# Coil Around A Tube - Iron Cylinder Inside Tube - How Many Turns Needed?

• I
• Mahonroy
In summary: has the following properties:- opposes the motion of the object it is attracting- can only do so up to a certain point- will eventually wear down and weaken the electromagnet
Mahonroy
TL;DR Summary
Coil Around A Tube - Iron Cylinder Inside Tube - How To Determine How Many Wire Turns And Power Required To Hold About 500 Pounds On Iron Cylinder
Hello, I am wanting to wrap a coil of wire around a tube, suspend an iron cylinder in the tube, energize the coil, and have it be able to suspend around 500 pounds on the iron cylinder.
I was playing around with some online calculators for coils, and didn't really get anywhere, so I figured I would check with you guys.

I am under the impression that when I energize the coil, that it will create a magnetic field that will apply a constant force in one direction on the iron cylinder. So while its energized, the iron cylinder should be constantly wanting to travel in one direction. I understand that if the magnetic field is too strong, the cylinder will want to continue to travel up even with the weight. And if its too week, it won't be able to suspend the weight and it will fall. This is fine for the exercise - I'm just trying to figure out a ballpark. I am under the impression that I could fine tune this by adjusting the voltage slightly.

Am I understanding this correctly or do I have this wrong? Does anyone know how to calculate roughly what kind of coil I would need with some headroom? I'm thinking of using a 1" PVC pipe to wrap the coil around (1.315" OD, 1.029" ID), and then a 1" OD iron cylinder to fit in the PVC pipe.

Thanks and any help or advice is greatly appreciated!

Welcome to PF.

Mahonroy said:
Hello, I am wanting to wrap a coil of wire around a tube, suspend an iron cylinder in the tube, energize the coil, and have it be able to suspend around 500 pounds on the iron cylinder.
That's a lot of weight, kind of in the junkyard dog range. Can you give more details about the application? And the dimensions of the tube and how far you want to lift this weight? Thanks.

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BTW, is this a typo? A 1" coil to lift 500 pounds?

Mahonroy said:
I'm thinking of using a 1" PVC pipe to wrap the coil around (1.315" OD, 1.029" ID), and then a 1" OD iron cylinder to fit in the PVC pipe.

berkeman said:
Welcome to PF.That's a lot of weight, kind of in the junkyard dog range. Can you give more details about the application? And the dimensions of the tube and how far you want to lift this weight? Thanks.

View attachment 318526

Thanks!
I'm thinking of using a 1" PVC pipe to wrap the coil around (1.315" OD, 1.029" ID), and then a 1" OD iron cylinder to fit in the PVC pipe. The coil can be wrapped to whatever diameter is necessary.
berkeman said:
BTW, is this a typo? A 1" coil to lift 500 pounds?
Not a 1" coil, I said a 1" PVC pipe is 1.315" outer diameter, the coil can be wrapped to whatever diameter is necessary around the 1.315" PVC tube.

Mahonroy said:
Not a 1" coil, I said a 1" PVC pipe is 1.315" outer diameter, the coil can be wrapped to whatever diameter is necessary around the 1.315" PVC tube.
Sorry, I'm still not tracking. You are still talking about a coil with its inner windings at 1.3" diameter? Can you post a sketch of what you are thinking of? (Use the "Attach files" link below the Edit window)

berkeman said:
Sorry, I'm still not tracking. You are still talking about a coil with its inner windings at 1.3" diameter? Can you post a sketch of what you are thinking of? (Use the "Attach files" link below the Edit window)
Here is a sketch of what I am talking about:

Mahonroy said:
Here is a sketch of what I am talking about:
That helps. So you want to make a solenoid to lift some amount of weight. Have you done any Google searching yet to see what typical solenoids can lift?

berkeman said:
That helps. So you want to make a solenoid to lift some amount of weight. Have you done any Google searching yet to see what typical solenoids can lift?
Yes, I mentioned I even tried using some online calculators but I didn't have much luck with them.

Mahonroy said:
Yes, I mentioned I even tried using some online calculators but I didn't have much luck with them.
Yeah, I don't think you are going to be able to lift 500 pounds with a 1" ID solenoid. If anything, I'd guess it would take closer to 0.25 meters ID or so, but that's just a guess.

What is the application?

hutchphd
Also the geometry of the magnet is very important. Much more holding strength can be obtained for a lifting a solid object if the object completes "magnetic circuit": this is why a horseshoe magnet can hold much more than double the strength each of its pole faces individually.

Also one must be aware that an electromagnet core reaches saturation beyond which more current (or windings) does little to help your cause. This is why strong magnets (or power transformers) need to be big chunks of iron. There used to be nice software

berkeman said:
Yeah, I don't think you are going to be able to lift 500 pounds with a 1" ID solenoid. If anything, I'd guess it would take closer to 0.25 meters ID or so, but that's just a guess.

What is the application?
That is pretty much the application in that image I uploaded. I want to be able to dial in a voltage to be able to hold the weight up against the cap. If I put in a 400 pound weight, I want to be able to dial back the voltage until I get the weight to suspend.

The problem is I have no idea of the ballpark/general size/shape/power requirements to do this. For example, are we talking a coil of wire that is 28awg, 100 feet long, and 50 volts....... or does it need 12awg wire, 2 miles long, spun into a diameter of 2 meters, and require 200 volts (and a ton of amp draw). I have no idea what the ballpark is for this, so I am trying to see if its possible to calculate it to get an idea.

Regarding size, the size of this thing can be roughly the size of a 55 gallon oil drum. Obviously smaller is better, but that volume is completely acceptable.

Mahonroy said:
That is pretty much the application in that image I uploaded. I want to be able to dial in a voltage to be able to hold the weight up against the cap. If I put in a 400 pound weight, I want to be able to dial back the voltage until I get the weight to suspend.

The problem is I have no idea of the ballpark/general size/shape/power requirements to do this. For example, are we talking a coil of wire that is 28awg, 100 feet long, and 50 volts....... or does it need 12awg wire, 2 miles long, spun into a diameter of 2 meters, and require 200 volts (and a ton of amp draw). I have no idea what the ballpark is for this, so I am trying to see if its possible to calculate it to get an idea.

Regarding size, the size of this thing can be roughly the size of a 55 gallon oil drum. Obviously smaller is better, but that volume is completely acceptable.
You still haven't said much about your application. Is the target thing that you want to lift made of ferrous metal? Or will you hook a harness to it to lift it?

And did you understand what hutch said about the shape/geometry of the magnet? If you can use a closed magnetic path for the lift, that will make the magnet much stronger (and hence smaller).

BTW, if you just need a very strong magnet that you can switch on and off easily, you can look into something like this:

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berkeman said:
You still haven't said much about your application. Is the target thing that you want to lift made of ferrous metal? Or will you hook a harness to it to lift it?

And did you understand what hutch said about the shape/geometry of the magnet? If you can use a closed magnetic path for the lift, that will make the magnet much stronger (and hence smaller).
Thanks again for the response. No its just weight - could be plastic, aluminum, steel. Basically any non-ferrous material. The only thing ferrous would be the rod that is in the coil for it to operate.

The cylinder does need to be able to move up and down from within the cylinder. I'm guessing if only the tip of the iron rod is in the cylinder, you would get less pulling force, and would need to increase the voltage?

berkeman said:
This won't work - it needs to be the form factor of the image I drew. The cylinder should be able to move up and down within the coil. Activate the coil, get roughly 500 pounds upwards force. Less voltage, less pulling force.

Mahonroy said:
Thanks again for the response. No its just weight - could be plastic, aluminum, steel. Basically any non-ferrous material. The only thing ferrous would be the rod that is in the coil for it to operate.

The cylinder does need to be able to move up and down from within the cylinder. I'm guessing if only the tip of the iron rod is in the cylinder, you would get less pulling force, and would need to increase the voltage?This won't work - it needs to be the form factor of the image I drew. The cylinder should be able to move up and down within the coil. Activate the coil, get roughly 500 pounds upwards force. Less voltage, less pulling force.
Okay. The 1" ID dimension is likely too small, but we'll deal with that. How long of a stroke do you need? How high of a lift do you need?

Do you understand how a solenoid works to attract the ferrous rod into its interior? It has to do with the divergence (spreading) of the magnetic field at the end of the solenoid coil...

hutchphd
Mahonroy said:
This won't work - it needs to be the form factor of the image I drew. The cylinder should be able to move up and down within the coil. Activate the coil, get roughly 500 pounds upwards force.
A long solenoid does not provide a long throw of strong pull (as @berkeman points out). Once the leading edge of rod gets into the solenoid, the ferrous rod is pretty well magnetized all down its length and the pull becomes much diminished. The useful range will be ~the diameter of the pole opening. This is one reason the scrapyard uses a flat cup magnet (on a crane).
Also for a given available voltage, the strength of the pull will depend only on the magnet volume. More turns will draw less current because the wire is thinner with higher resistance and it is basicly a wash. But higher voltage will give more pull for the same magnet.
So your "throw" requirement is tough.

berkeman
What about something like this then:

The rod is much smaller, and not sticking out the end of the coil. Would that give a more consistant force in the middle area of travel? What kind of coil diameter and voltage would we be talking here?

A simple rule of thumb is that a magnetic field of strength one Tesla will exert a force of 58 lbs per square inch. That calculates to 45 lbs pull on a one inch diameter steel rod. The maximum practical field is about 1.6 Tesla, at which the force will be about 148 PSI. These numbers are for a magnet or electromagnet that clamps directly to a flat steel surface, where the area is the pole area of the magnet.

You have an air gap through which the magnetic field passes. I once designed an electromagnet to deliver 1600 lbs force on a flat steel surface through a 1/8" air gap. That electromagnet needed 4000 ampere-turns to deliver the desired force through the air gap. It was designed for use with a 50 ampere power supply, so had 80 turns. My recollection is that I specified 10 gauge wire. There are more details in US Patent #6,389,941.

The pull force is magnetic field strength multiplied by pole area. Then you need enough ampere-turns to push that field through the total magnetic reluctance. You can search electromagnet design and magnetic circuits for more information. I'm not familiar with the calculations for a solenoid electromagnet, but this should help you get started.

vanhees71 and berkeman
Mahonroy said:
The rod is much smaller, and not sticking out the end of the coil. Would that give a more consistant force in the middle area of travel? What kind of coil diameter and voltage would we be talking here?
You are misunderstanding the workings of magnetic force in this circumstance. A simple bar magnet in a strong uniform field will feel an aligning torque but no net force
Once the slug is "inside" the core of the solenoid, the upwards force rapidly drops to near zero. The force is actually strong only where there is a strong field (to polarize the ferromagnetic material) and a strong unbalanced gradient in the field (to then produce net force). This will occur only at the end of the solenoid, so a simple long solenoid is unlikely to meet your design criteria for strong force over a long distance..

Mahonroy said:
What about something like this then:
I think there is still a bit too much contrast between the light ink and the dark paper. Maybe a little darker paper would work better? Or a lighter and finer pen?

nasu
I think there is still a bit too much contrast between the light ink and the dark paper. Maybe a little darker paper would work better? Or a lighter and finer pen?
LOL. @Mahonroy -- What Gus is saying is that your uploaded picture is not very clear. I struggled to read it, and considered downloding and enhancing it. But that should really be your job, no?

vanhees71
I think there is still a bit too much contrast between the light ink and the dark paper. Maybe a little darker paper would work better? Or a lighter and finer pen?

berkeman said:
LOL. @Mahonroy -- What Gus is saying is that your uploaded picture is not very clear. I struggled to read it, and considered downloding and enhancing it. But that should really be your job, no?
I originally tried adjusting the contrast... it was making parts of the white background more dark, and parts of the lines darker, but parts of the lines also lighter. Basically it was not working well. But making the image darker in general made it easier to see the lines.

Its just a tube, with a coil, with a small slug in the middle of the tube. Attached to the slug via a cable is a weight.

hutchphd said:
You are misunderstanding the workings of magnetic force in this circumstance. A simple bar magnet in a strong uniform field will feel an aligning torque but no net force
Once the slug is "inside" the core of the solenoid, the upwards force rapidly drops to near zero. The force is actually strong only where there is a strong field (to polarize the ferromagnetic material) and a strong unbalanced gradient in the field (to then produce net force). This will occur only at the end of the solenoid, so a simple long solenoid is unlikely to meet your design criteria for strong force over a long distance..
So the slug will move towards the center of the coil/tube is that right? So the area of movement would be between the end of the tube, and the middle then? Would this not work between those two points?

It will experience strong axial force only while the slug is entering (or exiting) the ends of the tube. This is not what you desire.

hutchphd said:
It will experience strong axial force only while the slug is entering (or exiting) the ends of the tube. This is not what you desire.
I feel like I am missing something here. You mentioned the coil will put a force on the slug near the end of the tube, and pull it towards the center didn't you?

If the slug is short compared to the tube, the region of strong force depends upon the length of the slug not the length of the solenoid tube.

hutchphd said:
If the slug is short compared to the tube, the region of strong force depends upon the length of the slug not the length of the solenoid tube.
I have any choice of length for the tube/coil, and any choice of length for the slug. If I want a few feet of movement, then what does that mean?

For that geometry, you probably want the slug to be similar length to the solenoid. But you are constrained also by the maximium (saturation) magnetization of the slug. Short travel gives you more force over short distance before you saturate. So you need to consider a multitude of factors and "adding more coils" will not get you there.
There is a reason you do not see this geometry in common use. I do not believe you can reach anything like your goals with the design you propose because life is just not that simple.

## 1. How does the number of turns affect the magnetic field in a coil around a tube?

The number of turns in a coil around a tube directly affects the strength of the magnetic field. As the number of turns increases, the magnetic field becomes stronger. This is because each turn of the coil adds to the overall magnetic field, creating a cumulative effect.

## 2. What is the relationship between the diameter of the tube and the number of turns needed?

The diameter of the tube does not have a direct relationship with the number of turns needed. However, a larger diameter tube may require more turns to achieve the desired magnetic field strength compared to a smaller diameter tube.

## 3. How does the material of the tube affect the number of turns needed?

The material of the tube can affect the number of turns needed in a coil around it. Different materials have different magnetic properties, so the number of turns needed may vary. For example, a tube made of iron will require fewer turns compared to a non-magnetic material like plastic.

## 4. Is there an optimal number of turns for a coil around a tube?

The optimal number of turns for a coil around a tube depends on the specific application and desired magnetic field strength. It is important to consider factors such as the material of the tube, the diameter, and the desired strength before determining the optimal number of turns.

## 5. Can the number of turns be too high for a coil around a tube?

Yes, the number of turns can be too high for a coil around a tube. If the number of turns is too high, it can lead to overheating and damage to the coil. It is important to carefully consider the specifications and limitations of the materials and equipment being used before determining the number of turns needed.

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