# Homemade solenoids and professional solenoids

Hi. I tried to make a homemade solenoid and it sucks. The copper has tight little humps in it and it wants to spring out of the compressed coil configuration instead of staying compressed onto the iron.

I looked on youtube but I haven't found any good tutorials yet. What is the best way to make a homemade solenoid? I noticed that videos of professional solenoids seem to reverse the direction of the coils instead of looping back to the start of the coil with a straight line. Wouldn't this reverse the direction of magnetism and cancel it out?

hutchphd
Homework Helper
Use a variable speed drill. Any sailor knows that every time you "wind" a coil loop you put one complete twist in the rope.....so spin the mandrel.........no twists. You can make some nice coils with a little practice.
Yes reversing the direction is probably not wise for the reason stated.

Thanks. I will probably end up buying a new drill, the drill I have is too weak for my needs.

Do the twists cause problems with the actual electromagnetism? Or/and does it just cause problems such as just not coiling as tightly as it should, such as increased springing and less compression.

I looked in the rules, I don't see a rule against posting double posting (2 consecutive posts in a row), so I guess I will post this here. If double posting is not allowed, I would not mind if the post was added as an addendum to the post above this.

So, I guess my other question is, what is the best video to learn solenoids? I have looked at a lot of videos, they don't seem to address the math of coils stacked on coils. Most of the videos seem to be missing vital information. My physical health is not the best, so I like to have videos that have 3d or 2d animations and music, or else I start to feel physically unwell. I encountered a 5 minute video, that said the "ideal solenoid" has a length longer than its radius, this makes no sense in terms of the general magnetic equations, since its strength diminishes with length (/length.) Length meaning length of solenoid, I assume this means the length of the solenoid itself, not the total length of the copper wiring. For this to be resolved, I assume the induction equations play a role here which makes radius become a detrimental attribute. I would like a video to combine both the induction and magnetic equations into a comprehensible and ergonomic video that has 3d or 2d animations and music.

Third question, what is the equation that addresses humps or imperfections in the copper itself? For instance I buy a copper wire already poorly spooled onto a plastic spool in random config. The copper has various bends and imperfections in the shape of the wire, what is the equation that tells me how much a 1mm or 2mm hump in the wire will affect the overall magnetic output, in terms of deviation from a perfect circle?

Fourth question... would it be safe to use a household extension chord to create an electromagnet? Wrapping it around an iron core? Plugging it into some kind of charging device so the current moving forward is less current than going back into the wall?

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hutchphd
Homework Helper
1. Does a book work for you?
2. If the solenoid is not "long" then the simple equation for the field is not true
3. When you uncoil the wire do not pull it off the end of the coil That will put twist into the wire. Put the spool on an axle and let it rotate as wire unspools. Bought wire should be smooth. And use enameled wire because you can get more turns in a given space. All that matters is more turns (so smallest diameter loop and closest packing) for a given size wire
4. Safe depends upon how much current. Even with low voltage wire can get hot quickly. There is nothing unsafe about 18 gauge "zipcord" wire. Obviously household voltage is not safe at all.
Are there any design requirements for this project?

I generally don't have the attention span to read long books, but I will read a book if it has equations and next to each equation describes exact physical property and gives the context of application. Any particular book you recommend?

I am building a cylinder solenoid wrapped around the axis, not toroid fanning from axis. I assume the cylinder is what is meant by "long" solenoid.

Does copper having twist in it disrupt the flow of electricity/magnetism in the solenoid? The reason I ask is because I may have already twisted this wire already. I have also heard that twists can speed up the speed of water currents, so in that vein, I wonder if twists can enhance the solenoid, or if it has no effect on the current.

Would putting the 120v household wire into a coil, increase the temperature? The heat equations list current as the factor. What is the exact equation of heat produced from straight line compared to, heat produced from coiled around a ferrous core?

No requirements yet. Just trying to get a better and more solid understanding of solenoids.

berkeman
Mentor
Hi. I tried to make a homemade solenoid and it sucks.
Would putting the 120v household wire into a coil, increase the temperature?
Please don't try to use AC Mains power for your project directly. It is very apparent that you don't have the background to do it safely (deadly shocks, fire destroying your home, etc.). That is not meant as an insult, just a practical limit on what you can do so far in your projects.

Instead, use an off-the-shelf DC or AC power "brick" to give you a safe way to have power for your projects. If you need AC, use a safety-approved transformer to give you your AC source. If DC will work, you can use lots of available DC power "bricks" that are used to power laptops, etc.

Can you say more about what your project is, and why you need a solenoid? The more you can tell us, the better we can help you.

BTW, for winding good quality solenoids and transformer coils at home, consider purchasing a simple coil winder. They are fairly cheap, and are definitely worth the investment if you are going to be winding many coils for your experiments...

https://images-na.ssl-images-amazon.com/images/I/417FOYheouL._AC_.jpg

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hutchphd
Homework Helper
I absolutely concur with the above sentiments. The kinks and bends in the wire will make little direct difference in performance although they may produce mechanical failures (shorts or breaks in the wire). The only performance issue is the more compact winding gives more turns .....so neatness does count a little.
You need to be careful of hot wires and, if you have big coils, back emf when disconnecting. Be safe and have fun.

jrmichler
Mentor
tried to make a homemade solenoid and it sucks. The copper has tight little humps in it and it wants to spring out of the compressed coil configuration instead of staying compressed onto the iron.
Start with the wire that is designed for exactly this application. It's called magnet wire. Two sources (not the only sources) are McMaster-Carr https://www.mcmaster.com/magnet-wire and Allied Electronics https://www.alliedelec.com/wire/magnet-wire/. Lamp cord has very thick insulation, so you can only get a few turns.

Then you need to, as mentioned above, wind the coil by turning the iron core while the wire unwinds from the spool. The unwind spool turns, the wire does not curl off the end. You can do this with a coil winder or by rigging a hand crank. A hand crank will get the job done. When I was in high school, I made a 10,000 turn coil using a hand crank, and counting turns. It was tedious.

Normal practice is to start at one end, wind a single layer all the way to the other end with each turn tight against the previous turn, then wind another single layer on top of the first layer to the other end, then repeat until finished. If you can wind 5 or 10 layers and still have it laying flat, you are doing very well.

You need enough back tension on the wire to pull it down onto the iron core. If using a hand crank, you can hold the wire with one hand while using the other to turn the crank. Use just enough back tension to pull the wire down snugly onto the iron core. Too little back tension will cause the wire to flop around loosely, too much back tension will damage the insulation and cause short circuits.

When you stop winding, the wire will try to spin itself loose. Wrap it with tape to hold it in place. You need to hold the wire tight with one hand, keep the iron core from spinning backward with another hand, and wrap tape around the finished solenoid with your third hand. Either find a way to lock the core from turning, or ask somebody to help.

If you tell us what you want this solenoid to do, and tell us what you have available for power, we can help you figure out what size wire to use and how many turns will be needed.

Be aware of the danger of playing with mains voltages! Many. many years ago I attemped to make a transformer by winding a number of turns of household wire around a simple iron bar, wired a plug on the end and plugged it into a outlet(we use 240volts here ,by the way). Resulted in a nice flash and burned the wires off the back of the outlet. Luckily I had enough sense and knowledge to rewire the outlet but sadly not enough knowledge to replace the fuse wire(just as well it blew, or I would have been working on live wires). Parents wondered why the fridge wasn't working when they got home! Lesson, Don't mess with mains supply unless you know what you are doing!

DaveE
Gold Member
I noticed that videos of professional solenoids seem to reverse the direction of the coils instead of looping back to the start of the coil with a straight line. Wouldn't this reverse the direction of magnetism and cancel it out?
The direction of the magnetic flux doesn't really depend on whether the coils go from left to right or right to left across the solenoid. It depends on whether the windings look like they are clockwise or counter-clockwise as viewed from the coil axis. For example, if you have a coil wound on a spinning shaft, the only way to reverse the direction of the magnetic flux would be to reverse the rotation of the shaft.

There is a lot of technique to how magnetic windings are actually implemented and why you may wind in a"Z" pattern or crossover to wind in a parallel fashion, mostly related to dielectric strength and winding capacitance. But that stuff is much too subtle to get into here.

If you want to learn more search for transformer winding techniques, you'll find a lot more info than if you search for solenoids.

Finally, you don't need high voltage (like the mains voltage). You want high current which will be at a low voltage for any solenoid you make at home. Plus, as others have said, it's dangerous for people to mess with if you don't already know a lot about electronics.

Third question, what is the equation that addresses humps or imperfections in the copper itself? For instance I buy a copper wire already poorly spooled onto a plastic spool in random config. The copper has various bends and imperfections in the shape of the wire, what is the equation that tells me how much a 1mm or 2mm hump in the wire will affect the overall magnetic output, in terms of deviation from a perfect circle?
Small humps and and bends are quite common, but does not really matter as long as you have 1-layer coil. Difference like 1-2% in inductance. For multilayer coil, humps are interfering with the copper density, therefore for fixed volume solenoid, you will be losing inductance due imperfect packing (inductance is proportional roughly to square of number of turns).

I frequently winding an inductors by hand. To reduce humps, basic rule is to avoid bending or twisting of conductor before it is already in correct position. Grab wire by fingers only at one point near coil. Let source of wire to be as unconstrained as possible. If wire is already permanently bent, discard that wire.

Thanks, this has been very enlightening for me.

I don't have a particular solenoid in mind, I am looking to build various solenoids, such as a solenoid of max tesla, or a solenoid of max efficiency, also motor solenoids or generator solenoids. As well as just generally trying to understand solenoid theory. So that maybe I can eventually build a computer simulation of solenoids, without having to purchase the wire beforehand.

After reading this, I am definitely not going to wrap a household wire around anything lol. I don't have a handcrank, so I will have to purchase a coil winder. I am not sure if AC or DC is better at making solenoids, but I will look into transformer information instead of solenoids. The youtube videos I've seen that are about solenoids are pretty vague. I did purchase magnet wire from amazon, however I think it may be too short since it is 25 feet long. The wire has some kinks in it, so I thought about putting the wire through a long tube to flatten the kinks, but I'm not sure if that would work. Bending the wire with pliers isn't super effective and might damage the insulation.

I am also thinking about purchasing one of those devices you plug into the wall which gives you variable voltage. Although variable amps would be more practical so I should probably buy that instead. I was thinking about buying thicker coils since thick coils have less resistance and more amps, but means you get a few less turns.

jrmichler
Mentor
You can take kinks out of magnet wire by clamping one end in a vise, then grabbing the other end with a pair of pliers, and pulling (or jerking) just hard enough to slightly stretch it.

A variable voltage current limited power supply is very nice to have for this sort of tinkering. This is one that I built back in the 1980's, and still use. It uses an LLM317 1.2 to 12 volt linear regulator.

And this one, which I ordered yesterday, should be much better: https://www.newark.com/multicomp-pr...ly-bench-prog-1ch-5a/dp/42AH0483?ost=42ah0483.

berkeman
That is good advice, but I don't have a vise lol. The voltage regulator looks like a good buy, thanks.