Hi all,

I did more work on my phase convertor project this evening (I'll post
some pictures soon). I stripped a 230 V - 110 V transformer in
preparation for winding a new secondary to give me a 415 V output. It's
amazing how many individual pieces of iron make up a transformer core -
in this case it must be close to 1000.

Anyway, the laminations show a little surface rust. It's minimal but
still makes a mess and it would be good to clean it off in order to do a
really nice rebuild job. There are two sizes of lamination:
approximately 3" x 1.5" and 9" x 1.5" (and a third size in the centre,
which I can't yet measure). Both are about 1/64" thick.

Any ideas on how I might clean off the surface rust? They're too
delicate for tumbling in a concrete mixer, and I don't have a blast
cabinet. I've thought about electrolytic de-rusting, but haven't tried
it before. Does it work okay with a whole bunch of little components
resting in a metal basket? Cleaning 1000 laminations with steel wool
seems like an endless task!

Any thoughts would be appreciated.

Best wishes,

Chris

Chris,

Why not just leave them alone? Conductivity between laminations is not much
of an issue in transformer and motor design. IMO, you'd do well to put them
back together again and make sure you have adequate protection where the new
wires will be in contact with the bare laminations.

Bob Swinney
"Christopher Tidy" wrote in message
...
Hi all,

I did more work on my phase convertor project this evening (I'll post some
pictures soon). I stripped a 230 V - 110 V transformer in preparation for
winding a new secondary to give me a 415 V output. It's amazing how many
individual pieces of iron make up a transformer core - in this case it
must be close to 1000.

Anyway, the laminations show a little surface rust. It's minimal but still
makes a mess and it would be good to clean it off in order to do a really
nice rebuild job. There are two sizes of lamination: approximately 3" x
1.5" and 9" x 1.5" (and a third size in the centre, which I can't yet
measure). Both are about 1/64" thick.

Any ideas on how I might clean off the surface rust? They're too delicate
for tumbling in a concrete mixer, and I don't have a blast cabinet. I've
thought about electrolytic de-rusting, but haven't tried it before. Does
it work okay with a whole bunch of little components resting in a metal
basket? Cleaning 1000 laminations with steel wool seems like an endless
task!

Any thoughts would be appreciated.

Best wishes,

Chris

Robert Swinney wrote:
Chris,

Why not just leave them alone? Conductivity between laminations is not much
of an issue in transformer and motor design. IMO, you'd do well to put them
back together again and make sure you have adequate protection where the new
wires will be in contact with the bare laminations.

Bob Swinney

Bob,

I might well do this. I just thought it would be nice to clean off the
rust as the dust makes quite a mess. But if I clean them, I want to do
it properly and then give them a fresh coat of insulating varnish. The
windings sit on a rubber/plastic former so that they aren't actually in
contact with the core.

Best wishes,

Chris

"Christopher Tidy" wrote in message
...
Robert Swinney wrote:
Chris,

Why not just leave them alone? Conductivity between laminations is not
much
of an issue in transformer and motor design. IMO, you'd do well to put
them
back together again and make sure you have adequate protection where the
new
wires will be in contact with the bare laminations.

Bob Swinney

Bob,

I might well do this. I just thought it would be nice to clean off the
rust as the dust makes quite a mess. But if I clean them, I want to do
it properly and then give them a fresh coat of insulating varnish. The
windings sit on a rubber/plastic former so that they aren't actually in
contact with the core.

Best wishes,

Chris

Chris,
don't clean them! The purpose of laminations is to prevent (or at least
reduce) eddy currents flowing through the thickness of the core, the
laminations are effectively insulated from each other (I think they oxidise
the surfaces of the laminations); cleaning them may well increase the
magnetic losses in the core by allowing high currents to flow between the
laminations.
Martin

--
martindot herewhybrowat herentlworlddot herecom

--
martindot herewhybrowat herentlworlddot herecom

"Hmmm"!

I may be misinformed, but over my many years of working on and around ship
and docks, I would hear a loud humming sounds coming from "some" very large
transformers. The electricians would refer to this a "lamination hum" and
was often blamed on rust between the laminations which would increase the
gap between them.

It never seem to be a detriment to the performance of the transformer other
than an annoying noise.

I often wondered if it didn't, to some small extent, effect the efficiency
of the transformer.

Just my experience, FWIW.

Steve

"Christopher Tidy" wrote in message
...
Robert Swinney wrote:
Chris,

Why not just leave them alone? Conductivity between laminations is not
much of an issue in transformer and motor design. IMO, you'd do well to
put them back together again and make sure you have adequate protection
where the new wires will be in contact with the bare laminations.

Bob Swinney

Bob,

I might well do this. I just thought it would be nice to clean off the
rust as the dust makes quite a mess. But if I clean them, I want to do it
properly and then give them a fresh coat of insulating varnish. The
windings sit on a rubber/plastic former so that they aren't actually in
contact with the core.

Best wishes,

Chris

On Fri, 13 Jan 2006 00:14:16 +0000 (UTC), Christopher Tidy
wrote:

Robert Swinney wrote:
Chris,

Why not just leave them alone? Conductivity between laminations is not much
of an issue in transformer and motor design. IMO, you'd do well to put them
back together again and make sure you have adequate protection where the new
wires will be in contact with the bare laminations.

Bob Swinney

Bob,

I might well do this. I just thought it would be nice to clean off the
rust as the dust makes quite a mess. But if I clean them, I want to do
it properly and then give them a fresh coat of insulating varnish. The
windings sit on a rubber/plastic former so that they aren't actually in
contact with the core.

Best wishes,

Chris
Hey Chris,

Leave the laminations alone. No need to do anything. And note the
"Insulating Varnish" is not applied to make it look nice or to not to
let it rust, but in fact to assist in what another poster said, and
that is, while in use, to keep the windings from moving and rubbing
together, and rubbing the sharp edges on the laminations too. If you
feel you need this to look nice after you get laminations back
together, just wire brush the flat sides, and not the part where you
can see the ends of the laminations. You don't want anything to
"short them out". Best way to apply the varnish after re-winding is
to dip the whole thing in a pail of varnish and let it sit for a few
hours, then bake it in the oven, ******Yeah right!! I'd be dead in
my house!!!****** So, while it's in the dip, make up a cardboard
carton with a nice big light bulb (150 watt?) and figure out a way to
suspend the transformer in with it, and then let it sit there for a
day to bake dry.

If you can't do that, then use air-drying Glyptol instead of varnish.

Easiest way, of course, is to take your efforts into a motor shop and
let them do the dip & bake properly. Then megger it.

Take care.

Brian Lawson,
Bothwell, Ontario.

On Fri, 13 Jan 2006 00:14:16 +0000 (UTC), Christopher Tidy
wrote:

I might well do this. I just thought it would be nice to clean off the
rust as the dust makes quite a mess. But if I clean them, I want to do
it properly and then give them a fresh coat of insulating varnish. The
windings sit on a rubber/plastic former so that they aren't actually in
contact with the core.

Best wishes,

A soak in salt & vinegar or dilute muriatic acid will probably take
care of the rust -- but you will definitely then need to coat the lams
with insulating varnish before reassembly. That could increase the
height of the stack enough so not all of the lams will fit inside the
coil former. If you have fewer lams, then the voltage capability of
a given winding will be reduced: less core sectional area supports
and produces fewer volts per turn at given max flux density.

According to Christopher Tidy :
Hi all,
I stripped a 230 V - 110 V transformer in
preparation for winding a new secondary to give me a 415 V output. It's
amazing how many individual pieces of iron make up a transformer core -
in this case it must be close to 1000.

Anyway, the laminations show a little surface rust.

Any ideas on how I might clean off the surface rust?

I would advise not doing it.

The laminations are designed to be electrically separate to
minimize eddy currents. There is an insulator coating between
laminations, and your cleaning would remove this. It also keeps the
magnetic fields oriented along the laminations, not across them.

I'm not sure what process is used to generate the insulating
layer, but at least the rust will not conduct electricity like the
cleaned laminations would.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

DoN. Nichols wrote:


I would advise not doing it.

The laminations are designed to be electrically separate to
minimize eddy currents. There is an insulator coating between
laminations, and your cleaning would remove this. It also keeps the
magnetic fields oriented along the laminations, not across them.

I'm not sure what process is used to generate the insulating
layer, but at least the rust will not conduct electricity like the
cleaned laminations would.

Good Luck,
DoN.


The insulating coating on transformer and motor laminations is
generally a thin oxide layer that is put onto the steel, with some sort
of a steam process. It is a finish not entirely unlike some types of gun
blueing. Usually the transformer is varnished after the laminated core
is assembled onto the coils. They are immersed into a varnish tank, and
often the tank is closed and a vacuum drawn in the tank to help draw any
trapped air out from the windings and the laminations.

You don't want eddy currents in the core, and you want to minimize
any gaps in the magnetic circuit to minimize core losses and idle
currents. Coating the individual laminations with varnish will introduce
lots of gaps in the core, which is not good. that is why they are steam
finished, it forms a very thin insulating layer.

Don is correct. You would probably be best off to leave them alone,
stack your core and varnish.

A number of years ago, I stacked hundreds and hundreds of these things
by hand. Used to work for a custom transformer house.

Hope that helps.

Al A.

Al A. wrote:
DoN. Nichols wrote:


I would advise not doing it.

The laminations are designed to be electrically separate to
minimize eddy currents. There is an insulator coating between
laminations, and your cleaning would remove this. It also keeps the
magnetic fields oriented along the laminations, not across them.

I'm not sure what process is used to generate the insulating
layer, but at least the rust will not conduct electricity like the
cleaned laminations would.

Good Luck,
DoN.



The insulating coating on transformer and motor laminations is
generally a thin oxide layer that is put onto the steel, with some sort
of a steam process. It is a finish not entirely unlike some types of gun
blueing. Usually the transformer is varnished after the laminated core
is assembled onto the coils. They are immersed into a varnish tank, and
often the tank is closed and a vacuum drawn in the tank to help draw any
trapped air out from the windings and the laminations.

You don't want eddy currents in the core, and you want to minimize any
gaps in the magnetic circuit to minimize core losses and idle currents.
Coating the individual laminations with varnish will introduce lots of
gaps in the core, which is not good. that is why they are steam
finished, it forms a very thin insulating layer.

Don is correct. You would probably be best off to leave them alone,
stack your core and varnish.

A number of years ago, I stacked hundreds and hundreds of these things
by hand. Used to work for a custom transformer house.

Hope that helps.

Al A.

Alright, it looks like the consensus is that I should leave them alone.
I thought they were varnished to prevent eddy currents, but now you
mention it there is a noticeable green layer on the plates. I assume
that this is the oxide layer formed by the steam. I had to dismantle the
core to rewind, so that isn't wasted effort. The reason for cleaning off
the rust was to make reassembly a bit cleaner. The rust is thin and
dusty and gets everywhere. Perhaps I should just wipe them with a rag
soaked in white spirit as I reassemble?

Thanks for the suggestions.

Chris

Christopher Tidy wrote:


Alright, it looks like the consensus is that I should leave them alone.
I thought they were varnished to prevent eddy currents, but now you
mention it there is a noticeable green layer on the plates. I assume
that this is the oxide layer formed by the steam. I had to dismantle the
core to rewind, so that isn't wasted effort. The reason for cleaning off
the rust was to make reassembly a bit cleaner. The rust is thin and
dusty and gets everywhere. Perhaps I should just wipe them with a rag
soaked in white spirit as I reassemble?

Thanks for the suggestions.

Chris



Just wiping the loose dusty stuff off as you describe sounds
about right to me. You are correct, that green is the oxide layer.
On some laminations the oxide layer makes some really cool multi-colored
patterns.

have fun, and let us know how it comes out.

-AL A.

On Thu, 12 Jan 2006 23:41:23 +0000 (UTC), Christopher Tidy
wrote:

You _might_ need to de-rust the laminations, just to get the stack
height small enough to fit back in the coil former. If they're really
rusty, then they're also likely to hum more than usual.

You should re-varnish too, if they're particularly scabby. Missing
varnish increases losses in the core, leading to wasted heat.

I've thought about electrolytic de-rusting, but haven't tried
it before. Does it work okay with a whole bunch of little components
resting in a metal basket?

Yes - a rotating basket would be ideal, but just turn them over every
few hours. You need a big shallow basket, and to have the anode on the
lamination side of the basket. Generally a plastic basket works best, if
you can arrange good contact to the workpiece. A conducting basket tends
to steal too much current flow for itself.

Electrolysis may also leave the varnish intact, compared to abrasives.
Or it might strip it - you don't know for sure until you've tried that
particular varnish.

On Fri, 13 Jan 2006 01:08:41 +0000, (DoN.
Nichols) wrote:

According to Christopher Tidy :
Hi all,
I stripped a 230 V - 110 V transformer in
preparation for winding a new secondary to give me a 415 V output. It's
amazing how many individual pieces of iron make up a transformer core -
in this case it must be close to 1000.

Anyway, the laminations show a little surface rust.

Any ideas on how I might clean off the surface rust?

I would advise not doing it.

The laminations are designed to be electrically separate to
minimize eddy currents. There is an insulator coating between
laminations, and your cleaning would remove this. It also keeps the
magnetic fields oriented along the laminations, not across them.

I'm not sure what process is used to generate the insulating
layer, but at least the rust will not conduct electricity like the
cleaned laminations would.

Good Luck,
DoN.

You could sandblast the laminations with low pressure 80 grit, then
put a coat of Manganese Phosphate (parkerize) or Zinc Phosphate on
them. Soak them in a thinned varnish or drying oil (tung or linseed)
and assemble. The manganese or Zinc phosphate is a poor conductor, and
particularly when oiled keeps the silicon steel from rusting.When the
oil "dries" it forms a varnish type resin that keeps the laminations
from vibrating - then you just need to keep the windings and cores
from singing.
"Parkerizing" is a relatively simple process.

Jm

After you get the whole thing back together take it to a motor shop and
have them dipped in an epoxy type of material. They will evacuate the
chamber to remove all the voids and then bake and dry as needed.

Bob AZ

On Fri, 13 Jan 2006 00:15:34 GMT, "Martin Whybrow"
wrote:

,;
,;"Christopher Tidy" wrote in message
...
,; Robert Swinney wrote:
,; Chris,
,;
,; Why not just leave them alone? Conductivity between laminations is not
,;much
,; of an issue in transformer and motor design. IMO, you'd do well to put
,;them
,; back together again and make sure you have adequate protection where the
,;new
,; wires will be in contact with the bare laminations.
,;
,; Bob Swinney
,;
,; Bob,

,; I might well do this. I just thought it would be nice to clean off the
,; rust as the dust makes quite a mess. But if I clean them, I want to do
,; it properly and then give them a fresh coat of insulating varnish. The
,; windings sit on a rubber/plastic former so that they aren't actually in
,; contact with the core.
,;
,; Best wishes,
,;
,; Chris
,;
,;Chris,
,;don't clean them! The purpose of laminations is to prevent (or at least
,;reduce) eddy currents flowing through the thickness of the core, the
,;laminations are effectively insulated from each other (I think they oxidise
,;the surfaces of the laminations); cleaning them may well increase the
,;magnetic losses in the core by allowing high currents to flow between the
,;laminations.
,;Martin
,;
Yes they are coated to prevent Eddy currents. I believe we used a
magnesium oxide but too much time has elapsed to recall details.

,;martindot herewhybrowat herentlworlddot herecom

On Thu, 12 Jan 2006 23:41:23 +0000 (UTC), Christopher Tidy
wrote:

Hi all,

I did more work on my phase convertor project this evening (I'll post
some pictures soon). I stripped a 230 V - 110 V transformer in
preparation for winding a new secondary to give me a 415 V output. It's
amazing how many individual pieces of iron make up a transformer core -
in this case it must be close to 1000.

Anyway, the laminations show a little surface rust. It's minimal but
still makes a mess and it would be good to clean it off in order to do a
really nice rebuild job. There are two sizes of lamination:
approximately 3" x 1.5" and 9" x 1.5" (and a third size in the centre,
which I can't yet measure). Both are about 1/64" thick.

Any ideas on how I might clean off the surface rust? They're too
delicate for tumbling in a concrete mixer, and I don't have a blast
cabinet. I've thought about electrolytic de-rusting, but haven't tried
it before. Does it work okay with a whole bunch of little components
resting in a metal basket? Cleaning 1000 laminations with steel wool
seems like an endless task!

Any thoughts would be appreciated.

Best wishes,

Chris


Did you think about using a spray on rust converter? I use it for
anything from engines to rectifier assy's.

In article rs.com, DoN.
Nichols says...

I'm not sure what process is used to generate the insulating
layer,

It's varnish.

If the varnish is stripped off there will be one giant conductive
shorted turn. The transformer will smoke.

JIm


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

In article , Christopher Tidy says...

Any thoughts would be appreciated.

The laminations MUST be electrically insulated from each other when
you are done or there will be one large shorted turn. This is bad.

If you strip them down to clean metal you will have to re-varnish
them before putting it back together.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Thanks for all the suggestions. There is nowhere near enough rust to
make reassembly a problem. There's just a bit around the edges and some
dust between the plates. I would try electrolytic de-rusting, except
that I'm concerned that it may remove the intentional green oxide layer
(it is an oxide layer and not varnish in this case). I'll give the
laminations a wipe with white spirit before I reassemble. Before that I
need to build some kind of jig so that I can wind neat coils. It didn't
occur to me at first that using thick (2.5 mm) wire would make winding
more difficult, but it looks like I need to avoid twisting the wire as
it is transferred from the reel to the transformer bobbin. I'll post
some pictures when it's done (probably a week or two).

Chris

jim rozen wrote:

If the varnish is stripped off there will be one giant conductive
shorted turn. The transformer will smoke.

In this you are mistaken. The steel is a magnetic material. The
insulated laminations reduce the eddy current losses. It is not unusual
for laminated cores to be welded to reduce acoustic noise. A solid lump
of iron would still function as a (lousy) transformer core.

Kevin Gallimore

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

According to Christopher Tidy :

[ ... ]

laminations a wipe with white spirit before I reassemble.

That will probably do well enough.
Before that I
need to build some kind of jig so that I can wind neat coils. It didn't
occur to me at first that using thick (2.5 mm) wire would make winding
more difficult, but it looks like I need to avoid twisting the wire as
it is transferred from the reel to the transformer bobbin. I'll post
some pictures when it's done (probably a week or two).

Hmm ... I've seen transformers with heavy wire (around this
size) wound with *square* wire -- to maximize the conductor's
cross-sectional area. Otherwise, there are air gaps between wires which
are just waste space.

Obviously, this would require even more care in the winding,
assuming that you can find the square wire in the first place.

Older transformers that I've disassembled have had a very thin
waxed insulating paper between layers of the wire -- to keep the wire
from bunching up, and especially to minimize the voltage between closely
adjacent wires, which could otherwise be a problem if an upper layer
dropped into a much deeper layer.

obviously, if you are going to be using 2.5mm wire, round or
square, you won't be developing enough voltage to have to worry about
this unless the transformer is a *lot* larger than I have been thinking. :-)

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

"DoN. Nichols" wrote in message
rvers.com...
According to Christopher Tidy :

[ ... ]

laminations a wipe with white spirit before I reassemble.

That will probably do well enough.
Before that I
need to build some kind of jig so that I can wind neat coils. It didn't
occur to me at first that using thick (2.5 mm) wire would make winding
more difficult, but it looks like I need to avoid twisting the wire as
it is transferred from the reel to the transformer bobbin. I'll post
some pictures when it's done (probably a week or two).

Hmm ... I've seen transformers with heavy wire (around this
size) wound with *square* wire -- to maximize the conductor's
cross-sectional area. Otherwise, there are air gaps between wires which
are just waste space.

Obviously, this would require even more care in the winding,
assuming that you can find the square wire in the first place.

Older transformers that I've disassembled have had a very thin
waxed insulating paper between layers of the wire -- to keep the wire
from bunching up, and especially to minimize the voltage between closely
adjacent wires, which could otherwise be a problem if an upper layer
dropped into a much deeper layer.

obviously, if you are going to be using 2.5mm wire, round or
square, you won't be developing enough voltage to have to worry about
this unless the transformer is a *lot* larger than I have been thinking.
:-)

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html

I think the thin paper is called "fish paper" in the rewinding trade. I've
no idea where the name came from.
Bob Swinney

"jim rozen" wrote in message
...
In article , Christopher Tidy says...

Any thoughts would be appreciated.

The laminations MUST be electrically insulated from each other when
you are done or there will be one large shorted turn. This is bad.

If you strip them down to clean metal you will have to re-varnish
them before putting it back together.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

"jim rozen" wrote in message
...
In article , Christopher Tidy says...

Any thoughts would be appreciated.

The laminations MUST be electrically insulated from each other when
you are done or there will be one large shorted turn. This is bad.

If you strip them down to clean metal you will have to re-varnish
them before putting it back together.

Jim


Jim, go back and read axolotol's statement about 4 posts above. Insulated
lams are not required, and probably not desireable. There can be no shorted
turn effect because current in the windings cannot be diverted to the
lams -- unless, of course, there is a short between the windings and the
lams. Actually it would take 2 shorts in 2 different places on the winding
to cause appreciable current to flow in the lams. Read that, other than
eddy currents, which the lams are designed to suppress.

Bob Swinney

--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

On Fri, 13 Jan 2006 18:27:13 -0500, axolotl
wrote:

jim rozen wrote:

If the varnish is stripped off there will be one giant conductive
shorted turn. The transformer will smoke.

In this you are mistaken. The steel is a magnetic material. The
insulated laminations reduce the eddy current losses. It is not unusual
for laminated cores to be welded to reduce acoustic noise. A solid lump
of iron would still function as a (lousy) transformer core.

Kevin Gallimore

It would be a very hot lousy transformer!

On Fri, 13 Jan 2006 21:44:38 -0600, "Robert Swinney"
wrote:


Jim, go back and read axolotol's statement about 4 posts above. Insulated
lams are not required, and probably not desireable. There can be no shorted
turn effect because current in the windings cannot be diverted to the
lams -- unless, of course, there is a short between the windings and the
lams. Actually it would take 2 shorts in 2 different places on the winding
to cause appreciable current to flow in the lams. Read that, other than
eddy currents, which the lams are designed to suppress.

Bob Swinney

It isn't about current connected from windings to lams. It's about a
closed conductive path enclosing the time-varying flux in the core.
Any closed conductive path enclosing the flux linking the winding is
a shorted turn.

Individual lams are still little shorted turns, but they each
individually enclose relatively little flux so eddy currents induced
in them are minimized.

A weld along one side of the stack doesn't create a closed path so it
doesn't hurt anything. If you placed another weld on the other side
of the stack, it would be a very different situation.

In article , Don Foreman says...

It isn't about current connected from windings to lams. It's about a
closed conductive path enclosing the time-varying flux in the core.
Any closed conductive path enclosing the flux linking the winding is
a shorted turn.

Yep. Try that sometime, put a turn of coat-hanger wire fully through
a core sometime, with the ends connected.

Back when transformers were new, they had all kinds of tricks.

A****er Kent made them by winding the bobbin on a form, and then
slipping it over a bundle of steel wires. Then bend the wires
over to overlap to complete the flux circuit. Pot the whole thing
in tar and there it is, laminated core without the need to punch
the E and I pieces.

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

On Fri, 13 Jan 2006 23:35:06 -0600, Don Foreman
wrote:

On Fri, 13 Jan 2006 21:44:38 -0600, "Robert Swinney"
wrote:


Jim, go back and read axolotol's statement about 4 posts above. Insulated
lams are not required, and probably not desireable. There can be no shorted
turn effect because current in the windings cannot be diverted to the
lams -- unless, of course, there is a short between the windings and the
lams. Actually it would take 2 shorts in 2 different places on the winding
to cause appreciable current to flow in the lams. Read that, other than
eddy currents, which the lams are designed to suppress.

Bob Swinney

It isn't about current connected from windings to lams. It's about a
closed conductive path enclosing the time-varying flux in the core.
Any closed conductive path enclosing the flux linking the winding is
a shorted turn.

Individual lams are still little shorted turns, but they each
individually enclose relatively little flux so eddy currents induced
in them are minimized.

A weld along one side of the stack doesn't create a closed path so it
doesn't hurt anything. If you placed another weld on the other side
of the stack, it would be a very different situation.




Have to respectfully dissagree here, guys. Your "average" Microwave
oven transformer is welded in at least 4 or 5 places. It is an "E"
core with a straight closer welded on at both ends. The closer is also
welded across at the middle, and the "E" core is welded at both bottom
corners to the bracket, as well as being welded across the middle.
On the one on my bench (modified to be an isolation transformer) there
are SIX welds, well distributed around the core - and it wuns
perfectly cool.

In article ,
clare at snyder.on.ca wrote:

On Fri, 13 Jan 2006 23:35:06 -0600, Don Foreman
wrote:

On Fri, 13 Jan 2006 21:44:38 -0600, "Robert Swinney"
wrote:


Jim, go back and read axolotol's statement about 4 posts above. Insulated
lams are not required, and probably not desireable. There can be no
shorted
turn effect because current in the windings cannot be diverted to the
lams -- unless, of course, there is a short between the windings and the
lams. Actually it would take 2 shorts in 2 different places on the winding
to cause appreciable current to flow in the lams. Read that, other than
eddy currents, which the lams are designed to suppress.

Bob Swinney

It isn't about current connected from windings to lams. It's about a
closed conductive path enclosing the time-varying flux in the core.
Any closed conductive path enclosing the flux linking the winding is
a shorted turn.

Individual lams are still little shorted turns, but they each
individually enclose relatively little flux so eddy currents induced
in them are minimized.

A weld along one side of the stack doesn't create a closed path so it
doesn't hurt anything. If you placed another weld on the other side
of the stack, it would be a very different situation.




Have to respectfully dissagree here, guys. Your "average" Microwave
oven transformer is welded in at least 4 or 5 places. It is an "E"
core with a straight closer welded on at both ends. The closer is also
welded across at the middle, and the "E" core is welded at both bottom
corners to the bracket, as well as being welded across the middle.
On the one on my bench (modified to be an isolation transformer) there
are SIX welds, well distributed around the core - and it wuns
perfectly cool.

I assume that the welds were all on the outside. This can be OK, so
long as there is no complete circuit in the iron more or less
paralleling the path the copper in the coils takes.

Joe Gwinn

On Sat, 14 Jan 2006 14:57:31 -0500, Joseph Gwinn
wrote:

In article ,
clare at snyder.on.ca wrote:

On Fri, 13 Jan 2006 23:35:06 -0600, Don Foreman
wrote:

On Fri, 13 Jan 2006 21:44:38 -0600, "Robert Swinney"
wrote:


Jim, go back and read axolotol's statement about 4 posts above. Insulated
lams are not required, and probably not desireable. There can be no
shorted
turn effect because current in the windings cannot be diverted to the
lams -- unless, of course, there is a short between the windings and the
lams. Actually it would take 2 shorts in 2 different places on the winding
to cause appreciable current to flow in the lams. Read that, other than
eddy currents, which the lams are designed to suppress.

Bob Swinney

It isn't about current connected from windings to lams. It's about a
closed conductive path enclosing the time-varying flux in the core.
Any closed conductive path enclosing the flux linking the winding is
a shorted turn.

Individual lams are still little shorted turns, but they each
individually enclose relatively little flux so eddy currents induced
in them are minimized.

A weld along one side of the stack doesn't create a closed path so it
doesn't hurt anything. If you placed another weld on the other side
of the stack, it would be a very different situation.




Have to respectfully dissagree here, guys. Your "average" Microwave
oven transformer is welded in at least 4 or 5 places. It is an "E"
core with a straight closer welded on at both ends. The closer is also
welded across at the middle, and the "E" core is welded at both bottom
corners to the bracket, as well as being welded across the middle.
On the one on my bench (modified to be an isolation transformer) there
are SIX welds, well distributed around the core - and it wuns
perfectly cool.

I assume that the welds were all on the outside. This can be OK, so
long as there is no complete circuit in the iron more or less
paralleling the path the copper in the coils takes.

Joe Gwinn

Right. Welds in the plane of the lams don't count either because the
lams are already conductive in that direction.

According to Don Foreman :
On Fri, 13 Jan 2006 18:27:13 -0500, axolotl
wrote:

jim rozen wrote:

If the varnish is stripped off there will be one giant conductive
shorted turn. The transformer will smoke.

In this you are mistaken. The steel is a magnetic material. The
insulated laminations reduce the eddy current losses. It is not unusual
for laminated cores to be welded to reduce acoustic noise. A solid lump
of iron would still function as a (lousy) transformer core.

Kevin Gallimore

It would be a very hot lousy transformer!

But only because of magnetic eddy currents, not shorted turns..

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---

On Sat, 14 Jan 2006 22:26:34 +0000, (DoN.
Nichols) wrote:

According to Don Foreman :
On Fri, 13 Jan 2006 18:27:13 -0500, axolotl
wrote:

jim rozen wrote:

If the varnish is stripped off there will be one giant conductive
shorted turn. The transformer will smoke.

In this you are mistaken. The steel is a magnetic material. The
insulated laminations reduce the eddy current losses. It is not unusual
for laminated cores to be welded to reduce acoustic noise. A solid lump
of iron would still function as a (lousy) transformer core.

Kevin Gallimore

It would be a very hot lousy transformer!

But only because of magnetic eddy currents, not shorted turns..

Enjoy,
DoN.

And the difference is?

Hint: current is current. "Eddy" just connotes current circulating
in a small region. What constrains the region size?

I suppose one might argue that there is no "turn" unless there is a
physical entity, separate from the core metal, that looks like a
shorted turn. OK, absent that it's an eddy current -- one honker of
an eddy current!

If we have many such axially-adjacent regions, are they in
parallel?
(Ducking........)

On Sat, 14 Jan 2006 14:57:31 -0500, Joseph Gwinn
wrote:

In article ,
clare at snyder.on.ca wrote:

On Fri, 13 Jan 2006 23:35:06 -0600, Don Foreman
wrote:

On Fri, 13 Jan 2006 21:44:38 -0600, "Robert Swinney"
wrote:


Jim, go back and read axolotol's statement about 4 posts above. Insulated
lams are not required, and probably not desireable. There can be no
shorted
turn effect because current in the windings cannot be diverted to the
lams -- unless, of course, there is a short between the windings and the
lams. Actually it would take 2 shorts in 2 different places on the winding
to cause appreciable current to flow in the lams. Read that, other than
eddy currents, which the lams are designed to suppress.

Bob Swinney

It isn't about current connected from windings to lams. It's about a
closed conductive path enclosing the time-varying flux in the core.
Any closed conductive path enclosing the flux linking the winding is
a shorted turn.

Individual lams are still little shorted turns, but they each
individually enclose relatively little flux so eddy currents induced
in them are minimized.

A weld along one side of the stack doesn't create a closed path so it
doesn't hurt anything. If you placed another weld on the other side
of the stack, it would be a very different situation.




Have to respectfully dissagree here, guys. Your "average" Microwave
oven transformer is welded in at least 4 or 5 places. It is an "E"
core with a straight closer welded on at both ends. The closer is also
welded across at the middle, and the "E" core is welded at both bottom
corners to the bracket, as well as being welded across the middle.
On the one on my bench (modified to be an isolation transformer) there
are SIX welds, well distributed around the core - and it wuns
perfectly cool.

I assume that the welds were all on the outside. This can be OK, so
long as there is no complete circuit in the iron more or less
paralleling the path the copper in the coils takes.

Joe Gwinn
The laminations will be, by definition, at right angles to the
windings. ANd yes, the welds are on the outside. Would be quite a
trick to weld the inside with the coils installed.

Don Foreman wrote:

I suppose one might argue that there is no "turn" unless there is a
physical entity, separate from the core metal, that looks like a
shorted turn. OK, absent that it's an eddy current -- one honker of
an eddy current!


It is the "shorted turn" concept I have a problem with. A powdered iron
toroid core will show a low DC resistance. It will, however support a
respectable flux density due to the distributed air gaps (or, if you
prefer, multiple domains) in it.

Kevin Gallimore

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

"axolotl" wrote in message
...
Don Foreman wrote:

I suppose one might argue that there is no "turn" unless there is a
physical entity, separate from the core metal, that looks like a
shorted turn. OK, absent that it's an eddy current -- one honker of
an eddy current!


It is the "shorted turn" concept I have a problem with. A powdered iron
toroid core will show a low DC resistance. It will, however support a
respectable flux density due to the distributed air gaps (or, if you
prefer, multiple domains) in it.

Kevin Gallimore
Sorry Kevin,
I've got to disagree with you; powdered iron cores have high electrical
resistivity since they consist of iron powder and an insulating binder. The
whole reason for using them is that they don't support eddy currents which
is what makes them good for high frequency use.
Martin
--
martindot herewhybrowat herentlworlddot herecom

jim rozen wrote:
In article , Don Foreman says...

It isn't about current connected from windings to lams. It's about a
closed conductive path enclosing the time-varying flux in the core.
Any closed conductive path enclosing the flux linking the winding is
a shorted turn.

Yep. Try that sometime, put a turn of coat-hanger wire fully through
a core sometime, with the ends connected.

Back when transformers were new, they had all kinds of tricks.

A****er Kent made them by winding the bobbin on a form, and then
slipping it over a bundle of steel wires. Then bend the wires
over to overlap to complete the flux circuit. Pot the whole thing
in tar and there it is, laminated core without the need to punch
the E and I pieces.

Jim



step-lap cored transfomers are interesting too. They wind the core out of strip steel, then cut it apart,
and reassemble it around the coils. They're really efficient and used in distribution transformers.

Martin Whybrow wrote:


Martin,

You are absolutely right. I really do know better. I must plead a virus
and too many drugs. After some sleep the only thing I can figure out I
was trying to say was that the iron was an energy storage medium and
could not be considered a simple conductor. What makes this worse is
that long ago, in a land far away, I used to have to measure the bulk
resistivity of ferrites. I will now slink off and change my drug mix.

Kevin Gallimore

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

On Sat, 14 Jan 2006 13:52:53 -0500, clare at snyder.on.ca wrote:

Have to respectfully dissagree here, guys. Your "average" Microwave
oven transformer is welded in at least 4 or 5 places. It is an "E"
core with a straight closer welded on at both ends.

Now put a single weld (or bead of solder) on the central leg of the E
and try it again.

Aren't disposable scrap microwave parts fun ! 8-)

You can weld all you like on the "outside" of the lamination stack, but
this doesn't create a shorted turn, it just creates a long C-shaped
conductor, bent into a doughnut (and then joined to a friend on the
other side to make the completed figure 8). So long as there isn't also
a conductive path on the "inside" of the E, then it's OK. You can
connect up laminations all you like, so long as you only connect them
along a plane that's at more or less constant B (or maybe H - I could
never remember).

As the coil has relatively little flux outside the coil, as soon as you
get a small distance away, then it's easy to draw a roughly
equipotential surface. You can even approximate this and follow the
straight-line outside of the E laminations instead. The field varies,
but not by much. _Inside_ the core though, in that central leg, then
unless the core is very long and thin then there will also be a field
variation lengthways on the core. Trying to put the welds here instead
of on the outside would probably cause enough losses to be significant.

I think Andy is right here, although I can't quite visualise all the
C-shapes contorted into doughnuts and figures of 8. Let's suppose that
you only weld where you would in order to fix the laminations together,
i.e., any welds are perpendicular to the plane of the laminations. If
you put welds on the outer surfaces of both the outer legs of the E,
that's fine, because the loop you create encloses two equal and
opposite quantities of flux: the flux in the central leg is equal and
opposite to the flux in the two outer legs, so there will be no voltage
induced in the loop. But if you made two welds on one of the outer legs
of the E (one on the outer surface and one on the inner), or
alternatively one on the outer surface of each outer leg, and two on
both surfaces of the inner leg, you'd have a problem as the net flux
enclosed isn't zero. I think you get the idea.

Sorry I've taken a while to respond to this thread. My own computer
(faithful Sun Ultra 2) has broken down. The clock stopped working, so I
tried to replace the NVRAM chip and now I can't get the machine to
boot. If there are any Sun hardware experts here let me know - I'd be
very glad of the help. I asked the question at comp.unix.solaris but so
far haven't received much advice.

Best wishes,

Chris

On 15 Jan 2006 11:36:47 -0800, wrote:

I think Andy is right here, although I can't quite visualise all the
C-shapes contorted into doughnuts and figures of 8. Let's suppose that
you only weld where you would in order to fix the laminations together,
i.e., any welds are perpendicular to the plane of the laminations. If
you put welds on the outer surfaces of both the outer legs of the E,
that's fine, because the loop you create encloses two equal and
opposite quantities of flux: the flux in the central leg is equal and
opposite to the flux in the two outer legs, so there will be no voltage
induced in the loop. But if you made two welds on one of the outer legs
of the E (one on the outer surface and one on the inner), or
alternatively one on the outer surface of each outer leg, and two on
both surfaces of the inner leg, you'd have a problem as the net flux
enclosed isn't zero. I think you get the idea.

Sorry I've taken a while to respond to this thread. My own computer
(faithful Sun Ultra 2) has broken down. The clock stopped working, so I
tried to replace the NVRAM chip and now I can't get the machine to
boot. If there are any Sun hardware experts here let me know - I'd be
very glad of the help. I asked the question at comp.unix.solaris but so
far haven't received much advice.

Best wishes,

Chris


You have remembered to tell it where to find /vmunix haven't you?


Mark Rand
RTFM