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Custom mini push electromagnet & winding method

Custom mini push electromagnet & winding method

Custom mini push electromagnet & winding method

I have a small but urgent electromagnet project in process however the actuator I need doesn't seem to be readily available although although it's not anything new, except for the custom size I need. Attached is a reference sketch.

I ordered and received these 12mm OD buzzers 12mm WST-1212S Soberton Inc | 433-1050-ND| DigiKey and Digikey just confirmed that there are also permanent magnets (PM) inside, which makes sense since they are something like an audio speaker and they also include mini electromagnets.

No. 1 in the sketch sheet illustrates what I need to make with the electromagnets (EMs) that are inside the buzzers. These parts will all fit inside a tube. When the EM is intermittently powered, it will push away a permanent magnet (PM) with the same polarity facing the EM. The PM's opposite side rests against a pin which rests against a spring. The purpose of it is to replace a push solenoid's function with it, because the mini push solenoids I've found are still both too big and too expensive.

Exactly what the needed pushing force is I don't know but it's not a whole lot. I would very generally estimate that the minimum would be equivalent to say, if the described EM were on a surface, oriented so the push was upwards, and the end of a pencil rested on it and the other end of the pencil was on the same surface, if it would instantly lift the end of the pencil resting on it upwards. That should be the minimum for it to work out. Of course, the more pushing force the better. It also needs to work off a small battery (about an inch long) up to say up to 12v, preferred. So that doesn't give much in Amps to work with.

Besides hand tools, I also have a power source which is rated up to 30VDC and 5Amps and I also have a digital Gauss meter which I haven't used yet, to help figure this out.

No2. in the sketch sheet is my attempt to bring clarity to contradicting information I've found regarding the correct magnetic wire winding method to get the most magnetic flux. The question arises regarding the added layers. Is it best to wind as shown in method A or method B or something else? It would be good to know this to see how the little EMs in the buzzers are wound and how to best do the winding if I need to make custom EMs, in case the ones in the buzzers won't do the job.

Please let me know what the general specs of the EM should be along with the power and Gauss that would be needed to achieve at least the minimum push force required. Also about the best winding method for maximum Gauss. Thanks very much for your help.


RE: Custom mini push electromagnet & winding method

It has been a while since I've wound an inductor, but I believe the performance is very similar with either technique that you show, especially when the number of windings is high (although I was working with RF inductors, so there may be other dominant factors at low frequencies). The main difference is if you want to one lead on the right and the other on the left (top technique) or if you want both leads on the left (bottom technique). Don't forget that you complete the last turn in the return path on the PCB.


RE: Custom mini push electromagnet & winding method

Thanks. Interesting.

So you're saying at these low power levels it may not matter which method it's wound? The leads may need to be both on one end. Either method would allow that configuration as it's just a matter of when to stop winding, no? If not, then what you're suggesting is if method A is applied, then the full length return of the wire over the existing wound wire, back to the starting end "Start-L" will cause an issue to diminish the magnetic flux?


RE: Custom mini push electromagnet & winding method

Not so much the power levels as the frequency; as you aren't attempting to transfer the field (i.e. transformer) and going straight for the force it is a non-issue. Do you know of the right-hand-rule for electromagnetics? If not, you should research it. The 'full length return' won't be pointing in the same direction as the rest, so it may be slightly less efficient.


RE: Custom mini push electromagnet & winding method

You are working too hard, and on the wrong problem.

Normal multilayer coils are wound at high speed on automated machinery with 'level wind' mechanisms that just oscillate the wire back and forth as the coil core is rotated, so successive layers are handed, in the screw thread sense, right - left - right - left, and so on. The magnetic field doesn't care.

Normal push solenoids look pretty much like pull solenoids, except that a slender pin on the plunger extends through the pole piece or seat that the plunger hits when the gap closes. The pin is what does the pushing.

You have also omitted a very important part of the solenoid, a return path for the flux outside of the coil. This normally takes the form of a concentric shell, or a U shaped stamping, either made of soft steel. Note also that any joints in these iron circuits are crimped or interleaved, so that the only air gap of any size is between the plunger and the seat when the solenoid is de-energized.

The permanent magnet is a complication that you don't need in a push solenoid. It normally appears only in latching solenoids, which are the Devil's spawn, or a sure cause of insanity, and also a sure way to dissipate an unlimited amount of development money with no consistently positive result to show for it.

Mike Halloran
Pembroke Pines, FL, USA

RE: Custom mini push electromagnet & winding method

Yes, I'm familiar with handedness. The standardized push solenoids I've found are either too big or too expensive. This is why I came up with the design for the push EM. I have been able to locate this:http://www.magnetechcorp.com/push-pull.html which again, is too expensive but they may be able make what I need which is much smaller and requires less push force, which I think should also cost less.

My proposed design with a dipole EM is more basic and I had understood that the handedness of the windings contributed to not only the amount of magnetic flux produced from a given power/current/amps from a battery but also the direction the magnetic flux would move. So I want the most magnetic flux possible in the right direction, at the smallest possible size and lowest cost.

Basically then what you're saying is the handedness doesn't matter and my design ultimately will be a waste of time and money. Correct?


RE: Custom mini push electromagnet & winding method

I may have contributed to it, but you are confusing handedness of a screw with handedness of an electomagnet, which is not quite the same.

Let's start again, with a single turn of wire, which is necessarily planar.

A hypothetical and impractical way to make a solenoid coil from that is to displace both ends by half a wire diameter, turning the circle into a helix, and join it to an adjacent coil, also formed into a helix, and recurse.

It does not matter whether the helix is left handed or right handed. The fields of the adjacent coils still add, and the right hand rule for electromagnetism still applies, to a single coil, and to any number of adjacent coils, be they adjacent axially or radially.

Mike Halloran
Pembroke Pines, FL, USA

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