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Author Topic: Lots of cheap solenoids or something similar  (Read 1839 times)
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I just realized it really goes for metal stuff if I pass them into the center of it. So now I'm not sure...

Here the predicament... I believe it want's to sit in the middle of a metal rod when powered on. So if the rod is pretty long and I only allow it to move a centimeter, it is pretty strong. BUT I don't have any magnets that will fit into it so I have no idea of having a small magnet would be stronger or weaker than a large piece of metal.
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Maybe learn more about magnets and electromagnets.

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfie.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/solenoid.html

If you touch a magnet to iron or steel, the field will go into that object and it will effectively become part of the magnet. Like when you put a magnet on the head of an iron nail and can pick up iron objects with the tip.

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That still doesn't really answer whether I will get more force from a solenoid making a long rod into a magnet or just having a small magnet.

For the sake of economy I'd at least like to know the difference before trying both at the same time.
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Yes it does answer. The long thin coil has more concentrated field through the core with less distance from the windings to the center. The long thin magnetized rod has more length inside that core. But you have to learn and think or it's just meaningless lines in drawings.

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I think we are talking about two completely different things. It sounds like you are talking about the shape of the solenoid. The shape I'm using is simply because of what I found that I can test with. That's all I have to work with right now.

I'm talking about the actuating rod. I'm wanting to know if I should just use a ferrous rod as is normally in a solenoid or if a small neodymium magnet could be used instead. Getting a bunch of ferrous metal rods would be difficult and I don't really have a way to cut them.

It would be ideal to just use small magnets and have wood actuating rods. It would also seem to me that even though the magnet would be much much smaller, since it has its own magnetic field it should align with the solenoid with a great deal of force but I have none that fit into my solenoid so I can't test it.

I don't know if that is true though. That is my question. Will a just a small neodymium magnet attract the solenoid as well as a large temporarily magnetized rod?
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A magnetized rod inside the coil will be more affected than a magnet outside the coil. The lessons to understand that are available at many physics learning sites on the web. Knowing even the basics will let you make effective devices instead of heaters that don't do a lot else.

It's your choice.


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Getting a bunch of ferrous metal rods would be difficult and I don't really have a way to cut them.

Nails and a pair of pliers?
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Why cut nails? The head makes a good stop/place to stick a magnet. If the ferrous rod has a field it works better.
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Yeah I considered that but I want sure how big I could find them and how magnetic they would be. I got good pull on a screw driver, I don't know how well a nail might do. I'll go see whati can find.
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Big nails (9 penny spikes) weigh more, take more energy to start moving. Try different sizes.

Much of the heat will be from resistance in the wire. Fine wire carries less current before getting hot from just resistance (but making the field also makes heat), good for less voltage and more wrappings. With a more efficient solenoid you don't need as much anyway.

Where will these valves be? Possibly you can mount them on thick aluminum for heat sink and blow air over the lot?

You have a whole project just making a good valve design. Think about using levers.


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Would servos work to move a valve?
Can be had for as low as $8
http://www.hobby-lobby.com/8_gram_precision_micro_servo_1033986_prd1.htm
Mega can drive 48 servos I think I recall reading.
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It depends on where you shop. I can probably beat these below btw:

http://www.allelectronics.com/make-a-store/item/SOL-132/SOLENOID-VALVE/1.html
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12 Vdc, 100mA solenoid valve. Open when activated. Body: 24mm diameter x 31mm long. 62mm overall length, including inlet and outlet ports and terminals. 0.19" diameter ports. Used, removed from equipment.
$2.50 ea.

http://www.allelectronics.com/make-a-store/item/DCS-110/STANDARD-RACING-SERVO/1.html
Quote
Analog servo motor. Standard size, 1.55" x 0.73" x 1.46" (39.4 x 18.5 x 37.1mm). 49oz-in torque @ 6Vdc. Speed: 0.23sec/60 Degrees @ 4.8V, 0.19 sec/ 60 Degrees @ 6V. 6.5" leads with standard 3-conductor female connector.
$6.95 ea.

http://www.allelectronics.com/make-a-store/item/SOL-102/MINIATURE-12VDC-PUSH-TYPE-SOLENOID/1.html
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Ledex(TM). 0.5" diameter x 1" long tubular solenoid with 3/8" diameter threaded bushing for mounting. 1/16" diameter x 1/2" long plunger. 40 Ohm coil. Operates on 12 Vdc. 1" wire leads.
$2.75 ea --- some caveats, provide your own return action and armature hold

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A customer from CA US
armature not attached
I haven't used these in an application yet, but it should be noted that the armature (the actuating pin of the solenoid) is not retained within the solenoid body. In other words, if there is no power to the device, the pin can fall out the back. If you plan to mount the solenoid vertically (with the pointy end facing upwards), you will need to have something behind the solenoid to keep the armature from falling out.

A customer from Midwest USA
Wimpy little solenoid
Very limited push power. Maybe 1/8 inch of stroke is usable for any kind of push. Will push very lightly on 2 D batts, stronger on a 9 volt batt and a bit more on a 12v SLA. Still wimply and no way to hold in the piston from falling out.

A customer from Canada
removable body?
can anyone tell me if you can remove the body or outer shell from this solenoid? all i need is the coil inside.

A customer from Near Sacramento, CA
Doesn't have spring return
The solenoid does not have a spring to return it to a retracted position when power to the solenoid is cut. Like the other reviewer mentioned, it does not have a back to keep the pin in when turned upside down (so that the pin pushes up when power is applied). I mounted the solenoid upside down (making sure the rod didn't fall out the back) and the solenoid would not always retract with the force of gravity after I triggered it. I was able to drive it with 5V and 9V and it has nice holding force.
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I have the parts from a magnetic toy that I bought a few years ago. It consists of little plastic "sticks" with a magnet each end and steel balls. You can build interesting shapes with it. I can't remember what it was called but I see similar things on Google called Geomag and Manetix.

In the parts I have it is easy to take the little neodym magnets out of the sticks. They are about 4mm in diameter and 4mm high. They might fit through the centre of your bobbins.


...R
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It would have to go down to less than a dollar before I could consider buying what I need. Even making them myself I have to be really cautious with what I pick.

 Found a few different sizes nails, even some really big ones for pretty cheap and some new thread spools that are longer and should allow larger nails to pass through. If the nails are too heavy I might make the solenoids the moving part.
« Last Edit: May 31, 2013, 02:25:41 pm by stoopkid » Logged

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Thread spools.... You want the windings close to the armature.

Small diameter spools might be okay but every mm between windings and armature takes away effect, the fall-off is fast. For some bobbins you would be better off with cardboard or rolled card stock and tape.

Here they make strong solenoid and measure move force vs hold force.
https://www.youtube.com/watch?v=hsoggQOoG4s

Adding: and of course you put a capacitor across power and ground at each coil and I think a diode, all for circuit protection, right? ULN28xx Darlington driver chips have that built-in btw.
« Last Edit: May 31, 2013, 06:33:57 pm by GoForSmoke » Logged

I find it harder to express logic in English than in Code.
Sometimes an example says more than many times as many words.

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