# Why the efficiency of air core transformer changes (up and down)

The Electrician
Gold Member
In your chart check the primary voltage of 6.59 volts. The corresponding primary current appears to be about 10 times too large. Same thing for primary voltage of 11.11 volts. These two points on the graph appear to be outliers.

If you fix those two values your graph will look much better; although the very first two voltage values look questionable too.

In your chart check the primary voltage of 6.59 volts. The corresponding primary current appears to be about 10 times too large. Same thing for primary voltage of 11.11 volts. These two points on the graph appear to be outliers.

If you fix those two values your graph will look much better; although the very first two voltage values look questionable too.
Why does it have to be a straight line again?

mfb
Mentor
All currents and voltages should be proportional to each other if we can neglect nonlinear effects (e. g. heating-induced things).

jim hardy
Gold Member
2019 Award
Dearly Missed
Why does it have to be a straight line again?
Primary current is the MMF that pushes flux.
Secondary voltage is a measure of the resulting flux.

What is the formula that relates flux to current ? Which terms in that formula might be nonlinear ?

Explanation for trend:

Sudden increase:
• The induced magnetic field becomes stronger due to permeability of iron core which provides magnetic flux densities 10000 times that of air.high permeability means that the most of magnetic field is concentrated in the iron core and therefore allows a better inductance.n iron core is often used to provide a low-reluctance path for the magnetic flux
• The resistance of a given piece of wire depends on three factors: the length of the wire, the cross-sectional area of the wire, and the resistivity of the material composing the wire. All of the factors remain the same. Therefore, coil have a steady resistance.
• Copper losses are low as resistance is the same and the current is low.
• The iron core Magnetic Stray losses at minimum although it increases with negligible with higher voltage.
• At this point, the hysteresis and eddy currents are minimal (also because of insulated Iron core).
• As weak magnetic field produces weak eddy currents and hysteresis.
• Magnetostriction is low as well
• Electric hum low due to less magnetic stray.

At higher voltage the increase becomes less.
• More consistent value:
• Magnetostriction increases due to a strong magnetic field.
• Copper losses increases because of increase in current (A big source of energy loss).
• Eddy Current becomes a bigger problem because of increase in magnetic field that causes bigger current being made in the iron core.
• Hysterosis also increases. (Don’t exactly know)
• Magnetic stray loss is still negligible but increases.
• The induced magnetic field becomes stronger.
• Electric hum a little bit due to more magnetic stray (which causes friction and therefore energy loss).
Is this explanation of trend right or am i wrong or less somewhere?
Thank you

Primary current is the MMF that pushes flux.
Secondary voltage is a measure of the resulting flux.

What is the formula that relates flux to current ? Which terms in that formula might be nonlinear ?
Are you asking me or mfbd?

jim hardy
Gold Member
2019 Award
Dearly Missed
Why does it have to be a straight line again?
Are you asking me or mfbd?
I thought you were asking me about the graph in post 49.
Perhaps i responded to the wrong question.

old jim

I thought you were asking me about the graph in post 49.
Perhaps i responded to the wrong question.

old jim
The question i was asking you sir was the explanation in post 55

Thank you for your time everyone

In your chart check the primary voltage of 6.59 volts. The corresponding primary current appears to be about 10 times too large. Same thing for primary voltage of 11.11 volts. These two points on the graph appear to be outliers.

If you fix those two values your graph will look much better; although the very first two voltage values look questionable too.

Sorry, the graph is actually this one

can please everyone tell me whether the explanation i gave at post 55 is right or wrong or not enough info?

One part of the current is due to the secondary current being "reflected" to the primary.
I do not get this
What i wanted to see is -
Is measured flux linear with current ?
This tells us whether it behaves like a solenoid or not?

An explanation on magnetising current and it's losses please. I cannot find anything about it for some reason.

jim hardy
Gold Member
2019 Award
Dearly Missed
This tells us whether it behaves like a solenoid or not?
Tells us how closely it approximates the ideal properties of inductance

recall definition of inductance, L = ##\frac{NΦ}{I}##

jim hardy
Gold Member
2019 Award
Dearly Missed
try http://www.rfcafe.com/references/po...nsformer-october-1960-popular-electronics.htm

from an old magazine article he thankfully saved

Core Losses
Since the iron core itself, as well as the coils, is cut by the expanding and contracting magnetic field, a current is induced here, too. As this eddy current flows in the core, it steals energy from the primary circuit and dissipates it as useless heat. The eddy current flows at right angles to the magnetic flux. It can be reduced by substituting several thin layers of iron for the solid core. These thin layers - laminations - are separated by layers of glue which electrically insulate the laminations from each other. In practice, a small eddy current is set up separately in each lamination, but the total loss is much less than for a solid-core transformer.

Still another core loss is caused by the alternating current itself. Since this current reverses its direction 120 times a second, the iron core - in effect, an electromagnet - must continually reverse its polarity. And since the minute magnetic elements in the core tend to resist this change, power must be expended to realign them. This is called hysteresis loss. Engineers reduce it by building transformer cores of steels which change magnetic polarity with comparative ease, so that less power is consumed in making the switch.
https://www.bing.com/search?q=transformer+core+loss+scholarly&pc=MOZI&form=MOZTSB

The Electrician
Gold Member
"One part of the current is due to the secondary current being "reflected" to the primary."

I do not get this.
This is the essence of what a transformer does.

In an ideal transformer where there is no loss in the core (and the core has infinite permeability) or in the resistance of the wire making up the primary and secondary, there would be no current drawn by the primary when the secondary is unloaded. If a load were then connected to the secondary, current would be drawn by the primary and that would be supplying power to the secondary load. We say that the secondary load is "reflected" to the primary. The transformer with a load on the secondary would behave as though a load was in parallel with the primary terminals. The magnetic coupling of primary to secondary allows power to be transferred from primary to secondary even though there is no direct electrical connection between the copper wire of the primary and the copper wire of the secondary--the connection is only by means of the magnetic flux that links both windings. This "reflected" load current would be the only current in the primary.

BUT, in a real transformer some current is drawn by the primary even when there is no load on the secondary. This current supplies the losses (in the iron core and the resistance of the copper wire of the primary) and the reactive current drawn by the finite inductance of the primary (the permeability of a real iron core is not infinite as was the case with the ideal transformer). This current is called the "exciting current", and it's still part of the primary current even when there is a load on the secondary. The primary current drawn when there is a load on the secondary consists of two parts--the exciting current and the reflected load current from the secondary load.

Baluncore
2019 Award
Before I comment I need to:
1. See a definitive data set with the decimal points in the correct places.
2. Know what colour (temperature) the filament lamp glows at the highest currents.
3. Know the primary exciting current when there is no filament of other load present.
Without that there will be confusion.

Baluncore
2019 Award
An explanation on magnetising current and it's losses please. I cannot find anything about it for some reason.
Magnetising current is reactive current. It is not real power therefore it is not a real loss, apart from primary series resistance which is very small.

these graphs are all for the Iron core transformer.
As I thought the effency-voltage graph looked like an inverse-inverse relationship (1/x =1/y) (The last graph with no title)
But shouldn't it go through origin?

Before I comment I need to:
1. See a definitive data set with the decimal points in the correct places.
2. Know what colour (temperature) the filament lamp glows at the highest currents.
3. Know the primary exciting current when there is no filament of other load present.
Without that there will be confusion.
2. yellow
3. Cannot be checked due to the school being closed.
Data for Air core

Data for Iron core

from an old magazine article he thankfully saved
thank you

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Also, I was looking at what variables i had to control.
I know that the number of coil is controlled by me along with the temperature by using therostat and also the small breaks i took after the wire got too heated.
But when i thought that i controlled the impendance by using 50Hz AC Current and the same wire for all experiment; I remember that my graph says different impendance so i thought someone may help me clarify this.
Anything else that i controlled by using my method?

The method went like this:
• Powerpack attached to rheostat
• rheostat attached to digital ammeter
• Digital ammeter attached to Transformer coil (primary winding)
• Transformer coil attached back to powerpack.
• The digital voltmeter attached in parallel to the primary coil.
• The secondary winding was attached to another Digital ammeter.
• The digital ammeter attached to a bulb of 2 ohms.
• Bulb attached back to the secondary winding.
• Another digital voltmeter attached in parallel to secondary winding.
• All wires were copper wires.
• All the voltage and current readings were taken from the respective devices and recorded.
Same equipments was used for alll trials and experiment.

On side note:
I had some medical emergency in my family and that's why i had not been active.

I am sorry.

jim hardy
Gold Member
2019 Award
Dearly Missed
..
As I thought the effency-voltage graph looked like an inverse-inverse relationship (1/x =1/y) (The last graph with no title)
But shouldn't it go through origin?

i'm really confused.

Graph 1 says it's efficiency vs voltage but it doesn't look much like the last graph(untitled)
did you swap axes or something ?

How can you get to origin plotting Pout/Pin ? Origin for that ratio has zero in denominator, and you know one has to be wary of any ratio with a denominator that's infinitesimal. One arranges his experiments to avoid them.

old jim

jim hardy
Gold Member
2019 Award
Dearly Missed
By the way -

nice job with this one.

Gives one confidence when a result comes out just what physics says it should, doesn't it ?