How do I build an electromagnet?

Question

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.

Answer 1

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.

Answer 2

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.

Answer 3

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).

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

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.

Answer 4

You might look at Electroboom's video on coilguns to see what can happen to electromagnets...

Answer 5

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.