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Transformer power rating

Started by Unknown November 3, 2017
A radio museum thread contributor says:

"Note the mains transformer power rating is at 50Hz or 60Hz, so it can handle higher audio power as on average it's more than 10x the frequency and the core size needed is much less (that's one reason SMPSU uses 25KHz to 2MHz, to use a small transformer). A toroidal transformer needs well matched bias currents, avoid them."

I'm not convinced that's true. Comments?


NT
On Friday, November 3, 2017 at 12:37:54 PM UTC-6, tabb...@gmail.com wrote:
> A radio museum thread contributor says: > > "Note the mains transformer power rating is at 50Hz or 60Hz, so it can handle higher audio power as on average it's more than 10x the frequency and the core size needed is much less (that's one reason SMPSU uses 25KHz to 2MHz, to use a small transformer). A toroidal transformer needs well matched bias currents, avoid them." > > I'm not convinced that's true. Comments? > > > NT
The higher frequency will mean it can handle more power before saturation, but the problem is that the lamentations will be too thick and eddy currents will over heat the thing.
On 2017/11/03 11:37 AM, tabbypurr@gmail.com wrote:
> A radio museum thread contributor says: > > "Note the mains transformer power rating is at 50Hz or 60Hz, so it can handle higher audio power as on average it's more than 10x the frequency and the core size needed is much less (that's one reason SMPSU uses 25KHz to 2MHz, to use a small transformer). A toroidal transformer needs well matched bias currents, avoid them." > > I'm not convinced that's true. Comments? > > > NT >
Audiophoolery. John :-#(#
On Friday, 3 November 2017 18:43:22 UTC, DemonicTubes  wrote:
> On Friday, November 3, 2017 at 12:37:54 PM UTC-6, tabby wrote:
> > A radio museum thread contributor says: > > > > "Note the mains transformer power rating is at 50Hz or 60Hz, so it can handle higher audio power as on average it's more than 10x the frequency and the core size needed is much less (that's one reason SMPSU uses 25KHz to 2MHz, to use a small transformer). A toroidal transformer needs well matched bias currents, avoid them." > > > > I'm not convinced that's true. Comments?
> The higher frequency will mean it can handle more power before saturation, but the problem is that the lamentations will be too thick and eddy currents will over heat the thing.
AIUI the power limit at 50/60Hz is down to copper loss & core loss, of which copper loss dominates. Going up in frequency does not change copper loss - not over the audio band anyway. Core losses rise but not greatly over the audio band. Thus I'd expect little change in power rating for audio versus mains use. OTOH reusing a mains transformer for audio output is liable to cause lamentation at higher frequencies due to phase shift causing instability. NT
On 11/3/2017 1:37 PM, tabbypurr@gmail.com wrote:
> A radio museum thread contributor says: > > "Note the mains transformer power rating is at 50Hz or 60Hz, so it can handle higher audio power as on average it's more than 10x the frequency and the core size needed is much less (that's one reason SMPSU uses 25KHz to 2MHz, to use a small transformer). A toroidal transformer needs well matched bias currents, avoid them." > > I'm not convinced that's true. Comments? > > > NT >
A mains transformer can handle higher voltage at higher frequency up to a reasonable limit. Beyond that reasonable limit it will not produce what you want. It will never be able to conduct more current for which it was designed. Try to run a mains transformer (loaded) at 25kHz to 2MHz and see what happens. Leakage inductance will eat your lunch. Toroidals can be designed for many applications. It is a mistake to categorize them as you have.
DemonicTubes wrote...
> > tabbypurr wrote: >> A radio museum thread contributor says: >> "Note the mains transformer power rating is at 50Hz or >> 60Hz, so it can handle higher audio power as on average >> it's more than 10x the frequency and the core size >> needed is much less (that's one reason SMPSU uses >> 25kHz to 2MHz, to use a small transformer).
>> I'm not convinced that's true. Comments? > > The higher frequency will mean it can handle more > power before saturation, but the problem is that > the lamentations will be too thick and eddy > currents will over heat the thing.
A second problem is the winding may have too many turns, certainly that's true thinking of smps use. High winding inductance with high capacitances will cause severe suffering at higher frequencies. -- Thanks, - Win
On Friday, 3 November 2017 19:22:31 UTC, John S  wrote:
> On 11/3/2017 1:37 PM, tabbypurr wrote: > > A radio museum thread contributor says: > > > > "Note the mains transformer power rating is at 50Hz or 60Hz, so it can handle higher audio power as on average it's more than 10x the frequency and the core size needed is much less (that's one reason SMPSU uses 25KHz to 2MHz, to use a small transformer). A toroidal transformer needs well matched bias currents, avoid them." > > > > I'm not convinced that's true. Comments?
> A mains transformer can handle higher voltage at higher frequency up to > a reasonable limit.
yes, not something that will be made use of when used as an af output transformer though
> Beyond that reasonable limit it will not produce > what you want. It will never be able to conduct more current for which > it was designed.
and since the highest currents in af are normally low freq, it won't really do more volts either, so no more VA.
> Try to run a mains transformer (loaded) at 25kHz to 2MHz and see what > happens. Leakage inductance will eat your lunch. > > Toroidals can be designed for many applications. It is a mistake to > categorize them as you have.
I haven't categorised them as anything. The metal strip wound ones do lack core gaps though. NT
On Friday, 3 November 2017 19:53:44 UTC, Winfield Hill  wrote:
> DemonicTubes wrote... > > tabbypurr wrote: > >> A radio museum thread contributor says:
> >> "Note the mains transformer power rating is at 50Hz or > >> 60Hz, so it can handle higher audio power as on average > >> it's more than 10x the frequency and the core size > >> needed is much less (that's one reason SMPSU uses > >> 25kHz to 2MHz, to use a small transformer). > > >> I'm not convinced that's true. Comments? > > > > The higher frequency will mean it can handle more > > power before saturation, but the problem is that > > the lamentations will be too thick and eddy > > currents will over heat the thing. > > A second problem is the winding may have too many > turns, certainly that's true thinking of smps use. > High winding inductance with high capacitances > will cause severe suffering at higher frequencies.
Indeed. DAMHIKT. NT
tabb...@gmail.com wrote:

---------------------------
> > > > A radio museum thread contributor says: > > > > > > "Note the mains transformer power rating is at 50Hz or 60Hz, so it can handle higher audio power as on average it's more than 10x the frequency and the core size needed is much less (that's one reason SMPSU uses 25KHz to 2MHz, to use a small transformer). A toroidal transformer needs well matched bias currents, avoid them." > > > > > > I'm not convinced that's true. Comments? >
** It's bunkum.
> > AIUI the power limit at 50/60Hz is down to copper loss & core loss, >
** Neither, it due to core saturation effects setting in if the supply voltage is higher or frequency lower than specified. Saturation causes a massive and non-linear increase in primary current.
> Going up in frequency does not change copper loss - not over the audio band > anyway.
** The rated current of the winding does not change, but using a higher frequency allows a proportionally higher voltage to be applied. The main restriction to this is insulation failure. A frequency plus voltage increase of about 2 or 3 times it the limit.
> Core losses rise but not greatly over the audio band.
** Core losses diminish with rising frequency, since the core is magnetised less and less. In general, mains and audio (tube output) transformers are similar size for the same power rating. High quality tube output transformers are larger as they are rated to work saturation free down to 20 or 30 Hz. Also, toroidal mains transformers CAN be used for tube output if care is taken to keep DC balance within tolerance. A number of guitar amps use toroidals for mains and output. However, typical E-core mains transformers have very poor high frequency response and cannot be so used. E-core audio transformers have layered windings to overcome this. .... Phil
Winfield Hill wrote:

------------------------
> > DemonicTubes wrote... > > > > tabbypurr wrote: > >> A radio museum thread contributor says: > >> "Note the mains transformer power rating is at 50Hz or > >> 60Hz, so it can handle higher audio power as on average > >> it's more than 10x the frequency and the core size > >> needed is much less (that's one reason SMPSU uses > >> 25kHz to 2MHz, to use a small transformer). > > >> I'm not convinced that's true. Comments? > > > > The higher frequency will mean it can handle more > > power before saturation, but the problem is that > > the lamentations will be too thick and eddy > > currents will over heat the thing. > > > A second problem is the winding may have too many > turns, >
** One increases the frequency and voltage in proportion to get higher power throughput - so the number of turns used is just right.
> certainly that's true thinking of smps use. > High winding inductance with high capacitances > will cause severe suffering at higher frequencies. >
** Unlike SMPS transformers, Audio (tube output) transformers are *wide band* devices that operate with *flat response* from 20Hz to 60kHz or more. Core size sets the low frequency power handling and the number of turns depends on the supply voltage being used. By layering primary and secondary windings, leakage inductance is reduced to trivial levels. ..... Phil