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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.

aaaaa says reinstate Monica
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The Thinkrium
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    Picture? And a wiring diagram? – Solar Mike Aug 15 '21 at 18:44
  • Welcome to EE.SE. Add a photo and some punctuation. A 9 V (fire alarm) battery isn't going to be good enough anyway. – Transistor Aug 15 '21 at 18:44
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    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. – jay Aug 15 '21 at 18:45
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    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. –  Aug 15 '21 at 18:48
  • What do you mean by "I have to assume that connection from - to + = 0 "? – Peter Bennett Aug 15 '21 at 19:02
  • I am using a regular alligator clip to wrap the zinc plated bolt and applying a 9 volt battery to the aligator clip . 1 clip wrapped and the 2 ends are attached to the -/+ – The Thinkrium Aug 15 '21 at 19:05
  • Well I’m getting no current when I attach the leads and my first thought is that they cancel each other out- that assumption DOES NOT make sense to me- but it’s not working and I’m in problem solving mode – The Thinkrium Aug 15 '21 at 19:09
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    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. – DKNguyen Aug 15 '21 at 19:11
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    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. – Peter Bennett Aug 15 '21 at 19:17
  • I have edited the question to include a message and i have also tried regular copper wire but i wasn't sure if i scraped the ends enough – The Thinkrium Aug 15 '21 at 19:53
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    I was expecting a picture of your multimeter too to see if you were measuring current probably. But in your photo, too few turns and vastly overestimating how much current and power 9V battery can produce (as many beginners do). For that number of turns to have any strength you need a much higher amperage battery and it would produce a lot of heat. You WOULD notice this. – DKNguyen Aug 15 '21 at 19:59
  • Ok I can appreciate what you are saying I am not wrong about my procedure but need more wraps, power ( either/or/both). Have I got that right – The Thinkrium Aug 15 '21 at 20:01
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    Get like 22AWG wire at thickest that is SOLID, Solid wire maintains shape. You can see your stranded wire wants to pop off the coil. Don't use wire with clips on the end already. Magnet wire is made for this but requires scraping the insulation at the ends. Wind neatly, tightly and make many turns (100+) – DKNguyen Aug 15 '21 at 20:04
  • I really appreciate all your input I can’t work on it right now but I will update you guys soon with the results – The Thinkrium Aug 15 '21 at 20:12
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    Those look like cheap alligator jumpers. I got a bunch from eBay myself, and they are very poor quality, and only make connection if wiggled just right. Also, the wire inside cheap jumpers is very thin, you may have burned the connection open. You'll need to get more turns of wire to get a noticable magnetic effect. Find a very small gauge wire, and wind 100+ turns of it, and then see if it works. I think you'd be better off with a AA or C battery to power it. – Mike B Aug 15 '21 at 23:14
  • This might help a bit: ***Help with homemade electromagnet*** - Asked 3 months ago Active 3 months ago Viewed 2k times https://electronics.stackexchange.com/questions/562814/help-with-homemade-electromagnet/562827#562827 – tlfong01 Aug 16 '21 at 01:38
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    Is the battery dead? Short circuiting a battery like that is liable to make it discharge all its energy pretty quickly. If it's a rechargable battery, you might want to consider recharging it and trying again. – nick012000 Aug 16 '21 at 08:37
  • No current? Check using ohmmeter setting of your multimeter through the clip wire. Maybe it has an open. By the way this isn't the best way to do this. If you could invest in a small power supply it might go better. And someone mentioned magnet wire, which is a good idea for this case. I'd start with 28 AWG and use lots of turns. And also a lower voltage high capacity battery might work better, like a classic 1.5v cell. Also is the screw made out of ferric metal or is it aluminum ? – Patrick Taylor Aug 17 '21 at 12:15
  • Get a bigger nail too - even if your wire were longer, you wouldn't be able to fit enough loops around that thing to produce all that much of a magnetic field. – Darrel Hoffman Aug 17 '21 at 13:36
  • Too few turns and that battery is now dead. –  Aug 17 '21 at 18:33
  • I once did this and was very confused why current was flowing but there was no magnetic field. Turns out stainless steel nails don't work well for this purpose. – Stephen Collings Aug 17 '21 at 20:38
  • I wonder if the bolt is actually aluminum or stainless steel. Neither would work as well. Does the bolt stick to a permanent magnet? – computercarguy Aug 17 '21 at 21:58

6 Answers6

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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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    How much current flows through it? I’m surprised the coil seems to have so much resistance. – Michael Aug 16 '21 at 07:12
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    @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. – TooTea Aug 16 '21 at 09:13
  • @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. – TooTea Aug 16 '21 at 09:21
  • 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. –  Aug 16 '21 at 11:50
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    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. – AndreKR Aug 16 '21 at 12:24
  • Key point - AA (or C, D, AAA) batteries have a significantly higher short-circuit current than a 9V battery (which is really just 6x 1.5V cells in series). 9V is optimized to deliver higher voltage but lower current. AA/C/D delivers lower voltage,but at a higher current. – J... Aug 17 '21 at 16:55
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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.

Simon B
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  • Since magnetism is a vector and I can add them by wrapping more can I get away with a 9v – The Thinkrium Aug 15 '21 at 20:10
  • @TheThinkrium It all depends on how strong a magnet you want. With enough turns of fine wire, even a 9V battery could power a small and not very strong electromagnet. – Simon B Aug 15 '21 at 20:12
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    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. – Solomon Slow Aug 15 '21 at 20:14
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    @ 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. – Frog Aug 15 '21 at 20:22
  • @Frog, I stand corrected. I was guessing that a 9V, "alkaline" battery could source about one Amp into a dead short, but I couldn't find a data sheet to back up my guess. Seems like they're wimpier than I thought. Also, yeah, I've seen "industrial-grade" multimeters with a 10A scale and a special port for the (+) lead that goes through an internal shunt. But those cost more than the "hobbyist/homeowner" grade meters that some of us own. – Solomon Slow Aug 15 '21 at 20:45
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    @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. – DKNguyen Aug 15 '21 at 21:29
  • @DKNguyen I once (as a high school student) had a multimeter with no 10A range. 200mA maximum and of course I blew that fuse the first time I tried to measure something. – user253751 Aug 16 '21 at 08:48
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    @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. – TooTea Aug 16 '21 at 09:04
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    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. – Spehro Pefhany Aug 16 '21 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?

fraxinus
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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.

JRE
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effect
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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.

Spehro Pefhany
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2

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)

JRE
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richard1941
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