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AIUI you use iron cores for low frequency and ferrite for high frequency
because ferrite doesn\'t get magnetized,
AIUI you use iron cores for low frequency and ferrite for high frequency
because ferrite doesn\'t get magnetized, so why couldn\'t aluminum do the
same?
Iron is good in low-frequency transformers because it has a high
saturation field and high permeability, so you can get away with
relatively few turns for the windings. Its disadvantage is that it
is conductive, so there will be eddy current losses, which get
rapidly worse with higher frequency. Those losses can be reduced
by making the core out of thin insulated laminations, but this
gets impractical quite fast.
Jeroen Belleman wrote:
===================
Iron is good in low-frequency transformers because it has a high
saturation field and high permeability, so you can get away with
relatively few turns for the windings. Its disadvantage is that it
is conductive, so there will be eddy current losses, which get
rapidly worse with higher frequency. Those losses can be reduced
by making the core out of thin insulated laminations, but this
gets impractical quite fast.
** Typical iron core transformers intended for 50/60 Hz can be used to 20kHz and beyond with no such issue.
As the operating frequency rises, core magnetisation falls cancelling any rise in losses.
....... Phil
Phil Allison wrote:
-----------------------------------------
Iron is good in low-frequency transformers because it has a high
saturation field and high permeability, so you can get away with
relatively few turns for the windings. Its disadvantage is that it
is conductive, so there will be eddy current losses, which get
rapidly worse with higher frequency. Those losses can be reduced
by making the core out of thin insulated laminations, but this
gets impractical quite fast.
** Typical iron core transformers intended for 50/60 Hz can be used to 20kHz and beyond with no such issue.
As the operating frequency rises, core magnetisation falls cancelling any rise in losses.
Why isn\'t laminated iron good for RF transformer cores then?
Jeroen Belleman wrote:
Phil Allison wrote:
-----------------------------------------
Iron is good in low-frequency transformers because it has a high
saturation field and high permeability, so you can get away with
relatively few turns for the windings. Its disadvantage is that it
is conductive, so there will be eddy current losses, which get
rapidly worse with higher frequency. Those losses can be reduced
by making the core out of thin insulated laminations, but this
gets impractical quite fast.
** Typical iron core transformers intended for 50/60 Hz can be used to 20kHz and beyond with no such issue.
As the operating frequency rises, core magnetisation falls cancelling any rise in losses.
Why isn\'t laminated iron good for RF transformer cores then?
** You have misunderstood my post.
...... Phil
** Typical iron core transformers intended for 50/60 Hz can be used to 20kHz and beyond with no such issue.
As the operating frequency rises, core magnetisation falls cancelling any rise in losses.
Why isn\'t laminated iron good for RF transformer cores then?
** You have misunderstood my post.
It\'s true I assumed constant Bmax. I should have said so.
Constant voltage, as you assumed, is indeed more natural.
** Well, I deal lot with audio transformers - from mic input to hundreds of watts.
I measured the frequency response of a few iron core
transformers: A 75VA rectangular-core worked well up
to 40kHz,
while a similar sized toroid went up to only
about 10kHz (-3dB), measured between the two independent
15V windings of each.
Jeroen Belleman wrote:
==================
** Typical iron core transformers intended for 50/60 Hz can be used to 20kHz and beyond with no such issue.
As the operating frequency rises, core magnetisation falls cancelling any rise in losses.
Why isn\'t laminated iron good for RF transformer cores then?
** You have misunderstood my post.
It\'s true I assumed constant Bmax. I should have said so.
Constant voltage, as you assumed, is indeed more natural.
** Well, I deal lot with audio transformers - from mic input to hundreds of watts.
I measured the frequency response of a few iron core
transformers: A 75VA rectangular-core worked well up
to 40kHz,
** Yep. Audio output types go to about 60kHz or more.
while a similar sized toroid went up to only
about 10kHz (-3dB), measured between the two independent
15V windings of each.
** That is odd, toroidals are usually the best with -3dB responses to 100kHz.
Just the fact the secondary is wound all over the primary does the trick.
What cannot be done is having a tiny laminated iron core running at 100kHz and high power.
As well as ferrite there are \"powdered iron\" cores and toroids that will.
Another material is \"amorphous steel\" which as very low losses.
...... Phil
Jeroen Belleman wrote:
==================
** Typical iron core transformers intended for 50/60 Hz can be used to 20kHz and beyond with no such issue.
As the operating frequency rises, core magnetisation falls cancelling any rise in losses.
Why isn\'t laminated iron good for RF transformer cores then?
** You have misunderstood my post.
It\'s true I assumed constant Bmax. I should have said so.
Constant voltage, as you assumed, is indeed more natural.
** Well, I deal lot with audio transformers - from mic input to hundreds of watts.
I measured the frequency response of a few iron core
transformers: A 75VA rectangular-core worked well up
to 40kHz,
** Yep. Audio output types go to about 60kHz or more.
while a similar sized toroid went up to only
about 10kHz (-3dB), measured between the two independent
15V windings of each.
** That is odd, toroidals are usually the best with -3dB responses to 100kHz.
Just the fact the secondary is wound all over the primary does the trick.
What cannot be done is having a tiny laminated iron core running at 100kHz and high power.
As well as ferrite there are \"powdered iron\" cores and toroids that will.
Another material is \"amorphous steel\" which as very low losses.
** That is odd, toroidals are usually the best with -3dB responses to 100kHz.
Just the fact the secondary is wound all over the primary does the trick.
It surprised me too. I also measured an inter-winding capacitance of
2nF, which strikes me as high. The drop-off was a resonance dip.
Tom Del Rosso wrote:
AIUI you use iron cores for low frequency and ferrite for high
frequency because ferrite doesn\'t get magnetized, so why couldn\'t
aluminum do the same?
You *want* a transformer core to be easily magnetized! You don\'t
want it to *stay* magnetized when the current goes to zero.
Jeroen Belleman wrote:
====================
** That is odd, toroidals are usually the best with -3dB responses to 100kHz.
Just the fact the secondary is wound all over the primary does the trick.
It surprised me too. I also measured an inter-winding capacitance of
2nF, which strikes me as high. The drop-off was a resonance dip.
** You did have a suitable resistive load on the secondary ??
Jeroen Belleman wrote:
Tom Del Rosso wrote:
AIUI you use iron cores for low frequency and ferrite for high
frequency because ferrite doesn\'t get magnetized, so why couldn\'t
aluminum do the same?
You *want* a transformer core to be easily magnetized! You don\'t
want it to *stay* magnetized when the current goes to zero.
Of course that\'s what I meant. It has to conduct a magnetic field but it
must not fight the induced field when it reverses.
I asked about the behavior of ferrite vs aluminum.
** You did have a suitable resistive load on the secondary ??
Just the 50 Ohm ports of my network analyzer.
Jeroen Belleman wrote:
===================
** You did have a suitable resistive load on the secondary ??
Just the 50 Ohm ports of my network analyzer.
** So you paralled the windings or had them in series ?
15V or 30 V ?
Suitable = close to full VA *if* the primary was operated at rated V.
Unloaded trannys always ring like a bell.
An RF network analyzer is a voltage source with a 50 ohm internal
impedance and a receiver with another 50 Ohm internal impedance.
I connected the source to one of the 15V windings of my transformer
and the receiver to the other. The source voltage is well below 1V
rms. Pretty far from the normal operating conditions of the transformer,
is true.
On 2021-08-26 04:25, Tom Del Rosso wrote:
Jeroen Belleman wrote:
Tom Del Rosso wrote:
AIUI you use iron cores for low frequency and ferrite for high
frequency because ferrite doesn\'t get magnetized, so why couldn\'t
aluminum do the same?
You *want* a transformer core to be easily magnetized! You don\'t
want it to *stay* magnetized when the current goes to zero.
Of course that\'s what I meant. It has to conduct a magnetic field
but it must not fight the induced field when it reverses.
I asked about the behavior of ferrite vs aluminum.
The short answer is that aluminium is worse than nothing as a
transformer core. It *will* fight changing fields.
Jeroen Belleman wrote:
On 2021-08-26 04:25, Tom Del Rosso wrote:
Jeroen Belleman wrote:
Tom Del Rosso wrote:
AIUI you use iron cores for low frequency and ferrite for high
frequency because ferrite doesn\'t get magnetized, so why couldn\'t
aluminum do the same?
You *want* a transformer core to be easily magnetized! You don\'t
want it to *stay* magnetized when the current goes to zero.
Of course that\'s what I meant. It has to conduct a magnetic field
but it must not fight the induced field when it reverses.
I asked about the behavior of ferrite vs aluminum.
The short answer is that aluminium is worse than nothing as a
transformer core. It *will* fight changing fields.
That implies that it will \"stay magnetized\" as you put it, so the answer
is too short but thanks for trying.
The short answer is that aluminium is worse than nothing as a
transformer core. It *will* fight changing fields.
That implies that it will \"stay magnetized\" as you put it, so the answer
is too short but thanks for trying.