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While the problems I am having span across several projects of mine, the common denominator is the electromagnet present in each project. I have made three electromagnets and none of them seem to be generating any magnetic flux. My research tells me that the determining factors of electromagnetic field strength are amperage and the number of turns of enameled wire, and my gut is telling me that amperage is the problem, but I'd like to be sure before I post another question regarding amperage.

I am using 30 gauge enameled copper for all three. Separate tests indicate that the wire is operating as it should.

Electromagnet #1 has a ferrite core that is 0.5" long and with 150 turns of wire using a total of 21.875' of wire.

Electromagnet #2 has a stainless steel bolt for the core, is 2.25" long, and has 450 turns of wire using 37.5' of wire.

Electromagnet #3 is a toroidal inductor that I wound myself. It uses a ferrite core, has a median circumference of 3", and has two wires turning around it. Each wire has 300 turns and uses 31.25' of wire, for a total of 600 turns using 62.5' of wire.

The power source for each electromagnet is a generic alkaline 9-volt battery. My gut tells me that this battery does not provide enough current, but even adding more batteries does not improve the electromagnet.

Which factor is to blame for my failing electromagnets? Am I missing something?

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    \$\begingroup\$ Your cores. If you want an electromagnet that acts like a regular magnet, then you need an iron core. Something soft, like a large nail. Hardened steel doesn't work well, neither does stainless steel. Ferrite cores don't make good magnets, either. Soft iron is the way to go. \$\endgroup\$
    – JRE
    Aug 30, 2017 at 21:21
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    \$\begingroup\$ Place a magnetic compass close to your electromagnets and see if it moves when you turn on the electromagnet. \$\endgroup\$
    – JRE
    Aug 30, 2017 at 21:23
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    \$\begingroup\$ Your project needs an electromagnet, but you actually don't know what an electromagnet is. Ferrite core - no big permeability, stainless steel - even less permeability, toroidal core - the flux has a closed path in the core. \$\endgroup\$ Aug 30, 2017 at 21:46
  • \$\begingroup\$ Different grades of stainless have different properties - most are non-magnetic. Check if a permanent magnet attracts yours - it probably doesn't. \$\endgroup\$
    – user16324
    Aug 30, 2017 at 21:55
  • \$\begingroup\$ Regarding my cores, wouldn't I still be able to perceive at least a miniscule magnetic field, almost as if I had no core at all? And also about the ferrite, I was under the impression during my research that it was a desireable core. Since it is not, under which circumstances would ferrite be beneficial? \$\endgroup\$ Aug 31, 2017 at 0:07

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This sounds like a combination of inappropriate cores with inappropriate power supply.

Do some math. The stainless steel bolt magnet has 37.5 feet of wire. #30 wire has a resistance of 103 mΩ/ft. The total resistance of your coil is therefore 3.9 Ω.

Now consider what happens when you connect that to a 9 V batteries. With 9 V across the wire, it should draw 2.3 A. That's way more than one of those wimpy 9 V clip-on batteries can source. As a result, the battery is abused and the voltage collapses. It's hard to say what current you actually get. It might be as much as a amp for a short while, but then will go down as the battery rapidly dies.

Ferrite isn't a good core for making magnets that go clink. It doesn't have the permeability of iron. Stainless steel is also not very good magnetically. With a toroidal core, it will be hard to tell from the outside whether there is much of a magnetic field inside or not. That's actually one of the points of using a toroidal core. The magnetic field largely stays inside. It therefore doesn't interfere much with the outside, and is likewise less susceptible to outside magnetic fields.

So:

  1. Use a iron rod or soft iron bolt as the core. Mild steel is OK, but stainless not, and ferrite definitely not. Test the core you plan to use with a permanent magnet. You want the one with the best clink factor.

  2. Use a straight or U-shaped core. Definitely not a O-shaped core.

  3. Use a real power supply. One of those wimpy 9 V batteries is OK for powering small transistor circuits, but not for something that takes real current like a electromagnet.

  4. Consider the power dissipation. If you had actually managed to put 9 V across your 3.9 Ω piece of wire, it would have gotten hot fast. Think about it. (9 V)2/(3.9 Ω) = 21 W! That would have gotten too hot to touch in well under a minute.

    A 5 V supply would be better. (5 V)2/(3.9 Ω) = 6.5 W. That's still a lot, but you'll have more time before things get too hot.

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  • \$\begingroup\$ Ok, so I'll work on getting some better cores. Regarding the heat of the magnet, it does actually get extremely hot very quickly, you're right. Thank you so much, that answers the first two problems. The toroid, however, is still kinda fuzzy. I know I can't really tell if it works due to it being a magnetic circuit; the reason I suspect it is not working is because my joule thief is not working properly. Excluding all other component factors in a joule thief, what might be hindering the toroid? It was my understanding the ferrite is necessary for a joule thief \$\endgroup\$ Aug 31, 2017 at 0:10
  • \$\begingroup\$ @Omni: You are confusing several different things. Inductors that use ferrite as the core material may are commonly used in switching power supplies, such as the joule thief. But, that's for a totally different purpose than a electromagnet to pick up magnetic things. Again, just skip the toroid for now. It's going to be difficult to tell when it's doing anything, and there is nothing useful it will do for your purpose anyway. Toroidal inductors are used for the electrical properties. \$\endgroup\$ Aug 31, 2017 at 12:37
  • \$\begingroup\$ Ok, thank you. This was an extremely useful post for me, as I now know where I need to do more research. Take care \$\endgroup\$ Aug 31, 2017 at 22:36

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