# Create an electromagnet stronger than a fridge magnet

• Electrical

## Main Question or Discussion Point

Hello, I have a question. I would like to create an electromagnet that is generally stronger than a standard fridge magnet... Right now I have this set up, (please tell me if what Im doing is wrong or unpractical). I have 10 AA batteries ligned in parallel to a 3 inch iron nail. I spliced a telephone wire (to get the 4 isolated copper wires) and I rapped around 10 meters worth of copper wire around the nail. Then stripped the ends and connected it with the batteries. However this doesn't seem to good. Is there a better way? Thanks!

Homework Helper
Gold Member
What you did seems ok. You might try a larger diameter piece of iron. The magnetic field strength will be limited by the saturation level of the magnetization of the iron, but a larger diameter piece of iron will result in more force with larger poles. You could even wrap several nails together to effectively increase the diameter.

What you did seems ok. You might try a larger diameter piece of iron. The magnetic field strength will be limited by the saturation level of the magnetization of the iron, but a larger diameter piece of iron will result in more force with larger poles. You could even wrap several nails together to effectively increase the diameter.
That sounds very interesting, I will definitely try that. I just want to make sure what I'll do is ok. Do I put the nails together and wrap at all in one? Or do I wrap the nail one by one and then wrap it even more together?

Homework Helper
Gold Member
That sounds very interesting, I will definitely try that. I just want to make sure what I'll do is ok. Do I put the nails together and wrap at all in one? Or do I wrap the nail one by one and then wrap it even more together?
Put the nails together=cut of the heads if you can. Additional suggestion is to put a small resistor=e.g. $R=10 \, \Omega$ or even 1-2 $\Omega$ in series with the batteries and wire so the batteries last longer. That will reduce the current somewhat, but I don't think the magnet will be substantially weaker with lower current.

Put the nails together=cut of the heads if you can. Additional suggestion is to put a small resistor=e.g. $R=10 \, \Omega$ or even 1-2 $\Omega$ in series with the batteries and wire so the batteries last longer.
Ok perfect I will try this, thank you so much!

Tom.G
Such a thing is used as an Electric Fire Door Release, use a Google search. The large part, which is an electromagnet, is mounted on the wall behind a door and is powered 12VDC, 24VDC, or 120VAC, drawing around 20mA to 100mA depending on model. The small part is mounted on the door to give the electromagnet something to attract. Different models have a holding power of 20lbs. to over 100lbs.

Fire doors in a building are often left open for convenience. When a Fire Alarm goes off, power is removed from the electromagnet and an ordinary door closer closes the door.

The bullseye pattern is the two magnetic poles of the electromagnet. This design concentrates the magnetic field where you want it, all at one end. The internal construction is similiar to the image below (if you don't have that notch cutout) and a coil of wire fills the empty space in this "pot core" shape.

The Physics Forums magnetics specialist is @jim hardy, who may be able to give more details and some design tips.

Hope this helps.

Cheers,
Tom

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Such a thing is used as an Electric Fire Door Release, use a Google search. The large part, which is an electromagnet, is mounted on the wall behind a door and is powered 12VDC, 24VDC, or 120VAC, drawing around 20mA to 100mA depending on model. The small part is mounted on the door to give the electromagnet something to attract. Different models have a holding power of 20lbs. to over 100lbs.

Fire doors in a building are often left open for convenience. When a Fire Alarm goes off, power is removed from the electromagnet and an ordinary door closer closes the door.

View attachment 227036

The bullseye pattern is the two magnetic poles of the electromagnet. This design concentrates the magnetic field where you want it, all at one end. The internal construction is similiar to the image below (if you don't have that notch cutout) and a coil of wire fills the empty space in this "pot core" shape.

View attachment 227035

The Physics Forums magnetics specialist is @jim hardy, who may be able to give more details and some design tips.

Hope this helps.

Cheers,
Tom
wow that is amazing... thank you so much!

jim hardy
Gold Member
2019 Award
Dearly Missed
Speaking real simply here,
any magnet has two poles and magnetic flux flows from one pole to the other. It makes a closed loop, just like Kirchhoff's current does.

The two poles of your electromagnet are separated by the length of your nail.
Your magnetic field has to traverse that distance through air.. and air is a terrible conductor of magnetic flux.
Reducing your air gap will give a stronger field. Try bending your nail into a horseshoe shape..

Look at hardware store magnetic door catches. They all have their poles close together for that reason.

https://www.kjmagnetics.com/blog.asp?p=gap-calculator

Iron is an excellent conductor of magnetic flux.
That iron yoke lets the flux flow easily around the external part of the magnetic circuit, from top of upper magnet to bottom of lower one. One of those will be a North pole and the other a South.
That way all the magnetic "push" (MMF is what we call it) is acting on the air gap, practically none gets wasted externally.

What clever mechanical construct can you come up with to minimize your air gap and put your flux where you want it ?

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Speaking real simply here,
any magnet has two poles and magnetic flux flows from one pole to the other. It makes a closed loop, just like Kirchhoff's current does.

The two poles of your electromagnet are separated by the length of your nail.
Your magnetic field has to traverse that distance through air.. and air is a terrible conductor of magnetic flux.
Reducing your air gap will give a stronger field. Try bending your nail into a horseshoe shape..

Look at hardware store magnetic door catches. They all have their poles close together for that reason.

View attachment 227044

https://www.kjmagnetics.com/blog.asp?p=gap-calculator
View attachment 227045

Iron is an excellent conductor of magnetic flux.
That iron yoke lets the flux flow easily around the external part of the magnetic circuit, from top of upper magnet to bottom of lower one. One of those will be a North pole and the other a South.
That way all the magnetic "push" (MMF is what we call it) is acting on the air gap, practically none gets wasted externally.

What clever mechanical construct can you come up with to minimize your air gap and put your flux where you want it ?
Wow that helped even more... Thank you so much! I'm trying to create a sort of 3D design using magnets (there's an actual purpose for this) Im 17 years old and I do a lot to help other people... If I could get this to work I believe it could do a lot... Thanks!

Homework Helper
Gold Member
Just an additional input: The magnetization and the magnetic field will generally have an upper limit around $B \approx 1.0 \, T$, and that is determined by the saturation level. The magnetic field can be made to be slightly higher by making the poles adjacent/in close proximity to each other. $\\$ @jim hardy suggestion to minimize the air gap between the poles will have the biggest effect in the linear region of the magnet, where you can save on current in the wires and battery power by putting a resistor in series. If you minimize the ar gap, you will get much stronger magnetic fields for a given current. Also, the more windings you have, the stronger the magnetic field you can get, until you saturate and start to approach the $B \approx 1 \, T$ upper limit. Once you reach this limit, increasing the current and/or the number of windings will do very little to increase the magnetic field strength.

Just an additional input: The magnetization and the magnetic field will generally have an upper limit around $B=1 \, T$, and that is determined by the saturation level. The magnetic field can be made to be slightly higher by making the poles adjacent/in close proximity to each other. $\\$ @jim hardy suggestion to minimize the air gap between the poles will have the biggest effect in the linear region of the magnet, where you can save on current in the wires and battery power by putting a resistor in series. Also ,the more windings you have, the stronger the magnetic field you can get, until you saturate and start to approach the $B \approx 1 \, T$ upper limit. Once you reach this limit, increasing the current and/or the number of windings will do very little to increase the magnetic field strength.
yes that too, I created a program with all the info I could get (mathematical equations) and with my first concept of one nail and 10 batteries in parallell I found that at around 230 windings it was not doing any difference.

Homework Helper
Gold Member
yes that too, I created a program with all the info I could get (mathematical equations) and with my first concept of one nail and 10 batteries in parallell I found that at around 230 windings it was not doing any difference.
I presume that is without a resistor in the circuit. Suggestion is to use a small resistor, e.g. $R=10 \, \Omega$, and I think you will find that more windings is helpful, up to maybe 1000 or more. A resistor in the circuit will save on your batteries. Also, recommend going with maybe 10-20 or more nails. That will increase considerably the diameter of the electromagnet.

anorlunda
Mentor
Wow that helped even more... Thank you so much! I'm trying to create a sort of 3D design using magnets (there's an actual purpose for this) Im 17 years old and I do a lot to help other people... If I could get this to work I believe it could do a lot... Thanks!
Your enthusiasm sounds great. But there might be an easier way. Can you try making your 3D thing with simple "refrigerator" magnets? Perhaps a lightweight design where the magnets do not need to be as strong. Or perhaps just a prototype.

Here's the problem. You say that refrigerator magnets are not strong enough. OK, so you want to make stronger magnets. Suppose you make some 3x stronger. Is that strong enough for your 3D project. Might you need 10x stronger. I sounds like you don't really know how strong you need.

So the better approach might be to experiment with designs that need less strong magnets.

Another approach is to try Neodymium Disc Magnets that you can buy inexpensively.

It is up to you to decide which part of your project is most fun, making the magnets, or using the magnets.

jim hardy
Gold Member
2019 Award
Dearly Missed
You can buy really strong permanent magnets mail order.
You won't find them in retail shops because they'll pinch fingers, and if infants swallow more than one of them they get tangled in their intestines because they stick together.. Hard learned lessons...

So you're 17, that's old enough to know if there are tiny fingers in your household and how to protect them.

We don't help with dangerous projects so will need some idea what you're up to, and assurance you're serious about keeping it safe.

The formula for flux as you know includes the product of amps and turns in the numerator. So invcreasing either raises flux.
It also has length in the denominator. So decreasing length raises flux. That'll be mostly the air gap length because iron is a short circuit for magnetic flux, at least up to the 1 Tesla @Charles Link mentioned.

old jim

Your enthusiasm sounds great. But there might be an easier way. Can you try making your 3D thing with simple "refrigerator" magnets? Perhaps a lightweight design where the magnets do not need to be as strong. Or perhaps just a prototype.

Here's the problem. You say that refrigerator magnets are not strong enough. OK, so you want to make stronger magnets. Suppose you make some 3x stronger. Is that strong enough for your 3D project. Might you need 10x stronger. I sounds like you don't really know how strong you need.

So the better approach might be to experiment with designs that need less strong magnets.

Another approach is to try Neodymium Disc Magnets that you can buy inexpensively.

It is up to you to decide which part of your project is most fun, making the magnets, or using the magnets.
Ish kinda correct yes, I want a magnet at the base of the platform, and over that I want electromagnets (created), the point of it is so that once an electromagnet is activated (current goes through) the poles will be the same and the nail(electromganet) will thrust upwards. The force itself would just be touch (like a fingers touch)

You can buy really strong permanent magnets mail order.
You won't find them in retail shops because they'll pinch fingers, and if infants swallow more than one of them they get tangled in their intestines because they stick together.. Hard learned lessons...

So you're 17, that's old enough to know if there are tiny fingers in your household and how to protect them.

We don't help with dangerous projects so will need some idea what you're up to, and assurance you're serious about keeping it safe.

The formula for flux as you know includes the product of amps and turns in the numerator. So invcreasing either raises flux.
It also has length in the denominator. So decreasing length raises flux. That'll be mostly the air gap length because iron is a short circuit for magnetic flux, at least up to the 1 Tesla @Charles Link mentioned.

old jim
yes I want this completely safe cause the hope is to heklp others and im not a fan of getting myself hurt so safety is a priorety. I dont think I need really strong magnets however.