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B Magnetic Lock

  1. May 4, 2017 #1
    Today I just learnt the concept of magnetic lock.. where pure electromagnetic force was used to lock doors.. My experience with magnets shows you can still pull two magnets apart.. but for magnetic lock.. there is no moving part, the door is closed just by the turning the electromagnets on and it is just small pieces and small voltages.. so powerful stuff! Specification says 650 lbs to 1000 lbs of force. Would anyone know the electrical patterns the magnetic lock make compared to ref magnets? How could something so small able to hold or pull 1000 lbs?
  2. jcsd
  3. May 4, 2017 #2


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    don't use the term "pure" em force ... there is no such term in science

    your statement is too vague
    depends on the strength of the magnets and what you are using to pull them apart ?
    I have a number of magnets that you cannot pull apart by hand

    again pretty vague .... what is your definition of small pieces and small voltages ??
    do you have any references ?

    do you have a link for this ?

    what is a ref magnet ?

    here is an example of a commercial electromagnetic door holder


    these are very similar to ones on doors of a building I visit regularly.... when the doors are held closed by these, they cannot be opened by hand

  4. May 4, 2017 #3
    Yes the above was exactly what I was describing. It is very small yet it can produce holding force of 350 lbs.. this is incredible stuff.. not even Maxwell could have guessed this can occur. I only hear about it today. Ref magnet means Refrigerator magnet.

    What kind of magnets do you have that can't be pulled by hands?

    Your device example has only 12 volts (and current of 380-430mA) and it has holding force of 350 lbs. I'd like to see it's lines of forces diagrams and how exactly it can reach such huge holding force with only 12 volts.
  5. May 4, 2017 #4


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    refrigerator magnets are very small and weak .... google Halbach array and have a read up about them

    readily available rare earth magnets

    depending on the coil turn count, number of coils and cores voltage and current strong electromagnets can be easily made

    haven't been able to find anything specific
  6. May 4, 2017 #5
    I was looking at youtube for how the winding core inside look like but couldn't find any.. any idea how it looks like or where to see it..

    350 lbs or 1200 lbs of force is huge.. how could mere 12 volts and 380mA turn into 1200 lbs of force.. where does the energy comes from I wonder...
  7. May 4, 2017 #6
    It is virtually impossible to judge force necessary to separate two magnets by just looking at the power consumption. The geometry, which in turns influences how the magnetic field lines run, has a huge influence. As an example, you can easily peel off a fridge magnet, but trying to pull it off all at once requires far more force.
  8. May 4, 2017 #7
  9. May 4, 2017 #8
    A normal magnetic door has a holding force of 600 lbs.. it's like have 4 people being carried by a mere pocket size 12 volts 350mA device.. which seems incredible.. later I will buy one to see how the inside works.. Has anyone actually calculated the magnetic force inside it how it can have a holding force of 600 lbs? Someone please compute it because it still sounds incredulous.. is this not indication of a new physics.. maybe the energy comes from the vacuum?
  10. May 4, 2017 #9


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    Force and energy are totally different things. Depending on how you do it, you can generate 1200 lb of force with zero energy input.
    It's been understood for over a hundred years -- and please don't idly speculate. We don't allow that here and it is much faster/more effective to just learn the real physics.
  11. May 4, 2017 #10
    Can you give an example of how to produce 1200 lb of force with zero energy input?

    There is no natural magnets that can hold 1200 lbs? But the tiny magnetic lock can. So induced electromagnetic force is indeed stronger than natural magnets? How come?

  12. May 4, 2017 #11


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    Every permanent magnet generates force with no energy input. For a non-magnet, you can just pile up 1200 lb of rocks.
    There are permanent magnets that can hold 1200 lb. This one holds 3,000 lb:
    Last edited: May 5, 2017
  13. May 5, 2017 #12


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    350lbs doesn't sound like enough to stop a strong person. The force will decrease rapidly with distance, so the lock only needs to be overpowered briefly.
  14. May 5, 2017 #13


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    A very large and very strong person probably not, but it isn't exactly easy to apply that much force to the door, since you have to rely on friction with the floor to generate the force.
  15. May 5, 2017 #14

    Ok. See picture above. I bought a magnetic lock with 600lbs holding force in order to figure out how such small device can hold 600 lbs (equivalent of 4 people hanging on it in the ceiling). I dismantle everything but couldn't open the black piece as it's one whole thing with black plastic integrated with whatever metal inside it at sides and bottom. Plugging it to a 12 volts 0.5A adaptor, it powers on and after sticking the shiny metal piece (below in the picture), it can't be removed by hands (because you need to apply 600 lbs pulling force). Testing it using a natural magnet.. the middle metal part of the black piece is positive and the sides negative. Ok. How does the coiling inside look like? I read using a core increasing the magnetic force many times. If you are to build it from scratch, how do you wind the magnetic wires in the cores? Clue: Also when I tried paper clips on the above compared to the natural magnets. The natural magnet can attract the paper clips at longer distance. While the paper clips stick to the magnetic lock only very close distance.
  16. May 5, 2017 #15
    Here are more zoom in pictures of the above magnetic lock EM core with a ruler at its side:


    Here are more specific questions:

    1. Why are there no similar sized natural magnet that has holding force of 600 lbs??

    2. What's so special about electrical electromagnets in general such as the above with mere 12 volts and 0.5 Ampere of electricity that can so much holding force?

    3. I plan to melt the plastic enclosure to reveal it's coiling patterns and metal core.. any idea how to melt the black plastic? Or any non-demolition scanning of its internal?
  17. May 6, 2017 #16


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    there's lots available as you were told earlier in the thread

    nothing special ... you are still attributing wonderful things to something very basic

    for safety reasons, I really don't want to go there .... I suggest it could be a bad thing to do

  18. May 6, 2017 #17
    the ones available are much bigger.. i'm talking of a natural 7 inches by 1.5 inches magnet that has holding force of 600 lbs. There seems to be none. Notice Russ_watters natural magnet weights 30 lbs.. while the above only weights 2 lbs... https://www.grainger.com/product/SU.../rp/s/is/image/Grainger/45PH65_AS01?$smthumb$

    If there is.. which one?

    Maybe in electromagnets the coils can be made closer? But what is the counterpart of the coils in magnets in terms of the faradays lines of forces...

    also why is there no electric motors made of natural magnets...

  19. May 6, 2017 #18


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    I will let you google that .... it really is time for you to start doing your own researching instead of making oddball comments with misunderstandings

    how did you come to that incorrect conclusion ?

    permanent magnets are used in motors. .... you can even build an electric motor at home with a permanent magnet and a coil of wire

  20. May 6, 2017 #19
    You mean anything that can be made in magnetic locks can be duplicated by permanent magnet with the same size.. well.. I used to go to stores to buy magnets as a child but couldn't find anything bigger with holding force of 600 lbs.. would be great to stick to refrigerator doors and let my friend pull it off...

    I mean why don't we have motors that run on permanent magnets without electrical current.. can't we make a permanent magnet with the same function as the electric current so we don't need fuel to run the motors?
  21. May 6, 2017 #20


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    To make a motor, you need to vary the magnetic field somehow. For example, if you have a fixed magnet at the 12:00 position, you need the force between that magnet and the rotor to be attractive when the rotor is at the 11:00 position and repulsive when the rotor is at the 1:00 position to keep the rotor turning in a clockwise direction. You can't do that with fixed magnets; they'll either always attract or always repel.
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