Hopefully this is the correct forum,
If I place a relatively weak Neodymium magnet inside of an open air coil, and energize the coil in the same magnetic polarity as the magnet will the two magnetic forces; Add, be as powerful as the stronger of the two, create interference and weaken the output slightly.

The idea is to have a small permanent magnet always present to act upon a sensor and allow the coil to be energized to create a larger magnetic field in the same direction as the coil more or less col-linear to the field present and hopefully enhance the field.

What I don't know is if the permanent magnet will interfere with the air coils field and make the output slightly less than it could be with just the air coil alone.
Basically I hope to slightly enhance an air coil with a weak permanent magnet core that if the coil is powered down the permanent magnet still has it's full field available.

I have learned through reading that two magnets placed in the same plane close together (even touching) actual create less pull on a metal plate than if they are separated by a couple inches do to some unknown field interaction.


Thanks for any input and feel free to move this to the correct forum.
JC

 

So if an iron core enhances an electromagnet will a wire wound electromagnet with a n52 magnet as its core exceed the N52's permanent magnetic field to a higher effective field?

Another words if I wanted to enhance the field of a permanent magnet can using the winding of wire around the magnet be used to enhance the field in much the same way as the magnet is first created?

Thanks JC

 

The total magnetic field will be the combination of the fields created by the permanent magnet and the current flowing coil of wire. So if they are in the same direction they will add.

 

Thanks Marley,
The guys over at KJ magnetics said that a Neodymium magnet wouldn't make a good magnetic core as it is not much more permeable than air.
I can understand that and so the coil won't add nearly as much to the total magnetic field created by the coil as plain old iron.

Just trying to figure out a way to make an electromagnet twice the physical diameter size as a Neodymium without expensive core materials and still get as much magnetic force as an N52 magnet and without huge currents.

Building a little motor project and everyone tells me to go AC since I can do field weakening to increase RPM and overcome BEMF.

Just looking for a cheap way to get N52 power in a small size without expensive (and hard for hobbyists to find) electrical steels.
Since it would be in DC mode it could be a solid (no hysteresis) so I was wondering about using an existing magnet as the core (much less than N52) and use the coil to bring the power up. I guess that is a bad idea and I would be better off using steal for the core but now I have to do crazy math (which I suck at) to figure out the power of how many turns vs what core material and what shape to get the same power as the perm magnet... Any suggestions?

 

Hello there,

If you start with an unmagnetized steel core and add a winding and energize that winding with a DC current teh core becomes magnetized and the field becomes greater than just the coil itself can produce.
If you start with a magnet, that material is a little different in that it is made to be magnetized and stay that way. Depending on the material, the field may or may not raise the magnetization of the core, but the air core should produce more magnetic strength than with just the magnet core alone.
The problem is just how much more. It's very hard to get useful pull force with an air core so although it should increase it will be hard to detect any change unless you use a lot of turns and a decent amount of current.
You can look up the formula for the force on the web.

Electromagnets always use a steel core because the steel core takes the magnetizing force and amplifies it by the permeability of the material and this can be a factor of 1000 or more (100 to 10000 roughly). You'd need a current 1000 times that with an air core, so you can get some idea how ineffective an air core really is.
Since a magnet is not really made for this purpose, it is unlikely that it will help much either.

Magnetic circuits work in a way similar to electrical circuits. The magnetic flux travels through the material and circles around. There's no end to the flux path same as current in an electrical circuit.
To get this to work for you it may be better to form a magnetic circuit where you have the magnet as one branch of the circuit and have an electromagnet (with steel core) in the other branch but facing in the opposite direction. This would create the most pull force i think.

I am not sure of your application but it would help if you could draw a picture of everything you were thinking in your original idea. Show where you would put the magnet, and show your added coil. Show what it has to pull on too. This will help figure out the best way to proceed.

 

I am playing with printed disc motors and noticed they always have permanent magnets driving them. The efficiency is high but I was always told field weakening will get you higher RPM due to reduced BEMF such as an AC motor or alternator.

Perhaps it is different for Printed disc motors but I think not.

So I am wondering how to get large magnetic flux and still get field weakening bennefits without complicated mechanisms messing with the perm magnets.

The line of thought was to try weaker perm magnet and use a coil to increase torque at low rpm but I now know that isn't feasible.

Maybe a short magnet with iron on either end and windings around the iron. Sorta like a electro / PM / electro sandwich.

Energized i get large flux but without energized a much weaker flux but probably the best choice is regular old windings with a good core material... i am just trying to conserve space and PM is like free flux vs using some of the power to generate the field....
JC

 

Hi again,

Yes motor design requires a delicate balance between the physics of physical mechanisms and the physics of electromagnetics and electronics and thermodynamics. There's a lot to consider here so if you are serious about this it would be best to consult with an engineer that actually designs high efficiency motors. There are often insider tricks that are used in different areas of industry that the run of the mill engineer that does not do that work on a regular basis wont know.
Magnetic circuits are very sensitive to distance, so when you add length to something you reduce something else, and you add mass and volume and surface area for cooling, etc. In the end you have to be able to set up an optimization equation that will show you the best of each parameter and then you go with that. The wire diameter and length play a part too and there is even an optimization based on the target operating voltage. A voltage of 12v vs 14v would require a different gauge wire, and the actual power source would also change it (lead acid battery vs NiCd vs power line driven power supply, etc.).
What this boils down to is a problem in several dimensions where you have to know exactly how each dimension changes the design efficiency, speed, torque, etc.

 

some late info. two words, conductor size. WHAT SIZE WIRE ARE U USING. there are two aspects to solenoids that many folks do not understand. the use of too-small conductor results in greater internal resistance. and, the presence of Too many Layers in a coil results in MORE back-emf. why is this true. the current flow in any two adjacent layers is 180 mechanical degrees OUT of phase. in a generating coil, this condition is not all bad; it results in self-inductance; making a coil more efficient. up to a point. in other words, there should be Only a Few layers in a generating coil. in the case of motor field coils, all this is still true. however, a field coil should NOT be too efficient. that is, a certain amount of impedance is Desirable; so that current flow is not, effectively, a 'short'. my knowledge of field coil design is limited. so all i can say is, do Not use too-small conductor and do not have hundreds of winds. . regarding coil core material - ONLY mild, not hardened, steel should be used. because, over time, hard steel will become Permanently magnetized; and coil function will be reduced. you may know that silicon steel is 'best'. otherwise use nails or other source of mild steel.

 

Not sure, but there may be an issue with saturation.

Bob

 

not sure, why you think this or why you felt it needed saying.
i AM SURE that the ONLY way to minimize saturation issues is via the use of SILICON STEEL.