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Small electromagnet to release neodymium magnet

03/27/2010 9:43 PM

Hello,

I would like to know if it is possible to do the following:

I have a 1/4" diameter x 1/8" thick neodymium magnet recessed approximately 1/8" down into a plastic mold. A piece of steel is attached to the top of the plastic mold, held in place by the magnet. I would like to mount a tiny electromagnet on top of the magnet (or in the space between the top of the magnet and the top of the mold) so that when the electromagnet is activated it repulses against the neodymium magnet and allows the piece of steel to be pulled away. I understand that the steel would be attracted to the activated electromagnet, but my hope is that the attraction would be minimal and that the steel could be released without much work.

Will this work? Thank you.

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#1

Re: Small electromagnet to release neodymium magnet

03/27/2010 10:04 PM

Your post is not clear.

My initial response is, just move the magnet away from the steel piece and it will be released.

Do you have a sketch?

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#2
In reply to #1

Re: Small electromagnet to release neodymium magnet

03/27/2010 11:41 PM

Hi lynlynch. Thank you for your response.

The steel piece is not fixed; it is actually being picked up by the plastic/magnet system. The issue I am trying to resolve is how to release the steel.

I've attached a sketch - hope it comes through clearly...

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#3
In reply to #2

Re: Small electromagnet to release neodymium magnet

03/27/2010 11:55 PM

I'm stuck on this thought. Forget the electromagnet. Just move the green magnet away from the red plate by some distance and the plate will be released. Your drawing indicates that you have room to increase the depth of the hole that houses the magnet.

Does that make sense?

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#4
In reply to #3

Re: Small electromagnet to release neodymium magnet

03/28/2010 1:54 PM

I've attached a revised sketch that better represents the setup. You are correct, I could create a shaft below the magnet and pull it down and away from the steel plate. The problem with this is that the connection between the plate and the magnet is extremely strong. Pulling the magnet away from the plate requires a lot of strength/work. That is why I was hoping the electromagnet scenario may be possible. I would just need to send a current through the electromagnet and the neodymium-steel plate connection would be greatly reduced.

Thanks again.

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#5

Re: Small electromagnet to release neodymium magnet

03/28/2010 10:43 PM

In machinery shops, they use a magnetic table. The magnets can be easily lowered with a lever, combined with an ex-centric spindle. Also if you tilt the magnet around an axis. you can lower the attraction too.

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#14
In reply to #5

Re: Small electromagnet to release neodymium magnet

03/30/2010 6:04 PM

Thank you for your post. This is helpful. The only downside I can see is that I need to limit the amount of space below the permanent magnet. The perm magnet is 1/8" in thickness and I'd like to keep the space between the bottom of the magnet and the bottom of the plastic mold to less than 1/8" as well. That would mean the plastic mold will effectively be 1/4" in thickness. Thanks again.

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#6

Re: Small electromagnet to release neodymium magnet

03/28/2010 11:17 PM

You could also use a screw mechanism to move the magnet in and out.

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#15
In reply to #6

Re: Small electromagnet to release neodymium magnet

03/30/2010 6:06 PM

Yes, I have considered this. However, I am in need of a "quick release" type of solution. Something that is single action would be ideal. Thanks.

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Anonymous Poster
#7

Re: Small electromagnet to release neodymium magnet

03/28/2010 11:39 PM

This might bed what you're looking for.

http://www.gap-power.com/videos/videos.html

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#8

Re: Small electromagnet to release neodymium magnet

03/29/2010 12:18 AM

Your idea won't work because setting up a (strong) electromagnet to diminish the attraction forces between thr neodymium magnet and the steel will create another magnetic connection between the electromagnet and the steel - with one possible result being that both the electromagnet and the steel would be repelled away from the neodymium magnet together. Of course you could let that happen and then after the steel had moved a bit, switch off the electromagnet. But I don't think that is what you want.

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#9

Re: Small electromagnet to release neodymium magnet

03/29/2010 5:34 AM

Hi,

if your magnet is SmCo or FeNdB then you will need a current in your electromagnet that is near 1000 amperes per mm length of the permanent magnet.

1/8 " thickness is 3.175 mm, so with Nd the current would be 1.2 * 3.175 * 1000 A or near 4500 A.

This is not an easy task.

But you may use short-circuiting a big capacitor by an IGBT.

Make sure that the current pulse is not too short to allow for the eddy-currents to decay. (20 ms needed in magnetising equipment.)

Have fun but be careful: you may shoot some debris around.

RHABE

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#10

Re: Small electromagnet to release neodymium magnet

03/29/2010 8:34 AM

Why not just use an electro magnet alone???

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#13
In reply to #10

Re: Small electromagnet to release neodymium magnet

03/30/2010 6:00 PM

Thank you for your response. An electromagnet alone will not work as I will need magnet to steel connection for long periods of time. The system will have limitations, one of which will be that it will not be able to be connected to a large, continuous power source. The best I will be able to achieve is a few D-cell batteries. I realize that this restriction throws many of the suggestions out the window.

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#11

Re: Small electromagnet to release neodymium magnet

03/30/2010 4:29 AM

Have you looked at magswitches.

Use your electromagnet to turn the knob.

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#19
In reply to #11

Re: Small electromagnet to release neodymium magnet

03/31/2010 5:03 PM

Thanks for the suggestion Randall. This type of device seems like it could work. Apparently, the mechanism is made up of (2) diametrically polarized neodymium magnets. Seems fairly simple/straight-forward. Now I just have to find a place that sells them in the size I need (3/4" diameter x 1/8" width). The suppliers I had looked at so far only carry them in larger sizes.

Does anyone have any experience working with a mechanism like this? Is it as simple as it seems (i.e. when upper magnet is positioned with N pole over S pole of lower magnet, the magnets form an active magnetic shunt. But, when N pole overlaps N pole, it provides a significant external magnetic field)?

Thanks again for all the insights.

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#12

Re: Small electromagnet to release neodymium magnet

03/30/2010 2:06 PM

Theoretically it could work as conceived, but it may not be very practical. If the required holding force of the magnet is large, the ampere turns needed for your electromagnet could be limited by the available current and/or volume of space needed for it's windings. One or more smaller vertical axis oriented magnets each surrounded by a reversing field coil surrounding it(them) may provide a more practical approach. It all depends on the specifics of your actual needs.

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#16
In reply to #12

Re: Small electromagnet to release neodymium magnet

03/30/2010 7:11 PM

Hi - thanks for the insights. Specifics are:

3/4" diameter x 1/8" thick neodymium magnet recessed in plastic mold (sketch is displayed in the original posts)

Magnet is attracted/attached to a steel plate. For the connection to be strong enough, I need the magnet to be no more than appx 1/16" from the steel.

I need a way to "quick release" the plastic mold/magnet system from the steel plate. The system will not have access to a substantial or continuous power supply. At most, a few D-cell batteries. I also need the release to be relatively jerk-free. By this, I mean that I need the disconnection to happen in a way that causes little movement to the steel plate (which is fixed, but in an unstable manner).

The magnet could be moved away from the steel plate, but ideally I want to keep the width of the plastic mold to less than 1/4". That would mean the magnet could move appx 1/8" away from the steel. I'll have to run some tests, but I believe that at a distance of 1/8", the steel could be detached fairly easily which would work for me.

Thanks again. I appreciate all of the comments and insights.

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#20
In reply to #16

Re: Small electromagnet to release neodymium magnet

04/01/2010 8:34 AM

As the specifics limit the size & volume it seems to limit a simple solution. Either the plastic part with the magnet inserted could have a lever (or screw as previously suggested) mechanism to apply the release force, or the magnet could be spring loaded laterally with a side release rod and be moved under a non-magnetic insert in the steel plate to release the holding force.

Just some open thoughts. Work on small and large relay failsafe and magnetic latching actuators (most electrical not manual actuated), but the concepts are the same - energy to magnetically latch & release.

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Anonymous Poster
#17

Re: Small electromagnet to release neodymium magnet

03/30/2010 8:03 PM

I saw a metal picker-upper that consisted of an aluminum can with a magnet inside.The magnet was released to contact the bottom of the can.The object it picked up was released by moving the magnet away from the bottom of the can.The metal stayed where it was put, and the can/magnet assembly was moved away.No electricity required.A small hand held one could be built using parts from a caulking gun to gain required leverage to pull the magnet away from the can bottom.Very simple.

HTRN

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#18

Re: Small electromagnet to release neodymium magnet

03/31/2010 3:15 AM

Just an "off the wall" suggestion: could you use a rubber suction cup instead:-

And, use your solenoid to release a valve to allow air into a hole in the back/top.

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