permalloy

Hello. I need to make two strong electromagnets. I have made one with an iron core I bought at Home Depot. I wrapped some wire around it and when I hooked it up to a battery it turned out to be 0.15 Tesla. This is not strong enough for my purpose.

Would it be better if I used permalloy? (Permalloy also goes under the names Mu-metal, supermalloy, ultraperm..) What strength of the electromagnet could I expect if I used permalloy?

Where can I get permalloy? I need it in rod form, about 1.5 cm in diameter and 15 cm long, to make the electromagnets.

Thanks in advance.

Reply to
rahemanvelji
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Wrong material - saturates too easily, hideously expensive, and very touchy mechanically. Intended for very low magnetic fields.

Use transformer steel, which is easily acquired from scrap transformers.

You probably need a better magnetic circuit, and/or a bigger winding as well.

Joe Gwinn

Reply to
Joseph Gwinn

I would suggest that your problem is air-gap rather than poor choice of steel. Even though Mumetal has got a maximum permeability of about 100,000 compared with mild steel's 2,000 the mild steel still has 2,000 times the permeability of air. So a 1 thou air gap is the same as 2 inches of steel.

As it happens the saturation strength of Mumetal appears to be about 0.77 Tesla.

Mark Rand RTFM

Reply to
Mark Rand

What is your purpose, and how many tesla *do* you need?

How uniform do you need it, and over what sort of area?

Jim

Reply to
jim rozen

You do not want to even try Mu-metal - it is anti-magnetic material.

Look up magnets. Don't research metals. Magnets that work are low grade steel - easy to magnetize. So soft metal is best. Remember heat kills. Also - know the turns ratio - assume you do as you speak of Tesla.

Martin

Martin H. Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH & Endowment Member NRA Second Amendment Task Force Charter Founder IHMSA and NRA Metallic Silhouette maker & member

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Reply to
Martin H. Eastburn

The gentleman who mentioned air gaps put his finger on your problem....probably..

First, talk about cores. Transformer iron and mild steel will hold about the same maximum flux density. Wrought iron will make a slightly stronger magnet, and Hyperco, a terrifically expensive high-cobalt material will make a stronger magnet. Hyperco will support 2.2 Tesla (

22000 gauss) while ordinary iron will support 1.5 Tesla.

You must design your magnet circuit to have as little air gap as possible. The magnetic flux path, and resulting flux can be thought of as being like current through a path with a fixed battery voltage and a series of resistors. The iron is represented as a low resistance, air as a high resistance, small cross section iron pathways as somewhere in-between. For a given battery voltage, you can build a current pathway that you just cannot get to conduct 1 ampere of current. Likewise, you can build a magnetic path that you cannot get to measure

10 Tesla's everywhere.

"10 Tesla's everywhere" requires a little explanation. As you move a gaussmeter probe around a magnetic pathway, you will measure all kinds of different values. The highest flux densities generated today are made with no iron core in the pathway. . The iron simply cannot support

140 Teslas. Any coil will make 1.5 Teslas, if you put enough current through it. The flux in your existing core can be increased to the maximum the core can support (1.6 Teslas or so) by increasing the number of turns on the core and/or the amount of current you run through your core. Flux is related to Amperes*turns. So you can get there with any coil and core, if you can find enough ampere turns. I suspect you are after a certain amount of magnet pull, not a theoretical Tesla value.

Roters wrote a book on Electromagnetic Devices in the '40s that is to-this-day the best plain English dissertation on magnetic things. The book is very expensive, and out of print...but you might get lucky at a big library.

Brownnsharp

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Reply to
brownnsharp

The more you explain about what you are trying to do, the better the answers will be. For example you might get what you need by discharging a capacitor into your coil. Works for magnetizing things, does not work for holding things.

Dan

jim rozen wrote: What is your purpose, and how many tesla *do* you need?

Reply to
dcaster

How big and how strong are the questions. For a lot of uses these days, the rare-earth permanent magnets are strong enough, you just have to be clever when designing a mechanism to turn them "off". Need more holding power, add more magnets. They're relatively cheap, cheaper than magnet wire these days. Check out this supplier's specs:

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I've done business with these guys, they're fast on shipping.

Stan

Reply to
stans4

From that site:

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1" diam x 1/4" thick. 65lbs holding power! 4500 Gauss, $4.

Question: when you stack these, do the fields add? To some max, in this case 13,200 Gauss.

Bob

Reply to
Bob Engelhardt

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