I have to make an electromagnet for my project. The role of the electromagnet is that I want it to repel a permanent magnet so that its hard to press down at that point an N42 ring Neodymium magnet (Outer diameter 26,75 mm: Inner diameter 16 mm: Height 5 mm) from around 2-3 inches distance. So that if a pulsing voltage is provided to it, it makes a vibration to be felt by permanent magnet.


I have now some results to talk about.

I bought few EM from market but they are too weak for this purpose probably not built for repulsion purpose. I have made 4 electromagnets so far with different specifications and have positive results. Now I want to get some feedback for what now on I am thinking to do based on what results I got so far.

Here are specifications & results of my 4 build EM:

I used Ferrit core of diff dia and height and enameled copper wire of diff dia. To give repulsion from more distance, I put a permanent NeoDem-magnet on top of core. It provided more distance for repul and finished attraction of core to magnet. Total distance of repulsion that felt becomes once I provide power to EM 30-35 mm with diff repulsion push from diff EMs, so 30 mm by permanent magnet that i put on the core and added 5-7 mm by EM. Under is a table listing specifications of core and wire & then how much repul each give to permanent magnet on switching ON/OFF EM. enter image description here

From these results, I concluded going for core with more diameter and using wire of 1.0 mm is way to go. Now I am thinking to use more thicker core i.e. 4cm, 6cm, and may be 8cm. I have few questions regarding this:

  1. Is there any formula or online tool available to calculate what size core with what size wire is optimum or is any rule to make maximum powerful magnet. I am thinking like there may be a saturation point so to use more thicker core than that has no effect or adding more turns only add resistance. There is one available but that is for air core online electromagnet calculator. It's very helpful though for finding resistance of coil and number turns.
  2. Any suggestion based on these results for what I am planning to do next will be very helpful.
  • \$\begingroup\$ Using a pair of fairly similar magnets I got some resistance (but not a real lot) at that distance so the real question is probably how to make an electromagnet of at least the same (but probably double) the strength of a 26.75 x 16 Neodymium magnet. I'm not sure how to calculate that but my gut feel is that it will need hundreds of watts of power. Did you anticipate having that sort of power available? \$\endgroup\$
    – PeterJ
    Nov 29, 2013 at 13:01
  • \$\begingroup\$ If I use two same N42 magnets of this measurement 2 repel,I can get a fair push at 2cm.Same kind of push I get with a 3x4cm coil where winding is 1cm & rest is metal inner core with 9V at 21 Ampere power supply.though the coil get hot very soon.I am thinking like some optimized coil may give more range?This is actually what I am currently thinking & looking.Off course increasing diameter & thickness of permanent N42 magnet can also be done.What I mentioned is what magnet currently I am using. \$\endgroup\$
    – enterprize
    Dec 2, 2013 at 15:24
  • \$\begingroup\$ 30 cm - are you sure you don't mean 30mm? Clearly your results indicate that a bigger diameter gives you force at a greater distance but this distance is only 7mm not 30 cm. What are you saying? \$\endgroup\$
    – Andy aka
    Dec 23, 2013 at 22:58
  • \$\begingroup\$ sorry,typo error,I corrected OP.Yes, 7mm by now but that much vibration is enough 2B felt as vibration is then from 30mm to 37mm.Bec from what distance repulsion is felt is one main issue so placing a permanent neodem magnet puts repulsion 2B felt at 30mm,removes attraction of core & 7mm is arm length of vib in this case.What now I want to know is about ration/extent how much can I add into diameter.I have 4,6,8cm ferrite core available,and then also current winding is 1cm deep,how about adding more layers of winding.Like if I inc core dia,should I also inc winding.Provided these r costly. \$\endgroup\$
    – enterprize
    Dec 24, 2013 at 1:06
  • \$\begingroup\$ If I place a more powerful magnet on core that is now option with increased dia of core and also use more powerful reader magnet, I hope the distance can be increased. Also when I used 1mm diameter wire with 2cm core, the repulsion felt is much more stronger. \$\endgroup\$
    – enterprize
    Dec 24, 2013 at 1:09

1 Answer 1


In my experience (using magnets and designing metal detection equipment), 3 inches is a very long way for coils that might only have a diameter of about 1 inch.

At 3 inches, if you used two similar magnets can you detect the repelling force (or attracting force)? If not then you cannot expect an electromagnet to produce anything like the same magnetic field so it won't work at that distance.

  • \$\begingroup\$ Plz see response to other comment.2 inches is what distance I am aiming but if it is less like 2 inches will also suffice. \$\endgroup\$
    – enterprize
    Dec 2, 2013 at 15:27

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