It was suggested that a medieval people, with a readily available source of electricity, would develop electric motors and horseless carriages. I had thought these would be too complicated to make until the 19th century. Benjamin Franklin discovered a primitive electric motor in the 18th century, but it wasn't until 1832 that it was usable for moving machinery.

The power the medieval people would have are batteries with, practically speaking, unlimited power. They can set the voltage and amperes to whatever the like, up to a gigawatt of power. There are quite a few of these batteries around, left by aliens, so I wondered what they might develop with so much electrical power.

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    $\begingroup$ My first guess is "the electric chair", but I'm a bit of a pessimist when it comes to human ingenuity. $\endgroup$
    – Erik
    Jan 9, 2021 at 20:59
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    $\begingroup$ For sure they would advertise it with "Deus lo volt" $\endgroup$
    – L.Dutch
    Jan 9, 2021 at 22:05
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    $\begingroup$ Welcome New Contributor! Just a heads up: even if you like it, don't award the green check mark until at least two days have passed. Give people a chance to find, read, and answer your question. "Accepting" an answer really puts a damper on other folks' efforts to help you. $\endgroup$
    – elemtilas
    Jan 10, 2021 at 0:58

6 Answers 6


Sort Of.

Making a thing that turns when power is applied is easy, if you have the power.
Making a practical electric motor is a wholly different matter.

Assuming you miraculously get a source of DC power. (supplied by aliens, it seems)
You still need a working knowledge of electricity and magnetism. But, again, with ample power source and minimal copperworking skill you can achieve this through trial and error.

Then you need to actually build the motor. This requires Steel (not iron).
It requires low-friction rotational mountings. Bearings. Although you might just get away with a well-greased smooth shaft.
And you need the ability and skill to make many,many,many meters of consistent thin copper wire that is also consistently insulated. Lumpy wiring or insulation leads to internal heating leads to motor burnouts.
You also need small things, like working switches, reliable wire splicing methods(not just twisting two wires together, you need soldering).

In developing your motors, you will most likely find yourself also inventing the portable, non-water fire extinguisher as an absolutely essential tool.

In short: Yes, given a free power source you can build motors. They may not be practical for use without a strong supporting technology of tool fabrication, metallurgy, and assorted other sciences.

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    $\begingroup$ What do you need the steel for? As far as I can tell, to make simple DC motor (the kind with brushes), all you need is some metal for the shaft (bronze works fine), some iron for the armatures, and lots of insulated wire. No steel. $\endgroup$
    – AlexP
    Jan 10, 2021 at 0:45
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    $\begingroup$ @AlexP you will need iron because it is ferromagnetic. It is significantly more difficult to construct an electric motor without iron. $\endgroup$
    – Alexander
    Jan 10, 2021 at 4:27
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    $\begingroup$ @Alexander: I am asking why the answer says they need steel. Iron and steel and different materials. And the point is that in the middle ages iron was cheap, but steel was rare and expensive. $\endgroup$
    – AlexP
    Jan 10, 2021 at 9:20
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    $\begingroup$ @PcMan wrought iron will work quite well, with low hysteresis and eddy current losses. $\endgroup$ Jan 10, 2021 at 14:15
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    $\begingroup$ @PcMan No, an electric motor is anything that generates a torque when exposed to an electrical potential. "Large amount" is not a requirement. As for water-cooling being a no-no, medieval people did figure out how to do things that were way more dangerous at the experimental stage than water on a motor, and once you figure out that it's important to insulate the water from the parts the electricity flows through, it's really not that hard to achieve that requirement, even with primitive materials and tools. $\endgroup$ Jan 12, 2021 at 9:55

From https://www.fleet.org.au/blog/spinning-wire/:

spinning wire

When the wire touches the top of the battery and the magnet, it is making a circuit, which allows electrons to flow – this is the current. There is also a magnetic field present due to the magnet on the bottom of the battery. When electrons move in the presence of a magnetic field, a force is created that is perpendicular to both the direction of the flow of electrons (current) and the magnetic field. This force, which is called a Lorentz Force, acts on the wire and causes it to move, which makes the wire spin around.

This would be easy to discover if the aliens have also left strong magnets. In a strong magnetic field anything with current flowing will move. It doesn't have to be a wire and doesn't need insulation.

From https://garethladley.tumblr.com/post/166922851287/homopolar-motor: homopolar motor

Without magnets the construction relies on a coil:

https://www.wired.com/2016/01/how-to-build-a-super-simple-electric-motor-out-of-stuff-you-already-have/ motor with coil

With an AA battery this would be hard to discover. It would run out and cannot put out a lot of power. But with an infinite alien battery?

  • Instead of thin wires, you can short circuit it with anything. Huge currents can flow, magnifying the slight forces that appear from incomplete coils (just a curved conductor).
  • The battery invites experimentation. It can melt metals without putting out heat. It can kill people. It can create sparks.

I think they can do it!

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    $\begingroup$ I basically just wanted to share these cool gifs. :) $\endgroup$ Jan 10, 2021 at 10:28

Building a primitive electric motor isn't that difficult--it just requires copper wire, magnetic material, and some sort of insulating material like cloth. Even though it would be be almost prohibitively expensive, it could be done far earlier than the 19th century, although due to the lack of high-density magnets, it would probably not be very effective. Here's how you'd build one:

  1. Draw copper wire. The less variation in diameter across the length, the better.
  2. Wrap copper wire in glue and fabric to insulate it and then form it into the necessary coil(s) for the motor
  3. If you want to build a DC motor, you'll need to build the graphite brushes too
  4. Spin your magnet in the coil and you've got a generator, run power through the coil and you've got a motor.

One of the major roadblocks would be the lack of permanent magnets. Neodymium was only discovered in ~1880 and modern rare earth magnets were invented in the 1900's. They would need to make extensive use of electromagnets and cumbersome lodestones if they can't find/synthesize magnetic material.

The biggest challenge is battery technology, in particularly, energy density. Only very recently (circa 2010) did batteries become good enough for high-performance applications like drones and only just now (2020) are batteries becoming good enough to seriously compete with combustion engines. If you have alien-given battery technology, it is very likely that electric motors would be discovered far, far earlier.

Many of the early electricity experiments struggled with the fact that to generate magnetic/electric fields that are measurable by primitive technology, you need a lot of electricity in the first place. For example, one of the earliest electromagnetic experiments was running power through a cable and then seeing how it affected nearby compass needles. People would presumably stumble across this much sooner if they were given infinite electrical power.

  • $\begingroup$ thanks for the answer! $\endgroup$ Jan 9, 2021 at 21:33
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    $\begingroup$ Permanent magnets are not needed -- electromagnets work just fine. We use permanent magnets for efficiency, not because we cannot build motors without them. $\endgroup$
    – AlexP
    Jan 10, 2021 at 0:46
  • $\begingroup$ Also, note that for dynamos (essentially, motors in reverse, for generating electricity at dams), the use small permanent magnets to "jumpstart" the current flow, which then feeds an electromagnet - this is because there's a maximum limit to the field strength available to permanent magnets (and practical considerations for manufacturing them), but using an electromagnet can overcome that. $\endgroup$ Jan 11, 2021 at 6:15

It's feasible, given the knowledge of what to do. Making, insulating, and winding the wire would be very expensive and manpower-intensive, and forming the shafts, bearings, etc would require some very specialized and very expensive craftsmen...things like standardized mechanical parts didn't exist before the industrial revolution, but the most exotic material you'd need is magnetically soft iron (wrought iron would work well), everything else could be brass, bronze, copper, etc. You wouldn't even need strong permanent magnets (you just need more of those expensive and difficult to fabricate coils).

However, a generator is just as easy to build, and in fact the same device can work as both. Benjamin Franklin was entirely capable of building a generator that could produce useful amounts of electricity, and motors to use it...he just didn't know how to do so. Designing an efficient and useful electric motor or generator is rather non-trivial, and required advances in scientific theory and mathematics.

These magic batteries would certainly help in developing electromagnetic machinery, but developing practical electric motors would still take a lot of time, and without an industrial revolution such machines would be incredibly expensive. They would also be difficult to repair, given the lack of standardized parts...you would need a craftsman capable of fabricating new parts from scratch.

  • $\begingroup$ Thanks for the answer! Yeah, it seems like it wouldn't be that useful, but might speed things up a bit. $\endgroup$ Jan 9, 2021 at 22:59

Frame challenge

This sort of question is quite common. It doesn't make a lot of sense in my opinion. Any society from the Ancient Greeks onwards (if not before) could have invented anything that we have today. All it requires is a stable enough civilisation which, in itself, is promoted by technological advance.

Humans were intelligent back then and could understand all sorts of concepts. If they had this magical source of power, they could use it to make simple machines which could be used to make more complicated machines which could be used to make even more complicated machines ...

All you do is shift the clock forward when exploring this sort of question. Medieval people would have been more advanced than they actually were. But so, what? If medieval people had lived in tower blocks and had iPhones, they wouldn't have been medieval in the sense we understand. You might as well construct a story in the modern world.

I hope this doesn't come off as too much of a rant. My intention is to avoid too much repetition of what I consider to be a common but unproductive line of enquiry.

Could medieval age people have built a missile?

Is it possible to erect an electric fence in medieval period?

How do medieval people fight if they can discharge powerful electricity?


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    $\begingroup$ ...to which I'll add that, per answers to the previous question, another side effect of having "free energy" is that they will likely discover improved metal smelting and (widespread use of) steam power much sooner, which is going to give them a big leg up on the other industrial processes needed to get to electric motors. $\endgroup$
    – Matthew
    Jan 11, 2021 at 13:53

what they lacked is knowledge and a drive, a purpose, and in our real history those sweet sweet infinite electricity source, gifts of gods.

in terms of craftsmanship, materials, and other necessities they were quite well equipped to the task(IDK, think of a clock, I bet u 99 percent do not know how they were made if haven't seen Click Spring videos), they just would not know how to put it all together. really, early bronze age technologies, and methods, and materials would suffice to build a practical electric motor.

but also do not forget those famous examples that - rockets were known in ancient china and some conspiratologists/historians/MythBusters even tried some of those as weapons, which may or may not be used by Koreans(?) at that time, with low-end partial success.

A steam engine, as a toy, was known since the roman empire/Greece, but it took half a millennia or more and a different civilisation to put it to work.

There is a saying that necessity is mother of inventions, and it not necessarily mean u invent when the hard time comes, but rather one puts together what u already know in a solution which then being used, along u can invent few other things but. There are multiple examples of early births of ideas or prototypes which didn't take off until later time or died prematurely or had a hard time spreading.

Bearings, wires, magnets, casting, insulation - none of that was a problem at medieval times. Heck, they even had conveyer approaches of manufacturing long before Ford made it a thing, again circa Rome empire time at least, the mass casting(mass production in some sense) was known even before them.

what were they lacking is a system of systematic knowledge and problem-solving and knowledge proliferation en masse - which today we call science or scientific methods.

So, could they - yes, absolutely; would they - unlikely, if not handwavium, batteries alone by far is not enough.

But the scientific and industrial revolution could come a few hundred years earlier.

Having a powerful electricity source you even do not need to use it in your typical electric motors to make a motor - start directly with ion engines, lol

Weekend Project: Ionic Space Thruster

Ion Propulsion - The Plane With No Moving Parts

or some turbine water combustion setup - electrolyze water and mix it with some water stream in a pipe and sparks inside and have u trusty water spitting pipe hitting water wheel type setup. as it quite easy to observe those effects, and the mechanically inclined mind can come with a certain setup.

electricity is very powerful and flexible - the way we use it is not the only way, we try to use it efficiently as it is not free, but if one has an abundance of it and does not know better ways - there are a lot of ways of how to use it.


about repacing horses, by the way, do u know what a replacement lacks of? Autopilot, and we still didn't solve that problem, lol. Yes, sure we had gotten plenty of perks by that relacement, too many to count, but autopilot was lost for a long time, until recent years.

so even if u have motors, u have to put more benefits on a plate to convince others it is a good replacement. roads are bad, so u may forget about speed, lol. No lights on roads, forget about 24.7 driving, etc. railroads are good because they solve some of those, but it is good only where it is.


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