In article
, T N Nurse
wrote:

Thanks to everyone who replied to this. The problem has now been
solved - intermittent fault in the probe lead. Grrrrrr!!!!
New probe leads now give the correct readings.

At least that is a lot cheaper to fix than the cost of a new
transformer.

-john-

--
================================================== ==================
John A. Weeks III 952-432-2708
Newave Communications http://www.johnweeks.com
================================================== ==================

On Tue, 28 Sep 2004 10:41:33 +0100, T N Nurse
wrote:


Thanks to everyone who replied to this. The problem has now been
solved - intermittent fault in the probe lead. Grrrrrr!!!!
New probe leads now give the correct readings.

---
So is the transformer burned up, or what???

--
John Fields

=20
On Tue, 28 Sep 2004 10:41:33 +0100, T N Nurse
wrote:
=20
{Centre tapped primary of a push-pull output transformer for audio =
amp}
=20
Looks like it. The two windings came in at 66 and 70 ohms respectively
with combined reading of 135 ohms. Looks like a partial short in
one of the windings. I measured it 3 ways just to be sure - using
the multimeter, using a constant voltage source and checking the
current and using a constant current and checking the voltage. All
3 came in with the same readings. I'm waiting to check with the
manufacturer to check if a 4 ohm difference is out of spec - I
suspect very much that it is.

It is not uncommon for the DC resistance of a center tapped winding to =
differ on each half. For the same number of turns, one half could have =
more length of wire because that part of the winding is further from the =
core piece and one turn uses more wire. A better way to test is to put =
an AC signal on each half separately and see if the secondary gets the =
same output.
David
..

On Wed, 29 Sep 2004 14:45:48 GMT, "David"
wrote:


It is not uncommon for the DC resistance of a center tapped winding to
differ on each half. For the same number of turns, one half could have
more length of wire because that part of the winding is further from
the core piece and one turn uses more wire. A better way to test is to
put an AC signal on each half separately and see if the secondary gets
the same output.

---
I disagree. Using EI laminations and winding the entire transformer on
the center leg, it makes nore sense, if only for the sake of economy,
to wind the CT primary bifilar and avoid using more wire than
necessary. After all, an extra ten feet per transformer is about two
miles of wire, 1000 transformers downstream. Putting down both halves
of the primary at the same time also saves time and tends to make both
halves of the primary look more alike than winding one half on top of
the other.

--
John Fields

"John Fields" wrote in message =
...
On Wed, 29 Sep 2004 14:45:48 GMT, "David"
wrote:
=20
=20
It is not uncommon for the DC resistance of a center tapped winding to
differ on each half. For the same number of turns, one half could have
more length of wire because that part of the winding is further from
the core piece and one turn uses more wire. A better way to test is to
put an AC signal on each half separately and see if the secondary gets
the same output.
=20
---
I disagree. Using EI laminations and winding the entire transformer on
the center leg, it makes nore sense, if only for the sake of economy,
to wind the CT primary bifilar and avoid using more wire than
necessary. After all, an extra ten feet per transformer is about two
miles of wire, 1000 transformers downstream. Putting down both halves
of the primary at the same time also saves time and tends to make both
halves of the primary look more alike than winding one half on top of
the other.=20
=20
--=20
John Fields
John,
That may be true, but this transformer may not have been wound with a =
bifilar primary. If bifilar I agree, if not, I stand by my original post =
and it should be tested by either measuring inductance or seeing if =
there is a difference in a secondary by feeding a signal into each half =
separately. I know a short on one side will affect both halves but a =
difference should still be seen.
David

On Wed, 29 Sep 2004 18:36:13 GMT, "David"
wrote:


John,
That may be true, but this transformer may not have been wound with a
bifilar primary. If bifilar I agree, if not, I stand by my original
post and it should be tested by either measuring inductance or seeing
if there is a difference in a secondary by feeding a signal into each
half separately. I know a short on one side will affect both halves
but a difference should still be seen.

---
I don't disagree with your measurement strategy except that I'd put a
signal into the secondary and then measure the primary output voltages
on either side of the center tap, the presumption being that if the
winding on one side has shorted turns, the voltage out of that side
will be lower than the voltage out of the other side.

--
John Fields

On Wed, 29 Sep 2004 12:13:11 -0500 John Fields
wrote:

I disagree. Using EI laminations and winding the entire transformer on
the center leg, it makes nore sense, if only for the sake of economy,
to wind the CT primary bifilar and avoid using more wire than
necessary. After all, an extra ten feet per transformer is about two
miles of wire, 1000 transformers downstream. Putting down both halves
of the primary at the same time also saves time and tends to make both
halves of the primary look more alike than winding one half on top of
the other.

I think this is only half right. Winding them bifilar would certainly
make them more "balanced" in both turns and impedance, but the total
amount of wire used would have to be the same.

Think of it this way: I still need the same number of turns in each
winding and the same number of total turns. Winding them bifilar
(assuming the same wire gauge) will still occupy the same amount of
the winding window.

So instead of "an extra ten feet" of wire in the outer winding, we end
up using five extra feet in each winding.

I don't know how a real transformer manufacturer would look at it, but
I suspect that the bifilar way has real appeal as long as the voltages
are small.

Once the voltages are large, we may want to spread out the ends and
wind them separately, which most likely means that we're back to the
original method of one on top of (and longer than) the other.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

"John Fields" wrote in message
...
On Wed, 29 Sep 2004 14:45:48 GMT, "David"
wrote:


It is not uncommon for the DC resistance of a center tapped winding to
differ on each half. For the same number of turns, one half could have
more length of wire because that part of the winding is further from
the core piece and one turn uses more wire. A better way to test is to
put an AC signal on each half separately and see if the secondary gets
the same output.

---
I disagree. Using EI laminations and winding the entire transformer on
the center leg, it makes nore sense, if only for the sake of economy,
to wind the CT primary bifilar and avoid using more wire than
necessary. After all, an extra ten feet per transformer is about two
miles of wire, 1000 transformers downstream. Putting down both halves
of the primary at the same time also saves time and tends to make both
halves of the primary look more alike than winding one half on top of
the other.

I would think that as far as toob transformers are concerned, the
voltages between the windings would be too great to wind them bifilar.

--
John Fields

On Fri, 1 Oct 2004 02:38:17 -0700, "Watson A.Name - \"Watt Sun, the
Dark Remover\"" wrote:


I would think that as far as toob transformers are concerned, the
voltages between the windings would be too great to wind them bifilar.

---
Using the proper insulation on the magnet wire and, if necessary,
vacuum-impregnating the transformers pretty much takes care of that
problem.

--
John Fields

On Wed, 29 Sep 2004 20:27:26 -0500, Jim Adney
wrote:

On Wed, 29 Sep 2004 12:13:11 -0500 John Fields
wrote:

I disagree. Using EI laminations and winding the entire transformer on
the center leg, it makes nore sense, if only for the sake of economy,
to wind the CT primary bifilar and avoid using more wire than
necessary. After all, an extra ten feet per transformer is about two
miles of wire, 1000 transformers downstream. Putting down both halves
of the primary at the same time also saves time and tends to make both
halves of the primary look more alike than winding one half on top of
the other.

I think this is only half right. Winding them bifilar would certainly
make them more "balanced" in both turns and impedance, but the total
amount of wire used would have to be the same.

---
You're right.
---

Think of it this way: I still need the same number of turns in each
winding and the same number of total turns. Winding them bifilar
(assuming the same wire gauge) will still occupy the same amount of
the winding window.

So instead of "an extra ten feet" of wire in the outer winding, we end
up using five extra feet in each winding.

---
I'm not sure I understand what you mean unless you're referring to the
penalty for not having two separate windings.

To find out I set up a hypothetical situation using wire with a
diameter of 0.1", a length of turn of 1" for the first layer and a
window width of 2" in order to get 20 turns per layer, and using
either bifilar winding or one winding on top of the other, for 10
layers the total length of wire was 765.3". For the bifilar case,
each winding's length was 382.65", but for one winding on top of the
other, the shorter winding was 225.58" and the longer winding 539.72"!

Taking the total number of turns per winding (100)and winding them
separately would require twice 225.58", or 451.16". Since either the
bifilar or "conventional" winding would require 765.3" for the same
number of turns, that's a savings of 314.14" of wire!
---

I don't know how a real transformer manufacturer would look at it, but
I suspect that the bifilar way has real appeal as long as the voltages
are small.

Once the voltages are large, we may want to spread out the ends and
wind them separately, which most likely means that we're back to the
original method of one on top of (and longer than) the other.

---
Dunno...


--
John Fields

Once the voltages are large, we may want to spread out the ends and
wind them separately, which most likely means that we're back to the
original method of one on top of (and longer than) the other.

Side by side works nicely too. Wind with a bobbin that has a
partition down the middle.


------+ +------
| |
------+ +------
| |
------+ +------


-Chuck

On Fri, 01 Oct 2004 13:36:38 -0500 John Fields
wrote:

I'm not sure I understand what you mean unless you're referring to the
penalty for not having two separate windings.

Now I'm the one who's confused, because any way we do this, there are
still 2 separate windings, unless you want to count the one on top of
the other as a single center-tapped winding.

To find out I set up a hypothetical situation using wire with a
diameter of 0.1", a length of turn of 1" for the first layer and a
window width of 2" in order to get 20 turns per layer, and using
either bifilar winding or one winding on top of the other, for 10
layers the total length of wire was 765.3". For the bifilar case,
each winding's length was 382.65", but for one winding on top of the
other, the shorter winding was 225.58" and the longer winding 539.72"!

Yes, note that 225.58 + 539.72 = 2 x 382.65. This was what I
predicted.

Taking the total number of turns per winding (100)and winding them
separately would require twice 225.58", or 451.16". Since either the
bifilar or "conventional" winding would require 765.3" for the same
number of turns, that's a savings of 314.14" of wire!

Yes, but the only way you can get this is to suddenly have more room
to do windings, so it's not really a fair comparison.

I don't know how a real transformer manufacturer would look at it, but
I suspect that the bifilar way has real appeal as long as the voltages
are small.

Once the voltages are large, we may want to spread out the ends and
wind them separately, which most likely means that we're back to the
original method of one on top of (and longer than) the other.

---
Dunno...

You'd have to assume that the voltage difference between adjacent ends
of the bifilar winding would be nearly as great as the B+ voltage. I'm
not sure how much I can expect to get out of magnet wire varnish, but
I'm pretty sure that I wouldn't want to count on this if I were making
a bunch of them to go out into the commercial world running on a 400V
B+ line.

Keep in mind also that this voltage difference would be AC, reversing
itself with the output. This is a lot harder on the insulation and is
a sure way to find flaws in the insulation. The ACVrms between wires
at either end would be about .7 x B+. The voltage difference in the
middle would actually be the same. Interesting how that works out....

Sure I could probably make one and show that it worked just fine, but
what would my return rate be when they went out into the field and
people covered the ventilation slots with magazines and dirty clothes,
while playing the stereo at full volume for hours on end. ;-)


-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

On Sun, 03 Oct 2004 12:13:08 -0500, Jim Adney
wrote:

On Fri, 01 Oct 2004 13:36:38 -0500 John Fields
wrote:

I'm not sure I understand what you mean unless you're referring to the
penalty for not having two separate windings.

Now I'm the one who's confused, because any way we do this, there are
still 2 separate windings, unless you want to count the one on top of
the other as a single center-tapped winding.

---
Separate windings as on two separate bobbins, each with the same width
and starting diameter and occupying a separate portion of the core.
---

To find out I set up a hypothetical situation using wire with a
diameter of 0.1", a length of turn of 1" for the first layer and a
window width of 2" in order to get 20 turns per layer, and using
either bifilar winding or one winding on top of the other, for 10
layers the total length of wire was 765.3". For the bifilar case,
each winding's length was 382.65", but for one winding on top of the
other, the shorter winding was 225.58" and the longer winding 539.72"!

Yes, note that 225.58 + 539.72 = 2 x 382.65. This was what I
predicted.

---
Yes, I know...
---

Taking the total number of turns per winding (100)and winding them
separately would require twice 225.58", or 451.16". Since either the
bifilar or "conventional" winding would require 765.3" for the same
number of turns, that's a savings of 314.14" of wire!

Yes, but the only way you can get this is to suddenly have more room
to do windings, so it's not really a fair comparison.

---
It's a perfectly fair comparison and reflects the savings to be
realized with utilizing more of the core. Consider a transformer wound
on EI laminations with one winding on the center leg and two other
windings wound around the outer legs. If the outer windings were
identical, then winding them separately would result in saving about
41% of the wire which would be needed to wind them either stacked or
bifilar.
---

I don't know how a real transformer manufacturer would look at it, but
I suspect that the bifilar way has real appeal as long as the voltages
are small.

Once the voltages are large, we may want to spread out the ends and
wind them separately, which most likely means that we're back to the
original method of one on top of (and longer than) the other.

---
Dunno...

You'd have to assume that the voltage difference between adjacent ends
of the bifilar winding would be nearly as great as the B+ voltage. I'm
not sure how much I can expect to get out of magnet wire varnish, but
I'm pretty sure that I wouldn't want to count on this if I were making
a bunch of them to go out into the commercial world running on a 400V
B+ line.

Keep in mind also that this voltage difference would be AC, reversing
itself with the output. This is a lot harder on the insulation and is
a sure way to find flaws in the insulation. The ACVrms between wires
at either end would be about .7 x B+. The voltage difference in the
middle would actually be the same. Interesting how that works out....

Sure I could probably make one and show that it worked just fine, but
what would my return rate be when they went out into the field and
people covered the ventilation slots with magazines and dirty clothes,
while playing the stereo at full volume for hours on end. ;-)

---
Folks who make transformers for a living know all that, and they
routinely hipot to 5kV winding-to-winding and winding-to-core, and
make stuff that can run at ungodly high temperatures, so I don't think
it's a big deal if it's planned for.

--
John Fields

On Sun, 03 Oct 2004 14:24:03 -0500 John Fields
wrote:

Separate windings as on two separate bobbins, each with the same width
and starting diameter and occupying a separate portion of the core.

Sure, you can do that, but you're changing the rules in the middle of
the game: You're giving yourself a larger winding window to work with.
(otherwise you would have slightly less than half as much length to
work with, so each winding would build up faster and taller. The extra
bobbin takes up some of your previous volume, so you come out behind.

Otherwise, separate bobbins is certainly a desirable thing to do, but
you have to allow extra space for it up front.

I could also suggest that I would just start with a longer core so
that I would need fewer layers, and that would save even more wire....

Folks who make transformers for a living know all that, and they
routinely hipot to 5kV winding-to-winding and winding-to-core, and
make stuff that can run at ungodly high temperatures, so I don't think
it's a big deal if it's planned for.

That's a MUCH easier problem than 300-500 AC volts between adjacent
turns.

-
-----------------------------------------------
Jim Adney
Madison, WI 53711 USA
-----------------------------------------------

On Tue, 05 Oct 2004 18:54:18 -0500, Jim Adney
wrote:

On Sun, 03 Oct 2004 14:24:03 -0500 John Fields
wrote:

Separate windings as on two separate bobbins, each with the same width
and starting diameter and occupying a separate portion of the core.

Sure, you can do that, but you're changing the rules in the middle of
the game: You're giving yourself a larger winding window to work with.
(otherwise you would have slightly less than half as much length to
work with, so each winding would build up faster and taller. The extra
bobbin takes up some of your previous volume, so you come out behind.

Otherwise, separate bobbins is certainly a desirable thing to do, but
you have to allow extra space for it up front.

I could also suggest that I would just start with a longer core so
that I would need fewer layers, and that would save even more wire....

---
At the expense of extra core or, for the same volume, a longer
magnetic path (not good). The game is to minimize the total cost of
the transformer while maximizing its performance, and blithely doing
this-and-that isn't likely to converge on a winning "design"
---

Folks who make transformers for a living know all that, and they
routinely hipot to 5kV winding-to-winding and winding-to-core, and
make stuff that can run at ungodly high temperatures, so I don't think
it's a big deal if it's planned for.

That's a MUCH easier problem than 300-500 AC volts between adjacent
turns.

---
Don't be ridiculous. The only problematic part about it is deciding
what insulation to use on the magnet wire, and since there are many
materials which can easily stand off higher voltages, that turns out
to be a non-problem as well.

Consider Kapton. At about 5kV/mil, a 0.0001" layer of it on adjacent
conductors would stand off a 1000V difference between them.

If you want to spout definitive information instead of mere opinion,
first go slogging through the spec's for the different magnet wire
insulation systems, then spout what you find.

In any case, I'm getting bored with this whole thing so if you choose
to reply you'll be talking to yourself.

--
John Fields