How Can I Design a Powerful Yet Low-Power Electromagnetic Lock?

AI Thread Summary
The discussion revolves around designing a powerful yet low-power electromagnetic lock controlled by an 8051 microcontroller for a digital security system. The user aims for a lock that can exert around 600 lbs of force while consuming only 3 watts of power. Participants suggest alternatives like using solenoids instead of continuous electromagnets to reduce power consumption and ensure reliability during power failures. The design includes a keypad and LCD for user interaction, with a backup power system to address potential load shedding issues. Emphasis is placed on safety and the need for a mechanical exit mechanism to ensure functionality in emergencies.
felix_cat
Messages
19
Reaction score
0
hey guys
Well I've searched the net quite a lot but all in vain. Every website comes up with their product rather telling about how to design. Well guys i am a student of 5th semester electronics engineering, have not specifically designed an electromagnet but have studied the basic course for physics and of electric machinery that involves different types of generators and motors, transformers. Now you guys might be wondering what type of engineering am i doing, well i can't say much there
My problem is that I have to control a magnetic lock by 8051 controller. I am making a digital security lock. Now you guys must have seen the magnetic locks, well how to design one. It has to be POWERFUL around 600lbs of force and extremely low POWER CONSUMPTION around 3watts because i am trying to fabricate the market product. Guys please guide me in such a way that i learn not like giving me the complete solution. Dont worry about the controller because I can handle it. The one thing puzzling me is that if i were to make it stronger by increasing the turns, the power consumption would increase, is that so, then i must increase the diameter. Well please answer.
 
Engineering news on Phys.org
Why does it have to generate 600 lbs. of force? Nearly all hotel rooms now use electronic locks. How do you think their locks work?
 
so like how much force does it need ? i mean to lock the door secure ... so what's your guess .. ? the hotel and also work on the same principle. I would control it through the controller ...
 
Last edited by a moderator:
Errrr, these types of locks don't use an electromagnet as the locking mechanism; that woulds consume large amounts of power cointinually and when the battery power failed, the lock would open. Not smart. Instead, the use a solenoid to move a part either into or out of the locking chain. It only has to act with a force of a few pounds and only when the lock is correctly coded.
 
yup magnitron, well i did some googling and the type a solenoid you're talkin about is class C solenoid or what ever, it has a spring thingy and moves in and out .. well thanks bro , i'll look into it
 
Last edited by a moderator:
You do that. Good luck to you.
 
well there is another thing now. I am thinking of making the electromagnet lock instead, the one which i talked about before. Look it works continuously on power when locked. In the market there are products such as the one i am mentioning and they have a little as 3$ annual expense of electricity, now how about that. Help me make one such electromagnet please. They provide 1200lbs of force and work on 12V dc 310mA. At least give any ideas !
 
Greetings, Felis Catus.
My initial assumption about your question is that you are looking at a true electromagnetic lock, wherein the magnet gloms onto a steel plate on the top of the door. I had some very limited exposure to those when I was in the security business. They really don't draw a lot of power. You might want to check into EftonScience, which used to be Edmund Scientific Company. They sold electromagnets that were a couple of inches in diameter, an inch or so high, ran on two 'D' cell batteries, and had a 500lb lifting capacity. Weld a couple of those suckers to a support bracket, tie them into your 12VDC supply, and you could probably hold off a SWAT team for a couple of hours.
 
like ur style bro ... but I am in the south asia ... so might want to re-think my opportunities here ... i thought i would give it a go myself, make one of those but turns out it aint easy , lots of calculations involved.

Would be helpful if you guide me through the design procedure ... like how many turns are we looking for here ? .. the dimentions ...
 
Last edited by a moderator:
  • #10
I'm afraid that I can't be of help there. I know nothing of the design aspect for electromagnets. One of the electrical geniuses like Berkeman can probably set you straight. Good luck with it.
 
  • #11
Would it not be easier and use less power if you used enough permanent magnets to exert that amount of force and use the electromagnet to oppose the permanent magnets long enough to open the door?
 
  • #12
skeptic2 said:
Would it not be easier and use less power if you used enough permanent magnets to exert that amount of force and use the electromagnet to oppose the permanent magnets long enough to open the door?

I'm not sure you'd want to do it that way, either. If your electromagnet fails--say if the winding opens--the door becomes a wall.
 
  • #13
negitron said:
I'm not sure you'd want to do it that way, either. If your electromagnet fails--say if the winding opens--the door becomes a wall.

Therein is the reason for always first determining whether you want the device fail-safe (unlocked) or fail-secure (locked) in a power failure. The application is the deciding factor.
 
  • #14
Plus there should be a manual back-up part of the lock. A keyed means to open the failed electical lock (which should fail locked).
 
  • #15
OK guys ... i better tell ye all abt the whole project because u guys r makin fairy tails.

The project consists of a keypad, lcd and a lock. The key pad and lcd would be in front of the door. The door can be unlocked from the front by only entering the correct password. There is going to be a button in front that would lock the door straight if it were in a unlocked state.

At the back there is going to be the lock which would be set up on the top, where usually the magnetic locks are. Down in the middle would be two buttons that would instantly either lock or unlock the door. The lock would run on 12V DC supply. I plan to make a power supply myself which is not going to be a problem or maybe if i find a suitable adapter.

So rite now its cool, unless your in that part of the south asia where load shedding is a heck of a problem. Therefore I had a back up in mind. EITHER normal non rechargeable batteries, if they last, which i convincingly know won't because I'd be simply shorting the wires in the lock. Henceforth i had a rechargeable battery mechanism in mind. When no lights, battery comes into play, and when yes lights, then battery the charges ... ... ...

how about that guys. and how the heeeck am i goin to end up with a wall rather than teh cool, comfortable under control magneetoo lock :wink: i don think its gona malfunction now .. or would it ? .. open for debate ...
 
  • #16
eeeh ... i don't know who's ugly question was i answering ... i read the post again .. u guys were just refuting skeptics idea... :confused:
 
  • #17
felix_cat said:
how about that guys. and how the heeeck am i goin to end up with a wall rather than teh cool, comfortable under control magneetoo lock :wink: i don think its gona malfunction now .. or would it ? .. open for debate ...

I've only read a few of the posts, so apologies if this has been pointed out already. A much more efficient way to do an electronic lock is to have your small solenoid only act for a couple seconds after the valid password is entered, and that small solenoid pulls a blocking pin out of the manual doorknob mechanism to allow it to be turned. The blocking pin can be quite strong against, say, up-down motions as people try to force the doorknob without using the password, but it will still only take a little current for a few seconds to pull it out of the way for access after a valid password is entered.

That is how many of the door locks work here at my workplace. You swipe your cardkey, and then you hear a small "click" in the door knob area, which indicates that the blocking pin has been pulled back by the solenoid for about a 4-second timeout. You have that much time to turn the knob to open the door, or the solenoid releases and you have to re-swipe. 4 seconds is usually plenty, but of course that time is up to you. A shorter time let's you run longer on batteries if the power is out.

One thing you will learn rather quickly in Engineering is that you should always look for optimizations in your designs. Using lots of current to actuate and hold a door lock is definitely not an optimum use of power, especially for when you need to run off of a battery backup. Be smart in your designs! o:)
 
  • #18
great ideas there !

why i was designing for continuous power ? Because this lock is for home use where you have to lock the door usually at night but perhaps i might want to rethink it. Another reason is that i saw these magnetic locks on the internet and they work the same way. Check the link below

http://images.google.com.pk/imgres?...ges?q=magnetic+lock&hl=en&sa=N&biw=1280&um=1"

So give it a final thought. I would do as you say because you got more experience on your side. One think more, you think the lock would last an hour running on rechargeable battery ?
 
Last edited by a moderator:
  • #19
Definitely you do NOT want a fail-closed door lock for home use. For one thing, it'd be a fire code violation. So, the permanent magnet idea put forth earlier is right out. Your idea could work, but you better be sure of the reliability of your construction; if the coil opens or the power is interrupted for any reason, your door is wide open.
 
  • #20
eerrr ... you talk about fire codes ... we don't have fire alarms here ...
 
  • #21
felix_cat said:
eerrr ... you talk about fire codes ... we don't have fire alarms here ...

Well, he also means for basic life safety. I'm assuming the electronic lock is only for access from the outside. From the inside, the door opens with just a turn of the knob, correct?
 
  • #22
berkeman said:
Well, he also means for basic life safety. I'm assuming the electronic lock is only for access from the outside. From the inside, the door opens with just a turn of the knob, correct?

well kind of .. like i said , there are going to be two button behind the door, one for lock and the other for unlock. You can have a knob to pull the door open ...
 
  • #23
felix_cat said:
well kind of .. like i said , there are going to be two button behind the door, one for lock and the other for unlock. You can have a knob to pull the door open ...

The behind-the-door ability to exit needs to be 100% mechanical. Quiz Question -- why?
 
  • #24
bro ... if you're wondering the 'behind the door' buttons to malfunction, just pull the plug out and the doors open ...

i hate quizzes though .. aint that sharp ...
 
Last edited by a moderator:
  • #25
felix_cat said:
bro ... if you're wondering the 'behind the door' buttons to malfunction, just pull the plug out and the doors open ...

i hate quizzes though .. aint that sharp ...

Not sure I understand your point (and not sure I want to be in a building that you have designed the electronic locks for...).

A big part of being a good engineer is thinking ahead. Safety is a huge part of what you do as a design engineer. If I gave you an interview question to describe to me an electronic door lock mechanism and system, and you fed me what you have posted in this thread, what do you think would happen?

Quiz Question -- Why?
 
Last edited:
  • #26
cmon dude ... don't be that harsh ... I've read your post again ...
look yours idea changes my design. I am not making a mechanical lock, its a MAGNETIC LOCK. My design is similar to those that are out there in the market. I gave the link too. I mean guys making those kinda locks aint fooling around .. are they ? .. or are the designs so flawed that they are marketing on the internet ?

I am trying to make one thing different. Normal Maglocks open when entered the right password. Close automatically when the door swings back (door swing back is automatic too). These are the one's which i saw at a university i went to. The different thing I am doing is that my design provides security from the outside but easily open from the inside. To make that happen I have to insert 'behind the door' control. AND i am not making the actuator solenoid lock thingys, its a purely MAGNETIC LOCK , no mechanics involved. Please stick to my design if you can ... and i hope i aint getting on your nerves because from the way your last post sounded ... :S :$
 
  • #27
I don't think you're getting on berkemans nerves. What he is concerned about is safety. Note the rules about posting about dangerous activities:
Explicit "how to" discussions of illegal and/or dangerous activities, or posts advocating such activities, are prohibited;...
https://www.physicsforums.com/showthread.php?t=5374"
We don't want to see someone get locked in when there's a fire and the door won't open.
 
Last edited by a moderator:
  • #28
berkman ... I am a newbie . ... let's face it ... i don't have answers to ur so called 'quiz questions', rather dealing me with sarcasm you could have some positive attitude and help me. I am in my 5th semester here, not working for a company like you.
I just asked you to help me make a friggin solenoid. that's it ... and my design won't let anyone lock em self up. YOU can just pull the plug out and the MAGNETISM IS HISTORY ... for godsake ...

and you josh cum here and sayin ... "we got rules mister. no one dies burning in the fire with a faulty design ... we don help peeple make that kinda stuff here" ... WELL for crying out loud I am not making such a thing. Skeptic gave the stupid idea for the PERMANENT magnet design... that's how u make peeple locked in PERMANENTLY... i think i wasted my time coming here on the forums .. buncha fyzists .. buh !
 
  • #29
close this thread because i aint comin back
 
  • #30
felix_cat said:
berkman ... I am a newbie . ... let's face it ... i don't have answers to ur so called 'quiz questions', rather dealing me with sarcasm you could have some positive attitude and help me. I am in my 5th semester here, not working for a company like you.
I just asked you to help me make a friggin solenoid. that's it ... and my design won't let anyone lock em self up. YOU can just pull the plug out and the MAGNETISM IS HISTORY ... for godsake ...

and you josh cum here and sayin ... "we got rules mister. no one dies burning in the fire with a faulty design ... we don help peeple make that kinda stuff here" ... WELL for crying out loud I am not making such a thing. Skeptic gave the stupid idea for the PERMANENT magnet design... that's how u make peeple locked in PERMANENTLY... i think i wasted my time coming here on the forums .. buncha fyzists .. buh !

I ask Quiz Questions all the time, son. It's a teaching/learning tool. As I mentioned earlier, a big part of learning to be a good engineer is learning to optimize your designs. And another part of real-world engineering is thinking about safety and reliability in your designs. You'll come to understand that as you continue in your engineering eductaion.
 
  • #31
Well I have got a lot of text warnings. Sorry for my disrespectful attitude Sir.

My request to you is just to look at the following link and explain the structure and design. It would be very thankful,grateful,utmost kind of you.

http://www.sdcsecurity.com/shared/eblast/081507_sdcsecurity/modularkit_datasheet.pdf"

This is the lock. Please explain why has he not coiled the solenoid directly on to the iron core rather he uses some black material. Could you kindly explain what that black material is and why the solenoid is coiled onto that. Give your guess of the dimensions of the core too.

And the reason why quiz questions are irritating is that you reply the answer to them very late. The other person has project deadlines to meet with if you are not aware.

Regards
 
Last edited by a moderator:
  • #32
felix_cat said:
Well I have got a lot of text warnings. Sorry for my disrespectful attitude Sir.

My request to you is just to look at the following link and explain the structure and design. It would be very thankful,grateful,utmost kind of you.

http://www.sdcsecurity.com/shared/eblast/081507_sdcsecurity/modularkit_datasheet.pdf"

This is the lock. Please explain why has he not coiled the solenoid directly on to the iron core rather he uses some black material. Could you kindly explain what that black material is and why the solenoid is coiled onto that. Give your guess of the dimensions of the core too.

Sorry, I'm not able to understand that pamplet with just a quick look. Maybe others are able to understand it...
 
Last edited by a moderator:
  • #33
Then do not take a quick look please . this is the forums , you have to help others, give time to them , come on , this is not fair. Berkeman, help please ...
This is a burning issue on forums, not a single forum on the internet deals with designing the electromagnet properly, you have to answer for the sake of science.
 
  • #34
felix_cat said:
berkman ... I am a newbie . ... let's face it ... i don't have answers to ur so called 'quiz questions', rather dealing me with sarcasm you could have some positive attitude and help me. I am in my 5th semester here, not working for a company like you.
I just asked you to help me make a friggin solenoid. that's it ... and my design won't let anyone lock em self up. YOU can just pull the plug out and the MAGNETISM IS HISTORY ... for godsake ...

and you josh cum here and sayin ... "we got rules mister. no one dies burning in the fire with a faulty design ... we don help peeple make that kinda stuff here" ... WELL for crying out loud I am not making such a thing. Skeptic gave the stupid idea for the PERMANENT magnet design... that's how u make peeple locked in PERMANENTLY... i think i wasted my time coming here on the forums .. buncha fyzists .. buh !

I'm very interested! I would love to find out more inforamtion related to this topic. Thanks in advance.
me too, I need more detailed info

simulation taux banque credit immobilier de France[/color] - Credit immobilier de France, simulation credit immobilier. Résultat mitigé pour le crédit immobilier de France.[/color]simulation taux banque credit immobilier de France[/color]
 
  • #35
felix_cat said:
Well I have got a lot of text warnings. Sorry for my disrespectful attitude Sir.

My request to you is just to look at the following link and explain the structure and design. It would be very thankful,grateful,utmost kind of you.

http://www.sdcsecurity.com/shared/eblast/081507_sdcsecurity/modularkit_datasheet.pdf"

This is the lock. Please explain why has he not coiled the solenoid directly on to the iron core rather he uses some black material. Could you kindly explain what that black material is and why the solenoid is coiled onto that. Give your guess of the dimensions of the core too.

And the reason why quiz questions are irritating is that you reply the answer to them very late. The other person has project deadlines to meet with if you are not aware.

Regards

felix_cat said:
Then do not take a quick look please . this is the forums , you have to help others, give time to them , come on , this is not fair. Berkeman, help please ...
This is a burning issue on forums, not a single forum on the internet deals with designing the electromagnet properly, you have to answer for the sake of science.

We don't give out designs or do your work / homework for you (which seems to be the case here). You might exhort us to spend time and effort upon your behalf (which we do, despite this being 'leisure' or a hobby for all of us) but you'd better do the same. As Jerry Maguire says, "Help us help you!" And in your very first post, you stated explicitly that you didn't want to be spoon fed a solution, you wanted us to do it in such a way(?) that you learned!

Okay, TA in me aside... As a 5th semester student in EE / Electronics Engineering, you should've taken an electromagnetics class. And, as you say, you know that an electromagnet depends upon both the number of turns as well as the current that goes through it:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html

Now, you may or may not know that you can multiply the effect of an electromagnet using a core with high magnetic permeability (yes, there are things that are much better than the iron / steel core):
http://en.wikipedia.org/wiki/Permeability_(electromagnetism)

With these in mind, you should be able to figure out how SDC does it. If you have to design your own system for authentication / control and locking (and it sounds like time's running out), don't do it the most complicated and sophisticated way possible (by designing and building your own electromagnet), do it the easiest, and most probably-successful way of doing it: with an off-the-shelf solenoid that pulls / engages a latch, as others have been suggesting!

Is the point of the course to design / build your own electromagnet which can rival commercial products? No? Then breathe, quit panicking, and figure out what you actually have to do (in the time available to you), and not what you wanted to do at the start of the project. This is what I counsel when the students I TA in my final-year electronics design project start freaking out with a month to go.
 
Last edited by a moderator:
  • #36
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.
 
  • #37
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.
 
  • #38
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.
 
  • #39
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 ??:rolleyes::confused:

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

looking from side on.
 
  • #40
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!
 
Last edited:
  • #41
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 !
 
  • #42
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.
 

Similar threads

Need an electromagnet to play Chess
Replies
37
Views
3K
Possible to connect two electromagnets perfectly together?
Replies
14
Views
2K
Electromagnetic field vs electromagnetic wave "radiation"
Replies
7
Views
2K
System design for charging battery from turbine alternator
Replies
8
Views
2K
How Do You Calculate the Force of a Solenoid to Lock a Neodymium Triangle?
Replies
9
Views
6K
How Do I Design an EMI Filter for a Converter with Only Voltage and Power Specs?
Replies
8
Views
2K
US Split-Phase to EU Heat Pump Not Working
Replies
1
Views
2K
How to Design a Donut Electromagnet
Replies
12
Views
4K
PVC Induction Heating Coil Design (early thoughts)
2
Replies
51
Views
3K
What's the normal low-load working temperature for an SMPS transformer?
Replies
27
Views
5K

Hot Threads

Recent Insights

Back
Top