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Ferrite electromagnets

Ferrite electromagnets

Good day,

I need to build a two dimensional magnetic levitation , but the problem i'm having is that the electromagnets are very sluggish in response time.

Would a ferrite core work better then normal mild steel? I'm controlling the current with a PWM signal at about 4kHz.

What other materials (for cores) would be suitable for quick response?

Thank you,
Brett Duncan

RE: Ferrite electromagnets

Ferrite cores will have a faster response time.

RE: Ferrite electromagnets

thanks MagMike,

I have searched extensively to try and locate ferrite rods with diameters between 15mm and 25mm in South Africa, do you perhaps now of a good source to purchase similar sized ferrite rods?

Could I also get a bunch of smaller rods and bind them together with epoxy to form a larger core? Will this work?

Thank you,


RE: Ferrite electromagnets

I'm based in the US.  Unfortunately, I do not know of a source in South Africa.

Smaller rods bunched together will work, although any spaces between neighboring rods will "dilute" the performance a bit.

RE: Ferrite electromagnets

Thank you once again MagMike,

I have searched extensively regarding ferrite rods? Will you be willing to help me out in getting some rods and shipping them to me. I will wire the money from a bank here to you over there.


RE: Ferrite electromagnets

Sorry, I won't be able to help you with that.

RE: Ferrite electromagnets

thanks MagMike,

Just a question regarding want I want to do. The formula that I'm using to calculate the number of turns, etc. is

V = 4.44 * N * f * Omax

where Omax = area * Tesla rating

Do you thin that this formula will actually work?

Thank you,


RE: Ferrite electromagnets

I can't say if a given formula will work.  You haven't provided nearly enough information to make a decision.  Aside from mentioning magnetic levitation, you haven't given much information as to what you are trying to do.

Formulas are just useful for describing behavior within certain parameters.  You need to have an understanding of what goes into them, why certain variables are present and, most importantly, their range of validity.

RE: Ferrite electromagnets

Thanks again MagMike,

Here is a break down as to what I'm trying to do.

It needs to be a two dimensional levitation system whereby a user can change the position in the vertical and the horizontal axis. Firstly, the system must perfectly levitate the object and then be able to externally (via a POT)change its position.

Please find attached my current design that I'm working on.

I will be using a DSP. The output of my DSP will use PWM (at a frequency of about 25kHz - it doesn't have to be this frequency though) that will control the current throught the magnets. That is why I will need to use a ferrite core electromagnet so that I can swtich at those speeds. I will be using Hall effect sensors as feedback for my system

My first biggest problem is designing the magnet. The formula that I posted earlier is the one that I will use for the design of the electromagnet.

Can you please give me some feedback as to what perhaps I should look out for and perhaps help me out with the electromagnet design using a ferrite core.

Thank you and kind regards,



RE: Ferrite electromagnets

Magnetic levitation is very unstable. As you have begun to understand the response time in your electromagnets is an issue. There is only going to be one 'sweet' spot here and the forces that want to move the object out of that are much faster than your electromagnets can respond.  


RE: Ferrite electromagnets

I couldn't agree with MJR2 (Mike) more.  The magnetic interation of the side electromagnets is going to prevent any stable levitation.  The fields from the side electromagnets will travel to the center electromagnet as well as the permanent magnets in ways to prevent stable levitation.

RE: Ferrite electromagnets

no this is not a school project.


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