antenna sticks as the
> conductors. So, yeah, 12V on parts that are more or less meant to be
> touched while live.
>

Denny gets the (highly virtual) prize for 1st mention but others are
obviously aware of them.

Bare metal telescoping arms supporting a lamp head.
Arms used for 12 VAC supply.

You can connect extra loads along the arms.

I tried shorting a - 8A AC into a meter and no sign of dropping current 5+
seconds into test - I chickened out before it did.

Semi random 1.X Ohm resistor loaded to 6V.

An example in use as an occasional bedlamp lit an added 30mm LED strip
(with added half wave diode and largish cap) without visible (to me) change
in halogen brightness. Fires could be made with these devices. I'd be
surprised if they hadn't been caused accidentally to date.



          Russell
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2015\05\06@025629 by RussellMc

face picon face
On 6 May 2015 at 16:45, James Cameron <quozlspamKILLspamlaptop.org> wrote:

> I've several.  They match your description.  On two of them I've
> ripped out the halogen bulb and reflector and fitted an MR16 LED.
> Ugly, but works.
>

For extra points take out the bulb and drape series parallel LEDs between
arms.
Double bonus  -

more fun and even uglier.


       Russell
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2015\05\06@045422 by emcq-jrcr

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face
RussellMc wrote:
>
> Domestic market appliance.
> 12 VAC 2A+ iron core transformer
> Assume transformer meets requlatory requirements for isolation etc  - ie
> there are no short to mains or similar issues.
> This is about the low voltage aspects.
>
> 12VAC accessible on extremely easily accessible largish area [tm] contacts.

About the same as a model railway then -  bare conductors (that need to be) in use by unharmed infants for years...
See Marklin 3-rail AC

George Smith

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2015\05\06@054945 by alan.b.pearce

face picon face
> > Domestic market appliance.
> > 12 VAC 2A+ iron core transformer
> > Assume transformer meets requlatory requirements for isolation etc  -
> > ie there are no short to mains or similar issues.
> > This is about the low voltage aspects.
> >
> > 12VAC accessible on extremely easily accessible largish area [tm] contacts.
>
> About the same as a model railway then -  bare conductors (that need to
> be) in use by unharmed infants for years...
> See Marklin 3-rail AC

Or any 2 rail DC layout, which will also have a couple of amps capability typically.



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2015\05\06@073254 by Spehro Pefhany

picon face
At 11:44 PM 5/5/2015, you wrote:
{Quote hidden}

Hi, Russell:-

Here's a couple photos of something that's over my head (literally) as I write.

http://www.speff.com/photo2.JPG
http://www.speff.com/photo1.JPG

There are several hanging fixtures (not shown, but just below photo1.JPG) that carry
MR11 halogen or equivalent LED bulbs to light my desk surface. The wires strung across
the ceiling are insulated with clear PVC (speaker-wire type insulation) and carry no
approval markings- and the metal clamps and the terminals in the supply are
non-insulated and 12V is exposed. Dusting the wires would expose the cleaner to 12V
every time. The supply is a switching supply "transformer" so fully isolated and
carries normal approval markings for this market (UL/CSA). Naturally, the supply is
short-circuit protected (it just shuts down if you overload or short it).

So I would say the answer to all the questions 1..5 is "yes". 2 is a bit trickier--
I have a suspicion it would meet requirements but may not have been subjected to
full testing- in particular the part after it becomes low voltage and galvanically
isolated.

Best regards,
Spehro Pefhany

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2015\05\06@085941 by David VanHorn

picon face
All we need here is a curtain or clothing with sparkly mylar thread to
contact the lamp.   Great article called low voltage the incompetent
ignition source comes to mind.
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2015\05\06@092127 by alan.b.pearce

face picon face
> Here's a couple photos of something that's over my head (literally) as I write.
>
> http://www.speff.com/photo2.JPG
> http://www.speff.com/photo1.JPG
>
> There are several hanging fixtures (not shown, but just below
> photo1.JPG) that carry
> MR11 halogen or equivalent LED bulbs to light my desk surface. The wires
> strung across the ceiling are insulated with clear PVC (speaker-wire type
> insulation) and carry no
> approval markings- and the metal clamps and the terminals in the supply are
> non-insulated and 12V is exposed. Dusting the wires would expose the
> cleaner to 12V every time. The supply is a switching supply "transformer" so
> fully isolated and carries normal approval markings for this market (UL/CSA).
> Naturally, the supply is short-circuit protected (it just shuts down if you
> overload or short it).

I don't know what is in the photos, but if I try and open either of them I get a message from our firewall that access has been denied because "Prohibited by URL database (Pornography & Adult Material)." !!!



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2015\05\06@094234 by Jason White

picon face
part 1 1218 bytes content-type:text/plain; charset="utf-8" (decoded base64)

See attached

On Wed, May 6, 2015 at 9:21 AM,  <.....alan.b.pearceKILLspamspam.....stfc.ac.uk> wrote:
>> Here's a couple photos of something that's over my head (literally) as I write.
>>
>> http://www.speff.com/photo2.JPG
>> http://www.speff.com/photo1.JPG
>>
>> There are several hanging fixtures (not shown, but just below
>> photo1.JPG) that carry
>> MR11 halogen or equivalent LED bulbs to light my desk surface. The wires
>> strung across the ceiling are insulated with clear PVC (speaker-wire type
>> insulation) and carry no
>> approval markings- and the metal clamps and the terminals in the supply are
>> non-insulated and 12V is exposed. Dusting the wires would expose the
>> cleaner to 12V every time. The supply is a switching supply "transformer" so
>> fully isolated and carries normal approval markings for this market (UL/CSA).
>> Naturally, the supply is short-circuit protected (it just shuts down if you
>> overload or short it).
>
> I don't know what is in the photos, but if I try and open either of them I get a message from our firewall that access has been denied because "Prohibited by URL database (Pornography & Adult Material)." !!

--
Jason White

part 2 10885 bytes content-type:image/jpeg; name="photo2.low.JPG" (decode)


part 3 19799 bytes content-type:image/jpeg; name="photo1.JPG" (decode)


part 4 197 bytes content-type:text/plain; name="ATT00001.txt"
(decoded base64)

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2015\05\06@095531 by Justin Richards

face picon face
>
> All we need here is a curtain or clothing with sparkly mylar thread to
> contact the lamp.   Great article called low voltage the incompetent
>

Curtain, yes.  I watched a curtain gently waft over a candle and burst into
flames.  If I had not been there as it occurred, I suspect my house would
have burnt down.
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2015\05\06@103727 by smplx

flavicon
face


On Wed, 6 May 2015, EraseMEalan.b.pearcespam_OUTspamTakeThisOuTstfc.ac.uk wrote:

>
> I don't know what is in the photos, but if I try and open either of them I get a message from our firewall that access has been denied because "Prohibited by URL database (Pornography & Adult Material)." !!!

Naked contacts :-)
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2015\05\06@105839 by David VanHorn

picon face
I was waiting for a sim to complete one evening and decided to google
lightsaber.  The first link i hit got the corp firewall. Blocked. Weapons.

I would have assumed they knew lightsabers aren't real..
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2015\05\06@111718 by alan.b.pearce

face picon face
>
> See attached
>
> >
> > I don't know what is in the photos, but if I try and open either of them I get
> > a message from our firewall that access has been denied because "Prohibited
> > by URL database (Pornography & Adult Material)." !!

I figured that was the style of lighting you were talking about, and is probably what the safety considerations for the desk lamp Russell is describing is based on.

But I wonder what else is hosted by the same provider to cause our firewall to use some published URL list to block it.



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2015\05\06@113842 by RussellMc

face picon face
I'm aware of the model railway and overhead light wiring arrangements.
I suspect that if the latter was designed for a 2A load that it would be
designed to go hi-z (PTC)  if shorted and not deliver the steady 8A that
mine does.

But what surprised me was the common use of such sources unidentified in
standard household settings. Model railroads demonstrate their capabilities
and are used because they do power things via the metal conductors. And
anyone who has tried to keep one working becomes rapidly aware of issues
such as continuity and  contact point cleanliness.

Some may use the overhead light system "unawares" but you'd hope not.

But the lamps have typically 200 to 500mm of bare metal telescoping rods
about 50mm apart. I can bridge the ones on one lamp by holding two NZ $2
coins overlapped.

I'm trying to think of how I can make a rectifier from household materials
- which would allow me to fashion a cellphone charger "on the spot" - with
due care, A good party trick if nothing else - for a limited range of
parties :-).

QUESTION:  How can I make a rectifier from typically available household
products - breaking open the TV, GPS, I-Phone (while a good idea) etc
doesn't count. Need not be perfect - as long as mean current is net
unidirectional it will work "in some cases".



        Russell
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2015\05\06@121747 by Ryan O'Connor

picon face
I saw a video once where someone successfully made a diode using a
razer blade and aluminium foil (I think that's what they used). You
might be able to fashion a half rectifier, though I doubt it would
work for anything above microvolts lol.

Ryan

On 7 May 2015 at 03:37, RussellMc <apptechnzspamspam_OUTgmail.com> wrote:
{Quote hidden}

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2015\05\06@123616 by Denny Esterline

picon face
>
>
>
> Denny gets the (highly virtual) prize for 1st mention but others are
> obviously aware of them.
>
>
Whoo hoo! I get a (virtual) prize for a (nonexistent) contest that I didn't
know I was entering with my (unintentional) entry. :-)




> Bare metal telescoping arms supporting a lamp head.
> Arms used for 12 VAC supply.
>
>

I assumed you had something else in mind, I was just pointing out that such
things are not at all "rare" as even a quick search shows several different
versions from different manufacturers. I have not studied in depth, but it
seems likely that there is a range of versions from "reasonably safe"
through "cheap and cheerful" all the way to "negligent homicide". Telling
them apart when purchasing probably involves divining rods. But on the plus
side, I'm sure there's an instructable somewhere showing how to hack
together divining rods from one of these lamps.. so... :-)


As to the quest for a home-brew diode for aforementioned party tricks - in
the USA at least, I would probably reach for a penny (one cent coin if not
obvious). Current version is copper clad zinc, older versions are solid
copper. I suspect, with a bit of effort, a copper oxide rectifier could be
lashed together.

google google, google. Yep.

Homemade copper oxide diode for crystal radio receiver:
http://www.hpfriedrichs.com/radioroom/cu-diode/rr-cu-diode.htm

and a zinc-oxide version
http://sparkbangbuzz.com/zinc-oxide-diode/zinc-oxide-diode.htm

So the pieces are there. The rest, as they say, is left as an exercise for
the student.

-Denny


(if a suitably motivated student is thwarted by the lack of access to US
pennies, contact me off list and I may be able to assist)
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2015\05\06@125104 by Dwayne Reid

flavicon
face
At 09:44 PM 5/5/2015, RussellMc wrote:
>Questions:
>
>1. Would you expect the arrangement described below in a domestic appliance
>(Say a halogen bulb based desk lamp).
>
>2. Would you expect it to meet regulatory standards?
>(Bonus - what standards does or doesn't it meet. )

Yes.  Class 2 wiring: current limited with non-field-repairable over-current device (self-resetting over-current device is acceptable).


>3. Is it safe?

Usually.  A dead short is definitely safe.


>4. Would you have such in your home?

Yes.  12V desk lamps are common.


>5. Do you know f you have one?

Yes - I have two desk lamps that meet your description.  Both currently do NOT work due to dead bulbs.  Because I like the look of one of the units, I plan to eventually replace the halogen lamp with LED.  Eventually.


{Quote hidden}

-- Dwayne Reid   <@spam@dwaynerKILLspamspamplanet.eon.net>
Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
(780) 489-3199 voice          (780) 487-6397 fax
http://www.trinity-electronics.com
Custom Electronics Design and Manufacturing

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2015\05\06@142050 by Spehro Pefhany

picon face
At 11:17 AM 06/05/2015, KILLspamalan.b.pearceKILLspamspamstfc.ac.uk wrote:
> >
> > See attached
> >
> > >
> > > I don't know what is in the photos, but if I try and open
> either of them I get
> > > a message from our firewall that access has been denied because
> "Prohibited
> > > by URL database (Pornography & Adult Material)." !!
>
>I figured that was the style of lighting you were talking about, and
>is probably what the safety considerations for the desk lamp Russell
>is describing is based on.

If you disallow that, what about things like AC adapters that have 19VDC at several amperes capability exposed? I'm
pretty sure that if you go and stick the end of such an AC adapter into a steel wool pad (don't go and do it..sheesh)
you'll see some fireworks. One could force the makers to put some kind of spring-loaded dielectric hood on each
and every barrel plug, but really...

Whenever there is a potential to deliver more than a watt or two the possibility for starting a fire exists if something
gets connected that happens to have the right resistance, and most cheap devices don't have any approvals past the AC adapter.
It's also perfectly possible to cause a fire (or cause serious burns) with unapproved and unregistered batteries, purchased
without a license or even a cursory ID check.

I have a lot more concern if it's something that could end up sitting on a desk surface- if it looks anything like any
of my dozen or so desks and workbench surfaces there are ample opportunities for issues.. more likely damage to something
electronic than fire in my case. I have a fully charged lithium 18650 cell in a holder with flying leads under some papers here..
allegedly with over-current protection built in (have not tested it).

>But I wonder what else is hosted by the same provider to cause our
>firewall to use some published URL list to block it.

From the original URL- I'm pretty sure nothing**, but it's a redirect through GoDaddy which (I think) might allow
questionable stuff. The actual hosting is on a major provider with a TOS policy prohibiting obscenity etc. <shrug>
I wonder how much legitimate stuff gets blocked by this kind of nanny filter.

** Well, unless some image recognition program misinterpreted this: http://www.speff.com/haggis.jpg

--sp





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2015\05\06@144710 by RussellMc

face picon face
On 7 May 2015 at 04:51, Dwayne Reid <RemoveMEdwaynerTakeThisOuTspamplanet.eon.net> wrote:


> >3. Is it safe?
>
> Usually.  A dead short is definitely safe.
>

Of the two I have here, one provided 8A into a meter (near short circuit)
and I gave up after 5+ seconds.  It doesn't have a "polyfuse type cutout as
they would show some actions by then. It MAY have a slow blow fuse but I
suspect the main fuse is a transformer winding.
TBD.

I could definitely set a house on fire with one of these.

Murphy could too.



       Russell
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2015\05\06@144946 by RussellMc

face picon face
On 7 May 2015 at 06:24, Spehro Pefhany <spamBeGonespeffspamBeGonespaminterlog.com> wrote:


> ** Well, unless some image recognition program misinterpreted this:
>

Ah. Haggis. True obscenity.


          R
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2015\05\06@171610 by IVP

face picon face
> But the lamps have typically 200 to 500mm of bare metal
> telescoping rods about 50mm apart. I can bridge the ones
> on one lamp by holding two NZ $2 coins overlapped.

I can blow the fuse by shoving a 20c piece up the socket

These college kids can put a man on the Moon but where's
the plastic-coated money ?

Pffft


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2015\05\06@183837 by IVP

face picon face
part 1 262 bytes content-type:text/plain; charset="iso-8859-1" (decoded quoted-printable)

> About the same as a model railway then -  bare conductors
> (that need to be) in use by unharmed infants for years...

And Scalextric model cars. I remember mine had some wonky
wiring after a few years

Joe

part 2 6125 bytes content-type:image/jpeg; name="dont_touch_sm.jpg" (decode)


part 3 180 bytes content-type:text/plain; name="Certification"
(decoded base64)

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Version: 2015.0.5863 / Virus Database: 4342/9711 - Release Date: 05/06/15
part 4 197 bytes content-type:text/plain; name="ATT00001.txt"
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