Re: Toroids for power transformers



There isn't any use talking to Ian Iveson about transformers.

He is an ignorant fool and no need to reply any further to his hopeless
reply post to mine below.

He has NO experience at ever winding any transformers, and is Usernet's
greatest pretender, poseur, and BS artist.

Patrick Turner.

Ian Iveson wrote:

Patrick Turner wrote

Just forget the operation at the rated power and
consider
the situation
with NO LOAD.

***Bad idea*** , if you are at all inclined to leap to
false
conclusions.

Have a look at the wave form of the **current** running
through the
transformer's inductance, ie, the magnetizing current.

If the transformer has much inductance and low
hysterisis
behaviour,
you'll
maybe see a current wave not unlike the mains voltage
wave, although
there won't be so much HF content because the L
obstructs
the HF.
No spikes, right?

Such a tranny might have GOSS cores, and B about
0.85Tesla.

Heat loss per Kg will be very low.

So in this case the designer would have used ample
turns
per volt.

But as the turns per volt are reduced, the inductance
falls, Bmax rises
and more Im flows
and at some voltage level the current wave of
magnetizing
current
will have distortion in excess of 3% which is visible
as
kinks in the
up/downs of the wave. Spikes. Many poorer trannies with
low TPV and high
Bmax will show much more than
3%, maybe 15% or more harmonic distortion which shows
the
iron is
becoming unable to create an opposing field
to the applied emf, or voltage propelled I flow.
The type of iron may still not get very hot, but many
are
beginning to
get noisy.
As TPV are further reduced, the cos of phase x Im
indicates heat lost is
becoming high enough
cause the iron to heat up considerably, and it happens
withouty a load
connected.
The full load causes additional losses i the copper
further heating the
whole thing.

**No.**

A loaded transformer passes much greater primary current
than an unloaded one that is not saturating. This greater
current causes a voltage drop across the primary
inductance,
resulting in lower magnetising current. The difference
between unloaded, and loaded as rated, will normally
ensure
that the core will not saturate, even if it does when the
secondary is unloaded.

Obviously, the current will become worse with load if the
tranny is
saturating.

Obvious only if it continues to saturate just as badly,
which it won't.

I have elaborated elsewhere. I'll post pictures if anyone
honestly wishes to learn. No point in your case

But first you should examine the unloaded current wave to
see
the quality of the design.

***Bad idea***, if you are inclined to leap to unfounded
conclusions, you could get confused.

Low Afe combined with low turns per volt give
high Bmax,
and the saturation shows up like dogs balls without having
any load.

Perhaps you have not designed, wound and tested many
transformers like I
have.

You carefully avoid selling to anyone who might report back
here on the quality of your work.

Guess who I wouldn't buy a transformer from.

I thought not.

Perhaps you have not wound as many as the manufacturers you
blindly criticise.

There is an important lesson here: be very careful if you
"over-specify", by buying a transformer bigger than you
need. Neither should you reckon on squeezing more than
the
rated voltage from a toroid by under-loading it and
taking
advantage of its regulation. If you underload, it may be
driven into the saturation region.

Just buying/ordering a higher VA tranny won't fix the
problem of the
Bmax being too close to
saturation. The Bmax must remain low for quiet cool
running.

If one buys a toroid with all the usual horrid problems
most of them
have
then one may add 50 turns by hand around the outside, then
re-insulate,
and this will increase the turns per volt, decrease the
Bmax, but also
decrease
all the secondary output voltages. Its usually too
difficult to
find a toroid which allows such sec reductions after
adding primary
turns.
So I wind all my own trannies because the commercials are
such poor
crap....

Toroids by their nature don't lose heat so easy,
especially
from the core. That may be why they all use GOSS, BTW.

It is one reason why toroids are GOSS, but one could use
NOSS,
and use a 400VA rated core size for where 200VA is needed,
with no
change to turn numbers.



A poor transformer gets quite warm just sitting there
connected to mains
with no load.

***Bad idea*** It may get much less warm if properly
loaded.

But a well designed tranny won't get hot any time, period.

Rubbish.

Equipment which by its nature demands widely varying
current
from the transformer should be careful to specify the
transformer to suit the application. "Standby" circuits
should run on an auxiliary transformer, and disconnect
the
main transformer from the mains.

I often instal auxilliary mains trannies of a few VA to
run fault
protection circuits and bias monitoring in tube amps.

But all my trannies don't get hot unloaded...

So you say.

Neither do those of most reputable makers.

You're just guessing.

And the artful and despicable bean counter likes to
have
about a 20C
rise in T because it means he's
saved enough copper and iron to buy that BMW he firqing
well wanted.

Manufacturers meet the requirements of application
designers. Accounting is a necessary part of that.

Its amazing how you defend the undefendable bean counters
always trying
to maximise profits at the expense of quality.

Accounting has a function to count, but not to control
production
methods.

How would you know.

Our
requirements may be different from the norm, and to that
extent we should not expect commodity transformers to
meet
our needs. This is just as true of an EI as it is of a
toroid or anything else.

Who is "Our?"

Valve audio enthusiasts.

All transformers should be good quality period.

Turner for president!

Most GOSS don't have the poor performance as NOSS, but
you
can easily
build a toroid or E&I tranny
with GOSS that WILL get scorching hot and you can't
keep a
hand on it
because its well over 40C.

Most designers don't use too little GOSS in a toroid,
because the design
becomes far too noisy
before it gets too hot.

MANY toroidals I have seen and a number I have bought
are
way too noisy
to use in hi-fi gear
even though they don't over heat. So although they say
GOSS can be run
at 1.3T which is approaching saturation
the noise is the problem, and the only way I have
addressed this is to
unwind the toroid by hand with a shuttle, and add 30%
more primary turns and then rewind the secondary over
the
top.
The last two 300VA and 500VA took a couple of days each
to
fix this way.

But they now run with only a few mA for Im, and with a
rectifier they
are tolerably quiet.
Still not as quiet as a well wound E&I.

The GOSS E&I I get now has maximum µ = 17,000 when
fully
interleaved,
and losses are comparable to a spiral core of GOSS used
in
a toroid.
With equal Afe for either toroid or E&I, ( or decent
C-cores ),
the weight of the toroid is only marginally lower than
the
E&I.

In Oz, the problem of hopelessly inadequate toroid and
E&I
trannies
entering Oz
in consumer items became so bad that all imports were
forced by govt
regulations to have a thermal fuse
mounted between the primary and secondary, so when the
item
got hot, it would go open even though there was not
enough
current to
blow a mains fuse.

Sometimes one would be lucky, and able to put a link
across the leads of
the fuse after it blew,
and place a new fuse of lower T rating on the outside
of
the sec.
But many makers concealed the thermal fuse to prevent
the
tampering, and
you need to buy a new
tranny to repair the item.

Makers were constantly whittling down the copper and
iron.

Planned obsolescence.

*Recognition of the inevitability of future progress.*

They want you back after it fails, and if you hate the
Yamaha when it
fails, you'll buy a Sony,
but their transformers are no better. The consumer has
NO
ESCAPE.

My Sony CD player transformers are beautiful, and clearly
better for the purpose than anything I can buy off the
shelf
from RS or Digikey. Closest would be something of Sowter
quality, with all the bells and whistles like copper band
and internal shields. Same with my cheap little Denon
CD/radio.

Yes, but its unlikely sources blow their transfromers.

Its mostly power amps or receivers which smoke their
trannies.

Often because a channel has been labouring into a low load
for too long,
or the ampo
is in a closed cupboard, and it just gets hot in there...

Anyway, a constant stream of mainly SS amps pass my bench
for repairs
and some include those needing a new tranny.


Toroids usually fail because the windings get too hot,
not
the core,

Is this different for EI? Considering how easy it is to
cool
the core of an EI, I wouldn't have thought so.

Cool cores are larger than bean counters want them to be.

In E&I trannies, core losses are often arranged to be
slightly
higher than copper losses, and because the wire is a bit
cooler,
it matters not if the core gets hotter, as the core
surrounds the wire.
However, the core blankets the wire passing through the
windows,
so the T difference is negligible. Many designs have equal
core and
copper losses
at rated working load of say 5% of the VA for each.

Toroids using GOSS nearly always have lower core losses.
The copper losses determines the temperature, and the core
follows the
copper,
because the copper fully blankets the core.



and
because there
are crossed over turns all around the windings with no
insulation
between them,
the presssure of the mounting bolts and rubber squeeze
the
hot wires
together an pinch through the
insulation in pressure spots. The shorted turn as a
result
does the
rest.

Again, a matter of specification. You could just as well
say
that an EI could fail because the bobbin has corners
which
concentrate the pressure on windings.

The winding of many toroids I have seen is attrocious,
with
very many crossed turns all piling up without insulation.

Some E&I are also "random wound", ie, not neatly layer
wound, which is
far
more reliable than random or toroidal. The corner turns
don't matter if
insulation is used
between all layers.
Pressure spots don't occur in E&I the way they occur in
toroids unless
the toroid
is potted well after varnishing properly and thus is not
subject to
dynamic stress due to a bolt
and a way too thin rubber washer.

Indeed they may fail
that way, but not very often as long as they do not stray
from their safe operating area. Manufacturers are of
course
aware of the potential weak spots, and generally take
measures accordingly. Disreputable manufacturers don't
last
very long in the market. It is up to all of us to make
wise
purchasing decisions.

Hmm, the Chinese seem to remain in the market place as do
many
other dodgy brands of gear I'd like to see hunted off.

The Chinese is not a single manufacturer. Xenophobia has got
the better of your judgement. It does happen to be the case
at the moment that many short-lived manufacturers are based
there, who have no reputation as yet. If they make rubbish
they don't last long. There is nothing about being Chinese
that allows them to defy competition in the world market.

One has to say a few prayers for the trannies if the
country
they came from is Dodgymaya.

But in 1955, if you bought a Leak, and had a tube
saturate, it often
wrecked
an OPT, then a PT as well...

Still possible with most new stuff I would guess. But it's
only a guess.

Similar happened to many old brandname amps.

Bean counter designed crap has always been with us.

Luckily, or we'd have no transformers. You, because of your
"bean counting", won't supply us.

Ian
.

Relevant Pages

  • Re: Toroids for power transformers
    ... with NO LOAD. ... If the transformer has much inductance and low hysterisis ... If one buys a toroid with all the usual horrid problems most of them ... from the core. ...
    (rec.audio.tubes)
  • Re: Toroids for power transformers
    ... with NO LOAD. ... A loaded transformer passes much greater primary current ... If one buys a toroid with all the usual horrid problems ... from the core. ...
    (rec.audio.tubes)
  • Re: Toroids for power transformers
    ... If the transformer has much inductance and low hysterisis ... from the core. ... That may be why they all use GOSS, ... toroid or anything else. ...
    (rec.audio.tubes)
  • Re: Transformer flux imbalande solutions
    ... Or a gapped ETD49 or 59 core may be the thing aswell? ... magnetizing current as transformer current. ... When you approach the limits it is a softer entry into hard saturation. ... long as you're careful with the design I don't think flux walk will be a ...
    (sci.electronics.design)
  • Re: Saturation in transformers.
    ... > in or approaching saturation. ... If your toroid weighs 4 lbs. and you had ... so these losses are not prohibitive. ... > core materials in the 26Ga. ...
    (rec.audio.tubes)