Making strong magnets without electricity, or making electricity from weak magnets

Continuing the discussion from Could a radio detector be built with 12th century tech?:

Every discussion about re-inventing technology days of yore gets around to the issue of magnets. Copper wire will be available far back into time, given a source of ore copper could be smelted to produce wire if necessary. Magnets are a different story. Lodestones exist in nature, magnetized iron ore that is fairly permanent. But lodestones are not easily available and what is found may be very weak magnets

Mr. Dibble presents the best way I know of to make a permanent magnet with limited resources in the linked thread:

An cold iron rod can be hammered while aligned with the Earth’s magnet field and it will become slightly magnetized. It will hold it’s field longer if kept in magnetic alignment but it has the problem that if the material is magnetically ‘soft’ enough to be magnetized that way it will lose it’s magnetic alignment easily from stray magnetic fields. By heating the metal past it’s Curie point it loses it’s magnetic alignment and then hammering it as it cools will get it aligned with the Earth’s magnetic field and it will be more permanent when it cools. But still weak. Able to pick up iron filings and tiny bits of metal only.

Now if you have magnets even weak ones, is that sufficient to make an effective generator to produce magnets the easy way with an electrical field? IIRC correctly the voltage produced from typical magnet and coil generators is based on the number of coils, but what kind of current do you get from weak magnets?

If you can’t make a practical generator with weak magnets is there a way to increase the strength of magnets through the use of multiple magnets? If you make a two large bundles of weak magnets and then hammer a new piece of iron aligned between the fields of those big magnets, do you get any more strength in that new magnet? I would assume there is some improvement over using only the Earth’s magnetic field to align the new magnet, but does it make a difference in getting to a magnet useful to use in a generator?

I’m sure someone can do a better job than I can at explain exactly how a chunk of iron becomes magnetized and what is being measured in a magnet that is significant for making generators, so I’ll just let this continue in responses.

I probably wouldn’t bother making a generator. You can create a fairly strong magnetic field using a large chemical battery and a coil of decently thick wire (thick enough that the current doesn’t melt the wire). It’s a nice, simple, electromagnet.

Chemical batteries are easy to make. Generally you just need two dissimilar metals and some electrolyte in the middle. A car battery uses lead and lead oxide as the metal plates and a mixture of sulfuric acid and water for the electrolyte. A lemon battery uses a copper penny and a zinc nail for the two metal bits and the lemon (mostly the lemon juice) as the electrolyte. The lemon battery’s big brother is called the Smee battery (named after a guy name Smee who invented it in the 1800s, I don’t remember his first name). Like a lemon battery, a Smee battery uses copper and zinc for the two metals, but instead of using a lemon as the electrolyte, a Smee battery uses sulfuric acid. I don’t think they had sulfuric acid back in the 12th century but someone with enough modern chemistry knowledge could probably synthesize it using what was available.

The amount of current that your chemical battery can produce is related to the surface area of the metal plates. If you want a more powerful battery, use bigger metal plates. A lemon battery is weak because the two bits of metal are a roofing nail and a penny, which are small. Smee batteries were designed for industrial use and were typically much larger.

I do understand batteries are a potential solution. Probably an excellent solution if you can make permanent magnets to make a generator from. Done well you could use electromagnets and only need the batteries to start it up. IIRC correctly copper, and silver if you can afford it, will make a decent battery. I’m not sure how common zinc would be if you go back far enough, but copper and silver were certainly available very far in the past.

I am still interested in finding out if it’s possible to increase the strength of magnets as described. And also curious how strong a magnet you need to make a generator. And as just mentioned, only enough to jump start a generator would be needed.

For the 12th century, zinc alloys were certainly in use (brass is rather well known!) but like a lot of metals, I don’t think anybody had yet figured out how to isolate metallic zinc. But as stated, copper and silver would probably work.

IIRC, magnesium would work but I think magnesium had also not been isolated until later.

Iron and copper should also work but probably not as well.

Also, I’m guessing you can’t use weak magnets in bulk to make more powerful magnets. Just doesn’t make sense.

If you have multiple permanent magnets, you can arrange them into a Halbach array to enhance the magnetic field (on one side).

They did, it was called Oil of Vitriol. It only starts getting written about in the next century, but it certainly existed before then, just as a guild secret of metalworkers and engravers.

Interesting. I understand how the a Halbach array makes a set of magnet act is if largely one-sided, but I don’t really know what effect that would have on making more powerful magnets. I’m not even sure what units describe the strength of magnets that applies here. Clearly it’s possible to make physically larger magnets by bundling them together, but for a given shape/size/material combination if it possible to make them stronger using more magnets.

If you can put together some batteries you should be in good shape for making a generator and magnetizing some steel. The batteries could be costly, I assume you end up with a pile of oxide when the batteries are used up. But if you can get a generator jump started and make some decent permanent magnets you shouldn’t need batteries anymore.

Bootstrap and feedback: Start by using weak magnets to make a weak generator, then feed the current back into electromagnets in the generator.

Theoretically, an automotive alternator couldn’t work unless there is some current from an outside source to boot up the field windings. Actually the residual magnetism in the rotating claw poles can be enough to start things working.

Sure, but for future use you’d want to make some better permanent magnets so you aren’t bootstrapping every time. And I’m not sure how far you’d get with bootstrapping the very weak magnets you can make without electricity. I have a feeling you can’t produce much useful current that way and your feedback will do virtually nothing.

If you do get around to making coils for any of your 12th century technology you’d do it the old fashioned way. Since you can’t pick up insulated wire at the hardware store you’d have to wrap your wires carefully around a wooden dowel or something, then coat each layer of coils with a non-conductive resin before adding another later of coils. I don’t know if common pitch extracts are conductive, but i think any similar substance properly distilled won’t be a problem. Simpler wiring could be wrapped in cloth if any insulation is needed.

Allegedly, oil of vitriol was extracted by Jabir ibn Hayyan as early as the 8th century. There is some dispute about the discoveries, or even whether the man actually existed (vs. being a pseudonym of multiple people). Regardless, it’s plausible given that it’s a fairly simple process given the right reagents (sulphate minerals).

Insulating material is easy, if it doesn’t have to flex. I’d probably use wax, but tar or pitch should be just fine, too. Even into the 20th century, cotton soaked in tar was commonly used to insulate wires.

You also don’t need very much insulation for a functional magnetic coil, because the voltage difference from one loop of the coil to the next will be very small. In modern coils, it’s usually just a thin layer of oxide or enamel, so thin as to be transparent.

Silk was the traditional insulator.
For many years shellac served to insulate coil wire so talking to the local artisan woodworker would likely yield a suitable lacquer. As noted above, tar, pitch or wax would probably also work.
I suspect that a suitable coil winding wire could be made by drawing a hot wire through pitch.

Quenching a red hot rod of carbon steel whilst it is immersed in a magnetic field would probably yield a magnet of good permanence.

Soft iron can be used to create useful magnetic circuits, and arraying magnets used to bootstrap up higher fields. So maybe from little magnets great ones can grow.

Otherwise, big coil and big battery. Sulphuric acid, copper and zinc, all available are enough for a Daniel Cell. Again, build a proper magnetic circuit around the target and experiment with quenching a hot steel target.

If there’s a way to increase the strength of magnets using other magnets of not greater strength than it is well hidden, and I think impossible. The unit of measurement of concern is gauss. Pull strength is a popular measure of magnets also but wouldn’t apply in making generators. The total power produced through a coil passing through a magnetic field is calculated from the square of the gauss, and using Faraday’s law (I think) you can derive more about the power a generator can extract based on the number of coils and how fast you can move the coils through the magnetic fields (or vice versa). Also, the optimal size and shape of magnet for a given weight of material, fully saturated is a cylinder with a length equal to it’s diameter. Lengthening the magnet may reduce it’s strength because more material is further away from the pole end of the magnet. Widening the magnet reduces it’s strength at any point on the pole end. It does not seem like the gauss strength of magnets can be increased without greater gauss.

The rest I’m not sure about, but I think current produced is limited by the magnetic field you have. A magnet produced by hammering while aligned with the Earth’s magnetic field can be several orders of magnitude stronger than the Earth’s magnetic field but it’s still extremely light. A generator can be rotating magnets or coils at ridiculously high speed with such very small magnets, far smaller than practical to extract maximum power based on such weak magnets, so bootstrapping a generator with weak magnets will require a very large number of coils and magnets to produce enough power to make larger magnets, if it works at all, I don’t know if there is enough current to overcome resistance alone in the coils, plus something I have to look up about generators, there may be different force resisting the generation of power that I don’t understand yet (aside from the force needed to move the generator).

Certainly for the purpose of travel to the past a battery will be the easiest way to get a generator started. If done with some foresight you’ll only need the batteries to work for a short time.

Final thought, lodestones are chunks of magnetite that are believed to have been magnetized by lightning strikes. There should be a powerful magnetic field around a lightning bolt that would magnetize the right kind of material. Let your imagination run wild on that concept.

These statements appear to be at odds with each other.

I meant using magnets alone in the first statement, but that doesn’t really matter. If does seem the initial magnet made by hammering has increased in strength from the Earth’s magnetic field, or so it seems.

I did not uncover anything to explain that and it leaves an open question, can the hammering process make a stronger magnet in the magnetic field from two magnets previously made by hammering? What is exactly happening with hammering that allows that initial magnet to be stronger than Earth’s magnetic field?

The simple explanation for magnetization of a hammered piece of steel is that the hammering allow magnetic domains in the material to align with an external magnetic field.

The earths magnetic field is very weak:
*Earth’s magnetic field is about 0.00005 tesla.
*The Earth’s magnetic field has aflux density of 25–65 microteslas (according to Wikipedia) whereas typical flux densities used in generators are nearer to 1 Tesla.
So, the Earth’s field is ~50 millionths of that used in a typical generator. Not really a practical proposition.

The Earth’s magnetic field does not appear to be very ‘strong’ by some measure or else we would see iron filings or magnetite sticking to nearly every piece of magnetic material. There is a ton of magnetite everywhere, drag a magnet along the ground in most places and you’ll find bits of black magnetite stuck to it. This doesn’t happen with any old piece of steel or iron. So a magnet made by hammering must be ‘stronger’ by some measure, but what measure?

Lots more questions than answers now. But site after site says you can only increase the ‘strength’ of a magnet with a stronger magnetic field, whether from a permanent magnet or an electromagnet, yet something is happening when a piece of steel or iron is hammered in the Earth’s magnetic field that appears to be an increase in ‘strength’.

ISTM one fundamental constraint is Gauss’s law, namely that the divergence of the magnetic field be zero. But you still have the possibility of “increasing the strength” of magnetic circuits using ferrite cores and other arrangements possibly involving multiple magnets and/or electric current.

The term strength of a field is I’ll defined here. It is quite possible to create a local increase in the field with material of low reluctance. But as noted above, Gauss’s Law requires that the divergence is zero. Not that a given small volume cannot contain a stronger field. Lots of weak magnets can create a small region of high strength in a suitable circuit.
A good example of this is the gap in a loudspeaker motor where the voice coil is placed. Local field strength in the gap is much higher than would be found around the naked magnet.

Making a magnet by striking iron on an anvil is probably helped by a local increase in field strength around the anvil.

I think you can make a pretty strong permanent magnet with the wire that grounds a lightning rod, if it gets struck. I think ferromagnetic objects close to the conductive path lightning takes get magnetized without even being wound, just being near a single pass of wire.