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?
- posted
2 years ago
-- Defund the Thought Police
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?
-- Defund the Thought Police
Tom Del Rosso wrote: ==================
** LOL - wrong.Most loudspeakers use FERRITE magnets !
** Or a piece of wood ?FYI
the whole point of a core is that it DOES get magnetised. And as easily as possible and with the least energy losses when cycled in each direction. Iron / Silicon alloys are is the only materials that do that well at low frequencies.
Ferrite has very low losses at at ALL frequencies but cannot compare with iron at low ones for sheer brute force.
.... Phil
You *want* a transformer core to be easily magnetized! You don't want it to *stay* magnetized when the current goes to zero.
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.
Ferrite has a lower permeability and lower saturation field, but it's an insulator, so it doesn't sustain eddy currents.
That's the simple view. Magnetic materials are complicated and lots of effort has been spent on finding the best materials for specific applications. There are hundreds of different kinds of magnetic materials, maybe thousands.
Jeroen Belleman
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........ Phil
Why isn't laminated iron good for RF transformer cores then?
Jeroen Belleman
-----------------------------------------
** You have misunderstood my post....... Phil
It's true I assumed constant Bmax. I should have said so. Constant voltage, as you assumed, is indeed more natural.
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. This was with a tiny excitation voltage, which may mess up the results.Jeroen Belleman
Jeroen Belleman wrote: ==================
** Well, I deal lot with audio transformers - from mic input to hundreds of watts. ** Yep. Audio output types go to about 60kHz or more.** 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
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.I use transformers for RF. I've used ferrite, of course, but also metglas and similar materials. The cores are mostly there for the low end of the frequency range. Beyond a few MHz, you really want to keep the flux out of the core, which is done by using transmission lines for the windings. Some of my transformers are good to 9GHz, but those bear little resemblance to a traditional wound transformer.
Jeroen Belleman
Jeroen Belleman wrote: ====================
** You did have a suitable resistive load on the secondary ??...... Phil
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.
Just the 50 Ohm ports of my network analyzer.
Jeroen Belleman
The short answer is that aluminium is worse than nothing as a transformer core. It *will* fight changing fields.
Jeroen Belleman
Jeroen Belleman wrote: ===================
** 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.
...... Phil
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.
Jeroen Belleman
Jeroen Belleman wrote: ===================
** Drive voltage makes no difference at mid and high frequencies. Only a low ones when approaching core saturation. Toridals use GOSS wound cores with tiny Imags.Fun fact:
GOSS = grain oriented silicon steel. First invented by an engineer who's surname was Goss.
..... Phil
That implies that it will "stay magnetized" as you put it, so the answer is too short but thanks for trying.
-- Defund the Thought Police
Aluminium is a good conductor. There will be eddy currents induced in it that will oppose any /change/ of magnetic field. Lenz law and all that.But once external fields are removed and enough time has passed for eddy currents to decay, there will be no field left over.
Jeroen Belleman
Tom Del Rosso Total Fuckhead wrote: ============================
** FUCK OFF you vile, arrogant, POS, wog assholeNever dream of coming back.
..... Phil
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