Discover the Power of Magnetic Locks: 650-1000 lbs of Force

[oquen]

Today I just learned 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?

 

[davenn]

where pure electromagnetic force was used to lock doors

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

My experience with magnets shows you can still pull two magnets apart..

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

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!

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

! Specification says 650 lbs to 1000 lbs of force.

do you have a link for this ?

Would anyone know the electrical patterns the magnetic lock make compared to ref magnets?

what is a ref magnet ?

here is an example of a commercial electromagnetic door holder

http://www.tomtop.com/alarms-secuit..._term=4576785870769436&utm_content=AU_Catalog

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

Dave

 

[oquen]

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

http://www.tomtop.com/alarms-secuit..._term=4576785870769436&utm_content=AU_Catalog

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

Dave

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.

I have a number of magnets that you cannot pull apart by hand

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

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 ?

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.

 

[davenn]

Ref magnet means Refrigerator magnet.

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

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

readily available rare Earth magnets

Your device example has only 12 volts and it has holding force of 350 lbs.

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

I'd like to see it's lines of forces diagrams

haven't been able to find anything specific

 

[oquen]

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

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...

 

[rumborak]

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.

 

[gleem]

This website https://www.kjmagnetics.com/calculator.asp?calcType=block calculates the force to pull a given type of neodymium magnet from a steel plate where forces can reach almost a 100 lb/in² with a surface field intensity of 0.64 Tesla.

 

[oquen]

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?

 

[russ_watters]

how could mere 12 volts and 380mA turn into 1200 lbs of force.. where does the energy comes from I wonder...

Force and energy are totally different things. Depending on how you do it, you can generate 1200 lb of force with zero energy input.

is this not indication of a new physics.. maybe the energy comes from the vacuum?

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.

 

[oquen]

Force and energy are totally different things. Depending on how you do it, you can generate 1200 lb of force with zero energy input.

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?

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.

 

[russ_watters]

Can you give an example of how to produce 1200 lb of force with zero energy input?

Every permanent magnet generates force with no energy input. For a non-magnet, you can just pile up 1200 lb of rocks.

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?

There are permanent magnets that can hold 1200 lb. This one holds 3,000 lb:
https://www.grainger.com/product/SU.../rp/s/is/image/Grainger/45PH65_AS01?$smthumb$

 

[Khashishi]

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.

 

[russ_watters]

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.

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.

 

[oquen]

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.

 

[oquen]

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?

 

[davenn]

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

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

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?

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

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?

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

 

[oquen]

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

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?

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

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...

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

 

[davenn]

If there is.. which one?

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

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

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

Dave

 

[oquen]

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

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...

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

Dave

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?

 

[Nugatory]

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?

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.

 

[Nugatory]

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?

If I have a single turn of wire, with .5A flowing through it, I'll get a magnetic field of a certain strength. Add a second turn to my coil, and I'll get twice the field, and so forth - I can make the field as strong as I want just by adding more turns. So .5A may not sound like much, but with more turns in the coil it will do just as much as a stronger current with fewer coils.

Natural permanent magnets are made from materials in which each individual atom is itself a tiny magnet. When we arrange the atoms so that their magnetic fields are mostly pointing in the same direction, we get a magnet. However, there's only so strong the magnet can be; we increase its strength by making more of the atoms line up, and once they're all lined up there's nothing more to do. But with the electromagnet... We can always add another turn to the coil, so in principle there's no upper limit.

 

[oquen]

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.

I think you need a current for motors to run.. so if you have a loop of superconducting wire with persistent current that goes around in loop.. and you have a permanent magnet surrounding it.. can you make the motor runs continuously without power input (theoretically)?

 

[Nugatory]

I think you need a current for motors to run.. so if you have a loop of superconducting wire with persistent current that goes around in loop.. and you have a permanent magnet surrounding it.. can you make the motor runs continuously without power input (theoretically)?

No. That would be a perpetual motion machine, not even theoretically possible.

 

[davenn]

You mean anything that can be made in magnetic locks can be duplicated by permanent magnet with the same size..

of course, but the problem is you cannot turn the magnetic field off so that the door can be opened, so that is why electromagnets are used

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..

I don't know how old you are, but if you are around my age, rare Earth magnets were not available
when I was a kid or a teenager and a bit older.
I don't remember rare Earth magnets being readily available in hobby type shops much before ~ 20
to 25 max years ago. over the last ~ 15 yrs, they have become easily available

Dave

 

[oquen]

No. That would be a perpetual motion machine, not even theoretically possible.

There are indeed Superconducting motors such as

Problem is you still have to supply energy to keep the temperature low, so there is still energy input which may be more to lower the temperature compared to a normal motor.

Can anyone answer if the currents and magnetic field induced between a normal wire carrying current and a superconductor is similar? Because in a superconductor, there is the so called Meissner effect where magnetic fields are excluded.. so can they interact with the North/South magnet/electromagnetic inside a motor at all to make it rotate?

 

[oquen]

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.

A monopolar motor works without any commutators or varying magnetic field.. what commercially available monopolar motors are available (are there)?

 

[rude man]

@oquen, the video states that half the insulation on the coil leads is removed where the leads contact the supporting wires connected to the battery. That FYI consitutes a commutator. At the end the video asks why half the insulation is removed. You should not rest until you have that figured out!

 

[mrad]

These magnetic door locks work on the principle of keeping the magnetic field tightly focused, either with a C-shape-to-I-shape interface (CI when put together looks like a backwards D, so the magnetic flux has a nice, tight, circulating path) or a solenoid interface (imagine a T dropping into a U). The energy required to pull away from a magnet is constant for a given magnetic field, but energy is the integral of force over distance, so a bar magnet will have low force over a longer distance, while these special shapes will have a high force over a short distance, but both will have the same area under the curve. A person can try to overcome the lock with a kick or jerking motion, to get a high force for a short period of time, so these devices typically have some sort of mechanical spring or shock mount that will give way, at a bit below the magnet's max force, to absorb that energy. The shock mounting, in effect, increases the distance and therefore the energy required to break the hold.

This points up what techniques can defeat these locks. A kick won't work, but if you can kick and then quickly insert a wedge to prevent the shock mount from recovering to its home position, and then repeat, that may ratchet the door apart until the shock mount reaches its limit, and then a kick against what is now a rigid body might momentarily exceed the magnet's max force. A pry-wedge-repeat technique may also work. The reliance on these special shapes makes them vulnerable to sabatoge, where someone slaps a sheet of aluminum over the steel plate (when the store is open, for example) so that everything looks ok, but the magnets max force is severely compromised. But lucky for us, hoodlum thieves don't hang around Physics Forums much.

 

[mfb]

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...

You need a suitable pair of objects for large forces - a fridge door is too thin (unless your other magnet covers half of the fridge or something like that).
Various online shops sell magnets that can give a force of hundreds of pounds on contact.

There are also switchable permanent magnets. Mechanical ones where you can establish or break the holding force by rotating a permanent magnet (sketch), and electromagnetic switches (electropermanent magnets).

 

[oquen]

@oquen, the video states that half the insulation on the coil leads is removed where the leads contact the supporting wires connected to the battery. That FYI consitutes a commutator. At the end the video asks why half the insulation is removed. You should not rest until you have that figured out!

It's not that. Nurgatory didn't want to give the answer so we can figure it the simple solution. The answer the video doesn't need commutator is because it's so light and it can make one full resolution even if only one half cycle is making it turn! (this is correct, other experts, right?) Making only half the insulation removed need to be exact so the one half cycle is in the inward force because if it's opposite.. it won't turn at all. So not a practical solution. Watch this and all shall be revealed.

 

[mfb]

It has "1/2 of a commutator". Half of the turn is unpowered, but the other half is sufficient to keep it moving through the whole rotation.

 

[oquen]

It has "1/2 of a commutator". Half of the turn is unpowered, but the other half is sufficient to keep it moving through the whole rotation.

Maybe it can move it faster, but it's not necessary. For example. Watch the following video especially at the 2:30 mark (just jump to it if you don't have time to watch the entire video), you can see the guy removing all the insulation around the end.. not just the 1/2 and the winding still runs:



I guess the reason it still rotates is because it's so light that it can overcome 1/2 of resistance, right?

 

[NTL2009]

Maybe it can move it faster, but it's not necessary. For example. Watch the following video especially at the 2:30 mark (just jump to it if you don't have time to watch the entire video), you can see the guy removing all the insulation around the end.. not just the 1/2 and the winding still runs:
...
I guess the reason it still rotates is because it's so light that it can overcome 1/2 of resistance, right?

Interesting. He clearly strips all the way around. I might build one to try myself.

My initial theory is the magnetic forces at some point push the coil up and away from contact, providing just enough switching to keep the force alternating, but I can't quite work that out on paper.

 

[davenn]

It's not that. Nurgatory didn't want to give the answer so we can figure it the simple solution. The answer the video doesn't need commutator is because it's so light and it can make one full resolution even if only one half cycle is making it turn! (this is correct, other experts, right?)

wrong
you are clearly not understanding what the commutator(s) is
both your videos clearly show the commutators of each of those motors
in your post #26 --- it's the 2 loops that the armature wires run through
in your post #32, they are shown as hooks rather than loops

the commutators in these 2 videos are serving a dual purpose
1) they are the bearings for the armature to run on and
2) they are the commutators ( the power transfer point ) the point where power is transferred
between the fixed sections and the rotating sectionsDave

 

[NTL2009]

...
both your videos clearly show the commutators of each of those motors
in your post #26 --- it's the 2 loops that the armature wires run through
in your post #32, they are shown as hooks rather than loops ...

Yes, but in post #32, how do the hooks provide any switching? If power is just transferred, with no switching, the armature will move towards, or away from the magnet (depending on polarity), and just "stick" there. But that motor spins. That is normally done by switching the polarity with a commutator, but in these simple motors, they just connect half the time and let inertia carry it through.

Maybe it's obvious and I'm just missing it.