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Copper wire primary and Iron wire secondary,what type of wave form will the transfomer have

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Mattski

Thu Jan 02 2014, 08:00AM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

Andy wrote ...

If you 'stretch' the wire, won't it require re-annealing before use?

, The resistance will be lower if its not annealed, and I think the permeability is increased if brittle.

If you have a voltage across a inductor(it just magically appears), what formula would you use for current.
T = L/R
A = V*L/Sec or (A=V/L/Sec)
X = 2pie*f*L
A = V/R

The circuit relationship of an inductor is defined as V=L*dI/dt. Voltage equals inductance times the time derivative of current.

So if you apply a voltage step to an inductor (voltage = 0 at time<0, voltage is a constant value V from time=0 onwards) then the current in the inductor rises linearly at a rate V/L. If L is in Henry's then V/L will give units of amps/second. The current flows into the terminal of the inductor which has the positive voltage relative to the other terminal.

wrote ...
Thanks Sulaiman, I'm getting really low values for amps, if a resistor is in place after the coil or the coil had high resistance, would that effect the X in the formula or be part of Z.

The conventional nomenclature for impedance is that:
I=V/Z
Z=R+jX.
Z = impedance
R = resistance
X = reactance which is 2*pi*f*L for an inductor.
j=sqrt(-1) which in most of the world is called 'i' but electrical engineers often use 'j' to avoid confusion with currents
Putting a resistor in series with an inductor will definitely lower the current. The resistance term should also include the resistance of the inductor's wire which will be high for an iron wire.

The imaginary numbers are a convenient trick to get magnitudes and phases of currents in response to sinusoidal stimulus. To get the magnitude of the current use the magnitude of impedance:
|Z|=sqrt(R^2+X^2)
|I|=|V|/|Z|= |V|/sqrt(R^2+X^2)

|Z| means magnitude of Z (also referred to as modulus or absolute value).

Ash Small

Thu Jan 02 2014, 11:23AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Andy wrote ...

If you 'stretch' the wire, won't it require re-annealing before use?

, The resistance will be lower if its not annealed, and I think the permeability is increased if brittle.

The first chapter of the book that PM linked to above confirms that reluctance increases with brittleness, and permeability decreases. It also states that annealed copper wire has less resistance than work hardened copper.

It also explains the magnetic differences, discovered by Faraday, in the early 1800's,
between soft, annealed iron, hard iron, and hardened steel.

I realise that this is slightly off-topic, and may not be completely relevant to this thread, however, some of it may be

Andy

Thu Jan 02 2014, 06:32PM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

@Mattski
Would ac be able to get to high amps if run at resonance with a cap, with a really high inductance value, compared to dc voltage.
Not asking to be spoon feed but....I'm after a >15joule of energy in a inductor, charged at 50hz, would this be possible.

Cheers

@Ash
Was certain that it said resistance went down with harder metals of the same type

Andy

Mattski

Thu Jan 02 2014, 07:39PM

Registered Member #1792 Joined: Fri Oct 31 2008, 08:12PM
Location: University of California
Posts: 527

A cap in series with the inductor will increase the current (You can get X of a series capacitor and inductor as 2*pi*f*L-1/(2*pi*f*C)) and at resonant frequency the reactance of a series LC pair goes to zero. Then the current will be limited by the resistance and saturation of the inductor and loss in the capacitor and wires (which shows up in the circuit as additional resistance).

Energy in an inductor is 0.5*L*I^2 so for a given inductance you know how much current you need. For any coil storing flux in a magnetic material it will saturate at a certain current value and the inductance will drop so it limits the ultimate energy storage.

You might want to pick up a simulator like LTSpice as for doing simple simulations on these types of circuits, you can do steady state AC to get magnitudes and phases of current and voltage or do a transient simulation to get waveforms. Though be careful because simulations can be misleading if you give it unrealistic inputs.

Ash Small

Thu Jan 02 2014, 08:11PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Andy wrote ...

@Ash
Was certain that it said resistance went down with harder metals of the same type

Andy

The book was written in 1904, and I've not checked with more recent publications, but I assume Faraday knew his subject.

Proud Mary

Thu Jan 02 2014, 08:23PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

The conductivity of copper is decreased by cold working and may be 2 to 3% less in the hard drawn condition than when annealed.

An approximate relationship between tensile strength of cold worked copper and its increase in electrical resistivity is:

P = T/160

Where P = % increase in electrical resistivity of cold worked copper over its resistivity when annealed.

T = tensile strength, N/mm2

Source:

Andy

Fri Jan 03 2014, 04:41AM

Registered Member #4266 Joined: Fri Dec 16 2011, 03:15AM
Location:
Posts: 874

Still not 100% sure, with two different sources.
Thinking about build a large coil that is a spiral/square, just wondering would four square coils each 2meters diameter when wired in series and facing the same way equal one coil 4meters diameter and the number of turns combined, or would it just be four smaller inductors added together.

No 14awg(i think) fencing wire for 900meters is about $120, which should make two coils.

Cheers

Sulaiman

Fri Jan 03 2014, 08:48AM

Registered Member #162 Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140

Please do not waste your time, effort and cash on making a coil of iron wire,
due to 'skin effect'

the a.c. resistance will be enormous.

Use the link above to determine the maximum size conductor required for your frequency,
e.g. for up to 100 kHz using copper wire, 0.63mm diameter, 22 awg.
Larger diameter copper wire will have lower ac resistance as the circumference is larger
(useful area of copper = circumference x skin depth)
but most of the copper will be 'wasted' at higher frequencies.

Copper pipe/tubing is often used to get a large circumference without wasting too much copper.

Very often one 'good' turn is better than many 'bad' turns at higher frequencies.

P.S. since most of the current will be flowing in the top 0.2 mm it is a good idea to clean/polish copper tubing then paint it to prevent surface corrosion,
or use 'magnet wire' which is prepared for you.

From winding Tesla Coil secondaries I think that at 100 kHz 'proximity effect' will have a worse effect than 'skin effect' if the 22 awg wires are close together.
Spacing the wires by just one diameter has a significantly good effect.
(but I am not saying space-wind TC secondaries, other considerations apply)

P.P.S. if you tell us your intended application you will get more applicable advice,
members have a very wide range of experience
and many of us have tried 'wondefull' and 'fancifull' ideas
(usually because we didn't know better ! , we all have to start somewhere)
so definitely keep experimenting, it's the best way to understand,
but often a little advice can save a lot of effort.

Dr. Slack

Fri Jan 03 2014, 10:56AM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

Iron wire might be useful to wind single layer 'self-damping' isolation inductors for Terry filters, the protection network between NSTs and SGTCs. But that is totally unsupported by any order of magnitude maths, that is I've no idea whether it would be slightly good or very good, but I do know it wouldn't be bad.

Where iron wire would be bad is anywhere where AC loss is a 'bad thing', like almost all transformers.

Proud Mary

Fri Jan 03 2014, 11:56AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Due to skin-efffect, an iron wire could be considered as a kind of low pass filter (LPF).

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