# secrets for solenoid construction?

#### Hamlet

Joined Jun 10, 2015
327
particularly long-throw solenoids...

I've been making solenoids for art projects. (Off the shelf solutions are short on availability, expensive and inadequate) .

I've had some luck, wasted a quantity of enameled wire, and ready for more.

I've used a number of online calculators, FWIW (for-what-it's-worth).

Is there any secret tips for what makes an adequate solenoid, or no?
My biggest concern is heat, not power. I'm not building pinball machines (but you never know...)

#### crutschow

Joined Mar 14, 2008
25,109
If the concern is heat, then you need to have enough resistance in the windings to limit the power to a few watts (V²/R).
So you determine how many turns you want, and calculate the approximate length of wire needed for the solenoid physical size.
Then you select a wire gauge to give the desired resistance for that length of wire.

To improve the magnetic characteristics of the solenoid, always have a complete magnetic path for the magnetic field through the solenoid.
Any added air gap, besides the minimum needed for the solenoid movement, will significantly reduce the solenoid field and its force.

#### Hamlet

Joined Jun 10, 2015
327
Air gap, check.

My plunger has to move thru the axis of the coil, before, during, and after (like an arrow),
and return.

Can the magnetic path be improved? Betterment would result in more power/strength, less heat.

#### crutschow

Joined Mar 14, 2008
25,109
Can the magnetic path be improved?
Have to see the physical design.

#### BR-549

Joined Sep 22, 2013
4,938
A lot will also depend on specific function.

#### Hamlet

Joined Jun 10, 2015
327
Okay, fare enough. Let me say, solenoids and relays have an open end, and a closed end.
I'm thinking more like a reciprocating rail gun, both ends open.

#### BR-549

Joined Sep 22, 2013
4,938
What is your idea of a long-throw solenoid? Explain how one works.

#### Sensacell

Joined Jun 19, 2012
2,568
Long-throw solenoids are so horribly inefficient, so terrible that they are almost never used in any real application.

Remember that one you saw in a product or machine?
Right... you never saw it.

#### Hamlet

Joined Jun 10, 2015
327
What is your idea of a long-throw solenoid? Explain how one works.
A long-throw solenoid is any solenoid with movement longer than about 20mm. Imagine a coil 40mm diameter, 75mm long, with a 20mm diameter x100mm length plunger. They don't sell them anywhere, so I want to make them. The plunger could be 102mm, or 233mm in tenth, or whatever. The coil could be longer, or shorter than the movement, or plunger itself, since the apparatus is not closed on one end like a relay or traditional solenoid.

I can see that I need to build more coils and plungers, using different wire gauge, turns, etc., before I understand. Obviously, there are no tricks or shortcuts, or more importantly, rules-of-thumb to guide me (apart from the left hand rule.) I'm guessing I need as many turns and amps as space will allow, while dissipating any heat build-up/service factor, while maximizing pull-in, or (push-out for perm. mag. plungers.)

#### BR-549

Joined Sep 22, 2013
4,938
Is it repeated hammer action, or sling shot? (shoot and hold)

#### Hamlet

Joined Jun 10, 2015
327
Is it repeated hammer action, or sling shot? (shoot and hold)
The movement I want is repetition. It doesn't have to be supper efficient. This is for kinetic sculpture type of application, waving a flag,
or jiggling an arm. I don't intend to shove around locking bolts on a security safe, or door locks.

All I was looking for was a guide, ratio of turns to amps, or some bit of advise like that. I understand a 2 ohm coil is going to get very
hot at 12v with a 100% duty cycle, but it should have lots of power if it has enough turns!

#### BR-549

Joined Sep 22, 2013
4,938
So you want an oscillating rod. Maybe a permanent magnet for the armature. With 2 coils and armature travel between. Two fields holding armature in between both sides. Extensions on armature if necessary.

There are only fundamental equations. One can spend a lot of time with design and math.....OR just build one and see how much amp turns it takes to move your setup. You will have two opposing fields with armature controlled in middle.

Sorta a see-saw current setup, if you get my meaning.

#### AlbertHall

Joined Jun 4, 2014
10,014
You could use a short-throw solenoid operating a lever to give you the longer movement.

#### Hamlet

Joined Jun 10, 2015
327
You could use a short-throw solenoid operating a lever to give you the longer movement.
I could, but I feel that would be too "snappy". I was thinking of finding a circuit that could ramp the current up and down, but that's for later.

#### Hamlet

Joined Jun 10, 2015
327
So you want an oscillating rod. Maybe a permanent magnet for the armature. With 2 coils and armature travel between. Two fields holding armature in between both sides. Extensions on armature if necessary.

There are only fundamental equations. One can spend a lot of time with design and math.....OR just build one and see how much amp turns it takes to move your setup. You will have two opposing fields with armature controlled in middle.

Sorta a see-saw current setup, if you get my meaning.

Yes, I'm getting the feeling that the math isn't the territory. A good guide, perhaps.
I like your idea of two solenoids, I think I will built that! I have wound both short and long
coils, but not twin coils/electromagnets. When fooling with this sort of thing, it helps to
have the apparatus in your hands, to feel what's going on. For instance, when the plunger
is approaching a centeredness of mass withing the coil, the force decreases dramatically. I'm sure this could be
described mathematically, but this is neither my aim or forte.

#### AlbertHall

Joined Jun 4, 2014
10,014
The force from a solenoid increases as the gap reduces so this works like a positive feedback mechanism. As soon as it starts to move the gap gets smaller and the force increases so the speed increases and so on. Solenoids are by nature snappy.

If you don't want snappy then think about a motor/threaded rod kind of system or similar which can provide a more controlled action. Perhaps a model control servo.

#### atferrari

Joined Jan 6, 2004
4,004
Wasn't a thread recently here in AAC of someone trying to optimize an electromagnet-driven billiard cue? I recall posting there a YT link of an automated arm "playing" on a real table. It seemed somewhat bulky but with a weak drive.

Regarding of a "controlled" (non snappy) action, there was in the Web a project of a levitator where the object floated up and dow following a slow sinusoidal law. Not sure but maybe using an electromagnet. Just to spark some ideas.

xox

Joined Jul 18, 2013
20,875
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#### Bernard

Joined Aug 7, 2008
5,555
Just for kicks, you might look in Search Forums at top of this page below the title
"secrets for solenoid construction", put in "I Made a Solenoid". All of the strands were brought out so either parallel or series winding could be used. The split was to prevent circulating currents in the magnetic path.
Small linear actuators can be made for various lengths and speed.
Just give us some clues as to your need & maybe we can help.

#### KeepItSimpleStupid

Joined Mar 4, 2014
4,100
You can approach the problem from the driver side. It's standard practice to "kick" the solenoid to move the mass and then lower the power for holding. I did one design, but I just moved the heat to a lamp housing that had plenty of cooling. I did another where, I had to actuate a shutter "slowly" near a 1mm thick \$800.00 USD filter, PWM is generally your friend.

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