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I want to make an electromagnet that can lift a paper clip off of the ground from a short distance (probably 7 to 8 inches). I naively thought of making an electromagnet as a simple task (because of the short videos which make it seem so simple), and I was more worried about making a big enough one to accomplish the task. However, I can’t even make a small electromagnet! I tried so many ways:

  1. Nail with insulated wire wrapped around it
  2. Nail with straight copper wire wrapped around it
  3. Different battery (many times)
  4. New nail
  5. Scrape the outer coating off the nail with insulated wire wrapped around it
  6. Dumbbell with all the insulated wire wrapped around it (seen in pictures)

I always made sure the nail or dumbbell was ferromagnetic (a fridge magnet stuck to it). I always made sure the wire was wrapped tightly. I made sure I wrapped the wire in the same direction on the second layer (number 6). I am pretty sure this question has made some of the knowledgeable people that use this forum cringe, but I’m just trying to learn.

enter image description here

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    \$\begingroup\$ That 9V battery is now dead. Don't just replace it, you might have better luck with a beefy 1.5V D cell. But 8 inches range? no chance. \$\endgroup\$
    – user16324
    Commented Mar 13, 2022 at 14:53
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    \$\begingroup\$ 7 to 8 inches is a long distance, at least for an electromagnet of similar or smaller size. Wrapped tightly - not so important. Lots of turns - much more important. You seem to have a few 10s of turns of very thick wire, you need thousands to run from a low current battery like PP3. With those few turns, a volt at lots of amps would be more approrpaite. \$\endgroup\$
    – Neil_UK
    Commented Mar 13, 2022 at 14:59
  • \$\begingroup\$ There may be a way to do what you want to do, but you will need to do it in a much different way. You probably need to think in terms of what you can salvage and how you might assemble it. \$\endgroup\$
    – user80875
    Commented Mar 13, 2022 at 15:06
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    \$\begingroup\$ @user-1818839 Thank you, although I am curious why a lower voltage will work better? \$\endgroup\$
    – Will
    Commented Mar 13, 2022 at 17:38
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    \$\begingroup\$ Engineering is a discipline of numbers and mathematics. You should expect that anything assembled without first calculating its performance will most likely not do whatever you thought it would. The behaviour of electromagnets are governed by well-understood mathematical relationships. If you put the parameters from your construction into those equations they will tell you exactly how strong the magnetic field will be. What did you calculate the expected field to be? It would seem that the error was in that calculation. If you could show what you calculated we can help find the mistake. \$\endgroup\$
    – J...
    Commented Mar 14, 2022 at 18:54

5 Answers 5

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I'm sorry, but you need to find a new project. Lifting a paper clip at 8 inches will require an extremely powerful magnet.

If you still want to see what you can make, you need to change your wire choice. Standard insulated wire such as you are using has insulation which is much too thick and badly reduces the number of turns you can make. You need to look into magnet wire. Not only will you get more turns, the insulation resists heat much better than regular insulation, and that will become important.

You also need to stop messing around with batteries and get an adjustable power supply. If you reeeeally need to use batteries you need to get a couple of cheap DVMs, and at least monitor the current you're sending through the coil. If you also check the battery voltage at the same time you'll be amazed at how low the voltage will get.

If you work your way up to the sort of magnet you're looking for, you'll also need to learn about temperature sensors and how to read them. The reason for this is that you will be dissipating significant power in the coil, and if you don't provide adequate cooling for the interior of the coil it will do nasty things like catch fire.

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    \$\begingroup\$ Thank you, I picked up some magnet wire and my power supply should arrive soon. I have also made the decision to move to the garage rather than stay in a carpeted room. For so long I thought the electromagnetic didn’t work but it was just my alligator clamps. Upon seeing the magnetic pull created by my current setup I now realize I’ll be luck to get a one inch pull rang😅. Thanks again \$\endgroup\$
    – Will
    Commented Mar 13, 2022 at 18:57
  • \$\begingroup\$ Back in my youth six decades ago, the go-to battery for this kind of thing was a "#6 dry cell". A huge thing with a couple of orders of magnitude more current capability than a 9V rectangular "transistor radio" battery. \$\endgroup\$
    – John Doty
    Commented Mar 14, 2022 at 13:46
  • \$\begingroup\$ @Will - You have to be careful about power supplies. If you're just getting a wallwart, it may not put out its rated current if the load is too low. Again, I really suggest you get a DMM to measure your coil current. It will, at the very least, keep you from getting fooled by a bad connection. \$\endgroup\$ Commented Mar 14, 2022 at 21:58
  • \$\begingroup\$ A car battery will provide huge amounts of current, enough to set your magnet on fire (srsly, don't do this). Also, your phone will measure magnetic fields (in teslas) if you load a sensors type app. \$\endgroup\$
    – Rich
    Commented Mar 14, 2022 at 22:40
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    \$\begingroup\$ To elaborate on the distance issue: if we're modelling the magnet as a mono-pole, strength falls off as 1/r^2, so the power at needed at 7 inches is nearly 500 times as much as what's need at 1/10 of an inch. If we model it as a dipole, then the strength falls off as 1/r^3, giving a ratio of more than 4000 between 7 inches and 1/10 of an inch. \$\endgroup\$ Commented Mar 15, 2022 at 0:03
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Some facts about magnetism that you may not know about or understand:

  1. For a given distance in the material it is probably 100 to 2000 times more difficult for magnetic flux to flow through air than a nail or other random magnetic materials that you might have.
  2. The most magnetic force is exerted when a magnet can attract a piece of iron that forms a closed path for magnetic flux when it is added to the path.
  3. The coil of an electromagnet has very little resistance, so only a very small voltage is required to drive a lot of current through it.
  4. All batteries have internal resistance. When a battery is driving a very small resistance, the current is determined by the internal resistance of the battery. The internal resistance is determined by the physical size. D-cells have very much less resistance than AAA cells. 9-volt batteries are 6 tiny cells stacked on top of one another. Those cells add up to a very much higher resistance than an AAA cell.
  5. Magnets are often pictured as a "U" or "horseshoe shape. One of the items above explains that.
  6. Strong electromagnets are made using hundreds or thousands of turns of wire.
  7. A special wire called "magnet wire" is used to make magnets. There is a good reason for that.
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  • \$\begingroup\$ Thank you @Neil_UK. I wrote point 1 after just a quick glance at a chart and then didn't correctly copy what I looked at. I will refine that a bit more. \$\endgroup\$
    – user80875
    Commented Mar 13, 2022 at 15:47
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Here's an example electromagnet you can buy: ELECALL electromagnet.

The datasheet shows that the most powerful model (the ELE-P100/40) can run at 12 volts at 1 amp (12 Watts).

datasheet

The lifting force at various heights is shown in this datasheet:

datasheet2

So it can lift a 24kg weight (attached to a metal plate) from a height of 1mm.

It can lift:

  • 13kg at 2mm
  • 5kg at 3mm
  • 3.5kg at 4mm
  • 2.5kg at 5mm
  • 1.8kg at 6mm
  • 1.?kg at 7mm
  • 1kg at 8mm
  • 0.7kg at 9mm
  • 0.5kg at 10mm

Plot these numbers using excel, and then add a 'power' trendline. It gives the equation y=48.246x^(-1.908). This is close to an inverse square relationship, however it will go to an inverse cube relationship beyond a certain point (I'm just not sure where that point would be).

Assuming the inverse square relationship still holds, it appears to be possible that you could pick up a 1 gram paper clip at a distance of 7 inches (however I think the inverse cube relationship will kick in before you get to that height). You would have to experiment to see if it is possible.

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    \$\begingroup\$ As a rule of thumb, the force will start to drop in relation of distance cubed when the distance is in similar scale as the separation of the poles on the magnet. \$\endgroup\$
    – jpa
    Commented Mar 14, 2022 at 15:29
  • \$\begingroup\$ @jpa I'm wondering if you could stack one electromagnet on top another with a spacer in between to effectively form a longer electromagnet. This would increase the height of the inverse square zone. \$\endgroup\$
    – Xavier
    Commented Mar 14, 2022 at 20:03
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    \$\begingroup\$ The electromagnet linked in the answer is specifically constructed to bring the poles quite close together, for high holding force. An U-shaped magnet with large separation would have a longer reach, even though the maximum force near the magnet is smaller. \$\endgroup\$
    – jpa
    Commented Mar 15, 2022 at 7:13
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You might look at Electroboom's video on coilguns to see what can happen to electromagnets...

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Make sure you are winding the wire in proper way while building the electromagnet. Side-by-side windings that carry current in opposite directions cancel each other's magnetic field - you need to wind the electromagnet so that the current travels in the same direction in all turns of the coil.

Another thing, use a soft iron core rather than nails and dumbbells because those are made of steel. It will help you focus the magnetic flux better.

Instead of insulated wire, use thin enameled wire (bare wire coated with transparent enamel). It will allow you to place more turns per unit length. The thickness of insulation in case of the wire you are currently wastes a lot of space.

The power of magnetic force is proportional to the current, as well as the number of turnings in the electromagnet winding. Increase either of those to make your magnet stronger.

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