Electromagnet with lowest energisation times.

[sunny52266]

Hi there PF,

I am currently trying to make an electromagnet that is able to turn on and off at about 2-4Hz of frequency and is able to repel small neodymium magnets with about 16N of pull force.

I have tried various configurations of coils around ferrite cores. The power supply has been same with 20V of voltage and supplying 2A current. My goal is not to implement the frequency just now. I can do it later. The ferrite cores are about 1.2 cm in diameter.
1. this config had about a 100 turns of a 32SWG wire and was able to repel a neodymium magnet with about 5N of force. but the problem was that if the magnet got too close to the iron core, it would stick to the core, no matter what the polarity of the magnet or the electromagnet.
2. This config had about 200 turns of a 40SWG enamelled wire and was able to repel the 16N neodymium magnets. but the problem was the same. if it got too close to the core, it would stick to it as well.
3. This config had the same amount of turns as the second config but they were laid in a hap-hazard way. there was much air gap between the turns and there were many layers to it. the coils had the same direction of current flow, that is the layers were not opposite to each other. This config seemed to be providing the most push pull force of all, ironically. I know it shouldn't be the case.

I can build electronic circuit that changes the magnet's polarity. what I need is some advice just to build this magnet. Any help would be greaatly appreciated!

 

[Carl Pugh]

Can a non magnetic spacer be put next to the ferrite so magnet doesn't get too close?
You have all the parts required, have you tried it without the ferrite?

 

[sunny52266]

Can a non magnetic spacer be put next to the ferrite so magnet doesn't get too close?
You have all the parts required, have you tried it without the ferrite?

no mate. haven't tried it yet. Ill most probably try it today. and yes a spacer can be put in there. but this is the problem. I have yet to identify a safe distance and when the final vehicle is designed I can take that into account. Its basically part of a maglev vehicle system. I have done the levitation bit. and now this is the main concern of my project. An electro magnet.

And there is one more question, what if I use a thinner ferrite core? e-g an iron bolt or something? would it practically help the electromagnet to increase effective flux density?
It should in theory, but I was wondering if someone's tried it practically?

 

[Carl Pugh]

Ferrite generally saturates at about 3,000 gauss. Ferrite is also generally very brittle.
Iron generally saturates at 15,000 to 20,000 gauss.
An iron core say 4 inches X 4 inches may be able to operate at 4 Hz without excessive loss. Larger cores may have to be broken up into smaller cores.
An iron core is probably better for this application.

Above is strictly from theory and I have no test data to back it up.

Sounds like a fun project.
Good Luck
Carl

 

[sunny52266]

Ferrite generally saturates at about 3,000 gauss. Ferrite is also generally very brittle.
Iron generally saturates at 15,000 to 20,000 gauss.
An iron core say 4 inches X 4 inches may be able to operate at 4 Hz without excessive loss. Larger cores may have to be broken up into smaller cores.
An iron core is probably better for this application.

Above is strictly from theory and I have no test data to back it up.

Sounds like a fun project.
Good Luck
Carl

Thanks for your reply Carl. practically making these coils for myself is a challenge. I do not have the machine that makes solenoids and practically, much stuff is different from theory. Basically I do not have that kind of space to lay out my coils in the project this way. This is why I require an 'I' shape core and then have the solenoid over it. Today I measured the resistances of the coils. The 3rd design mentioned in my first post had a resistance of 5.2 Ohms and the 2nd design had a resistance of 2.4 Ohms.
And Plus, I do not have any idea where to get these Iron cores from. :S

And btw, thanks for your idea of non magnetic spacer. It worked out quite well. Thanks again.