Hi Ian,

When one writes on an ascii only medium, one must do something to
show emphasis. The only way I know to do that is write a word
or two in capital letters.

In the culture of email and news that I adopted, when I started
messing with DARPA back in the '70s, that is the way it was done.

For example:

I HATE YOU AND YOUR MOTHER'S NOSE! - that would be shouting.

I think it would best if we REALLY REALLY try and concentrate....

^^^^^^^^^^^^^
Emphasis.

I am not shouting at you, I don't think I have ever done. However,
lacking a method of underlining or italicizing a word, I capitalize.
Please don't take that as shouting. You will find that a large
number of people do the same as I. They aren't shouting either.

Shouting is when you write whole angry sounding sentences in
capital letters.



Ian Iveson wrote:
Now my ISP has switched me back on...

"Chuck Harris" wrote:


[see below]


I take capitals as shouting. That is usual, I believe. You shout
sometimes.

It has been said that saturation depends on voltage. It has been
said that in order to avoid saturation the core should be made
bigger. You began yourself by explaining that the problem would be
related to skimpy margins of iron and copper, neither of which is
relevant and seems a bit like axe-grinding to me. For the same
quality transformer at twice the voltage Casino requires the same
quantity of both.

The impression of emphasis, and I did say emphasis, is because much
has been said about size of core, and virtually nothing has been
said about number of turns.

It really doesn't matter to which you attribute the saturation. The
OP only had the transformer he had. He wasn't planning on changing
it so that it would work. That being the case, one can explain the
reason for its failure to work properly at 2x its rated primary voltage
as:

1) the core is too small for the flux...
2) there aren't enough turns...
3) the frequency is too low...

[note, ... means I left out the boring part of the sentence]

Pick one. Whichever makes you happy. They are all true, and they all
explain the deficiencies of the OP's transformer when run at twice
its design voltage.

There is no implication in any of the above statements that the only
way to make a transformer that would handle a higher primary voltage
is to make one with a larger core... not at all! If you kept the
turns the same, that would be one solution. But not necessarily the
best solution.

For instance, I can make a quite dandy 110v to 240v transformer with
one turn of wire on the primary, and two turns on the secondary. I
can make this transformer, and it will run cool as a cucumber, all
day long at 25Hz! How would I do this???

Simple, I would need a core the size of a volkswagon for a silly
couple hundred VA transformer. (No, I didn't calculate this...
I am purposefully exagerating.)

Yes, what you said about economy of materials is true, and yes you
can argue as has John that you merely meant that the symptom of
saturation appears in the core, rather than the cause.
Nevertheless, by not mentioning number of turns, which is the crux
of the matter, the impression was created. I was not the only one
who had difficulty following a thread that drifted towards the
moans of small producers in the face of the bean-counting
Juggernauts, blah.

I am one of those bean counting Juggernauts! When I design a
transformer, or anything else, I have to make it as cheaply as will
meet the design requirements. That is what it means to be an
engineer. I have certain preferences when it comes to transformers
that I use for myself. I don't want to ever have to redo one,
so I would prefer it run at a low flux so that it will run cool
and have a minimum amount of vibration. Why? Because the insulation
will last longer that way. Because I don't like burning myself on
transformers that are operating "normally".


The maths bits are fair enough but rather generalised with respect
to the original question of what would be the problem with that
particular transformer at that voltage. That left a gap, between
the reminiscences, the business interests, and the maths, where I
felt a simple answer might have been.

The answer was quite simple and was stated over and over again:

This transformer will saturate if run at 2x its rated voltage...
Don't do it!

The message was needlessly complicated when both you and William
came in and said ignore the above message, and go ahead. It'll
work just fine with reduced load current.

The message was further complicated by guys that tried to judge
the "book" by its cover, rather than its contents, and said the
"saturation" message is wrong, go ahead run the transformer backwards,
I do it all the time. Of course they meant they put 6V into a 6V
filament winding, or 110V into a 110V secondary of a 220-110V step
down transformer.

As far as "boning up" is concerned, I had failed previously to grasp
the point that currents due to load cancel, more or less, with
respect to saturation. Something I had not noticed in the fog of
knowledge
I already have. There is a reason for this that I have just been
wondering about. It explains why my spice transformer model still
has a linear core. I must have known everything else that is in the
model otherwise it wouldn't work, I suppose. Specified transformers
seem to work OK, so I guess I must have known something then...can't
really remember. Must have though because some of my transformers
are quite complicated and have quite a lot of wires coming out of
them.

Spice models for transformers are very simple if they don't take into
account core characteristics, leakage inductances, and capacitances.

Most of the time, an ideal transformer will adequately model the real
thing. It is cases like where you increase the primary voltage, or
drop the frequency so as to cause the core to head for the nonlinear
region that are not handled well by an ideal transformer model.

And for audio-intended transformers you don't really need to know.
Saturation will be outside the full-power bandwidth. Er...I think
that follows anyway...yes it must.

When you take the typical audio output transformer, and head for the
lower end, 20Hz, or so, the transformer is quite likely to be starting
to saturate... That is, with the typical garden variety transformer.
Some of the transformers that top off in the 12 lbs range will do much
better.

I am fundamentally uneasy about saturation. Coming from a
background with no practical electronic content, I still am
conscious of mapping mechanical dynamics onto electrical things.
But I have never needed to consider the saturation velocity of mass.
Or even its equivalent of the BH curve. Never been into rockets and
stuff, or really big things, or really small things moving very
quickly. Ballistics is about my limit.

Saturation is all about sudden nonlinearities. Some places you see
it in mechanical models are springs when they run out of range, (eg. a
compression spring that has its coils touching, a tension spring that
has its coils pulled all the way out... Or elastic deformation, a
spring that has been bent so much that it won't return.) There are
plenty of other examples, a shaft on a pot can be thought of as being
in mechanical saturation when it is turned against its stop.


What I say is related to my purpose here, which is not to
demonstrate what I know. I have never to my
knowledge been responsible for electrocution, and am careful to
frequently point out that I know virtually nothing about anything.

Your original comment to William:


Please don't give advice about things you don't understand.


Is pathetic and silly. This is a discussion group. I give opinions
on lots of things, and got sick of putting "IMO" in every sentence.
If there were only Chucks here, and no Williams, there would be no
point in coming. But William employs a similar strategy to me, it
seems, and it was his perseverance, despite your bullying, that
sorted the wheat from your chaff.

It puts my hackles up when someone like William tells the group to
ignore a person who provided a correct answer, and go with his
uneducated, and incorrect solution. That is where the bullying
occurred, not with me.

If William came in and stated that he didn't think this was right,
and gave his reasons, I would have entered this thread in a more
friendly manner. But he didn't. He flat out said the answer was
wrong! ... and he couldn't have been more wrong himself.



The rest of your first contribution was pure hyperbole, intended no
doubt to rub in your bullying with a bit of guilt-tripping.


If you try applying 120V, 60Hz to this 60V, 60Hz winding, you
will drive the transformer well into saturation. This will

cause

the primary current to approach that of the DC wire resistance.


In a word, You will let all the smoke out of your
transformer.

All of which is completely and verifiably true. Why do you call it
hyperbole? Just because you don't want it to be true isn't a good
reason.

As to your assertion that I believe current is measured in resistance,
do you really think I am that stupid? I left a couple of words
out in my haste to get the message done. Tell me you have never
done that.

"This will cause the primary current to approach that caused by the
DC resistance alone."

Does that sound better to you?

Only if he gets an arc. No poof. Much slower than that. Care to
bet? A current can't approach a resistance, BTW. Pedantry, yes,
but OTOH that sentence doesn't make sense anyway. Approach usually
implies that it gets close. We don't actually know how close it
would get, because we don't know for what proportion of the time the
core would saturate.

That is why I said "approach", rather than "will be". I have taken
the "I" laminations off of transformers and used them as demagnetizers,
so I do have a fair idea how long it would take to ruin the primary.
Even with a 50W light bulb in series, they get hot very fast.
It is not in my nature to needlessly destroy things. I would never
make a very good UL inspector.

The part that you are not aware of is that if you do this experiment
at 240V, the winding temperature will skyrocket immediately, and the
insulation will be damaged very quickly. No, a short won't
necessesarily happen right away, but the insulation will become
so brittle that it won't withstand any bending or vibration without
flaking off.

At saturation, a typical 1 ohm dc resistance 120V primary will be
sucking V*V/R watts at Vpeak. So, if you are sticking 240V into
the 120V primary, that will result in 240V*240V*2 = 115200Wpeak!

Do you think that might heat things up a bit?

Do you think it matters if it is only saturating 1/4 the time
at the peaks? (that drops the power to somewhere around a mere
28000W. I would have to integrate the waveforms to give you a
more exact answer.)

About the only thing that will keep these numbers from being
realized is the fact that the primary has some inductive reactance
even without a core, and the power cord you connect up with has
some resistance.

There will be a lot of margin to play with, in
terms of power rating of the windings, so I would expect minutes,
not seconds, before destruction. You'd notice, wouldn't you? The
buzzing, the noise, etc. You wouldn't just walk away and let it
burn.

Walk away from it? No, not me, I already know what will happen.
But some newbie might if folks such as you, and William,
convinced him that it would be ok as long as he just reduced
the load current.

-Chuck