230V AC Coil Contactor: Understanding Electromagnet Functionality & Alternating Magnetic Field

lolakr wrote:

After all, alternating current creates an alternating magnetic field, which would attract and sometimes repel contacts

Make yourself an experiment - take a metal screw, wind some coils on it with an enameled cord. Maybe some in thin isolation. Connect it to the 9V battery back and forth. In any of these cases, does this electromagnet repel other elements?
I will explain to you the principle of this magnetism. A coil wound around a metal core creates a magnetic flux. Don't look for what it is, unless you really want to. For now, assume that it creates and that's it. This flux magnetizes one end of the core as positive and the other as negative. When another metal object is in the same stream, it will be magnetized in the same direction. In this way, the positive pole (N) of the electromagnet will be at the negative pole (S) of the other object. So they will attract each other. If we change the coil polarity everything will work the same, but where the N pole was S will be S, and where S will be N.

lolakr wrote:

Another problem is when crossing zero the field disappears and nothing is holding the contacts.

You're kind of right. When passing through 0, there is no coil magnetism, but there is also residual magnetism, i.e. something like magnetic inertia. The coil's magnetism disappears, but for a while both pieces of the core (exactly the core and the so-called jumper) are attracted. Here I will add that the compact coil is used to reduce this residual magnetism, because it causes the relay to switch off a little longer, which is undesirable.
In addition, there is also mechanical inertia.

lolakr wrote:

I have a second question (partly related due to alternating current), namely, how does an alternating current welder work if the arc disappears when crossing zero

An electric arc is very hot air (gas, anyway). It conducts electricity very well, but when it is hot. As you can imagine, hot air with a temperature of several thousand degrees does not cool down too quickly

lolakr wrote:

Ok, I already understand what's going on (I don't have a permanent magnet at the moment) but if I put a permanent magnet on it and did not rotate it, it would be attracted once and repulsed when changing polarity?

Yes. Then let's say the N pole of the permanent magnet will still be close to the pole of the electromagnet ... and this is where the polarity depends on the polarity.

lolakr wrote:

Could I have a simplified drawing please? I can't imagine it (as if it would look like the whole thing

I did not find a nice picture quickly, but look here:

Approximately in the middle on the left you have the core along with the magnetic armature. The core is E-shaped and the jumper I is next to it. There is a coil on the middle column (the horizontal one here), which is not here. And the same situation - a current flows through the coil, which magnetizes the armature and the core itself, which attract each other. Both of these elements are made of soft magnetic steel, i.e. one that is easy to remagnetize and which does not become a permanent magnet when the current stops flowing through the coil.
The compact coil is usually located in the middle column. There is a slight groove in the center through which the coil also passes. It surrounds half the cross section of the middle column.

When the contactor is turned on, a high current flows through the coil - until the core attracts the armature. Then this current decreases. This is because the inductance of the coil changes. When the contactor is open, there is an air gap between the core and the armature, which conducts the magnetic flux less well than the metal core. The impedance (similar to the resistance) of the coil is proportional to its inductance and the frequency of the current, the greater the inductance or frequency, the greater the impedance, and therefore the lower the current. Since the impedance is low with the contactor open, a large current flows through it. When the contactor closes, there is no magnetic gap, so the coil impedance increases and the current decreases.
The nominal contactor working at 230V closes close to 160V. If you connected a lower voltage, the force attracting the armature would be too small and the current too high and the contactor would burn after a few minutes.

Added after 16 [minutes]:

lolakr wrote:

Are large industrial electromagnets AC or DC?

But where was it used?
In this type of elements, we distinguish various energy losses:
In copper - just the power lost to the coil's resistance.
Mechanical losses - in AC electromagnets it is the trembling of the sheets that make up the core. Why, in alternating current, the core is made of sheet metal and not solid, I will explain later.
Losses on magnetic hysteresis, i.e. remagnetization. There are steels that are easier to remagnetize, and there are ones that are difficult to remagnetize. Those that are more difficult to remagnetize require more energy for this process, and therefore have greater losses.
Eddy current losses. Here you would have to know how a transformer works, but in short it is like this:
Through the core made of steel flows a VARIABLE mangetic flux produced by an alternating current. This stream induces an electric current in the core. If the core was solid, i.e. cast from steel, the currents would be so high that the electromagnet / transformer would be a great heater. Instead, it divides the core into lamellae and thus divides the magnetic flux. The plates are isolated from each other with a layer of varnish. The lower the flux, the lower the eddy current. This is a simplified version.
In addition, the core is made of transformer steel, which has better magnetic properties, and two that it has higher resistance (resistance) which, according to the ohm law, reduces the eddy currents.

lolakr wrote:

Good question, I meant for example in electromagnetic lifts

I'm not sure but DC seems to be used there.

lolakr wrote:

I just didn't understand the sentence above. Would it look like this?

No. After all, I wrote that on the left side; P The core is marked as 4 and the magnetic armature is 5.
6 is the spring that pushes the armature away from the core.

lolakr wrote:

the coil that is not there should be where I drew it? or on the left in the extension of this column like here?

You have the core marked with the number 4. It looks like E. E has 3 horizontal lines. You have a coil wound on the middle one. [/ Code]