That is what I thought initially, that the outside of the magnet really doesn't matter. I noticed that only the area inside of the coil was creating a field, which is what I wanted. I have found a way to use about 1300 turns of wire will pull 7 amps. The only thing that worries me is that my current magnet was suppose draw 17 amps but i only read 6davenn said:That would be a minimum and it is more to stop the coil getting too hot because of high current flow
and draining the battery(s)
The Ohms required isn't your main requirement
In post #33, @Tom.G gave you the main requirements
the physics of the coil will already contain the magnetic field reasonably well ( sort of)
putting the coil in a metal box isn't going to help concentrate the magnetic field.Only an iron core will do that
absolutely tiny ... microTesla or less
Now that's a lovely word. It could be straight out of the lexicon of George W Bush. But it's meaning is very clear (clearer than most of Dubbya's utterances).Baluncore said:ampacity.
NathanSM said:What is the field strenght of the coil measured in? Tesla?
Could one of the reasons of my magnet being much weaker that projected was that it was winded poorly? The magnet made almost no force. I winded all 160 feet around a small spool and I did not do a very good job. All of the winding was clockwise but it is a little uneven. Thank you for the detailed explanation of ampacity and how I can use it.Baluncore said:You maximise the amp·turns by filling the largest possible winding cross-section.
If the winding is 75 mm long and 5 mm deep it has a section of 5 * 75 = 375 mm².
You can probably fill π/4 ≈ 80% of that section with round copper, the rest being insulation and air.
So the section of copper is 375 * 0.8 = 300 mm².
The ampacity of copper magnet wire is about 10 A/mm².
For a one turn winding that makes 300 * 10 = 3000 amp·turns.
It remains 3 kA·turns for a full section of any diameter copper wire.
If you know the DC voltage available you can select wire that is thin enough to limit the current by resistance, to the ampacity of that sized wire.
The attached file contains the calculations needed to evaluate different copper wire sizes.
Adjust the wire diameter to have actual current less than ampacity.
The wire is wrapped around an aluminum tube. This tube has a 1/2 diameter and is hollow. Ferrous items are supposed to be able to move through this tube and be affected by the magnet, if that makes sense. If i were using an iron tube would it not just turn the entire tube into a large magnet? The force of the magnet is supposed to be concentrated in one section of the tube.Baluncore said:If you scramble wind the coil, the same length of wire will have a few less turns, so the amp·turns will be slightly less. I do not think that is the real problem.
I think you need many more amp·turns, or a magnetic core.
If the former was aluminium it will act like a shorted secondary winding. You should have an insulated gap along the wall of the tube to prevent the shorted turn.
If the former was an iron tube it would greatly reduce flux through the air core because the flux would follow the iron path rather than the air path.
What material is the former?
Can you reduce the inner diameter by 1%, and so reduce the area of the former by 2%, to get a greater field density?
So are you saying that the aluminum tube is hindering the force of magnet inside the tube. As for the project imagine having a piece of metal inside the tube i want to toggle different magnets to hold the metal at different positions within the tube. I can certainly cut gashes into the tube on either end of the coil. The item only travels inside of the tube that the coil is wrapped around though.Baluncore said:You have a long magnetic coil. You will only notice a change when the magnetic material is near the ends of the coil.
The thick aluminium tube wall is a shield that will slow any changes within the air core. The presence of ferrous material in the tube will distort the field, but that change will be delayed by the aluminium tube.
Maybe change to a plastic tube, or cut an insulating slot along the aluminium tube in the region of the coil.
We do not know what you are trying to do so it is difficult to suggest more practical alternatives to your concept.
That will make no difference. You must cut the aluminium for the length of the coil and insulate the cut to make sure there is no circulating secondary current. You do not seem to understand that your coil is the primary of a transformer. The aluminium tube is a short circuited secondary of that same transformer.NathanSM said:I can certainly cut gashes into the tube on either end of the coil.
So it is big and heavy to fit the tube, while the magnet is weak. Is the tube horizontal?NathanSM said:The item only travels inside of the tube that the coil is wrapped around though.
Do you mean 6" rather than 6'?NathanSM said:I see what you mean. The tube is 2 1/2' but I am only coiling around about 6' of it.
This ONLY makes a difference when the current is changing. If AC (Alternating Current, maybe from a transformer) was used, their would be a problem. With DC from a battery, the only effect is when the current is actually changing, the magnetic field would change slightly slower than if the tube was an insulator.Baluncore said:You must cut the aluminium for the length of the coil and insulate the cut to make sure there is no circulating secondary current. You do not seem to understand that your coil is the primary of a transformer. The aluminium tube is a short circuited secondary of that same transformer.
There is an additional effect=the iron piece that is being attracted produces a changing magnetic field, so there is the possibility of Faraday EMF's in the aluminum.Tom.G said:This ONLY makes a difference when the current is changing. If AC (Alternating Current, maybe from a transformer) was used, their would be a problem. With DC from a battery, the only effect is when the current is actually changing, the magnetic field would change slightly slower than if the tube was an insulator.
That is what I thought. Today I am doubling the length of wire on the coil, so hopefully that will help.Tom.G said:This ONLY makes a difference when the current is changing. If AC (Alternating Current, maybe from a transformer) was used, their would be a problem. With DC from a battery, the only effect is when the current is actually changing, the magnetic field would change slightly slower than if the tube was an insulator.
For these first experiments, I suggest you continue with what you have and make changes later if needed for speed or other reasons. Right now your main problem is to make a magnet strong enough to move your ball bearing.
I did mean 6". I am not really farmiliar with saturation. Is this like a limit as to how fast I can make a ball bearing can go or with how much strenght it can be held within the field?JBA said:Do you mean 6" rather than 6'?
A small ball bearing (or item) has very little volume and will quickly become saturated regardless of the strength of the coil field.
That shouldn't be too signifigant should it?Charles Link said:There is an additional effect=the iron piece that is being attracted produces a changing magnetic field, so there is the possibility of Faraday EMF's in the aluminum.
It could be very significant, particularly if the iron ball is moving fast. It might be an interesting experiment to have one aluminum tube with a slot and another without a slot and compare results. Faraday EMF's in the aluminum would have currents whose magnetic fields would be opposite the magnetic field of your coil. The slot should reduce these "eddy" currents considerably.NathanSM said:That shouldn't be too signifigant should it?
Try dropping a permanent magnet thru the tube. You will get an idea of how much of a problem it can be. Of course your ball bearing will not be magnetized nearly as much as the permanent magnet, but there will be some effect.NathanSM said:That shouldn't be too signifigant should it?
Ill check those out, I will have to cut slots anyway for some sensors.Charles Link said:@NathanSM See https://www.physicsforums.com/threads/spherical-magnet-dropped-through-aluminum-pole-rotates.924489/
along with other threads on Physics Forums of Lenz's law with a tube. You may want to do a search of the topic. There are a number of posts that you might find good reading.
Please use the SI unit metre, m or mm. They are useful and can be understood. The fractional foot' and inch" just lead to confusion.NathanSM said:... The tube is 2 1/2' but I am only coiling around about 6' of it. ...
This, I believe, is somewhat inaccurate. The laminations and the slot block eddy currents. Upon blocking most of the eddy currents, there is very little magnetic field generated in the opposite direction. In the case of the laminated transformer, the magnetic field is that of the applied field from the current in the primary coil, ## \\ ##Baluncore said:The insulation between transformer laminations provide a rapid path for flux to reach the magnetic material deep in the core. Likewise, the slot in an aluminium tube provides the path for the external coil to interact with the surface of an internal ball.
If that is all they do then why is the thickness of a lamination related to the frequency and skin effect in the lamination. The magnetic flux that enters the magnetic material does it via the insulation between the laminations. The eddy current excuse is given to pacify trainee technicians.Charles Link said:The laminations and the slot block eddy currents.
In the link that I gave above, see post 20, especially the second part. The post is by Jim Hardy, and I think he gives a very good and accurate explanation.Baluncore said:If that is all they do then why is the thickness of a lamination related to the frequency and skin effect in the lamination. The magnetic flux that enters the magnetic material does it via the insulation between the laminations. The eddy current excuse is given to pacify trainee technicians.
There is a voltage drop of your battery . Use a voltmeter across the terminals of the battery while the current is flowing through the circuit to see it.NathanSM said:Currently I am having an issue I do not understand. When plug the 14V battery into a length of wire with 1.6 ohms of resistance I only read 7 amps.
Got not even a volt.zoki85 said:There is a voltage drop of your battery . Use a voltmeter across the terminals of the battery while the current is flowing through the circuit to see it.
Then for 1.6 ohms resistance, you should read about .7 amps of current. Did you get the decimal place correct in your current reading? Perhaps another factor is the resistance of the wire will increase if it heats up. Something is inconsistent here.NathanSM said:Got not even a volt.
How did you get .7 amps? I am rather confused, a lot have people said use thinner wire as my setup has too little turns/resistance. I double the amount of wire used instead. This still increases resistance and turns but I've got a weak magnet that is drawing 7 amps, and heating up.Charles Link said:Then for 1.6 ohms resistance, you should read about .7 amps of current. Did you get the decimal place correct in your current reading? Perhaps another factor is the resistance of the wire will increase if it heats up. Something is inconsistent here.
It is easier to calculate the best solution than to buy something, then wait to find it does not seem to work. Before you go looking for another power supply you should identify all the parameters for your coil.NathanSM said:I may purchase DC-DC boost converter and try to run the circuit at a much higher voltage and see how this affects the strength.