Something to do while watching some less engaging TV. Unwound another large
toroidal mains transformer. Suspecting doubled up winding of the primary and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at some
point it fails catastrophically. Yes, burnt spot weld buried in the middle
of the primary. Anyone know what this duff winding technique is called ?
(reduces the number of shuttle passes by 2 must be the reason). Is there a
way of testing an unknown , but good , transformer for this winding pattern
?
How come this wiring procedure is not outlawed ?
More generally, someone in production told me that a "goodness" test for a
mains transformer is an open secondaries, no load, monitoring of the primary
current is useful, any truth/rationale in that. ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

On Mar 20, 8:53*am, "N_Cook" wrote:
Something to do while watching some less engaging TV. Unwound another large
toroidal mains transformer. Suspecting doubled up winding of the primary and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at some
point it fails catastrophically. Yes, burnt spot weld buried in the middle
of the primary. Anyone know what this duff winding technique is called ?
(reduces the number of shuttle passes by 2 must be the reason). Is there a
way of testing an unknown, but good, transformer for this winding pattern?

Not that I know of.

How come this wiring procedure is not outlawed?

Most of the transformers wound in this way don't burn out?

More generally, someone in production told me that a "goodness" test for a
mains transformer is an open secondaries, no load, monitoring of the primary
current is useful, any truth/rationale in that. ?

It tells you the inductance of the transformer. It doesn't tell you
how much heat is being dissipated in the windings and the core - for
that you have load the seconaries and watch how fast the output
voltage falls off with incresing load.

Since the permeability of the core declines with increasing
temperature, the inductance falls away as the transformer heats up, so
that magnetising current - and the power dissipation - goes up as the
transoformer gets warmer.

--
Bill Sloman, Nijmegen

"N_Cook"

Something to do while watching some less engaging TV. Unwound another
large
toroidal mains transformer. Suspecting doubled up winding of the primary
and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at
some
point it fails catastrophically. Yes, burnt spot weld buried in the middle
of the primary. Anyone know what this duff winding technique is called ?

** " Standard practice " ??


(reduces the number of shuttle passes by 2 must be the reason). Is there a
way of testing an unknown , but good , transformer for this winding
pattern
?

** Only by testing to destruction.

How come this wiring procedure is not outlawed ?

** It works, is not a recognised safety hazard and saves cost.

BTW: I have a 300VA toroidal with EXACTLY the same kind of failure here
at the moment, waiting for a replacement to be made. But it is lasted 8 or
9 years before shorting.


More generally, someone in production told me that a "goodness" test for a
mains transformer is an open secondaries, no load, monitoring of the
primary
current is useful, any truth/rationale in that. ?

** Yes.

If you checked a run of transformers and found one with a significantly
higher I mag than the others - then the core assembly or the primary
winding has been bodged. For example - an E core tranny where the
laminations are not fully interleaved or tightly enough packed to eliminate
air gaps between the Es and Is will show high I mag on test.

Toroidals normally have very low I mag figures, 10 to even 100 times lower
than similar sized e-cores. However, if the primary voltage exceeds the
maker's design value, expect to see I mag go through the roof. It will also
go through the roof if you try to use a toroidal made for 60 Hz mains power
on 50Hz.



....... Phil

Phil Allison wrote in message
...

"N_Cook"

Something to do while watching some less engaging TV. Unwound another
large
toroidal mains transformer. Suspecting doubled up winding of the primary
and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at
some
point it fails catastrophically. Yes, burnt spot weld buried in the
middle
of the primary. Anyone know what this duff winding technique is called ?

** " Standard practice " ??


(reduces the number of shuttle passes by 2 must be the reason). Is there
a
way of testing an unknown , but good , transformer for this winding
pattern
?

** Only by testing to destruction.

How come this wiring procedure is not outlawed ?

** It works, is not a recognised safety hazard and saves cost.

BTW: I have a 300VA toroidal with EXACTLY the same kind of failure
here
at the moment, waiting for a replacement to be made. But it is lasted 8
or
9 years before shorting.


More generally, someone in production told me that a "goodness" test for
a
mains transformer is an open secondaries, no load, monitoring of the
primary
current is useful, any truth/rationale in that. ?

** Yes.

If you checked a run of transformers and found one with a significantly
higher I mag than the others - then the core assembly or the primary
winding has been bodged. For example - an E core tranny where the
laminations are not fully interleaved or tightly enough packed to
eliminate
air gaps between the Es and Is will show high I mag on test.

Toroidals normally have very low I mag figures, 10 to even 100 times lower
than similar sized e-cores. However, if the primary voltage exceeds the
maker's design value, expect to see I mag go through the roof. It will
also
go through the roof if you try to use a toroidal made for 60 Hz mains
power
on 50Hz.



...... Phil







I'm amazed they last as long as they do , 400 turns or so of paired primary
wires layed together touching and thermal cycling / chaffing possibility
along the lacquer . Certainly not produced in a clean-room so any amount of
microscopic grit between the wires, what is the thickness of 2 layers of
lacquer to resist pk-pk voltage of 350V , let alone mains surges?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

On Fri, 20 Mar 2009 07:53:39 -0000, "N_Cook"
wrote:

Something to do while watching some less engaging TV. Unwound another large
toroidal mains transformer. Suspecting doubled up winding of the primary and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at some
point it fails catastrophically. Yes, burnt spot weld buried in the middle
of the primary. Anyone know what this duff winding technique is called ?
(reduces the number of shuttle passes by 2 must be the reason). Is there a
way of testing an unknown , but good , transformer for this winding pattern
?
How come this wiring procedure is not outlawed ?
More generally, someone in production told me that a "goodness" test for a
mains transformer is an open secondaries, no load, monitoring of the primary
current is useful, any truth/rationale in that. ?

Way back in my dark past I worked in a plant where we wound our own
transformers. Indeed, the doubling of the primaries is standard
practice. Note that if your primary voltage is 240VAC the voltage
between the adjacent wires will be approximately 180V maximum.

Of course, these were using 'I and E' laminates. We tested the wound
bobbin for the correct number of turns and leakage between the wires
of the paired windings. After the laminations were added the entire
transformer was vacuum impregnated with varnish. Not much chance for
movement between the windings after that!

PlainBill

N_Cook wrote:

I'm amazed they last as long as they do , 400 turns or so of paired primary
wires layed together touching and thermal cycling / chaffing possibility
along the lacquer .

You are describing all transformers.


Certainly not produced in a clean-room so any amount of
microscopic grit between the wires, what is the thickness of 2 layers of
lacquer to resist pk-pk voltage of 350V , let alone mains surges?

The lacquer will resist plenty more than that.

Graham

PlainBill wrote in message
news
On Fri, 20 Mar 2009 07:53:39 -0000, "N_Cook"
wrote:

Something to do while watching some less engaging TV. Unwound another
large
toroidal mains transformer. Suspecting doubled up winding of the primary
and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at
some
point it fails catastrophically. Yes, burnt spot weld buried in the
middle
of the primary. Anyone know what this duff winding technique is called ?
(reduces the number of shuttle passes by 2 must be the reason). Is there
a
way of testing an unknown , but good , transformer for this winding
pattern
?
How come this wiring procedure is not outlawed ?
More generally, someone in production told me that a "goodness" test for
a
mains transformer is an open secondaries, no load, monitoring of the
primary
current is useful, any truth/rationale in that. ?

Way back in my dark past I worked in a plant where we wound our own
transformers. Indeed, the doubling of the primaries is standard
practice. Note that if your primary voltage is 240VAC the voltage
between the adjacent wires will be approximately 180V maximum.

Of course, these were using 'I and E' laminates. We tested the wound
bobbin for the correct number of turns and leakage between the wires
of the paired windings. After the laminations were added the entire
transformer was vacuum impregnated with varnish. Not much chance for
movement between the windings after that!

PlainBill

Did you ever metal saw across any of them to actually check on the
impregnation. ? Not transformers, but I've seen such a check on a similar
process with much the same viscosity of fluid and most of the interior was
not impregnated, vacuum gave out to viscosity down fine pathways.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N_Cook" wrote in message
...
Something to do while watching some less engaging TV. Unwound another
large
toroidal mains transformer. Suspecting doubled up winding of the primary
and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at
some
point it fails catastrophically. Yes, burnt spot weld buried in the middle
of the primary. Anyone know what this duff winding technique is called ?
(reduces the number of shuttle passes by 2 must be the reason). Is there a
way of testing an unknown , but good , transformer for this winding
pattern ?
How come this wiring procedure is not outlawed ?
More generally, someone in production told me that a "goodness" test for a
mains transformer is an open secondaries, no load, monitoring of the
primary
current is useful, any truth/rationale in that. ?
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Sounds like fun, in front of the telly, something I would do.

But.................

I would really worry about inhaling/handling the slightest amount of PCBs.
Especially if the unit was manufactured before the '70s. (@_@)

N_Cook wrote:

Did you ever metal saw across any of them to actually check on the
impregnation. ? Not transformers, but I've seen such a check on a similar
process with much the same viscosity of fluid and most of the interior was
not impregnated, vacuum gave out to viscosity down fine pathways.

You're worrying about stuff that's not important.

Graham

"Kalarama" wrote in message
...
"N_Cook" wrote in message
...
Something to do while watching some less engaging TV. Unwound another
large
toroidal mains transformer. Suspecting doubled up winding of the primary
and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at
some
point it fails catastrophically. Yes, burnt spot weld buried in the
middle
of the primary. Anyone know what this duff winding technique is called ?
(reduces the number of shuttle passes by 2 must be the reason). Is there
a
way of testing an unknown , but good , transformer for this winding
pattern ?
How come this wiring procedure is not outlawed ?
More generally, someone in production told me that a "goodness" test for
a
mains transformer is an open secondaries, no load, monitoring of the
primary
current is useful, any truth/rationale in that. ?
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Sounds like fun, in front of the telly, something I would do.

But.................

I would really worry about inhaling/handling the slightest amount of PCBs.
Especially if the unit was manufactured before the '70s. (@_@)


Was this PCB stuff overblown about being dangerous? I worked for
Westinghouse motor and transformer repair in the 40's. Was up to my elbows
some times in PCB oil on transformers. I am still here. As for all coils and
motor windings they were submerged in varnish over night. then drained and
baked. No failures. WW

PlainBill wrote in message
news
On Fri, 20 Mar 2009 07:53:39 -0000, "N_Cook"
wrote:

Something to do while watching some less engaging TV. Unwound another
large
toroidal mains transformer. Suspecting doubled up winding of the primary
and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at
some
point it fails catastrophically. Yes, burnt spot weld buried in the
middle
of the primary. Anyone know what this duff winding technique is called ?
(reduces the number of shuttle passes by 2 must be the reason). Is there
a
way of testing an unknown , but good , transformer for this winding
pattern
?
How come this wiring procedure is not outlawed ?
More generally, someone in production told me that a "goodness" test for
a
mains transformer is an open secondaries, no load, monitoring of the
primary
current is useful, any truth/rationale in that. ?

Way back in my dark past I worked in a plant where we wound our own
transformers. Indeed, the doubling of the primaries is standard
practice. Note that if your primary voltage is 240VAC the voltage
between the adjacent wires will be approximately 180V maximum.

Of course, these were using 'I and E' laminates. We tested the wound
bobbin for the correct number of turns and leakage between the wires
of the paired windings. After the laminations were added the entire
transformer was vacuum impregnated with varnish. Not much chance for
movement between the windings after that!

PlainBill


In the ideal yes, but this Tx and another similar there is no interlayer
insulation between each of the 3 or 4 primary "layers".
Compact winding only on the inside diameter, not the outside , where
windings
could easily slip a "layer". So worst case voltage could be 240/0.707 , peak
to peak, without any mains spikes.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

In article ,
"Kalarama" wrote:

I would really worry about inhaling/handling the slightest amount of PCBs.
Especially if the unit was manufactured before the '70s. (@_@)

Then you'd be somewhat less than brilliant. No mention of transformer
oil was involved, and nobody is likely to uncan an oil filled
transformer in their living room. A dry, varnished/lacquered transformer
has no oil, so no PCBs.

--
Cats, coffee, chocolate...vices to live by

Ecnerwal wrote in message
...
In article ,
"Kalarama" wrote:

I would really worry about inhaling/handling the slightest amount of
PCBs.
Especially if the unit was manufactured before the '70s. (@_@)

Then you'd be somewhat less than brilliant. No mention of transformer
oil was involved, and nobody is likely to uncan an oil filled
transformer in their living room. A dry, varnished/lacquered transformer
has no oil, so no PCBs.

--
Cats, coffee, chocolate...vices to live by


I did think elf 'n' safety a week ago, opening a pack of silicone rubber
sleeving. All this fine glistening deposit everwhere , will I get silicosis
?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"Eeysore"
N_Cook wrote:

I'm amazed they last as long as they do , 400 turns or so of paired
primary
wires layed together touching and thermal cycling / chaffing possibility
along the lacquer .

You are describing all transformers.


** Totally off with the fairies ********.


Certainly not produced in a clean-room so any amount of
microscopic grit between the wires, what is the thickness of 2 layers of
lacquer to resist pk-pk voltage of 350V , let alone mains surges?

The lacquer will resist plenty more than that.


** Totally off with the fairies ********.


....... Phil

"N_Cook"
PlainBill


Way back in my dark past I worked in a plant where we wound our own
transformers. Indeed, the doubling of the primaries is standard
practice. Note that if your primary voltage is 240VAC the voltage
between the adjacent wires will be approximately 180V maximum.

Of course, these were using 'I and E' laminates. We tested the wound
bobbin for the correct number of turns and leakage between the wires
of the paired windings. After the laminations were added the entire
transformer was vacuum impregnated with varnish. Not much chance for
movement between the windings after that!


Did you ever metal saw across any of them to actually check on the
impregnation. ? Not transformers, but I've seen such a check on a similar
process with much the same viscosity of fluid and most of the interior was
not impregnated, vacuum gave out to viscosity down fine pathways.


** Nevertheless, vacuum impregnation works very well with transformers.

The basic idea is to remove all the air spaces between windings and fill
them with insulation material - so the unit will never suffer from "corona"
discharge.

http://en.wikipedia.org/wiki/Corona_...a_dischar ges

Corona discharge is the biggest killer over time of transformers that handle
AC mains or higher voltages - particularly valve output transformers and
EHT transformers.

Until fairly recent times, vacuum impregnation was standard practice for all
mains voltage transformers - toroidal types were wound with porous cloth
tape insulation to allow this step to be done.

Now makers use polyester tape insulation along with tougher, flexible
enamels and impregnation is impossible.

IMO - a mains toroidal with dual primaries ought to have them wound
separately and with at least one layer of poly tape in-between.



...... Phil

On 2009-03-20, N_Cook wrote:

I'm amazed they last as long as they do , 400 turns or so of paired primary
wires layed together touching and thermal cycling / chaffing possibility
along the lacquer . Certainly not produced in a clean-room so any amount of
microscopic grit between the wires, what is the thickness of 2 layers of
lacquer to resist pk-pk voltage of 350V , let alone mains surges?

peak to peak is half of that between series-connected windings.

N_Cook wrote:

I did think elf 'n' safety a week ago, opening a pack of silicone rubber
sleeving. All this fine glistening deposit everwhere , will I get silicosis
?


Though if the deposit had been from something dowsed down from a fire at
over 300degC, it's likely to be bloody painful amounts of Hydrofluoric
acid. Be ready to lose fingers :-(

--
Adrian C

Fred Abse wrote:

On Fri, 20 Mar 2009 23:34:55 +0000, N_Cook wrote:

I did think elf 'n' safety a week ago, opening a pack of silicone rubber
sleeving. All this fine glistening deposit everwhere , will I get silicosis
?

Probably French chalk, AKA talc. Put there as a lubricant.

Yup, totally normal.

Graham

Phil Allison wrote:

"Eeysore"
N_Cook wrote:

I'm amazed they last as long as they do , 400 turns or so of paired
primary wires layed together touching and thermal cycling / chaffing
possibility
along the lacquer .

You are describing all transformers.

** Totally off with the fairies ********.

Well not ALL, but lots.


Certainly not produced in a clean-room so any amount of
microscopic grit between the wires, what is the thickness of 2 layers of
lacquer to resist pk-pk voltage of 350V , let alone mains surges?

The lacquer will resist plenty more than that.

** Totally off with the fairies ********.

5 - 10 kV according to this site.
http://www.awtad-fzco.com/ecwire.htm

Graham

"Ecnerwal" wrote

A dry, varnished/lacquered transformer

So, you're willing to bet there are never any toxic additives (as in
polyvinylchloride) in these varnishes and/or lacquers?

On Mar 20, 9:43*am, "WW" wrote:
"Kalarama" wrote in message


I would really worry about inhaling/handling the slightest amount of PCBs.
Especially if the unit was manufactured before the '70s. * * (@_@)

Was this PCB stuff overblown about being dangerous? *I worked for
Westinghouse motor and transformer repair in the 40's. Was up to my elbows
some times in PCB oil on transformers. I am still here.

There's three issues with PCB oils. First, they're fireproof (a
safety plus).
Second, the oil can overheat and decompose, into dioxins and other
toxins/carcinogens. This, is a safety minus. I've heard of a
contaminated
animal feed episode that got LOTS of political attention. The third
one,
is kinda scary: like DDT, the compound persists and spreads in the
natural environment, so it can cause problems in future decades or
centuries if it isn't collected and neutralized. No one wants to
take the risk of causing the next species extinction and/or lawsuit
flood.

On Fri, 20 Mar 2009 10:43:18 -0600, "WW"
wrote:


"Kalarama" wrote in message
m...
"N_Cook" wrote in message
...
Something to do while watching some less engaging TV. Unwound another
large
toroidal mains transformer. Suspecting doubled up winding of the primary
and
then for UK use joining opposite ends and so relying on 2 thicknesses of
lacquer to resist high voltage. Of course somewhere near the middle at
some
point it fails catastrophically. Yes, burnt spot weld buried in the
middle
of the primary. Anyone know what this duff winding technique is called ?
(reduces the number of shuttle passes by 2 must be the reason). Is there
a
way of testing an unknown , but good , transformer for this winding
pattern ?
How come this wiring procedure is not outlawed ?
More generally, someone in production told me that a "goodness" test for
a
mains transformer is an open secondaries, no load, monitoring of the
primary
current is useful, any truth/rationale in that. ?
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/


Sounds like fun, in front of the telly, something I would do.

But.................

I would really worry about inhaling/handling the slightest amount of PCBs.
Especially if the unit was manufactured before the '70s. (@_@)


Was this PCB stuff overblown about being dangerous? I worked for
Westinghouse motor and transformer repair in the 40's. Was up to my elbows
some times in PCB oil on transformers. I am still here. As for all coils and
motor windings they were submerged in varnish over night. then drained and
baked. No failures. WW

PCBs are really dangerous stuff. They are carcinogenic, mutagenic
bioaccumlative toxins. I must have waded through thousands of pages
of technical and medical data on them. The parts i printed stacked up
to a couple of inches.

On Fri, 20 Mar 2009 17:09:21 -0400, Ecnerwal
wrote:

In article ,
"Kalarama" wrote:

I would really worry about inhaling/handling the slightest amount of PCBs.
Especially if the unit was manufactured before the '70s. (@_@)

Then you'd be somewhat less than brilliant. No mention of transformer
oil was involved, and nobody is likely to uncan an oil filled
transformer in their living room. A dry, varnished/lacquered transformer
has no oil, so no PCBs.

It ain't necessarily so.

Start with this for current US regulation:

http://ecfr.gpoaccess.gov/cgi/t/text...61_main_02.tpl

Anyone care to speculate on the timeline of failure?
There was no local hotspot and no lacquer damage more than a mm from the
"spot weld", and a bit of very localised smoke staining travelling a cm or
so along the affected wires in each direction. Nothing to suggest that the
initial bridge was between the 2 bifilar wires of the primary, so not
running a 120 volt primary in effect on 240V ac for any time. For 240V use
the 2 primaries seriesed to give about 2.8 ohm originally , after failure
then about 0.4 ohm.
The 2 primaries broke into 5 lengths
9.6,14.6,20.1,20.1 and 25.3m long , measured to about 0.2m accuracy.
So originally probably 2 x 45m. Don't know for sure as did not think to
check but the weld was probably 20.1m from one end, but I would suggest that
bridge occured after an arc to another layer (higher pd) and then localised
heating to bridge across to the bifilar fellow wire.

In summary , no evidence that bifilar wiring itself was the reason for
failure but more due to the lack of any interlayer insulation. Because of
the uneven wire spacing between inside and outside faces of the toroid it is
too easy for the layers to be jumbled.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N_Cook" wrote in message
...
Anyone care to speculate on the timeline of failure?
There was no local hotspot and no lacquer damage more than a mm from the
"spot weld", and a bit of very localised smoke staining travelling a cm
or
so along the affected wires in each direction. Nothing to suggest that
the
initial bridge was between the 2 bifilar wires of the primary, so not
running a 120 volt primary in effect on 240V ac for any time. For 240V
use
the 2 primaries seriesed to give about 2.8 ohm originally , after failure
then about 0.4 ohm.
The 2 primaries broke into 5 lengths
9.6,14.6,20.1,20.1 and 25.3m long , measured to about 0.2m accuracy.
So originally probably 2 x 45m. Don't know for sure as did not think to
check but the weld was probably 20.1m from one end, but I would suggest
that
bridge occured after an arc to another layer (higher pd) and then
localised
heating to bridge across to the bifilar fellow wire.

In summary , no evidence that bifilar wiring itself was the reason for
failure but more due to the lack of any interlayer insulation. Because of
the uneven wire spacing between inside and outside faces of the toroid it
is
too easy for the layers to be jumbled.

It would also be helpful to know how the toroid was mounted, and if the
failure occurred where pressure was applied. Toroids are usually mounted
either flat with washers and rubber gaskets with a single screw through the
hole, or vertically in an "Omega" bracket, with some rubber cushioning
material around the periphery. But in either case there may be additional
pressure on a "high spot" where two windings may be crossed, and softening
of the insulation from overheating may also contribute to a short.

It is fairly easy to check for dielectric breakdown between the bifilar
windings, but nearly impossible to detect a weakness between adjacent turns
of a single winding. But it might be possible to use a higher frequency, or
PWM pulses of higher peak voltage, to produce a higher potential between
turns of the same winding, and observe spikes of current due to breakdown.

Paul

Paul E. Schoen wrote in message
...

"N_Cook" wrote in message
...
Anyone care to speculate on the timeline of failure?
There was no local hotspot and no lacquer damage more than a mm from the
"spot weld", and a bit of very localised smoke staining travelling a cm
or
so along the affected wires in each direction. Nothing to suggest that
the
initial bridge was between the 2 bifilar wires of the primary, so not
running a 120 volt primary in effect on 240V ac for any time. For 240V
use
the 2 primaries seriesed to give about 2.8 ohm originally , after
failure
then about 0.4 ohm.
The 2 primaries broke into 5 lengths
9.6,14.6,20.1,20.1 and 25.3m long , measured to about 0.2m accuracy.
So originally probably 2 x 45m. Don't know for sure as did not think to
check but the weld was probably 20.1m from one end, but I would suggest
that
bridge occured after an arc to another layer (higher pd) and then
localised
heating to bridge across to the bifilar fellow wire.

In summary , no evidence that bifilar wiring itself was the reason for
failure but more due to the lack of any interlayer insulation. Because
of
the uneven wire spacing between inside and outside faces of the toroid
it
is
too easy for the layers to be jumbled.

It would also be helpful to know how the toroid was mounted, and if the
failure occurred where pressure was applied. Toroids are usually mounted
either flat with washers and rubber gaskets with a single screw through
the
hole, or vertically in an "Omega" bracket, with some rubber cushioning
material around the periphery. But in either case there may be additional
pressure on a "high spot" where two windings may be crossed, and softening
of the insulation from overheating may also contribute to a short.

It is fairly easy to check for dielectric breakdown between the bifilar
windings, but nearly impossible to detect a weakness between adjacent
turns
of a single winding. But it might be possible to use a higher frequency,
or
PWM pulses of higher peak voltage, to produce a higher potential between
turns of the same winding, and observe spikes of current due to breakdown.

Paul




But the primary is buried under the heavy gauge secondaries windings and
then three layers of 0.05mm polyester film strip, each layer of that
probably overlapped by a factor of 3. So I would have thought immune from
any external mechanical effects, exccept vibration perhaps.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

This one is mounted by central coach bolt and dished disk plus rubber disk.
In use the bolt is vertical and when amp is carried it is horizontal.
I should say I've seen the result of an amp set for USA use used on 240V ,
extensive areas of bare copper due to lacquer melting or burning off and
large amounts of smoke damage.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N_Cook"

This one is mounted by central coach bolt and dished disk plus rubber
disk.
In use the bolt is vertical and when amp is carried it is horizontal.
I should say I've seen the result of an amp set for USA use used on 240V ,
extensive areas of bare copper due to lacquer melting or burning off and
large amounts of smoke damage.


** Now I know for sure you are a posturing BULL**** ARTIST.

The only thing that fails when a toroidal of several hundred VA is fed with
double the rated primary voltage is the damn FUSE !!!!




...... Phil

Phil Allison wrote:
"N_Cook"
This one is mounted by central coach bolt and dished disk plus rubber
disk.
In use the bolt is vertical and when amp is carried it is horizontal.
I should say I've seen the result of an amp set for USA use used on 240V ,
extensive areas of bare copper due to lacquer melting or burning off and
large amounts of smoke damage.


** Now I know for sure you are a posturing BULL**** ARTIST.

The only thing that fails when a toroidal of several hundred VA is fed with
double the rated primary voltage is the damn FUSE !!!!




..... Phil




Assuming the correct value/type of fuse was in place and hadn't been
"repaired" by wrapping aluminum foil (aka ciggy paper) around it.
In my experience not many 120vac transformers survive even momentary
240vac,fused correctly or not. Maybe you are talking about much larger
transformers than I deal with.
JC

"Archon"
Phil Allison wrote:
"N_Cook"
This one is mounted by central coach bolt and dished disk plus rubber
disk.
In use the bolt is vertical and when amp is carried it is horizontal.
I should say I've seen the result of an amp set for USA use used on 240V
,
extensive areas of bare copper due to lacquer melting or burning off and
large amounts of smoke damage.


** Now I know for sure you are a posturing BULL**** ARTIST.

The only thing that fails when a toroidal of several hundred VA is fed
with double the rated primary voltage is the damn FUSE !!!!


Assuming the correct value/type of fuse was in place and hadn't been
"repaired" by wrapping aluminum foil (aka ciggy paper) around it.


** 100% WRONG !!


In my experience not many 120vac transformers survive even momentary
240vac, fused correctly or not.


** So YOU only deal with flea powered trannys - right ?


Maybe you are talking about much larger transformers than I deal with.


** Did you bother to read what I posted ????

A dual-primary tranny of 300VA has 5 ohms of resistance if connected for
230/240 volts and 50 Hz operation

If the same tranny is connected for 120 volts - that 5 ohm value falls to
a tiny 1.25 ohms !!!

When 240 is applied in error, the AC current draw is limited only by that
1.25 ohms of resistance - since the core is instantly driven into * total
magnetic saturation* and effectively disappears.

The resulting AC current flow is in the order of **150 ** amps - so any
tubular glass or ceramic fuse blows INSTANTLY.

Any domestic power circuit (ie thermal magnetic, 15 or 20 amp rated )
breaker will open in a few milliseconds under such a gross overload.

Get real pal.



....... Phil

Phil Allison wrote in message
...

"N_Cook"

This one is mounted by central coach bolt and dished disk plus rubber
disk.
In use the bolt is vertical and when amp is carried it is horizontal.
I should say I've seen the result of an amp set for USA use used on 240V
,
extensive areas of bare copper due to lacquer melting or burning off and
large amounts of smoke damage.


** Now I know for sure you are a posturing BULL**** ARTIST.

The only thing that fails when a toroidal of several hundred VA is fed
with
double the rated primary voltage is the damn FUSE !!!!




..... Phil






It was someone who brought their 160VA Alchemist APD22 Nemesis Amplifier
over from the USA, transformer survived long enough for the electrolytics
to short , then they overloaded the primary enough to blow the , still set
for USA use, mains fuse.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N_Cook" wrote in message
...
Phil Allison wrote in message
...

"N_Cook"

This one is mounted by central coach bolt and dished disk plus rubber
disk.
In use the bolt is vertical and when amp is carried it is horizontal.
I should say I've seen the result of an amp set for USA use used on
240V
extensive areas of bare copper due to lacquer melting or burning off
and
large amounts of smoke damage.


** Now I know for sure you are a posturing BULL**** ARTIST.

The only thing that fails when a toroidal of several hundred VA is fed
with double the rated primary voltage is the damn FUSE !!!!


It was someone who brought their 160VA Alchemist APD22 Nemesis Amplifier
over from the USA, transformer survived long enough for the
electrolytics
to short , then they overloaded the primary enough to blow the , still
set
for USA use, mains fuse.

So the fuse should be about 2 amp slow blow type, which should blow within
0.1 sec at 20 amps and within 1 or 2 cycles at higher current. For 240 VAC
use, it would be about half that. But the parallel primary connection would
also be able to handle twice the current, so the fuse should have been
adequate.

I have tested some toroidal trannies that seem to saturate quite slowly
with increased primary voltage. In a 2 kVA unit rated 240 VAC I had about
50 mA at 240V, 100 mA at 280V, and 600 mA at 320V. Of course it would have
drawn a lot more current at 2x rating, but perhaps not enough to blow a
properly rated fuse instantly. I have seen a rather severe failure in a
toroidal 480 to 240 VAC autotransformer that was connected backward to a
high capacity mains source, thus placing the protective fuse on the load
side.

Paul

Paul E. Schoen wrote in message
...

"N_Cook" wrote in message
...
Phil Allison wrote in message
...

"N_Cook"

This one is mounted by central coach bolt and dished disk plus rubber
disk.
In use the bolt is vertical and when amp is carried it is horizontal.
I should say I've seen the result of an amp set for USA use used on
240V
extensive areas of bare copper due to lacquer melting or burning off
and
large amounts of smoke damage.


** Now I know for sure you are a posturing BULL**** ARTIST.

The only thing that fails when a toroidal of several hundred VA is fed
with double the rated primary voltage is the damn FUSE !!!!


It was someone who brought their 160VA Alchemist APD22 Nemesis Amplifier
over from the USA, transformer survived long enough for the
electrolytics
to short , then they overloaded the primary enough to blow the , still
set
for USA use, mains fuse.

So the fuse should be about 2 amp slow blow type, which should blow within
0.1 sec at 20 amps and within 1 or 2 cycles at higher current. For 240 VAC
use, it would be about half that. But the parallel primary connection
would
also be able to handle twice the current, so the fuse should have been
adequate.

I have tested some toroidal trannies that seem to saturate quite slowly
with increased primary voltage. In a 2 kVA unit rated 240 VAC I had about
50 mA at 240V, 100 mA at 280V, and 600 mA at 320V. Of course it would have
drawn a lot more current at 2x rating, but perhaps not enough to blow a
properly rated fuse instantly. I have seen a rather severe failure in a
toroidal 480 to 240 VAC autotransformer that was connected backward to a
high capacity mains source, thus placing the protective fuse on the load
side.

Paul



I was trying to find a table or formula for toroidal inrush current versus
power rating, but nothing found. A toroidal Tx , power for power comparison
to conventional Tx, has to be larger fuse rating, to avoid blowing at switch
on or after a few switch-ons.
If a toroidal Tx has nothing wrong with it at switch one then there is more
headroom for some later failure inducing problem not to blow the fuse. But
does this headroom increase with higher wattage ? does the ratio of
practical fuse rating/ normal maximum power consumption rise with higher
wattage toroidals ?


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/

"N_Cook"
Phil Allison


** Now I know for sure you are a posturing BULL**** ARTIST.

The only thing that fails when a toroidal of several hundred VA is fed
with double the rated primary voltage is the damn FUSE !!!!


It was someone who brought their 160VA Alchemist APD22 Nemesis Amplifier
over from the USA,

** Has a 3 ohm primary.

Current draw on a 240 volt supply is circa 70 amps !!!


transformer survived long enough for the electrolytics
to short,

** Pure fantasy.


then they overloaded the primary enough to blow the , still set
for USA use, mains fuse.

** Pack of lies.

The supply side fuse would have blown in milli-seconds.

The electros would not have be over voltaged.


...... Phil

"Paul E. Schoen"


I have tested some toroidal trannies that seem to saturate quite slowly
with increased primary voltage.


** Not true of any normal commercial toroidal sold for use with AC supply,


In a 2 kVA unit rated 240 VAC I had about 50 mA at 240V, 100 mA at 280V,
and 600 mA at 320V.


** Memory plays tricks and your test results are probably wrong.



...... Phil

N_Cook wrote:

I was trying to find a table or formula for toroidal inrush current versus
power rating, but nothing found.

Well of course you won't you mental retard. It depends on the exact construction
of the transformer, the load and the instant at which it is switched on in the
mains cycle.

Why do you have to clog up these groups with your infantile questions ?

If in doubt fit a Surge-Gard in series.

Graham

"Eeyore" wrote in message
...


N_Cook wrote:

I was trying to find a table or formula for toroidal inrush current
versus
power rating, but nothing found.

Well of course you won't you mental retard. It depends on the exact
construction
of the transformer, the load and the instant at which it is switched on
in the
mains cycle.

Why do you have to clog up these groups with your infantile questions ?

If in doubt fit a Surge-Gard in series.

Toroidal trannies do seem to have higher inrush currents due to remanent
magnetism. If there are an unequal number of positive and negative
half-cycles applied, the effect is a net DC component that magnetizes the
core. Depending on the phase of the next application of voltage, this could
add to the normal surge and cause very high inrush for a couple of mSec,
which can trip some sennsitive breakers or pop fuses.

I have tried adding series thermistors, but they only work when they are
cold, and in our application we applied multiple surges that heated them
and reduced their effectiveness. In normal applications where power is
switched infrequently, they work well. Another method is to apply soft
turn-on or gradual turn-off using a triac with phase modulation to
demagnetize the core or reduce the turn-on surge.

Paul

Paul E. Schoen wrote:

"Eeyore" wrote in message
...


N_Cook wrote:


I was trying to find a table or formula for toroidal inrush current
versus
power rating, but nothing found.

Well of course you won't you mental retard. It depends on the exact
construction
of the transformer, the load and the instant at which it is switched on
in the
mains cycle.

Why do you have to clog up these groups with your infantile questions ?

If in doubt fit a Surge-Gard in series.


Toroidal trannies do seem to have higher inrush currents due to remanent
magnetism. If there are an unequal number of positive and negative
half-cycles applied, the effect is a net DC component that magnetizes the
core. Depending on the phase of the next application of voltage, this could
add to the normal surge and cause very high inrush for a couple of mSec,
which can trip some sennsitive breakers or pop fuses.

I have tried adding series thermistors, but they only work when they are
cold, and in our application we applied multiple surges that heated them
and reduced their effectiveness. In normal applications where power is
switched infrequently, they work well. Another method is to apply soft
turn-on or gradual turn-off using a triac with phase modulation to
demagnetize the core or reduce the turn-on surge.

Paul


Where did the trannie get the sex change?

"Paul E. Schoen"


Toroidal trannies do seem to have higher inrush currents due to remanent
magnetism.

** Nonsense.

If there are an unequal number of positive and negative half-cycles
applied, the effect is a net DC component that magnetizes the core.

** Utter ********.




...... Phil

Paul E. Schoen wrote in message
...

"Eeyore" wrote in message
...


N_Cook wrote:

I was trying to find a table or formula for toroidal inrush current
versus
power rating, but nothing found.

Well of course you won't you mental retard. It depends on the exact
construction
of the transformer, the load and the instant at which it is switched on
in the
mains cycle.

Why do you have to clog up these groups with your infantile questions ?

If in doubt fit a Surge-Gard in series.

Toroidal trannies do seem to have higher inrush currents due to remanent
magnetism. If there are an unequal number of positive and negative
half-cycles applied, the effect is a net DC component that magnetizes the
core. Depending on the phase of the next application of voltage, this
could
add to the normal surge and cause very high inrush for a couple of mSec,
which can trip some sennsitive breakers or pop fuses.

I have tried adding series thermistors, but they only work when they are
cold, and in our application we applied multiple surges that heated them
and reduced their effectiveness. In normal applications where power is
switched infrequently, they work well. Another method is to apply soft
turn-on or gradual turn-off using a triac with phase modulation to
demagnetize the core or reduce the turn-on surge.

Paul



I thought the disjunctures between the laminations of conventional Tx set up
miniature magnetic circuits in opposition to the magnetising field and so
reduced the current inrush. Toroidal formers don't have these.