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Calculating electromagnet strength

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Calculating electromagnet strength

Unread postAuthor: JDP12 » Mon May 14, 2007 7:51 pm

Hey all,

I am experimenting with electromagnets, and I want to know how can i calculate how much weight an electromagnet can take??

I need to know because I am using it for a specific purpose...to be unveiled later.

So basically I need to know how to calculate how much weight an electromagnet can take.

Thanks guys
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Unread postAuthor: jrrdw » Mon May 14, 2007 7:53 pm

Spring scale, like the kind you weight fish on.
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Unread postAuthor: pyromaniac » Mon May 14, 2007 7:54 pm

weigh a paper clip and hang paper clips off of each other till it falls and ten count them and time's it by the weight.
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Unread postAuthor: JDP12 » Mon May 14, 2007 7:56 pm

ah..I suppose a spring scale would work good.

Anyone have any good links to making small, high power magnets?? Like able to lift 100 pounds..but small, like 1.5" in diameter.

That seems a little ridiculous..I may come up with another idea though.
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Unread postAuthor: Scope » Mon May 14, 2007 8:19 pm

Hand wrap the coils.

look into real coil guns. Same principle except you would want less of a snap in voltage and more of a steady flow.
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Unread postAuthor: jrrdw » Mon May 14, 2007 8:57 pm

Earth magnets, buy them from Ebay.
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Unread postAuthor: shud_b_rite » Tue May 15, 2007 12:51 am

This is a tricky one. Electromagnets have many different variables that can affect their performance. Instead of calculating the weight it can take you calculate the weight force in newtons. I cant find my physics book with all the equations in it but go to this site for some answers:

Scroll down to where it says "calculating the magnetic force"
http://en.wikipedia.org/wiki/Magnet
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Unread postAuthor: integral » Tue May 15, 2007 1:45 am

The paperclip idea doesn't give you the max weight, it just shows the decreasing magnetic field strength. And should we be waiting in anticipation for a potato rail gun? :lol:
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Unread postAuthor: jimmy101 » Tue May 15, 2007 10:06 am

What you want to do is not going to be easy.

Since you asked for an electromagnet, I assume it is important that it can be turned on and off (hence you can't use rare earth magnets)

An electromagnet that'll lift 100 pounds and is only 1.5" diameter is a pretty kick ass electromagnet. Probably start with a 1.5" diameter iron rod and a lot of magnet wire. I would suspect that it would take perhaps a 100' of say 20~24 gauge magnet wire.

Then you need a pretty serious power supply. A couple AA's or 9V's won't even come close. Perhaps a 12V car battery or a 10~20 Amp car battery charger. (Need to calculate the current draw and power dissipation to make sure you won't melt the wire.)

One thing to consider would be a couple 1" diameter rare earth magnets that'll hold say 80 pounds. Then add an electromagnet that'll hold the additional 20 pounds. As long as the load on the magents is greater than 80 pounds then it can be released by turning off the electromagnet.

<a href="http://www.leevalley.com/hardware/page.aspx?c=2&p=32065&cat=3,42363,42348&ap=1">Here</a> is a source of rare earth magnets (not necisarily the cheapest one). They have 1"D by 1/8" thick magnets that hold 30 pounds each (when properly backed with iron).
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Unread postAuthor: joannaardway » Wed May 16, 2007 4:00 am

I think you'll need more than 20 AWG.

I have used rare earth magnets about that size, and they have a 3,000 gauss rating, and that wouldn't come close to lifting 100 pounds of anything - they'll crush your fingers if two of them come together, but you'll struggle to lift 100 pounds with them.

My family have got this huge neodymium slab magnet that will lift about 150 pounds (it's for fishing items out of canals and rivers - we have a canal boat), but it is vast, and that only happens when the flux from both poles is linked round onto the object.

I suggest something else, like one of these lifting magnets (which will lift about 65 to 70 lbs, and can be turned on and off by some magic), or one of these, which will do the same, but about 130-140 lbs.

Ok, that's a UK site, but I'm sure that you could acquire such a thing in the US.
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Unread postAuthor: boilingleadbath » Wed May 16, 2007 2:46 pm

No magic - the lifting magnets are simply pulled away from the targeted ferrous surface by a lever (the release trigger).

And because magnetic force drops off as 1/X<sup>3</sup> or so, they are rendered incapable of pulling on the target surface very hard - they "let go".
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