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enter image description hereI’m trying to teach myself electrical engineering. I am trying to make an electromagnet using a 9V battery, alligator clips, and a steel bolt.

Steps ->

  1. Wrap wire
  2. Connect power

I have no magnetism.

In fact my multimeter shows no current.

The battery is new and has the correct voltage when I connect it directly.

I have to assume that connection from - to + = 0 but everything I see online says to do what I’m doing.

It’s so simple but I’m missing something.

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    \$\begingroup\$ Picture? And a wiring diagram? \$\endgroup\$
    – Solar Mike
    Aug 15, 2021 at 18:44
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    \$\begingroup\$ Hey, don't worry. No one born as an EE. Could you explain a little more about what you did, like 1) My wire was pulled out from my old headset plug, 2) this is the picture of what I have, etc. You are at a right place to ask the question. \$\endgroup\$
    – jay
    Aug 15, 2021 at 18:45
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    \$\begingroup\$ Multimeters often have a fuse in the current circuit. It could be blown. How familiar are you with using your meter? Multimeters vary somewhat in how they do the current connection. Some require the one of leads to be plugged into a different jack for current readings. There are other possible meter-use errors. \$\endgroup\$
    – user80875
    Aug 15, 2021 at 18:48
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    \$\begingroup\$ Photos...if you're new your descriptions are nonstandard and can't be relied upon since you may not know what you are looking at or did. \$\endgroup\$
    – DKNguyen
    Aug 15, 2021 at 19:11
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    \$\begingroup\$ If you are using "magnet wire" (wire with a clear varnish-like insulation), you will need to scrape the insulation off to make contact with the actual wire - an alligator clip will not cut through the insulation to make contact. \$\endgroup\$ Aug 15, 2021 at 19:17

6 Answers 6

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Here is a nail with 80 turns of 22 AWG magnet wire connected to a AA cell that showed 1.2 V unloaded and 0.4 V connected to this coil. The electromagnet is strong enough to hold a small washer, but not attract it from any distance at all.

If you tightly wind all of the clip-lead wire around the bolt and tape it so it doesn't unwind, you might get the same magnetic results with a D cell, perhaps even a fresh C or AA. The wire may get hot and the battery may not last long.

enter image description here

Additional Information

The electromagnet shown was able to hold the approximately 750 mg washer with about 1.3 A produced by a substantially depleted alkaline AA battery. The connections were improved somewhat for the current measurement, made on the 10A range of the TEKDMM 155.

Note that the magnetic field around a single conductor produced by a few hundred milliamps can be detected with an inexpensive compass or even a compass made from a bread-wrapper twist-tie balanced on the point of a pin.

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    \$\begingroup\$ How much current flows through it? I’m surprised the coil seems to have so much resistance. \$\endgroup\$
    – Michael
    Aug 16, 2021 at 7:12
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    \$\begingroup\$ @Michael 22AWG has a resistance of 80 mΩ per meter. Comparing with my pencil I guess the diameter of the coil might be around 5 mm, that gives approximately 1.25 meters of wire with a total resistance of 0.1 Ω. My (rechargeable) AAs will deliver >4A into a dead short, so I guess roughly half of the resistance might be in the connections/contacts. \$\endgroup\$
    – TooTea
    Aug 16, 2021 at 9:13
  • \$\begingroup\$ @Michael Actually, the contact resistance won't be so bad, I messed up the last part of my back-of-the-envelope calculation (but can't edit the comment anymore). There's 0.4V across the coil, which would perfectly fit 4A across 0.1 Ω. \$\endgroup\$
    – TooTea
    Aug 16, 2021 at 9:21
  • \$\begingroup\$ The contact and lead resistance may not be trivial. The battery is in a holder with an added cheap slide switch. At 1.2 volts, the alkaline battery is considerably depleted. A alkaline AA will produce a strong deflection of a cheap compass from a single-wire magnetic field flowing through a narrow strip of aluminum foil. \$\endgroup\$
    – user80875
    Aug 16, 2021 at 11:50
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    \$\begingroup\$ In my experience those alligator cables in the OP have a resistance of about 1 Ω each. You can't really use them for anything power related. \$\endgroup\$
    – AndreKR
    Aug 16, 2021 at 12:24
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If the multimeter is showing no current then you have probably connected it wrong.

The magnet you've shown in the photo will be extremely weak. It doesn't have enough turns of wire around the nail. The more turns, the better. "Magnet wire" is a very thin wire with a thin transparent insulator. What you've used is thick plastic insulated wire.

The battery you have used isn't up to the job. Those 9V batteries are not designed to deliver high currents. If you connect a voltmeter across the terminals, you will find that the voltage goes from 9V with the magnet disconnected, to barely more than 0V with it connected.

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    \$\begingroup\$ If OP connected the multimeter "right," and if "right" means, all the current flowed through the meter, then OP almost certainly blew a fuse in the meter. \$\endgroup\$ Aug 15, 2021 at 20:14
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    \$\begingroup\$ @ Solomon Slow I wouldn’t agree ‘almost certainly’; a 9V alkaline will deliver something like 400mA at short, which is the same value as the fuse rating for some meters. That said, my $10 meter only has a 10A fuse. It’s certainly common to find that meters of unknown provenance have the fuses blown because of previous trauma. \$\endgroup\$
    – Frog
    Aug 15, 2021 at 20:22
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    \$\begingroup\$ @SolomonSlow "Industrial grade"? I thought those were just multimeters =/ I've not seen a multimeter with anything less than 10A. Not even the $5 no-name ones I get for free sometimes. \$\endgroup\$
    – DKNguyen
    Aug 15, 2021 at 21:29
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    \$\begingroup\$ @SolomonSlow They have to be way wimpier than anything else. A 9V "block" battery contains six 1.5V cells in series. Each of those cells is thus super tiny (button-cell-sized), much smaller than even an AAA. Connecting them in series makes the voltage add up, just like their internal resistance, so the current into a dead short stays roughly the same as for a single cell. \$\endgroup\$
    – TooTea
    Aug 16, 2021 at 9:04
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    \$\begingroup\$ A fresh 9V alkaline battery will deliver almost 2.5A (source: tested just seconds ago with a Panasonic consumer-grade battery from the dollar store). NiCd 9V batteries have been measured to deliver about 90A (before rapid unscheduled disassembly). It will blow the fuse on a 200mA scale very quickly. \$\endgroup\$ Aug 16, 2021 at 16:51
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In contrast with other answers I think your electromagnet should, at least marginally, work.

BUT:

9V batteries like yours have their short-circuit current in the range of 1A (and your magnet is pretty much a short circuit).

Those 9V batteries that I have used don't have any kind of protection and will become very hot as quick as 30 to 60 seconds when shorted. And it will generally be good for ~10 munites of such use if it doesn't catch fire beforehand.

If it doesn't work - something breaks. Either the battery has some "fuse" component, or the wire gets burnt somewhere (probably around the clips).

Another reason why your magnet may fail is the bolt being made of stainless steel. Is it attracted to other magnets?

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    \$\begingroup\$ "magnet is pretty much a short circuit" By magnet, you mean coil. \$\endgroup\$
    – winny
    Aug 16, 2021 at 13:15
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In addition to the other great answers mentioning you'll want to use a thinner wire (so you can get more wraps around your nail), something else you'll want to check: your nail looks like it might be stainless steel. Many types of stainless steel are not ferrous (not magnetic), so it would not be a good core for your electromagnet. You can test this by seeing how well your nail is attracted to other magnets. An iron nail would work better.

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I think if you try about 1,000 turns of AWG30 (0.25mm) on a 3" nail (should be about 6 ohms) you'll get a quite noticeable response. I tried about 300 turns and it attracted another nail from a few mm away.

Note that the open magnetic circuit is not ideal.

You have around a dozen turns actually around the core (other turns essentially don't count) and the current is being limited by the battery so the effect will be quite small.

You are getting perhaps 24 ampere-turns vs 450 ampere-turns for my test and about double that again for my suggested winding.

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Your experiment looks exactly like something I did in middle school in 1953; gives me a funny feeling that we might be related.

You probably learned Ohm's law: voltage = current x resistance. There is another form of Ohm's law for magnetism: ampere-turns = flux x reluctance. You want to maximize flux, and you are stuck with the reluctance that is determined by the size, shape, and material properties of your nail (as Effect mentioned above, make sure it is magnetic iron by testing with a magnet,) so you need to increase the ampere-turns. Since, as others have pointed out, your amperes are limited by the internal resistance of your battery, you need to make the most of them by increasing the number of turns.

There is a limit to what can be achieved, however. Once all of the magnetic domains in the nail are aligned, increasing the ampere-turns further will only slightly increase the flux. That is called saturation. If you achieve this, the nail is likely to retain some of its magnetization after the current is removed. So read more about the magnetic properties of iron, and keep playing with it.

For safety's sake, do NOT try a car battery; with the short length of heavy wire your photo shows, the very high current from a car battery will burn everything up very quickly, including your fingers if you are touching the setup! Also, do not modify your setup to create a high-velocity nail gun. You may injure someone.

You may want to look at the history of how magnetic fields around current carrying wires were first detected. I found this in Wikipedia:

"In 1820, Ørsted published his discovery that a compass needle was deflected from magnetic north by a nearby electric current, confirming a direct relationship between electricity and magnetism.[7] The often reported story that Ørsted made this discovery incidentally during a lecture is a myth. He had, in fact, been looking for a connection between electricity and magnetism since 1818, but was quite confused by the results he was obtaining.[8][9]"

The next discovery was how changing magnetic flux could induce voltage in a wire. Once those two ideas were put together, we got all kinds of devices-- motors, generators, transformers, electrical communication, and ultimately Tesla's creation of our electrical power system and radio wave transmission. (In the end, the patent office threw out Marconi's patents.) It was in the early 1800's and was an exciting time of great discoveries in mathematics, physics, chemistry, and other sciences. So connect your meter to the coil and pull the magnetized nail out of it to see if you can induce a voltage. (If that does not work, apply a permanent magnet to the head of the nail and try again.)

Here is a book you will love: The Scientific American Book of Projects for The Amateur Scientist Hardcover – January 1, 1960 by C.L. Stong (Author)

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  • \$\begingroup\$ @JRE hey, thanks for the edit! \$\endgroup\$ Aug 27, 2021 at 1:20

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