electromagnetic project

[jake598]

I have an idea. Well that is the first step I guess, but with limited to no experience in electronics this is going to be a long road ahead.

I want to be able to control the magnetic force from an electro-magnet with a dimmer switch (if this is possible). Rather than a 'sucking' type magnet I am after a 'pushing' type (i know that isn't the right terminology).

The dimmer switch is there as I want to be able to control the distance static magnets will be pushed away from the elctro-magnet. The maximum distance it will have to propel the static magnet away from the electro-magnet is 50cm.  Hopefully I can get a smooth transition when dimming the electro-magnet.

I know this is slightly confusing as I am un-aware of the correct terminology but if anyone is able to help me with what sort of magnet and materials I would need to start, and if you have any ideas to constructing this apparatus, it would be greatly appreciated.

Cheers!

[Bluechip]

Hi Jake
 
Welcome to Madmodder ...
 
If the solenoid is AC, then you can, in theory control it with a dimmer.
 
You do need a solenoid that is continuously rated, many have a duty cycle.
 
However ...
 
Electromagnetic force at 50 cm 
 
You will need one helluva  solenoid ....
 
I think we need some more details ...
 
Unless I've got something wrong ... not unknown     
 
 
Dave BC

[HS93]

I think you may need a yard of track from a magnetic levitation train. 

Peter

[andyf]

Hi Jake,

Apart from the distance, which would probably involve currents far beyond the rating of a dimmer switch, there is another problem. Dimmer switches run on AC, and if you run your electromagnet on AC the magnetic flux will switch with the AC, with the poles  switching rapidly between (in normal magnetic terms) north and south. This doesn't usually matter if you are trying to attract a piece of iron as in an AC relay coil, but if you are trying to attract or repel a magnet with its own N and S poles, there will be a problem.

I suppose you could rectify the AC coming out of the dimmer and run the electromagnet on DC, but again the currents involved would be huge for the distance involved. The coil would heat up, too.

If you just want to levitate an object magnetically, see http://en.wikipedia.org/wiki/Magnetic_levitation , but note that it only works with materials which can't themselves be magnetised either temporarily or permanently and the distances involved are generally short.

Andy

[jake598]

blue chip,

This is my amateur cartoon sketch of generally what I would like to achieve. By having a blanket of magnetic beads (I was thinking of the magnetic stone hematite) on top of a 'electro-magnet'. Hopefully this moveable 'skin' is able to be contracted and retracted through magnetic force, and hopefully the amount that the 'skin' (beads) retracts is controlled through a device similar to a dimmer switch.

I just thought that the dimmer switch would be a practical solution but I think this is proving much more difficult than I imagined.

It seems a bit abstract but it is all in my head

[John Hill]

I think the dimmer idea is OK in as much as that is likely to be the least of the challenge.  If you want to make a variable electro magnet then yes you can plug your simple rectifying power supply (i.e. DC power pack) into a lamp dimmer and you will get variouable strength of the electromagnet.

But I am having problems visualising the magnetic circuit of what you are trying to do,  can you confirm this is a 'blanket' and not just a string of beads you are trying to control?

[jake598]

John Hill, It will be a membrane of tightly woven beads so that it can cope with the flexibility of changing shape. I have seen there are a few types of electro-magnets. Would you have an idea of what to purchase, and the amount of force on it needed to achieve what I am am trying to do. Thanks a bunch for your help.

[picclock]

Hi Jake

I don't think the dimmer approach is likely to work - especially over the 12" 50cm distance you require. If you just want to control it with a knob have you considered using another magnet with a rack/pinion drive. This would allow you to turn a knob, raising or lowering the controlling magnet as required. If it needs to be controlled electrically you could use a stepper motor to do the raising/lowering. Controlling an electromagnet which could lift the weight of your 'blanket' to a height of 50cm will create real issues, especially to anyone with magnetic material standing near.

Good Luck

Best Regards

picclock

[HS93]

also keep people with pacmakers as far away as possable.

Peter

[BillTodd]

Rather than a 'sucking' type magnet I am after a 'pushing' type (i know that isn't the right terminology).

I think you need to do a little research... 

A magnet will only repel a like pole of another magnet i.e.  a north pole will repel a north pole. Unfortunately, magnets always have two poles; There are no magnetic monopoles in nature.

A magnetic field will normally only strongly attract ferromagnetic materials  e.g. Iron, Nickel and their compounds.

There are a couple of odd exceptions:

One is the special state of Super-conductivity.  In a super-conductor, the electric currents induced by the external magnetic field will produce an opposing magnetic field, so producing an opposing force between the magnet and superconductor.

The other is a weak force called Diamagnetism. Some materials (e.g. water) can produce a weak opposing field in the presence of a strong magnetic field  (enabling a crazy scientist to float a tiny frog in a bead of water, placed between the poles of a very strong magnet see - http://en.wikipedia.org/wiki/Diamagnetism)


In effect this means your electro-magnet will always attract your beaded material.

Bill

[edit]

Another approach to 'floating' on a magnetic field is to use an AC field to induce a field in a non-magnetic conductor

For instance you can use an AC electro-magnet to lift an aluminium sheet. The problem here is the induced current in the aluminium will heat it considerably, and the force of the field drops with the square of the distance.

[John Hill]

Jake, I suggest starting with a strong magnet  ( you can buy 'super' magnets that are strong enough to be dangerous) and experimenting with your beads.

Magnets dont come in 'sucking' and 'blowing' varieties, a simple magnet has two poles which are usually at each end and are referred to as 'north' and 'south'.  When the north pole of one magnet comes near the south pole of another they attract, but two like poles will repel. 

This means the magnetic beads must all be aligned with all the beads having the same pole on one side of your fabric, the beads will not like this and will try to flip around!

So, again, my suggestion is to experiments and find the major issues using permanent magnets,  the electro magnet questions will be easier to solve when we know more about what is required (which we learn from your experiments)

John

[jake598]

Thanks for all of your feedback so far, I’m going to attempt to see how it eventuates this weekend. I’ll keep you posted with the results. This is project is quite different to my usual occupation and interests so the results should be ‘interesting’.