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# Need assistance with an electromagnet? Answered

Hi, let's say i have a permanent magnet and an electromagnet
The permanent magnet is strong probably 50-100mt, the electromagnet is week less than 10mt, (the electromagnet being just a loop of wire, nothing inside, just air)
I need the electromagnet to capture all the lines of the magnetic field of the permanent magnet and thus make my electromagnet  stronger, They can be placed at a distence of 3-5mm from each other
I can isolate them and put them in an environement where once activated the electromagnet would offer to the permanenet magnet a path of least magnetic reluctance
Since the electromagnet is weaker (and probably has less magnetic lines) will it still be able to capture all the  lines and strength of the permanent magnet and direct it with almost no losses to the other end of the electromagnet (cause the electromagnet is quite long )
How much weaker can it be untill it becomes useless in capture and directing the entire field of the PM (10 times, 100 times)? Any advice?

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II think the magnetic fields produced by bound currents obey superposition. That is to say, if you have a current loop number 1, and you know the field surrounding it is B1(x,y,z), and a nearby current loop number 2, and its field is B2(x,y,z), then the magnetic field due to both current loops is just:

Btot = B1(x,y,z) + B2(x,y,z)

In fact this idea of superposition is sort of the basis for the Biot-Savart law,

http://en.wikipedia.org/wiki/Biot%E2%80%93Savart_l...

It assumes that every little piece of current I*dL makes a magnetic field dB(x,y,z), and you can integrate, add all the little dBs together, to find the whole field.

However, what you are suggesting is there is some kind of non-linear (not obeying superposition)

http://en.wikipedia.org/wiki/Nonlinear_system

relationship between the field of an electromagnet and that of a permanent magnet.

And I don't know if permanent magnets actually work that way or not.

I mean I had always just assumed, or been led to believe, the field of a permanent magnet looked just like that of an electromagnet, but with an unchanging DC current in it. I.e. the field of a permanent magnet is, um, "permanent", like the name suggests.

But in truth, I don't actually know how permanent magnets work. So I think the best way for you to proceed is by experimenting. Sorry if this answer seems kind of long winded.

Actually I just need a conductor that I could switch on and off at will; a small electromagnet could be a more energy efficient solution than shielding, working with a ferromagnetic conductor or trying to neutralize the field. I think that you are right, even a very weak magnetic field could still offer a path of list resistence to a stronger magnetic field.

:)

If you use a pot like design similar to the lifting magnets in wrecking yards you might be good to go.
Drill out the center of the inner "stump" to take your magnet.
The winding goes around the stump till full - you can use a spool like design and simply add the outer metal ring when done.
Door holding nagnet might be a good start point if they are not too big.
They are available in a similar design with a permanent magnet too.
Magnet can just hold the door, together with the electromagnet it is strong enough that the door is forced to stay open (can't be closed by accident).
If the electromagnet is activate with reverse polarity is is stronger than the permanent magnet and cancels the magnetic field out - the door is released and closes.

I hope this is what you are looking for as it is the only thing I found that combines magnets.
Only in ignition coils magnets are used too to created a stronger negavite spark, same pricinple though.
Coil generates a magnetic field that is the same or stronger than the one from the permanent magnet.
When the field collapses the resulting pulse with the added magnets is much stronger resulting in sparks with higher voltage and current.

Thank you for your reply, this is actually very interesting, I will take a look at those devices. Much appreciated :)

Also, I have previously seen mention of this idea of using an electromagnet with a small magnetic field, to sort of switch, or direct, the magnetic field of a big permanent magnet. For example, this patent,

http://www.freepatentsonline.com/6362718.html

includes this idea. Although superficially, it seems like this idea couldn't possibly work, because this is one of those "free energy" machines. It allegedly produces more electrical energy than it consumes.

Not sure if this is what you were looking for, but it might be, so I thought I'd mention it.

Here is how to use a PM to decrease the power loss (I^2xR) in an electromagnet while increasing the flux (attraction) and still be able to zero the flux out in order to drop a weight when you want to.

Hmmm, similar type of question, different user.....
To sum it up: you don't combine permanent magnets with electro magnets.

see latching relays then....