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Electronic circuit design discusions
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About those custom wound line freq transformers - part 1
Thanks for all your comments. They covered a wealth of areas so I realise I should have followed my own usual advice and concentrated on one aspect at a time. Firstly, for the most part I'm mostly interested in toroidal construction. So
please ignore any aspects relating to EI and other constructions.
Secondly, I'm especially interested in designs with LOWER FLUX operation, since
stray field is a particular concern to me especially with 'restoring' and
improving to more current specs certain older specialist items of 'boutique'
audio gear for example. What may have been an acceptable noise floor a couple of
decades ago looks very second-rate by modern standards you see.
There is also the advantage of elimination of 'switch-on surge' but that's a
relativley minor consideration for equipment of < ~ 100VA. but I am also
interested in this for other applications).
So, I like the idea of operation at reduced flux. The stray field will reduce in
proportion to the reduced magnetising force but I presume will also reduce since
the magnetic material retains it's permeabilty best at lower fluxes.
Additionally, the distortion in Imag will be lower with a lower magnetising
force resulting in less of the very annoying harmonic content in the stray flux.
So, there are some reasons for wanting to work with a lower flux level.
I'd be additionally interested in suggestions for other methods of reducing
stray flux.
The symmetry ? of the windings appears that it may have some influence and I
noticed that transformers from a certain manufacturer which had a thick 0.4mm
polyproplylene barrier between pri and sec appeared to have higher leakage flux.
I'm hoping that I may be able to reduce this stray flux by improving coupling
with the use of triple insulated winding wire which doesn't require a solid
barrier like that.
Graham
Eeyore wrote:
(snip) > I'd be additionally interested in suggestions for other methods of reducing
> stray flux.
(snip) Make sure the windings (but especially the low voltage, high
current ones) fold back on themselves to their starting
point, instead of going around the hole one or more times.
Such circles produce a magnetic field out the ends of the
toroid.
-----------------------------------------------Reply-----------------------------------------------
On Sun, 13 May 2007 16:48:12 GMT, Eeyore
<rabbitsfriendsandrelati @hotmail.com> wrote: >Thanks for all your comments. They covered a wealth of areas so I realise I >should have followed my own usual advice and concentrated on one aspect at a >time. >Firstly, for the most part I'm mostly interested in toroidal construction. So
>please ignore any aspects relating to EI and other constructions.
>Secondly, I'm especially interested in designs with LOWER FLUX operation, since
>stray field is a particular concern to me especially with 'restoring' and
>improving to more current specs certain older specialist items of 'boutique'
>audio gear for example. What may have been an acceptable noise floor a couple of
>decades ago looks very second-rate by modern standards you see.
>There is also the advantage of elimination of 'switch-on surge' but that's a
>relativley minor consideration for equipment of < ~ 100VA. but I am also
>interested in this for other applications).
>So, I like the idea of operation at reduced flux. The stray field will reduce in
>proportion to the reduced magnetising force but I presume will also reduce since
>the magnetic material retains it's permeabilty best at lower fluxes.
>Additionally, the distortion in Imag will be lower with a lower magnetising
>force resulting in less of the very annoying harmonic content in the stray flux.
>So, there are some reasons for wanting to work with a lower flux level.
>I'd be additionally interested in suggestions for other methods of reducing
>stray flux.
>The symmetry ? of the windings appears that it may have some influence and I
>noticed that transformers from a certain manufacturer which had a thick 0.4mm
>polyproplylene barrier between pri and sec appeared to have higher leakage flux.
>I'm hoping that I may be able to reduce this stray flux by improving coupling
>with the use of triple insulated winding wire which doesn't require a solid
>barrier like that.
>Graham
All those things are good but they will all cost dearly in watts/pound (in both senses of "pound"). Toroids leak so little flux it's probably not worth adding a lot of
turns to reduce flux density. An evenly wound primary is probably
worth the effort. If you use a bridge+capacitor off the secondary, the
current surges in that wiring will usually radiate more nasty harmonic
flux than the transformer. Transformers sometimes get blamed for this.
John
-----------------------------------------------Reply-----------------------------------------------
John Larkin wrote: > Eeyore wrote: > >Thanks for all your comments. They covered a wealth of areas so I realise I
> >should have followed my own usual advice and concentrated on one aspect at a
> >time.
> >Firstly, for the most part I'm mostly interested in toroidal construction. So
> >please ignore any aspects relating to EI and other constructions.
> >Secondly, I'm especially interested in designs with LOWER FLUX operation, since
> >stray field is a particular concern to me especially with 'restoring' and
> >improving to more current specs certain older specialist items of 'boutique'
> >audio gear for example. What may have been an acceptable noise floor a couple of
> >decades ago looks very second-rate by modern standards you see.
> >There is also the advantage of elimination of 'switch-on surge' but that's a
> >relativley minor consideration for equipment of < ~ 100VA. but I am also
> >interested in this for other applications).
> >So, I like the idea of operation at reduced flux. The stray field will reduce in
> >proportion to the reduced magnetising force but I presume will also reduce since
> >the magnetic material retains it's permeabilty best at lower fluxes.
> >Additionally, the distortion in Imag will be lower with a lower magnetising
> >force resulting in less of the very annoying harmonic content in the stray flux.
> >So, there are some reasons for wanting to work with a lower flux level.
> >I'd be additionally interested in suggestions for other methods of reducing
> >stray flux.
> >The symmetry ? of the windings appears that it may have some influence and I
> >noticed that transformers from a certain manufacturer which had a thick 0.4mm
> >polyproplylene barrier between pri and sec appeared to have higher leakage flux.
> >I'm hoping that I may be able to reduce this stray flux by improving coupling
> >with the use of triple insulated winding wire which doesn't require a solid
> >barrier like that.
> All those things are good but they will all cost dearly in watts/pound
> (in both senses of "pound").
Of little concern in this context. > Toroids leak so little flux it's probably not worth adding a lot of
> turns to reduce flux density.
They leak enough to matter. I'd like to get my hands on some O-cores actually. Have you seen those ? R-cores are good too but try getting a custom one ! > An evenly wound primary is probably worth the effort.
That's the sort of thing I was getting at. How can one optimise the winding ? > If you use a bridge+capacitor off the secondary, the
> current surges in that wiring will usually radiate more nasty harmonic
> flux than the transformer. Transformers sometimes get blamed for this.
Indeed. In my recent 'experiments' I was adding external series resistance to stretch the conduction period. Graham
-----------------------------------------------Reply-----------------------------------------------
John Popelish wrote: > Eeyore wrote: > (snip) > > I'd be additionally interested in suggestions for other methods of reducing > > stray flux. > (snip) > Make sure the windings (but especially the low voltage, high
> current ones) fold back on themselves to their starting
> point, instead of going around the hole one or more times.
> Such circles produce a magnetic field out the ends of the
> toroid.
So, ideally you want each winding to be arranged equally through 360 degrees ? Or presumably, multiples therof. Graham
-----------------------------------------------Reply-----------------------------------------------
On Sun, 13 May 2007 17:57:14 GMT, Eeyore
<rabbitsfriendsandrelati @hotmail.com> wrote: >John Larkin wrote:
>> Eeyore wrote:
>> >Thanks for all your comments. They covered a wealth of areas so I realise I
>> >should have followed my own usual advice and concentrated on one aspect at a
>> >time.
>> >Firstly, for the most part I'm mostly interested in toroidal construction. So
>> >please ignore any aspects relating to EI and other constructions.
>> >Secondly, I'm especially interested in designs with LOWER FLUX operation, since
>> >stray field is a particular concern to me especially with 'restoring' and
>> >improving to more current specs certain older specialist items of 'boutique'
>> >audio gear for example. What may have been an acceptable noise floor a couple of
>> >decades ago looks very second-rate by modern standards you see.
>> >There is also the advantage of elimination of 'switch-on surge' but that's a
>> >relativley minor consideration for equipment of < ~ 100VA. but I am also
>> >interested in this for other applications).
>> >So, I like the idea of operation at reduced flux. The stray field will reduce in
>> >proportion to the reduced magnetising force but I presume will also reduce since
>> >the magnetic material retains it's permeabilty best at lower fluxes.
>> >Additionally, the distortion in Imag will be lower with a lower magnetising
>> >force resulting in less of the very annoying harmonic content in the stray flux.
>> >So, there are some reasons for wanting to work with a lower flux level.
>> >I'd be additionally interested in suggestions for other methods of reducing
>> >stray flux.
>> >The symmetry ? of the windings appears that it may have some influence and I
>> >noticed that transformers from a certain manufacturer which had a thick 0.4mm
>> >polyproplylene barrier between pri and sec appeared to have higher leakage flux.
>> >I'm hoping that I may be able to reduce this stray flux by improving coupling
>> >with the use of triple insulated winding wire which doesn't require a solid
>> >barrier like that.
>> All those things are good but they will all cost dearly in watts/pound
>> (in both senses of "pound").
>Of little concern in this context.
>> Toroids leak so little flux it's probably not worth adding a lot of
>> turns to reduce flux density.
>They leak enough to matter. I'd like to get my hands on some O-cores actually. Have
>you seen those ? R-cores are good too but try getting a custom one !
>> An evenly wound primary is probably worth the effort.
>That's the sort of thing I was getting at. How can one optimise the winding ?
>> If you use a bridge+capacitor off the secondary, the
>> current surges in that wiring will usually radiate more nasty harmonic
>> flux than the transformer. Transformers sometimes get blamed for this.
>Indeed. In my recent 'experiments' I was adding external series resistance to stretch
>the conduction period.
>Graham
As John P points out, the secondary can be a single-turn winding in the plane of the toroid, pushing its flux through the hole. In that case, that rather large loop, fed with nasty rectifier surges, could be a mean source of radiated harmonics. More math to deal with. I've pretty much gone over to switchers. I can buy a 150 watt
universal-input PFC corrected switcher for about what I'd pay for a
150-watt toroid.
John
-----------------------------------------------Reply-----------------------------------------------
Eeyore wrote: > Thanks for all your comments. They covered a wealth of areas so I realise I > should have followed my own usual advice and concentrated on one aspect at a > time. > Firstly, for the most part I'm mostly interested in toroidal construction. So
> please ignore any aspects relating to EI and other constructions.
> Secondly, I'm especially interested in designs with LOWER FLUX operation, since
> stray field is a particular concern to me especially with 'restoring' and
> improving to more current specs certain older specialist items of 'boutique'
> audio gear for example. What may have been an acceptable noise floor a couple of
> decades ago looks very second-rate by modern standards you see.
> There is also the advantage of elimination of 'switch-on surge' but that's a
> relativley minor consideration for equipment of < ~ 100VA. but I am also
> interested in this for other applications).
> So, I like the idea of operation at reduced flux. The stray field will reduce in
> proportion to the reduced magnetising force but I presume will also reduce since
> the magnetic material retains it's permeabilty best at lower fluxes.
> Additionally, the distortion in Imag will be lower with a lower magnetising
> force resulting in less of the very annoying harmonic content in the stray flux.
> So, there are some reasons for wanting to work with a lower flux level.
> I'd be additionally interested in suggestions for other methods of reducing
> stray flux.
> The symmetry ? of the windings appears that it may have some influence and I
> noticed that transformers from a certain manufacturer which had a thick 0.4mm
> polyproplylene barrier between pri and sec appeared to have higher leakage flux.
> I'm hoping that I may be able to reduce this stray flux by improving coupling
> with the use of triple insulated winding wire which doesn't require a solid
> barrier like that.
> Graham
Without regard to the shape of the core, remember how magnetic losses happen: movement of magnetic domains, if i remember correctly (been 30 years) is a lossy mechanism. Rotation of magnetization in the domains may be a secondary aspect. The first appears to be non-linear, and the second appears to be linear; it is the non-linear aspects that will cause distortion. Therefore, it appears that the larger the field within reason, the smaller percentage the non-linear aspects will be = less distortion (due to magnetic effects). Concerning symmetry, especially for toroids, simplified theory seems
to teach that one can have a winding "piled" high in a small arc of the
toroid and achieve the same results as if uniformly wound on the toroid.
As long as the permeability of the toroid material is at least 1000
times that of air, then it would seem the error in that simplified
theory would be less than 0.1%.
-----------------------------------------------Reply-----------------------------------------------
John Popelish wrote: > Eeyore wrote: > (snip) >> I'd be additionally interested in suggestions for other methods of
>> reducing
>> stray flux.
> (snip)
> Make sure the windings (but especially the low voltage, high current
> ones) fold back on themselves to their starting point, instead of going
> around the hole one or more times. Such circles produce a magnetic field
> out the ends of the toroid.
Good point, especially if the number of turns is fairly small (eg: N=100, wrapped uniformly full 360 degrees would give the equivelant of a one turn circle the diameter of the toroid for a 1% vertical field. Wrapping 50 turns for 180 degrees CW and the other 50 turns back the same 180 degrees CCW would give reasonable cancellation between the two halves. If one wants to be rather picky, wind the 180 degrees *bifilar* and connect the two windings appropiately. -----------------------------------------------Reply-----------------------------------------------
Eeyore wrote: > John Popelish wrote:
>> Eeyore wrote:
>> (snip)
>>> I'd be additionally interested in suggestions for other methods of reducing
>>> stray flux.
>> (snip)
>> Make sure the windings (but especially the low voltage, high
>> current ones) fold back on themselves to their starting
>> point, instead of going around the hole one or more times.
>> Such circles produce a magnetic field out the ends of the
>> toroid.
> So, ideally you want each winding to be arranged equally through 360 degrees ? Or
> presumably, multiples therof.
I was not addressing the fraction of the toroid covered by each winding. I was addressing the external field caused by windings that enclose the center hole. This can be prevented either by back winding a second layer over the first, till you get back to the starting point, or by just returning back over the winding with the end wire, around the outside circumference, so that no winding encircles the center hole, circumferentially. This prevents production of any field out the ends of the hole. -----------------------------------------------Reply-----------------------------------------------
Robert Baer wrote:
> Good point, especially if the number of turns is fairly small (eg:
> N=100, wrapped uniformly full 360 degrees would give the equivelant of a
> one turn circle the diameter of the toroid for a 1% vertical field.
> Wrapping 50 turns for 180 degrees CW and the other 50 turns back the
> same 180 degrees CCW would give reasonable cancellation between the two
> halves.
> If one wants to be rather picky, wind the 180 degrees *bifilar* and
> connect the two windings appropiately.
Better to space those turns so that the first half of the winding covers 360 degrees and the second half of the winding retraces back around the core to the start. But it works almost as well to wind a 360 degree layer and wrap the wire around the outside circumference back to the start to either end, or start another layer. -----------------------------------------------Reply-----------------------------------------------
John Popelish wrote: > Eeyore wrote: > > John Popelish wrote: > >> Eeyore wrote: > >> (snip) > >>> I'd be additionally interested in suggestions for other methods of reducing > >>> stray flux. > >> (snip) > >> Make sure the windings (but especially the low voltage, high
> >> current ones) fold back on themselves to their starting
> >> point, instead of going around the hole one or more times.
> >> Such circles produce a magnetic field out the ends of the
> >> toroid.
> > So, ideally you want each winding to be arranged equally through 360 degrees ? > Or
> presumably, multiples therof.
> I was not addressing the fraction of the toroid covered by
> each winding. I was addressing the external field caused by
> windings that enclose the center hole.
I'm not following your terminology here. What do you mean by " windings that enclose the center hole " ? > This can be
> prevented either by back winding a second layer over the
> first, till you get back to the starting point, or by just
> returning back over the winding with the end wire, around
> the outside circumference, so that no winding encircles the
> center hole, circumferentially. This prevents production of
> any field out the ends of the hole.
Nope. I didn't get that at all. It sounds like it might be important though. Graham
-----------------------------------------------Reply-----------------------------------------------
Eeyore wrote: > John Popelish wrote:
>> Eeyore wrote:
>>> John Popelish wrote:
>>>> Eeyore wrote:
>>>> (snip)
>>>>> I'd be additionally interested in suggestions for other methods of reducing
>>>>> stray flux.
>>>> (snip)
>>>> Make sure the windings (but especially the low voltage, high
>>>> current ones) fold back on themselves to their starting
>>>> point, instead of going around the hole one or more times.
>>>> Such circles produce a magnetic field out the ends of the
>>>> toroid.
>>> So, ideally you want each winding to be arranged equally through 360 degrees ? > Or
>> presumably, multiples therof.
>> I was not addressing the fraction of the toroid covered by
>> each winding. I was addressing the external field caused by
>> windings that enclose the center hole.
> I'm not following your terminology here. What do you mean by " windings that enclose
> the center hole " ?
>> This can be
>> prevented either by back winding a second layer over the
>> first, till you get back to the starting point, or by just
>> returning back over the winding with the end wire, around
>> the outside circumference, so that no winding encircles the
>> center hole, circumferentially. This prevents production of
>> any field out the ends of the hole.
> Nope. I didn't get that at all. It sounds like it might be important though.
Okay, forget the windings that encircle the cross section of the core. Those produce flux around the core, and that is what you want. But if the current path from start of winding to end of winding makes a circle all the way around the circumference of the hole, (winding covers entire toroid, and end exits near the start) then magnetic flux will also be produces through the hole (because 1 turn encircles the hole as a solenoidal winding) and that flux will spray out each flat side of the toroid. Two otherwise identical toroidal transformers can have a
measurable difference in external flux if the winder took
the trouble to retrace each full layer, back around the
circumference to the starting point (or to wrap a second
layer back to the start), to avoid encircling the hole.
-----------------------------------------------Reply-----------------------------------------------
John Larkin a crit :
> On Sun, 13 May 2007 17:57:14 GMT, Eeyore > <rabbitsfriendsandrelati @hotmail.com> wrote: >> John Larkin wrote:
>>> Eeyore wrote:
>>>> Thanks for all your comments. They covered a wealth of areas so I realise I
>>>> should have followed my own usual advice and concentrated on one aspect at a
>>>> time.
>>>> Firstly, for the most part I'm mostly interested in toroidal construction. So
>>>> please ignore any aspects relating to EI and other constructions.
>>>> Secondly, I'm especially interested in designs with LOWER FLUX operation, since
>>>> stray field is a particular concern to me especially with 'restoring' and
>>>> improving to more current specs certain older specialist items of 'boutique'
>>>> audio gear for example. What may have been an acceptable noise floor a couple of
>>>> decades ago looks very second-rate by modern standards you see.
>>>> There is also the advantage of elimination of 'switch-on surge' but that's a
>>>> relativley minor consideration for equipment of < ~ 100VA. but I am also
>>>> interested in this for other applications).
>>>> So, I like the idea of operation at reduced flux. The stray field will reduce in
>>>> proportion to the reduced magnetising force but I presume will also reduce since
>>>> the magnetic material retains it's permeabilty best at lower fluxes.
>>>> Additionally, the distortion in Imag will be lower with a lower magnetising
>>>> force resulting in less of the very annoying harmonic content in the stray flux.
>>>> So, there are some reasons for wanting to work with a lower flux level.
>>>> I'd be additionally interested in suggestions for other methods of reducing
>>>> stray flux.
>>>> The symmetry ? of the windings appears that it may have some influence and I
>>>> noticed that transformers from a certain manufacturer which had a thick 0.4mm
>>>> polyproplylene barrier between pri and sec appeared to have higher leakage flux.
>>>> I'm hoping that I may be able to reduce this stray flux by improving coupling
>>>> with the use of triple insulated winding wire which doesn't require a solid
>>>> barrier like that.
>>> All those things are good but they will all cost dearly in watts/pound
>>> (in both senses of "pound").
>> Of little concern in this context.
>>> Toroids leak so little flux it's probably not worth adding a lot of
>>> turns to reduce flux density.
>> They leak enough to matter. I'd like to get my hands on some O-cores actually. Have
>> you seen those ? R-cores are good too but try getting a custom one !
>>> An evenly wound primary is probably worth the effort.
>> That's the sort of thing I was getting at. How can one optimise the winding ?
>>> If you use a bridge+capacitor off the secondary, the
>>> current surges in that wiring will usually radiate more nasty harmonic
>>> flux than the transformer. Transformers sometimes get blamed for this.
>> Indeed. In my recent 'experiments' I was adding external series resistance to stretch
>> the conduction period.
>> Graham
> As John P points out, the secondary can be a single-turn winding in
> the plane of the toroid, pushing its flux through the hole. In that
> case, that rather large loop, fed with nasty rectifier surges, could
> be a mean source of radiated harmonics. More math to deal with.
If correctly wound (ie 360 for each winding) the surge induced mag fields cancel out. The single turn JP spoke about just sees the magnetizing current. --
Thanks,
Fred.
-----------------------------------------------Reply-----------------------------------------------
Fred Bartoli wrote:
> If correctly wound (ie 360 for each winding) the surge induced mag
> fields cancel out.
How can this be ? The surge is the result of temporary core saturation caused by the combination of remanent magnetism at turn-on and the undefined start point of the magnetisation cycle. Graham
-----------------------------------------------Reply-----------------------------------------------
Eeyore a crit : > Fred Bartoli wrote:
>> If correctly wound (ie 360 for each winding) the surge induced mag
>> fields cancel out.
> How can this be ? The surge is the result of temporary core saturation caused by the
> combination of remanent magnetism at turn-on and the undefined start point of the
> magnetisation cycle.
Quoting JL : >In that case, that rather large loop, fed with nasty rectifier surges,
>could be a mean source of radiated harmonics.
I wasn't speaking of the turn on surge, which is almost a no problem,
but rather of the peak rectified current involved by the capacitor
charging. In that case the secondary ampere-turn product compensate for
the primary ampere-turn product, except for the magnetizing current.
--
Thanks,
Fred.
-----------------------------------------------Reply-----------------------------------------------
Fred Bartoli wrote: > Eeyore a crit : > > Fred Bartoli wrote: > >> If correctly wound (ie 360 for each winding) the surge induced mag
> >> fields cancel out.
> > How can this be ? The surge is the result of temporary core saturation caused by > the
> combination of remanent magnetism at turn-on and the undefined start point of > the
> magnetisation cycle.
> Quoting JL :
> >In that case, that rather large loop, fed with nasty rectifier surges,
> >could be a mean source of radiated harmonics.
> I wasn't speaking of the turn on surge, which is almost a no problem,
> but rather of the peak rectified current involved by the capacitor
> charging. In that case the secondary ampere-turn product compensate for
> the primary ampere-turn product, except for the magnetizing current.
Oh I see. Yes, a large loop will indeed radiate more of course. That's an interesting aspect I
hadn't previously considered as such within the context of transformer design. I see what
you're driving at now.
I had perhaps imagined that the permeability of the core would preferentially retain most
of that flux within the core adequately.
Graham
-----------------------------------------------Reply-----------------------------------------------
Fred Bartoli wrote:
> I wasn't speaking of the turn on surge, which is almost a no problem,
> but rather of the peak rectified current involved by the capacitor
> charging. In that case the secondary ampere-turn product compensate for
> the primary ampere-turn product, except for the magnetizing current.
Possibly, but John didn't mean the winding proper, but the additional one-turn winding formed by the fact that each winding forms a single 360 degree loop around the perimeter of the core. Proper winding methods which are probably not employed for normal off-the-rack mains toroids can eliminate the stray effects of those though. --Daniel
-----------------------------------------------Reply-----------------------------------------------
Haude Daniel a crit : > Fred Bartoli wrote: >> I wasn't speaking of the turn on surge, which is almost a no problem,
>> but rather of the peak rectified current involved by the capacitor
>> charging. In that case the secondary ampere-turn product compensate for
>> the primary ampere-turn product, except for the magnetizing current.
> Possibly, but John didn't mean the winding proper, but the additional
> one-turn winding formed by the fact that each winding forms a single
> 360 degree loop around the perimeter of the core.
I was too. Just picture the primary and secondary equivalent additional single turn, incoming currents... Oops, currents are in 1:n ratio, so you need nx360/360 windings to
balance this. Surely never done, and probably impracticle.
> Proper winding
> methods which are probably not employed for normal off-the-rack
> mains toroids can eliminate the stray effects of those though.
-- Thanks, Fred. -----------------------------------------------Reply-----------------------------------------------
On Mon, 14 May 2007 14:59:55 +0200, Fred Bartoli
<fred._canxxxel_this_bartoli@RemoveThatAlso_free.fr_AndThisToo> wrote: >Haude Daniel a crit : >> Fred Bartoli wrote: >>> I wasn't speaking of the turn on surge, which is almost a no problem,
>>> but rather of the peak rectified current involved by the capacitor
>>> charging. In that case the secondary ampere-turn product compensate for
>>> the primary ampere-turn product, except for the magnetizing current.
>> Possibly, but John didn't mean the winding proper, but the additional
>> one-turn winding formed by the fact that each winding forms a single
>> 360 degree loop around the perimeter of the core.
>I was too. Just picture the primary and secondary equivalent additional
>single turn, incoming currents...
>Oops, currents are in 1:n ratio, so you need nx360/360 windings to
>balance this. Surely never done, and probably impracticle.
I almost did a post declaring that the primary NI canceled the secondary NI until I realized that most likely N=1 in both windings but "I" is sure different. John
-----------------------------------------------Reply-----------------------------------------------
John Larkin wrote:
> I almost did a post declaring that the primary NI canceled the
> secondary NI until I realized that most likely N=1 in both windings
> but "I" is sure different.
And if the winder is not aware of the effect, the two I*T factors may add instead of subtract. The direction the current takes around the toroid with each winding is completely optional. -----------------------------------------------Reply-----------------------------------------------
John Popelish wrote: > John Larkin wrote: >> I almost did a post declaring that the primary NI canceled the
>> secondary NI until I realized that most likely N=1 in both windings
>> but "I" is sure different.
> And if the winder is not aware of the effect, the two I*T factors may
> add instead of subtract. The direction the current takes around the
> toroid with each winding is completely optional.
Just to be clear, T in the above product is the solenoidal turns, not the toroidal turns. Perhaps I should have used an L for layers. -----------------------------------------------Reply-----------------------------------------------
Haude Daniel wrote: > Fred Bartoli wrote: > > I wasn't speaking of the turn on surge, which is almost a no problem,
> > but rather of the peak rectified current involved by the capacitor
> > charging. In that case the secondary ampere-turn product compensate for
> > the primary ampere-turn product, except for the magnetizing current.
> Possibly, but John didn't mean the winding proper, but the additional
> one-turn winding formed by the fact that each winding forms a single
> 360 degree loop around the perimeter of the core. Proper winding
> methods which are probably not employed for normal off-the-rack
> mains toroids can eliminate the stray effects of those though.
This sounds very interesting. I am indeed confident that the typical off-the-shelf toroid does not pay
attention to these matters.
Graham
-----------------------------------------------Reply-----------------------------------------------
Eeyore wrote: > Haude Daniel wrote:
>> Possibly, but John didn't mean the winding proper, but the additional
>> one-turn winding formed by the fact that each winding forms a single
>> 360 degree loop around the perimeter of the core. Proper winding
>> methods which are probably not employed for normal off-the-rack
>> mains toroids can eliminate the stray effects of those though.
> This sounds very interesting.
> I am indeed confident that the typical off-the-shelf toroid does not pay
> attention to these matters.
You are probably right, yet many amplifier designers take proper care to pair all AC circuit pairs, outside of the transformer, to cancel their magnetic fields. Even cheap tube amplifier filament circuits were usually wired with tightly twisted pairs. -----------------------------------------------Reply-----------------------------------------------
On Mon, 14 May 2007 11:07:32 -0400, John Popelish <jpopel @rica.net> wrote: >John Larkin wrote: >> I almost did a post declaring that the primary NI canceled the
>> secondary NI until I realized that most likely N=1 in both windings
>> but "I" is sure different.
>And if the winder is not aware of the effect, the two I*T
>factors may add instead of subtract. The direction the
>current takes around the toroid with each winding is
>completely optional.
Yikes! John
-----------------------------------------------Reply-----------------------------------------------
John Larkin a crit : > On Mon, 14 May 2007 11:07:32 -0400, John Popelish <jpopel @rica.net> > wrote: >> John Larkin wrote:
>>> I almost did a post declaring that the primary NI canceled the
>>> secondary NI until I realized that most likely N=1 in both windings
>>> but "I" is sure different.
>> And if the winder is not aware of the effect, the two I*T
>> factors may add instead of subtract. The direction the
>> current takes around the toroid with each winding is
>> completely optional.
> Yikes!
Well, for a N:1 ratio, that'll be a (N+1)/(N-1) mag field change. Given that N is often well above unity, it's not as disastrous as it might first seem. --
Thanks,
Fred.
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