Electromagnetic lock design

[felix_cat]

Firstly its a hobby thing.

Secondly, I have got a design, you just do not go by opposing the design and present a whole new mechanism, you provide small alterations to the design. All I wanted was how to construct an electromagnet that could lift 600lbs with 24/12Volts power supply. Building it from scratch was never taught in the course, only numerical questions where you are given the dimensions already, have to calculate the amperes or turns. That is the reason I came to the forums.

Thirdly: I told you guys that I am in a 3rd world/part of the world where research is at the lowest and people making solenoids and coils by just endlessly coiling the iron core. I do not want that, of course that is the difference between an engineer and a technician. That is 6th grade science stuff and has not changed at the College level either, that flux is proportional to permeability, cross sectional area, current and inversely to length. How technically, keeping in mind the changes in permeability as magnetic intensity increases and the magnetic saturation, am I suppose to design it, that was my problem.
Well thanks a lot you guys, certainly, i think i was not even told what was cooking tonight, talk about being spoon fed.
And Maria baby, do not worry. Daddy is going to figure out soon.

 

[MATLABdude]

Well then, that's a good starting point. If you already understand basic electromagnetic theory, and have a design, and you're just looking for some modifications, then go for a core made of permalloy or mu metal, or a laminate electrical steel one.

And now, I'm confused again; if you've got a design, and you understand the theory, and the modifications, then what are you asking of us? How to build this thing for real? You'll need to get a machine shop to build you a core, and to buy yourself some 30 gauge wire. Or, you can go to a motor / coil rewinder (unless you live in a country really, really bereft of infrastructure, like Cambodia, I can almost guarantee you that there'll be quite a few shops that do this) and have them build it to your specifications.

 

[Danger]

This is starting to weird me out big-time.
For safety of yourself and your family, you would want it fail-safe for exit and fail-secure to keep the baddies out if the power fails.
My thought right now (keeping in mind that I've had over a dozen beers) is that you could accomplish both by having the electromagnet mounted on a physically disconnectible mounting bracket. In that case, the permanent magnet on the door would provide fail-secure in a power failure, but you could manually disconnect the electromagnet from the frame if you had to exit in a hurry.

 

[felix_cat]

Thanks a lot guys. That was the support I guess I needed. Well I did all the math, I would post it for maybe anyone of you to check it, the force I calculated was around 4300 Newtons. But I made an assumption of B=1.2T with Ur(mu R) being 3000.

A query if you might help me with, in the textbook, there are numerical questions given where two graphs, one of Relative Permeability(mu R) and second of Flux Density(B) against H(field strength A,turns/meter) are plotted. When the core is tested these results are plotted.

My question is that if I assumed that my core would have Ur 3000 and B=1.2, is it correct ? Should I too first plot a graph and test the core ?
With the calculations I did, I found out that 35 turns on a steel core that is similar to the shape of digit " 8 " (eight) were required, where the coiled wired is on the middle of the digit
Also I assumed that I=0.5A. I guess results are valid ??:uhh:

-->|(Armature Plate)
=|================<-- Magnetic Core E shaped
=|......=
=|......=
=|......=
=|......=
=|......=
=|......=
=|......=
=|...coiled...=
=|================
=|...here...=
=|......=
=|......=
=|......=
=|......=
=|......=
=|......=
=|......=
=|......=
=|================ <-- Magnetic Core E shaped
-->|(Armature Plate)

looking from side on.

 

[MATLABdude]

35 turns sounds suspiciously low (even though I haven't built one of these before); I think you may be off by an order of magnitude or two. With this whole endeavour, you'll probably need to go through at least two or three iterations (with appropriate analysis in-between) to create something that works to the specs that you're using.

I'm guessing $\mu_{R}$ is $\frac{\mu}{\mu0}$, however, yes?

Do you have the equipment necessary to determine B vs. H? If not, you're probably stuck with doing some experimentation to try to derive what $\mu$ is under a given set of conditions (and as I say, you're probably not going to build this perfectly first time through).

As Danger and some of the other posters have counseled, I urge you to consider the safety / emergency aspect. Whether it be a big red push button that kills power, or a manual (non-magnetic) unlock bracket that disconnects that frame from the magnet, allowing the (permanent) magnet to swing free with the door, and people to leave if the power fails, or just a big red sign that says "In case of Emergency, PULL POWER CORD TO EXIT!"

This is our duty as engineers: to not just build something, but to also think through failure modes, and ramifications of our design decisions. And what differentiates us from some guy that slaps stuff together without regards to design / thought. I guess we're also responsible when the unexpected happens, or when someone figures out a way around our safety constraints / recommendations, but that's a whole other discussion.

Anyways, good luck with your project, and let us know how it turns out!

 

[felix_cat]

NICE !

One mistake in my previous post by the way, its not a steel core , its an iron core.

Well, got to go to the hardware store now ...

And I would take full notice of safety issues, thanks for reminding me !

 

[Danger]

One clarification to MATLABdude's post is to point out that although I did recommend something that I thought might be a practical solution, I am not an engineer. I never finished high-school. I've built a lot of **** in my day, mostly from scratch, and I was a professional (technical-college educated) locksmith, but that doesn't count against the brainpower of most PF members. Listen to the professionals, not me.