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transformer core

K

Kevin Weddle

Jan 1, 1970
0
What I can I use for a transformer core? I think I need a piece of
steel with a large area. The example core that I have seen has a large
area as opposed to just length. Do I have to find a steel shop to get
a core?
 
R

ron doctors

Jan 1, 1970
0
What I can I use for a transformer core? I think I need a piece of
steel with a large area. The example core that I have seen has a large
area as opposed to just length. Do I have to find a steel shop to get
a core?

This is a very open question.
Lets have some answers and we can help!

1. Function? What are you going to do with the transformer. The ans.
to this will lead to more ? but without knowing the end use it is far
too open a ?
Did you know that tfr. cores can be made of .. silicon steel, cobalt
steel, nickel steel, ferrite , even air! ..?

2. Why? You can buy transformers for almost every function for less
than it will cost for the parts! ( BTW see my trasnformers listed in
http://www.members.cox.net/rdoctors/clearall.html

3. What technical skills do you have?

4. Do you understand basic transformer design?


Hoping to help ...
ron
 
K

Kevin Weddle

Jan 1, 1970
0
This is going to be a power autotransformer. I need the voltage to be
right,so I need to wind my own. I have been told to use iron instead
of steel, but I don't want to glue a core together and I don't want to
strip a transformer. I can't measure the inductance but I can
calculate it. The question is how good will the transformer be.
 
B

Bill Vajk

Jan 1, 1970
0
Kevin said:
This is going to be a power autotransformer. I need the voltage to be
right,so I need to wind my own. I have been told to use iron instead
of steel, but I don't want to glue a core together and I don't want to
strip a transformer. I can't measure the inductance but I can
calculate it. The question is how good will the transformer be.

A solid core will have significant eddy currents and will
be inefficient. How well your application deals with that
sort of inefficiency is more to the point.

Bear in mind that transformer manufacturers go to the trouble
of laminated cores even for small wattage applications.
 
R

Robert Baer

Jan 1, 1970
0
Kevin said:
This is going to be a power autotransformer. I need the voltage to be
right,so I need to wind my own. I have been told to use iron instead
of steel, but I don't want to glue a core together and I don't want to
strip a transformer. I can't measure the inductance but I can
calculate it. The question is how good will the transformer be.

Since you clearly do not know what you are doing, the "transformer"
will not be too sucessful.
Iron or steel could "work" but neither is ideal, and a solid block
will result in gross heating and/or fire.
Get a surplus transformer, damnit, and strip the secondary, and wind
the desired new secondary to be connected in series with the primary:
aiding or opposing, depending on needs.
Or get a variac = variable auto-transformer.
 
K

Kevin Weddle

Jan 1, 1970
0
I imagine that the core material is small. For a stepup
autotransformer, the entire winding has to be on the core. This means
I would have to physically combine several cores together to make
this. Also, the magnet wire is going to be difficult to wrap on many
cores.
 
R

Robert Baer

Jan 1, 1970
0
Kevin said:
I imagine that the core material is small. For a stepup
autotransformer, the entire winding has to be on the core. This means
I would have to physically combine several cores together to make
this. Also, the magnet wire is going to be difficult to wrap on many
cores.

Not really.
Look at any non-toroid power transformer and note that the windings
are put on a cardboard (or plastic) slip-on form.
So when one gets a power transformer and removes the silicon-iron
laminations, then one sees that base and can remove the secondary togive
space for a new secondary.
If one makes a larger transformer from same-sized laminations "stolen"
fromtwo or three transformers, then one makes a winding form for use.
 
K

Kevin Weddle

Jan 1, 1970
0
Okay. So you suggest laminating several cores together, then winding
the magnet wire around a form made of cardboard. It sounds a little
bit like a ball of junk. But I think you have convinced me. You know
that a large transformer can be a little expensive to tear apart.
 
R

Robert Baer

Jan 1, 1970
0
Kevin said:
Okay. So you suggest laminating several cores together, then winding
the magnet wire around a form made of cardboard. It sounds a little
bit like a ball of junk. But I think you have convinced me. You know
that a large transformer can be a little expensive to tear apart.

I doubt that you need a transformer rated more than 1000 watts.
First you must determine the power that the new transformer is going
to handle.
There are many surplus transformers available, and the chances are
good that you can find one with a similar rating, which would mean that
you would not have to make your own winding form.
For E-I laminations, the total cross-sectional area = square root of
the power Times 0.290 .
If you only measure the center cross-section area, then double that
for the total.
And for cost, it pays to shop around; wierd voltage transformers at
times go for far less than standard voltages, as nobody can use the
wierdos.
Grab one and plunk it downatthe cash register and ask how much for
this hunk of metal.
If too much, leave it there and walk away...you may be called back and
given a better price.
Add in other stuff, maybe even really junky crap and call it a pile of
metal..
 
K

Kevin Weddle

Jan 1, 1970
0
There exists a chart for the power flux density. I have found that a
few square inches of cross-sectional area should cover most
applications. Also, I have found out that the core is square in shape
and the magnet wire can be wrapped around it. I had a different idea
for the electrical characteristics too. I am using the value of the
inductive reactance rather than the number of turns for my
calculations.
 
R

Robert Baer

Jan 1, 1970
0
Kevin said:
There exists a chart for the power flux density. I have found that a
few square inches of cross-sectional area should cover most
applications. Also, I have found out that the core is square in shape
and the magnet wire can be wrapped around it. I had a different idea
for the electrical characteristics too. I am using the value of the
inductive reactance rather than the number of turns for my
calculations.

I have never seen inductive reactance used with the dwesign of (sine
wave) transformers.
There are equations relating cross-sectional area, power ratine and
turns per volt to each other, given the core (material and shape) and
frequency.
I gave one part of that recently; i have used the formulas from a
booklet printed in the mid 1940s many times and never had to re-do any
of the hundreds of hand-wound power transformers (from 5 watts to 1000
watts at 50-60Hz).
The formulas do not mention flux density, but (obviously) the
relationships are based on the flux density (for the silicon steel used
then - but still work well for the more modern alloys that are more
efficent).
 
K

Kevin Weddle

Jan 1, 1970
0
You know that there is a formula for transformers incorporating
inductance. I don't have my book on it. This is, however, an
autotransformer. This means that it will obey the laws of the voltage
dividing. I would suspect that an ordinary transformer would be the
same. The number of turns is just not real enough to calculate the
voltage.
 
R

Robert Baer

Jan 1, 1970
0
Kevin said:
You know that there is a formula for transformers incorporating
inductance. I don't have my book on it. This is, however, an
autotransformer. This means that it will obey the laws of the voltage
dividing. I would suspect that an ordinary transformer would be the
same. The number of turns is just not real enough to calculate the
voltage.

Incorrect.
Knowing the core area (as i mentioned) and use of a simple formula
will enable one to calculate TURNS PER VOLT.
 
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