Constant Voltage Transformer Question

[Watson A.Name - \"Watt Su]

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:OHcm3kD8xV2BFw$p@jmwa.demon.co.uk...

I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
Dark Remover" <NOSPAM@dslextreme.com> wrote (in
10tiipltk1d31be@corp.su
pernews.com&gt about 'Constant Voltage Transformer Question', on Mon, 3
Jan 2005:
What really used to bother me was when I connected the thin ethernet
T
connector to a PC in the classroom. There were a dozen or more PCs
daisychained to each other and to the network. I could see a spark
when
I touched the T connector to the jack in the back. Shocking.

I doubt that the voltage was literally shocking. The PCs are all
connected together by the safety earth conductor, and current from
filter capacitors from line to earth in each PC flows in the earth
conductor. Contrary to popular belief, this conductor has finite
resistance, so a voltage is developed across it. When you connect the
parallel path formed by the net cable shield, you cause a proportion
of
the current to divert and flow in the shield. The voltage is very low,
but so is the impedance, so the current can be appreciable.

It felt like 50 or 60 volts to me. Shocking.

--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[John Woodgate]

I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
Dark Remover" <NOSPAM@dslextreme.com> wrote (in <10tkajvbpneqj70@corp.su
pernews.com&gt about 'Constant Voltage Transformer Question', on Mon, 3
Jan 2005:

It felt like 50 or 60 volts to me. Shocking.

Then somewhere in the system you had a piece of equipment that was not
earthed. It might be a fault, or it could be a legal Class 2 product.
The signal ground of such products normally floats at half the supply
voltage, but the current available should be too low to cause a shock.

Vintage Danish audio test gear is another matter. Here, the supply
voltage is 230 V and the capacitances to the signal ground are much
higher. You can get a real bite from these products.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Watson A.Name - \"Watt Su]

"John Woodgate" <jmw@jmwa.demon.contraspam.yuk> wrote in message
news:CBRFmDCLkj2BFw+f@jmwa.demon.co.uk...

I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
Dark Remover" <NOSPAM@dslextreme.com> wrote (in
10tkajvbpneqj70@corp.su
pernews.com&gt about 'Constant Voltage Transformer Question', on Mon, 3
Jan 2005:
It felt like 50 or 60 volts to me. Shocking.

Then somewhere in the system you had a piece of equipment that was not
earthed. It might be a fault, or it could be a legal Class 2 product.
The signal ground of such products normally floats at half the supply
voltage, but the current available should be too low to cause a shock.

Vintage Danish audio test gear is another matter. Here, the supply
voltage is 230 V and the capacitances to the signal ground are much
higher. You can get a real bite from these products.

I think you may have hit upon something. The capacitors of many PCs in
parallel, adding up to the point where the current and voltage are
hazardous.

--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[John Woodgate]

I read in sci.electronics.design that Watson A.Name - "Watt Sun, the
Dark Remover" <NOSPAM@dslextreme.com> wrote (in <10tl7vvahlldv29@corp.su
pernews.com&gt about 'Constant Voltage Transformer Question', on Tue, 4
Jan 2005:

I think you may have hit upon something. The capacitors of many PCs in
parallel, adding up to the point where the current and voltage are
hazardous.

The effect is recognized in EMC and safety circles. I did a calculation,
and obtained an unconvincing result for the likely voltage, but Y MMV.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Charles Edmondson]

Jim Thompson wrote:

On 31 Dec 2004 13:22:03 -0800, Winfield Hill
hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:


Jim Thompson wrote...

I was wondering how Constant Voltage Transformers would perform with
lamp loads. I'm thinking of room-by-room regulation for ceiling
fixtures... since, 15' up, it's tricky with a lamp changer pole :-(

Why not change to electronic mini-fluorescent lamps? I'd imagine
they aren't very voltage sensitive and now they're available with
decent color-temperature phosphors, and some can work with dimmers.
Save on electricity, cooling energy, and manpower.


Do they make those with floodlight shaping?

I haven't been impressed with the light output of the CFLs I've seen.

I have 5x 75W halogen floods just over the cooking area... 15' up,
that's barely adequate.

...Jim Thompson
Hi Jim,

Do you have undercabinet lighting as well? In my kitchen, the only time
I switch on the recessed lighting is when I have company! I just use
the undercabinent lights (flourescents) all the time. I find it a lot
easier on the old eyeballs than bright overheads that leave shadows.

--
Charlie
--
Edmondson Engineering
Unique Solutions to Unusual Problems

 

[David Lesher]

Rich Grise <richgrise@example.net> writes:

But it's cool watching a ferroresonant tranny regulate, especially when
you've got a variac and an AC ammeter. As soon as you apply any voltage at
all, the current goes WAY up. The first time I did it, I kinda panicked
when it was drawing 7 amps on the primary at about 3 VAC in. "It's
regulaging!" he said. He was beaming, probably because he designs them.
Of course, the current went to practically zero at no load and full V.

They were also inherently short-circuit protected. Well, current-limited;
I'm not sure if those are really technically different things.

Lorain Products used to test their many tens of KVAs 3 phase UPS's
with a 100HP motor. Drop it across the output, the UPS goes to limit
and sits there. Motor does not move. Then you see it creeeeeep oh
so slowly, then you can see it move. After many minutes the motor
was going full speed.....

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[David Lesher]

Jim Thompson <thegreatone@example.com> writes:

Back in the '70s a friend got a microwave oven, and I noticed that his
kitchen lights would dim and brighten when the microwave was on. And I
also noticed that at half heat settings, the lights would dim and
brighten at about ten second intervals, which led me to the conclusion
that all the microwave was doing was switching the magnetron on and off,
and not 'dimming' it on a per cycle basis.


AFAIK, that's the way most, if not all, microwaves adjust "power".

And inside the microwave is a ferroresonant xfmr.....

--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

[John Woodgate]

I read in sci.electronics.design that David Lesher <wb8foz@panix.com>
wrote (in <ctdlrl$s7g$6@reader1.panix.com&gt about 'Constant Voltage
Transformer Question', on Fri, 28 Jan 2005:

After a large effort; turns out the Mini-sized (as in British car)
copier machine was putting nasty spikes on the line/neutral, nasty
enough to degrade motor insulation and other windings. They fitted it
with (!) lightning protection (Poly-phaser or such) and that solved the
issue. One wonders how ?Xerox? got UL approval....

UL approval for what? There is no product safety issue. There IS an EMC
issue, but the US has not adopted IEC/EN 61000-3-3, which would probably
have caught the problem.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

 

[Rich Grise]

On Fri, 28 Jan 2005 15:15:23 +0000, David Lesher wrote:

Jim Thompson <thegreatone@example.com> writes:

Back in the '70s a friend got a microwave oven, and I noticed that his
kitchen lights would dim and brighten when the microwave was on. And I
also noticed that at half heat settings, the lights would dim and
brighten at about ten second intervals, which led me to the conclusion
that all the microwave was doing was switching the magnetron on and off,
and not 'dimming' it on a per cycle basis.


AFAIK, that's the way most, if not all, microwaves adjust "power".


And inside the microwave is a ferroresonant xfmr.....

It turns out, at least in the last one I took apart, it _looks_ like a
ferro, but that oil-filled cap is merely the filter cap in a half-wave
doubler. The tranny looks like a ferro, because the primary and secondary
are separate windings, with a space between them. But there are no shunts,
and no resonant winding. )-;

It's a linear transformer, and the cap is only a HV oil-filled cap.

How mundane. ;-)

The maggie _is_, however, the other diode in the half-wave doubler. ;-)

Cheers!
Rich

 

[Rich Grise]

Mark Zenier wrote:

In article <pan.2005.01.28.17.29.42.423374@example.net>,
Rich Grise <richgrise@example.net> wrote:
On Fri, 28 Jan 2005 15:15:23 +0000, David Lesher wrote:

And inside the microwave is a ferroresonant xfmr.....

It turns out, at least in the last one I took apart, it _looks_ like a
ferro, but that oil-filled cap is merely the filter cap in a half-wave
doubler. The tranny looks like a ferro, because the primary and secondary
are separate windings, with a space between them. But there are no shunts,
and no resonant winding. )-;

It's a linear transformer, and the cap is only a HV oil-filled cap.
The maggie _is_, however, the other diode in the half-wave doubler. ;-)

There are shunts (or some sort of welding trick), so that the transformer
current limits. It's like a Neon sign transformer.

Mark Zenier mzenier@eskimo.com Washington State resident

I tried to post this as an attachment, but my post seems to have gone
to the bit bucket. As I said in the other post, I stand corrected.
Thank you. I realized I have a uWT right here, so "I'll take a picture
to prove my point," I sez to meself.

Imagine my surprise!
http://www.neodruid.com/images/dscf0145.jpg

Cheers!
Rich