Electromagnet build... fence row nails and wire. rScotty

[Dadnatron]

I have been removing fences from all over my property and want to be as sure as reasonably possible, that I've picked up wire/nails/etc.

I've walked the lines, but each time I walk it again, I find something else I missed. And while I know there is no way to absolutely insure everything is gone, I do believe there are better ways than I have found thus far.

I've decided that I might try to make a strong magnet attached to something which will stir up the dirt and grass. I figure, if I can loosen up the things in and on the ground with some sort of implement, I can immediately drag an electromagnet across it to pick up whatever is loosened.

I've seen some online, but most of them are either for asphalt or are so expensive as to not make sense for me.

I can build/alter a cart/disc/springtooth/etc to work up the groung. Perhaps it needs to be nothing more than just small tines in front of the magnet. But I'm not quite as sure about the magnet itself.

I have seen options for microwave core modifications, which seems reasonable, but I am unsure how to transfer this 'focal' magnetism to something useful. So, my question is, how would you go about making a relatively inexpensive 84" wide electromagnet strong enough to pull crap off/out of the ground (reasonably) in such a manner? I'm not expecting to rip it from 6" down or anything, but what I'm hoping for is something that can pick up loose wire/nails from the ground or which are partially imbedded in/under some dirt. Would I need (I suspect) several of these along the course?

For an 84" (and I'm saying this simply because that is the width of my tractor, no other reason. It just has to be of a useful width) I suspect I would need more than one microwave core. But I could use a little help with the thinking, because I'm not sure whether to chuck this idea or proceed. And I'd like a better idea of what I can expect.

Would wrapping a bar and covering it so I can remove debris be better?

I don't think that available permanent bar magnets will be strong enough to do what I need or that one which will work will be reasonably enough priced to make this a useful endeavor. I'm in the thinking/planning stage. And didn't want to get in too deep if this is just not a reasonable thing to be doing or which will not be strong enough to do the job I need.

 

[Dadnatron]

And finally.... this is a technical question...

When wrapping the wire, will reversing the direction of the wire wrapping, negate the magnetism? ie, wrapping a wire, from left to right, down the shaft of a rod in a single layer, then adding a layer right to left.... does it, or why doesn't it, cause the magnetic force to be negated?

 

[Rosher18]

I made an electromagnet in school for a science project. As long as the wrap direction doesn't change (keep spinning clockwise, in other words) the field produced will be stronger with each successive wrap. Wrapping across the width of the core just has to be uniform. Going left to right and switching directions to add another layer is just how electromagnets are made.

 

[rScotty]

And finally.... this is a technical question...

When wrapping the wire, will reversing the direction of the wire wrapping, negate the magnetism? ie, wrapping a wire, from left to right, down the shaft of a rod in a single layer, then adding a layer right to left.... does it, or why doesn't it, cause the magnetic force to be negated?

As long as the wraps are in the same direction, wrapping down the rod and then back again will increase the magnetic force at the ends.

In fact, twice the wire will yield twice the magnetic force at the ends of the rod..... but only as long as the current through the coil remains the same. Since we have also doubled the resistance of the coil when we doubled the length then this would require doubling the voltage. If you were using a car battery originally, the longer coil wire would now need two of the same car batteries connected in series.

But don't start quite yet. There's another problem with a coil on a rod and we are going to have to change the shape of the electomagnet as well. It will work, but there are tricks...
I'll write some more after lunch.
luck,
rScotty

 

[Dave Pee]

I would buy a few of the magnetic "broom" used by roofers, for example, to pick up nails ans screws.

magnetic "broom" - Google Search

Or make you own for free with the magnets from old computer disc drives. Super strong.

 

[flyerdan]

A good source of electromagnets are the clutches from auto air conditioner pumps; they already have the mounting holes to attach to a board or whatever your drag is made from. Need a pretty big circuit to run five or six of them though, I think they pull about 4 amps each.

 

[PILOON]

You could have 2-3 'magnetic brooms' wide by attaching then to a length of wood or metal to cover a wider path.
However those 'brooms' will only collect loose steel items, not powerful enough to yank buried metal.
I have one and they are good to collect surface loose steel.

 

[mapper]

I use a large horseshoe magnet that came out of a WW2 era radar set. It will pick up stuff from about six inches away. I drop it into the bottom of a hefty garbage bag and swing it back and forth in front of me walking through the area I want to clean up, the challenge is to carefully pry the accumulation off without tearing the bag.
I am not sure where you could get one now, I inherited mine from my father-in-law.
Amazon has magnetic sweepers that will pick up thirty pounds for about $57.

 

[rScotty]

As long as the wraps are in the same direction, wrapping down the rod and then back again will increase the magnetic force at the ends.
I'll write some more after lunch.
luck, rScotty

The problem with a rod shape is that an electromagnet only projects a useful magnetic field at right angles to the coil winding. So winding a coil around a rod will concentrate the useful force at either end of the rod but there is almost no useful magnetism anywhere along the rod itself. Just at the ends.

Now if you do build it and then bend it into a horseshoe shape there will be a nice field where the ends are closest to each other as long as they are only a few inches apart. It will end up looking like an old fashioned permanent horseshoe magnet but larger and able to be switched on and off.

Or you could wind coils like dinner plates and bolt them flat to the bottom of a 2x4. That would work too. The field would project out away from each plate. Winding the coil around a big flat steel washer would enhance the strength of the electromagnet, and make it easier to mount. It would still only be good for an inch or so from the coil.
good luck, rScotty

 

[MossRoad]

I'd buy a metal detector and find the nails in one pass and be done with it. You might find some other neat stuff, as well. Plus, with a metal detector, you can sweep closer to objects like fence and trees than you can by dragging a large magnet around. Heck, you might find some buried treasure.