# Solenoids



## cfellows (Mar 25, 2008)

Didn't want to highjack Allthumbs' thread so thought I would start another. I've been doing some calculations and experiments with solenoids the past couple of days. I decided to build a solenoid 2" long and 1" OD. The inside diameter of the coil is .45". As shown below, I made the bobbin out of 1" diameter black delrin. I bored an 11/32" hole, 2 inches deep and epoxied a piece of thin walled brass tubing inside. This makes the bobbin stronger and, perhaps, wear better without having any affect on the magnetic properties.







Then I turned the inner part to .45" diameter and parted off the finished bobbin.






I drilled a very small hole in one of the flanges to feed the start of the wire through. Then I mounted the bobbin on a 5/16" bolt with a rubber washer over the end with wire protruding, started the wire, and chucked it in my lathe.






Here's a picture of the 8lb spool of wire






I wrapped about 350 feet of #28 wire on the bobbin and secured it with black electrical tape.






The measured resistance was about 20 ohms and the wire is rated at a maximum of about .32 amps. 

Continued on next Post...


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## cfellows (Mar 25, 2008)

I tried the solenoid with a 5/16" plunger which fit nicely inside the brass liner using 12 volts. I wasn't particularly happy with the amount of pull force. I figured it was barely enough to run a small, single cylinder engine. I could increase the pull proportionately by increasing the voltage, but I wanted to use 12 volts or less to run any future solenoid engines I build.

I unwound all the 28 gauge wire and rewound it with 24 gauge wire. 24 gauge is rated at about .81 amps and even though I got significantly fewer turns, the resistance was a lot lower at only 5.7 ohms for the finished coil. This time, with 12 volts applied, I got a lot stronger pull. That's because with the lower resistance, I was pushing 3 times as many amps through the coil. The coil started getting pretty warm after about a minute so I couldn't run the solenoid at 100% duty cycle for very long. However, I think at a 50% duty cycle, which would be 1/2 of every revolution, it would be fine.

The finished coil has 14 layers of tightly spaced turns. The total amount of wire is about 150 feet which is under 1/4 pound.

I've also learned a few things about physical coil parameters based on calculations:

1. If you use smaller gauge wire on the same size bobbin, your pull force will be less. So, if you use smaller wire, you need to use a smaller bobbin because the resistance goes up faster than the number of turns.

2. If you make the overal diameter larger resulting in more turns, the pull force will also be less, because, again, the resistance goes up faster than the affect from increased turns.

3. If you increase the inside diameter of the coil, you'll also get less pull force.

4. If you make the coil longer, increasing the number of turns, but using the same size wire, the same OD and the same ID, the pull force will remain the same. This is because the increased resistance is exacly balanced out by the increased number of turns. However, the current (amps) will be less and the effective stroke can be longer.

Encasing the solenoid in iron or steel doesn't much affect the pull force until the plunger gets close, maybe 80% in, to the end of the stroke. Then the pull beings to increase really dramatically.

That's all for now. More information as I go along.


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## AllThumbs (Mar 26, 2008)

Thank you. That is helpful.

E


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## zeusrekning (Mar 26, 2008)

Very good information here. Made some attemps at this a couple weeks ago with little luck. Could you go into more detail about the winding. Did you wind each layer left to right, right to left? Or did you wind left to right then come back to the left and wind left to right again? I couldn't think of a better way to word that. Hope it makes since. I was actually making a simple electro-magnet, should the principles be the same? I wanted my EM to repel magnets for a hall effect motor but I couldn't get it to repel a rare earth magnet. The magnet would still stick to my steel core. 
Keep the info coming Cfellows.
Tim


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## DICKEYBIRD (Mar 26, 2008)

Great info Chuck!
Where did you find your wire? I reckon the high price of copper brings the price of an 8 lb. roll of wire up there pretty high.

Using my meager knowledge of ohm's law, the amperage is roughly 2 amps? If so, what are you planning to power your motor with? That's a bit above the average wall wart. Maybe an old computer power supply?

Keep the info flowing! ;D
Milton


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## tattoomike68 (Mar 26, 2008)

I am no electrical wizzard but I did used to make many tattoo machines. the solenoids are much like what you are building. adjusting the points while the machine was running would light a person up good. ;D






For a power supply I used a tyco HO scale train set transformer.


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## cfellows (Mar 26, 2008)

zeusrekning  said:
			
		

> Very good information here. Made some attemps at this a couple weeks ago with little luck. Could you go into more detail about the winding. Did you wind each layer left to right, right to left? Or did you wind left to right then come back to the left and wind left to right again? I couldn't think of a better way to word that. Hope it makes since. I was actually making a simple electro-magnet, should the principles be the same? I wanted my EM to repel magnets for a hall effect motor but I couldn't get it to repel a rare earth magnet. The magnet would still stick to my steel core.
> Keep the info coming Cfellows.
> Tim



Starting on the left side, I just went back and forth winding the turns as tightly as I could. It's not terribly important to get the windings in nice even layers, but it does let you get more turns in a smaller space.

The principles for solenoids and electromagnets are basically the same. The only difference is that in a solenoid the steel or iron core is the plunger whereas it's usually fixed in an electromagnet.

The problem you've got with your rare earth magnet is that it's attraction to the steel core is stronger than the repulsion from the electromagnet. Increasing the voltage to the EM might work. It might also be worth trying it with the steel core of the EM removed.

Chuck


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## cfellows (Mar 26, 2008)

DICKEYBIRD  said:
			
		

> Great info Chuck!
> Where did you find your wire? I reckon the high price of copper brings the price of an 8 lb. roll of wire up there pretty high.
> 
> Using my meager knowledge of ohm's law, the amperage is roughly 2 amps? If so, what are you planning to power your motor with? That's a bit above the average wall wart. Maybe an old computer power supply?
> ...



I had bought the wire on eBay several years ago and it's been sitting on a shelf. You can still get pretty good prices on eBay. Just search for magnet wire.

I calculate the amps to be a little over 2 (Volts / Ohms). I have a number of Variacs with full wave rectifiers in the shop since some of my tools are powered with large DC motors. For those of you who aren't familiar, a Variac is a variable transformer than runs on AC, usually 120 volts but some are rated for 240 volts. The transformer has a rotary knob that lets you adjust the output voltage from zero to about 140 volts. These are availabe from about a 2 amp rating up to 30 amps or more. There's usually a lot of them for sale on eBay. The voltage has to be changed from AC to DC, but this is easy to do with what's called a bridge rectifier. These are a simple little device with two poles for AC in and two poles for DC out. They cost less than 5 bucks.  Just make sure they a high enough voltage and current rating.

Ultimately I plan to run the motor on a 12 volt rechargeable batter. These are available on eBay and hobby shops for RC models.


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## AllThumbs (Mar 26, 2008)

Mr Fellows,

Good information. I have been fiddling too. You are a lot smarter in that you are fiddling before building an engine, I am fiddling after building parts, so my coil is now limited by what I can squeeze into what I have built so far.

An observation/question. Do you filter the rectified DC out of the variac? if not, this will affect your testing, since the DC of of the variac will be choppy. This will add inductive reactance, (increasing the impedence) to the electrical circuit, causing calculated current to be more than actual current (ohm's law doesn't apply to AC or straight rectified DC when we are talking coils).

In other words, for coils, 6V rectified AC does not behave like 6 V DC (battery) unless it is filtered with a large capacitor.

Eric


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## cfellows (Mar 26, 2008)

Eric,

No, I don't filter the DC voltage. I do understand that the rectified DC is choppy, and that the actual current is probably less than calculated. When I get around to powering the engine with a battery, I plan to use a small, electronic controller to vary the speed, so hopefully the increased current won't be a problem.

Thx...
Chuck


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## cfellows (Mar 26, 2008)

I just uploaded an Excel spreadsheet that will let you change physical parameters of a coil such as wire size, coil length, outside diameter, inside diameter, and voltage. The spreadsheet will calculate the length of wire required, the resistance in ohms, the current in amps, and the amp turns which is a gauge of magnetic force.

Chuck


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## zeusrekning (Mar 26, 2008)

:bow:


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## rickharris (Mar 26, 2008)

The output of the bridge rectifier won't be all that choppy as the bridge rectifies both sides of the AC voltage, The inductance of the coil will have some smoothing effect anyway.

Sources for wire can include transformers from older electrical equipment, electric bells, motors and similar. So called Magnetic wire means enamel coated rather than plastic insulation. You should find 2 different gauges in the primary and secondary coils.

You must wind the coil in the same direction as this effects the direction of the magnetic field and changing direction will produce a field that opposes it's self and so reduces the over all effect.

If you want a stronger reaction replace you iron core with your rare earth magnetic, Switching a coil with reed switches or mechanical switches is no problem but be cautious when using electronics with the coil as the collapsing magnetic field creates a strong reverse electrical flow (Back EMF) this can distroy electronics connected to drive the coil - usually it is cut off by using a flywheel or snubbing diode across the coil.


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## AllThumbs (Mar 26, 2008)

By choppy I mean from 0 to max voltage 120 times a second. ;D

Just to clarify, it makes no diference if you wind from left to right and back or right to left and back. What you don't want to do is wind half the spool clockwise and the other half counterclockwise.

E


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## cfellows (Mar 27, 2008)

I wound another coil tonight to see if the diameter of the plunger had much affect. The construct of the coil was the same as the last one, #24 wire on a delrin spool with a thin wall brass tube pressed into the center. However, where the last one took a 5/16" diameter plunger and was 2 inches long, this one took a 7/16" plunger and was 3 inches long. I had to make this coil longer with fewer layers to get approximately the same number of amp turns. Running both coils on 12 volts, I didn't notice any appreciable difference in the pull. While the diameter of this plunger is only about 40% larger, the cross sectional area, which is what matters, is nearly twice as large. Perhaps a more objective test using a scale would measure some difference but I couldn't feel any.

From a technical standpoint, I think this means that the smaller plunger was more than adequate to conduct the magnetic lines of force without saturating and using a larger diameter plunger didn't really improve anything. As you increase the voltage and/or amps, the magnetic lines of force are increased and eventually the core (plunger) becomes saturaged. Once you've saturated the plunger, increasing the amps or voltage will not make any further increases in the pull strength on the plunger. Stated another way, I believe if the plunger is not saturated, increasing its diameter will not make any difference.

The three inch long coil I made tonight did provide pull over a longer stroke, so for a longer stroke engine, longer coils are the order of the day. I also discovered that if you insert a short bolt into the opposite end of the coil, the pulling force increases dramatically as the plunger gets closer to the end of the bolt inserted from the other end. This, however, does shorten the effective stroke.

Of course, the real test would be building a motor and seeing how well the coils perform. Too much pull and the engine is going to run too fast. But then, I guess I'd have to wonder how that could be a problem? :

By the way, as a disclaimer, I'm far from an expert in these matters and welcome any challenges to my proclamations!

Here is a link to a 5 page description of solenoid construction, how they work, and the different types. Very good reading.

http://www.sal.wisc.edu/pfis/docs/archive/public/Product%20Manuals/bicron/soldesop.pdf

Chuck


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## cfellows (Mar 30, 2008)

I started on an engine for my solenoid this weekend. I plan to use a larger diameter flywheel in the finished engine, mostly for looks.

I used the 2" solenoid, wound it with 24 gauge wire. The finished coil has 14 layers of tightly spaced turns. The total amount of wire is about 150 feet which is under 1/4 pound. The bobbin was made from 1" diameter delrin, with the inside of the spool turned down to .45 inch.

Not the best pictures, but you get the idea.
















The aluminum cylinder shroud is 2" tall and 1.25" diameter. The stroke on this engine will be around 5/8 inch.


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## Bogstandard (Mar 30, 2008)

Lovely engine coming along there Chuck,

If it runs as well as it looks, it will be a stunner when finished.

It's always nice to see homebuilds emerging from the ashes.

John


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## DICKEYBIRD (Mar 30, 2008)

Sigh, you guys make this stuff look so easy.

Chuck, is that an o-ring at the top? Destined to hold the outer "cylinder block" in place? Clever.


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## AllThumbs (Mar 30, 2008)

You wisely did some testing before building. A question or two: Does the piston ever come right out of the coil? Also, what will be the shape of your piston? I am thinking a "T" shape would be the best. Is that what you are planning?

E


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## cfellows (Mar 30, 2008)

AllThumbs  said:
			
		

> You wisely did some testing before building. A question or two: Does the piston ever come right out of the coil? Also, what will be the shape of your piston? I am thinking a "T" shape would be the best. Is that what you are planning?



I plan on using 5/16" plunger from an existing solenoid which is just a solid rod with a slot in the bottom to attach the connecting rod to. I would be worried about the lateral forces on the piston if the full diameter part were too short. What do you think would be the advantage of a T shaped piston?

I will have to experiment some with the length of the plunger and the connecting rod. My home wound solenoid is not encased in iron or steel, so it behaves differently than one which is. In a standard, steel encased solenoid, the pull on the plunger increases dramatically as it reaches the end of the stroke. Conversely, the amount of pull exerted by a coil not encased in steel drops off as the plunger approaches the centered point.

So, the short answer is, I'm not sure if the piston will come all the way through or not...

Chuck


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## Bogstandard (Mar 30, 2008)

Chuck,

You are doing it the right way.
You are being an experimental engine builder. 
Fixing it as you come across problems.

You can only get it near enough while building these little engines, it is the fine tuning afterwards that gets them spot on.

We have a saying for it in the UK.

It is 'suck it and see'.

John


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## AllThumbs (Mar 30, 2008)

I notice on my sol. the face of the coil does a lot to attract iron. In other words, even when only a slight pull could be felt when the iron piston was entering the cylinder, the piston could be made to stick to the face of the coil. I was then thinking that a t shaped piston made to enter the cylinder with the "t" part made to almost contact the face of the coil at TDC may be the way to go. I did not incorperate this into my engine, but perhaps I should have. 

E


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## cfellows (Mar 30, 2008)

AllThumbs  said:
			
		

> I notice on my sol. the face of the coil does a lot to attract iron. In other words, even when only a slight pull could be felt when the iron piston was entering the cylinder, the piston could be made to stick to the face of the coil. I was then thinking that a t shaped piston made to enter the cylinder with the "t" part made to almost contact the face of the coil at TDC may be the way to go. I did not incorperate this into my engine, but perhaps I should have.



My gut reaction, and this is far from scientific or even academic, is that the shape of the piston has little affect on the pull force. I think it has more to do with the mass and the way that the mass can conduct the magnetic lines of force as it gets closer to the coil. Given the shape of your cylinder and coil, my opinion, and it's just an opinion, is that a t-shaped piston would be of no advantage. Unfortunately (or fortunately if you like tinkering) the best way is to try both methods and see if it works better.

Chuck


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## cfellows (Mar 30, 2008)

Bogstandard  said:
			
		

> You are doing it the right way.
> You are being an experimental engine builder.
> Fixing it as you come across problems.



John, your point is well taken, and I've decided to do a sidebar here and make a test-bed engine that will let me change the stroke, the distance of the cylinder from the crankshaft, and other physical parameters as I think of them. There is very little documentation on the internet regarding the parameters of reciprocating engines that use electric coils and this looks like a good opportunity to add to that knowledge store.

While electric reciprocating engines will probably never be practical in replacing other engine types, it does afford a simple method for making model engines that simulate full size engine operation without the complexity of valves, ignition, fuel sources or external power sources such as compressors and boilers. In other words, if you want a small model engine that you can sit on your desk and looks and works like a full size engine, electric solenoid engines could be a good choice.

Chuck


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## Bogstandard (Mar 30, 2008)

Chuck,
I like to try anything once, just for the sake of learning something new.

I am a grubby hands man, and absolutely hate electrics. It is a shame really, I used to service, in one of my previous lives, miniature coil winding machines. Never took any notice of what they did, I just made them work again. The wife used to work on the machines, winding coils for going into card readers in ATM machines.

So this post has got me very interested, not on the coil winding side, but the method of operation. 
I am very lucky, I have contacts in all sorts of industries, so this Thursday, I should have a load of surplus solenoids being delivered, for me to play with. But that will be in the distant future, too much work is backing up now for me to play with things.
So what you are doing here will be the sum total of what I know about these fascinating engines.

Keep up the good work.

John


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## cfellows (Mar 31, 2008)

Well, I experimented with the engine some tonight. I determined that the maximum pull my homemade coil exerted on the plunger was when the plunger was between 1/2 and 2/3 of the way in.  It seems logical to me that the best efficiency would be gained by having the maximum pull ocurring at about mid stroke where you have the best mechanical advantage on the crank. All this means that I need to increase the distance between my solenoid and the crankshaft by about 3/4". Probably the best way to accomplish that is to increase the length of the vertical columns from 2 3/4" to 3 1/2". I could accomplish the same result by shortening the plunger but that would also shorten the range of the pull which I don't want.

Chuck


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## cfellows (Apr 5, 2008)

Got my solenoid engine to a point where it runs. Started right up the first time. It runs OK on 12 volts, but runs a lot better on 18 volts. I'm going to try some other coil configurations to see if I can get the performance I want on 12 volts.

[ame=http://youtube.com/watch?v=3fBnqWlGc30]http://youtube.com/watch?v=3fBnqWlGc30[/ame]


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## Bogstandard (Apr 5, 2008)

G-R-E-A-T

John


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## rake60 (Apr 5, 2008)

Looks Good Chuck!

Nice work!!!

Rick


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## AllThumbs (Apr 5, 2008)

Beauty!


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## Powder keg (Apr 5, 2008)

It even sounds like an engine) Good job!!!

Wes


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## Powder keg (Apr 5, 2008)

Here is a thought on these Solenoid engines. A lot of them pull a plate to the end of the solenoid. This is where the magnetic pull would be strongest. You could then have an iron core in the center of your coil and I think this would make a stronger engine? Here are a couple examples of what I'm trying to say)
[ame]http://www.youtube.com/watch?v=1k9BXvGNOOA[/ame]

[ame]http://www.youtube.com/watch?v=zRQkYWpeMsY[/ame]

Wes


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## zeusrekning (Apr 5, 2008)

The one in the first video is what Cedge brought by to show me today. 











I'm going to model it up soon.
Tim


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## Bogstandard (Apr 13, 2008)

I managed to get my claws on a few solenoids recently, and these looked the best of the bunch, the others were massive. They have 24 volt coils, but have very good pulling power at 12 volts.
Do you electric string lads think they will do for a future project, or should I go another route?






John


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## AllThumbs (Apr 13, 2008)

Is there a current rating on them? I am sure they would be awsome for a solenoid engine application.

Eric


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## rickharris (Apr 13, 2008)

Go for it - In the unlikely event of problems - ask again - It's so much easier to fix something that is in use rather than talk theory (which is so often wrong in practical terms anyway)


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## cfellows (Apr 13, 2008)

Bogstandard  said:
			
		

> I managed to get my claws on a few solenoids recently, and these looked the best of the bunch, the others were massive. They have 24 volt coils, but have very good pulling power at 12 volts.
> Do you electric string lads think they will do for a future project, or should I go another route?
> 
> John



John,

The solenoids you have pictured will work as either pull or push. The long, skinny tip protruding out the other end would operate in push mode. I think the solenoids would work in a small engine, probably better as a multiple "cylinder" version, maybe in a boxer configuration. I would keep the stroke pretty short, 1/2" - 5/8" since these solenoids don't exert much force until the plunger gets pretty well inside the coil.

The bigger solenoids you have could maybe be used in a beam type engine, either horizontal or vertical. I've thought of designs where the solenoids are located horizontally in the base of the engne, with a vertical beam at end connected to a horizontal crankshaft that doubles back over the top and connects to the crankshaft toward the back. 

Like this:


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## cfellows (Apr 13, 2008)

Got my solenoid engine finished this weekend. Here's the video:

[ame=http://youtube.com/watch?v=e3tcdiO2HCc]http://youtube.com/watch?v=e3tcdiO2HCc[/ame]

I replaced the aluminum casing on the coil with steel and added a cast iron cap on top. I also shortened the pillars (actually made new ones out of drill rod). All this seemed to give the engine more torque.

Chuck


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## PTsideshow (Apr 13, 2008)

Very very good,runs nice to. Along with looking good.
 ;D


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## Brass_Machine (Apr 13, 2008)

Cool deal! I like it a lot.

Eric


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## shred (Apr 13, 2008)

Very nice. 

I'd be real tempted to hide a battery in the base and carefully set it on the shelf in the 'off' portion of the cycle.. some unsuspecting person comes along and gives the flywheel a flip and watch 'em freak as it starts right up.. ;D ;D


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## rake60 (Apr 13, 2008)

Nice!

Rick


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## AllThumbs (Apr 13, 2008)

Sexy!


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