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DIY electromagnet vs rare earth magnet?

  1. Aug 14, 2013 #1
    Hi my name is HopelesslyFaithful (HF) (forum didn't allow all chars). I am from Notebookreview and while googling for my project. I came across this site a thread that was helpful but also made more questions. I posted this on NBR so i did a direct copy paste hoping i could get some expert help over here.

    So i have been wanting to either buy a very large rare earth magnet 1-2 feet in either direction. or created my own electromagnet. I plan on using this to regular clear the gravel drive way where my dogs run and my wife's horses walk.....Also where my cars drive down. My father-in-law is an idiot and throws crap everywhere so i use two different magnets right now but one is too weak and the other weighs 80 pounds and i hate dragging it around. I am too lazy to make a mount that keeps it 2 inches off the ground. Any higher it isn't strong enough to clear well. Hence why i want a rare earth magnet or an electromagnet that i can crank a ton of juice into and move it around the drive way/horse barn. I have never made and electromagnet but it doesn't seem to hard from what i have read. Anyone have any experience and can help me decide on what is best?

    I see some have 250 pounds of pull force so i am unsure what that means in actual performance....i assume it is ridiculous. Also if i get a 3 foot by 1 foot 2 inch REM that will have about 100-1000 pounds i think from what i have seen (i am unsure if that would be wise...i think that would pull me or things things heavy towards it right?). None are made that big so i'll have to put them together to make it. I know they are brittle as can be so i figure i would put a thin piece of steel or whatever metal would work as a base that would shield them from metal hitting them directly.

    I am wondering if an electro magnet would be better since i can turn it on and off. Though it wouldn't be as strong and would be limited to ~100 feet from an outlet plus cost more money over time. I think the several hundred pounds of pull would be near impossible to control with a REM that large....even a low quality one would have issues right? If i made a REM one i would want max 100-200 pounds right since that would be the max i could ever pull off.

    How expensive would an electromagnet be to build being let us say 2'x2' and 6'by2'? Also how much force would be generated and how much electricity needed? I'll take the 80 pound magnet and drag it once a month 50 feet and get about 1-2 pounds of random metal -_- (worse case) A few hundred square feet done real fast gets me a few pounds :/ hence why i want something better and faster. I also had a nail go into my foot a few months ago so it is a problem.

    The reason for one being 2'x6' is that i would mount it to my skid steer or my truck and drive it around. If i wanted to clear pasture i could barrow my father-in-laws 5kw propane generator and mount it all to the truck ^^ I figure this will be expensive but i can use this for the next 50 years of my life so i figure it is a worthy investment if possible so i don't have expensive vet bills or doctor bills or blown tires. My truck actually got a nail a year ago and i had to plug it :/

    Electromagnet - Wikipedia, the free encyclopedia

    ignore my last statement it was dumb
    -ok it wasn't dumb you can use permanent magnets for the core.....not sure how much better it is. Although, it is suppossed to be in a N/S,S/N,N/S way so making a core like that our of REM maybe undo able.

    Also i am always up for different ideas since i am sure someone has a better idea than me ^^ There was something else but i am blanking....

    BTW I do know i need to get a DC power supply so any ideas on what voltage and amps would be awesome.

    EDIT: Also i am wondering this too. If a magnet has 300lb of pull and has an area of 30 square inches does that mean it has 10 lbs of pull per square inch? I would assume that a the field of a 300lb force would over lab in pull but still wouldn't be as good as a 300lb square inch piece right? If you need me to further explain/elaborate what i am getting at just ask.
    Last edited: Aug 14, 2013
  2. jcsd
  3. Aug 14, 2013 #2
    Sounds like an awful lot of trouble just to collect the crap that happens to contain iron, nickel, or cobalt.

    What about the aluminum crap, plastic crap, wooden crap, glass crap...
  4. Aug 14, 2013 #3
    glass crap is an issue too but nothing i can do. The plastic and aluminum are not an issue. Father-in-law scraps aluminum and plastic isn't going to lamb an expensive horse or myself.

    From what i read it doesn't sound too expensive to make...the several foot sized one will be so i'll consider the cost into that but doing it myself won't be an issue if i get some guidance.

    I "should be" competent enough to make it with a general design guide and knowing what i actually need to make it. I am hoping someone knows this stuff and can save me a day or two of research into "reinventing" something that ha already been made.
  5. Aug 14, 2013 #4


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    I recommend strongly against large rare earth magnets. They are really dangerous. More so than the metal you are trying to pick up.

    You could build a metal detector loop using pvc and sweep a large area (6 to 8ft rectangle loop). A PVC loop metal detector is light and could be towed by hand. Also, metal detectors are fun way beyond just finding dangerous junk Use the detector to find the metal, a magnet on a stick to pick the magnetic stuff up (it will also detect non-ferrous metal). You will find lots of underground stuff too, if you turn it up, maybe even a treasure. Go to http://www.geotech1.com for lots of different plans. You probably want a pulse induction system. Hopefully someone else here knows more than I do about the practicality.
  6. Aug 14, 2013 #5
    the thing is crap is everywhere so the detector would just go over on every square foot....i am not kidding. years of build up. Also the stuff is not just sitting on the surface. It is partially in the group so i am hoping to get something strong enough to pull it out. Someone on NBR showed me these

    http://www.magnetsource.com/Consumer Pages/Sweepers.html

    but i doubt it'll be strong enough. Check this out from above..maybe you can answer it.

    Also i say this and if my thought above is true this might work but again at this force....i feel i really need something on and off.


    Last edited: Aug 14, 2013
  7. Aug 14, 2013 #6


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    If you are dealing with "years of buildup" then this sounds like a one off job. Worth while spending a bit of time and thought over, before you launch into an expensive purchase with doubtful success.
    You seem to be wanting a magnet that will pull buried magnetic material up from amongst the gravel. This is very demanding. Did you consider using a system / process where the gravel rolls past (or over) a stationary magnet mounted on a sloping board? It would involve shovelling all the gravel, a bit at a time, admittedly, but you would get a more reliable system and, you could incorporate a seive, to remove dust and sand. Plus, the other debris would be more visible and easier to remove. I'm really suggesting the sort of technique used in mining and general materials sorting.
    I realise it sounds attractive (no pun intended) just to drag your magnet up and down the yard and hope to pick up all the nasty bits but you could easily miss stuff. You could estimate the time taken for the job if you work out how many tons of gravel you have and how long it takes to sort a shovel's worth. That will probably put you off the whole thing!
  8. Aug 14, 2013 #7
    Your father-in-law throws a couple of pounds worth of sharp metal objects around your driveway each month?

    Not to state the obvious, but isn't it about time you nut up and tell him to stop doing that?
  9. Aug 14, 2013 #8
    do you have an example of this? I remember seeing something like that but this seems almost more expensive and time consuming. Would an electromagnet cost that much? I could easily go smaller.

    To the other guy. I tell him he is a moron every day and deal with his stupid *** all the time. Also i only do it every month or two real fast so i get new and old stuff. a skid steer, cars, wheel barrels, trucks, and back loader drive over it each month so older stuff gets kicked up a lot. Eat time i legit do it i get maybe 1-3 pounds. I have done it twice this summer so maybe once every 2 months in the summer....too cold and frozen in winter to bother.

    EDIT: what if i used the magnet first than racked the gravel than used the magnet again. I think that would get most of them.
    Last edited: Aug 14, 2013
  10. Aug 14, 2013 #9


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    It strikes me, from what you say about the junk, that you need to deal with all sorts of non-ferrous stuff too. Why not use a double seive - small holes to let the dust through and then large (gravel-sized) holes to let the gravel through. The big junk, made of all materials will be left at the end.
    I found this link, which may give you some ideas. Don't take it too seriously but you could think in terms of a scaled down version.
    I was thinking more of a sloping trough, perhaps on a trailer, which you load at the top and then agitate / bash it and the mixture finds its way down, sorting what you don't want and what you do want on the way. At some stage of the process, your magnet could come in handy.
    I remember my dad fashioned something of the sort with some perforated metal on a frame to get large stones and medium stones from garden earth. I was only a teenager at the time but it was interesting enough for me to get involved and help him. It did work, too.
    Unfortunately, how ever you do it, it will be tiring for you or expensive to pay someone else.
  11. Aug 14, 2013 #10


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    Oh well, these requests are good for a chuckle sometimes:

    A 4400 lb lifting capacity REM for lifting applications will run about US $2250.00
    The magnet itself weighs 275 lb.

    Here is a manual for such a beast:


    Of course, the manual doesn't state how you get the stuff off once it is attached to the magnet. I would also keep anything that uses magnetic media for info. storage (audiotapes, videotapes, credit cards, debit cards, floppy disks, hard drives, etc.) well away from this puppy, otherwise, all that info is likely gone for good.
    Last edited: Aug 14, 2013
  12. Aug 14, 2013 #11

    jim hardy

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  13. Aug 14, 2013 #12
    true i could take it apart and throw REM in it. Not a bad idea. I just figured that if i went with a larger version electromagnet would be cheaper. I know REM are not too expensive as long as you don't get into the large projects.
  14. Aug 14, 2013 #13

    jim hardy

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    The shop in my town is not the main factory, but they do have a fair inventory of small-ish magnets of various strengths. They have a lot of rectangular ones that you could stack between two pieces of angle iron.


    They "zapped" some for me in their big solenoid to make them quite strong.
    I'd say give them a call and see what they'd send you. The place is quiet as "the Maytag Repair Shop" so i'm sure they'll appreciate the call.

    old jim
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