Understanding coils for newbies

[mbrownn]

Understanding coils for newbies

This thread is about what coils do in simple terms, how to manipulate them and not the highly technical how and why. If you wish to do that start another thread to run along side this one so that we can all learn then do so but I dont want it getting too complicated on here as this can be quite complex as it is.

Now for the basics

1) When you apply a voltage to a coil of wire, a current will flow through it.
2) When a current passes through a coil of wire, a magnetic field forms in and around that coil.

So now we can use a coil as an electro magnet that can be switched on and off at will.

The first manipulation of the coil I will mention is the core. By placing a magnetic material in the core of a coil, there appears to be a gain in magnetic pull in the center of the core. (If someone world like to add a simple explanation why this happens feel free to do so but please keep it simple.)

This simple set up is used in many applications such as bells and relays, but if configured with other magnets or coils can make motors and transformers. Something we can discuss later.

Coils with or without cores can also be used as chokes in electronic circuits. (Again feel free to add a simple explanation of this)

There are two primary things that influence what voltage that is required to cause a given current to pass through a coil. These are the resistance of the wire and the inductance of the coil. (feel free to add a simple explanation of Inductance)

Generally it is not not possible to manipulate the resistance of a coil but it is possible to manipulate the inductance and this is normally done with the core by adding a magnetic material in this location. It can also be done by winding a second coil in or around the first coil and controlling the current flowing through it or both.

Inductance also has some interesting properties when dealing with alternating current and pulsed direct currents. For example when we pass AC or pulsed DC through our first coil at low frequencies Inductance has little effect upon what we are doing but as the frequency increases the inductance offers an apparent higher resistance.

We can manipulate this by shorting out the second coil and controlling the flow of current in this second coil by a variable resistor.

A shorted secondary coil will significantly lower the impedance (apparent resistance caused by inductance) of a primary coil, allowing a much higher AC or pulsed DC current to flow in the primary at high frequencies.

Another manipulation of a coil is achieved by applying a varying the magnetic field to the core of a coil from another source be it a moving magnet or another coil. This being different to the last manipulation by the fact that we would be applying current to the secondary coil in this case, not just allowing a current to flow in a transformer action. In this method is is possible to raise the inductance of a primary higher than would naturally occur with a normal coil and core.

Now we can manipulate the voltage and current in coils and the resultant magnetic fields in many ways.

Those that understand this feel free to post simple explanations of why this is the case, and those that dont, feel free to ask questions.

[Dog-One]

Shorted Secondary

Good topic. And if we really think about this simple device, great things may come of it.

A shorted secondary coil will significantly lower the impedance (apparent resistance caused by inductance) of a primary coil, allowing a much higher AC or pulsed DC current to flow in the primary at high frequencies.

This is the part that truly fascinates me. A shorted secondary, by definition doesn't put any electrical power directly into the transformer, but has a profound effect on how the transformer behaves/responds. In this video, observe what the short via a spark gap does to the electrical circuit on the primary:

High voltage HHO drive circuit - YouTube

Now do keep in mind this short (spark) is coupled in series with a capacitor. And yes, the primary now reacts very different.

[mbrownn]

Good topic. And if we really think about this simple device, great things may come of it.

This is the part that truly fascinates me. A shorted secondary, by definition doesn't put any electrical power directly into the transformer, but has a profound effect on how the transformer behaves/responds. In this video, observe what the short via a spark gap does to the electrical circuit on the primary:

High voltage HHO drive circuit - YouTube

Now do keep in mind this short (spark) is coupled in series with a capacitor. And yes, the primary now reacts very different.

I'm glad you like the Idea of the thread

As usual, an interesting video from Tinman, a brave man too poking his fingers around a MOT and capacitor just after it has been powered up

This is a different operation from the ones I described above that I would consider more advanced use. It has always been a problem to get sufficient power into a high inductance coil at higher frequencies and to prevent too much power at lower frequencies, by manipulating the coil in these ways it makes such things possible. We also have to consider any other operating coils or moving magnets that there may be around our device, Im thinking motors here.

[mbrownn]

Applying a voltage to a coil is like pushing a car, it is a force we apply. The result of this force is like what happens when we push, something moves. The more voltage we apply, the more something moves, and what moves is termed current.

When we push current through a coil with voltage, a magnetic field is produced. This is interesting in of itself because if we resist the magnetic field it has no effect on the voltage or current. i.e. it does not matter if the magnetic field is placing a force upon something else such as attracting or repelling, it does not alter voltage or current. Having said that, if a magnetic field is moving within our magnetic field an effect is seen, and this seems to be the source of BEMF in motors.

When our voltage is removed is when another special event happens Provided there is a conductor for the current to flow forming a path from one end of the coil to the other, a current continues to flow. Just like when we push a car, when we stop pushing the car continues to move. Of course the car slows and stops after a short time and this is also true of the current in the coil. This slowing is due to resistance.

If the path for the current has high resistance, the voltage across the now un-powered coil now rises above the voltage that we originally applied. If there is no path the voltage may rise many 10s or even 100s of times higher than the original voltage I compare this to the brakes on a car, depending how quickly we want the car to stop the braking force can be 10s or 100s of times greater than the force used to push the car forward in the first place.

This phenomenon is very important in many of the devices that have been discussed on this forum and in many is the source of the whole output power.

In truth it is not well understood. Some have compared it to momentum, such as that in a car, others have said that it is something entering into the coil from the environment.

I am not really sure, it could be both. I would go as far as to say that many people on this forum know more about it than the so called experts in our universities and there is more to it than can be explained by this simple analogy.