Electromagnetic lock design

  1. hey guys
    Well Ive 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 cant 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.
     
  2. jcsd
  3. 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?
     
  4. so like how much force does it need ? i mean to lock the door secure ... so whats your guess .. ? the hotel and also work on the same principle. I would control it through the controller ....
     
    Last edited by a moderator: Aug 4, 2009
  5. negitron

    negitron 842
    Science Advisor

    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.
     
  6. 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 thanx bro , i'll look into it
     
    Last edited by a moderator: Aug 4, 2009
  7. negitron

    negitron 842
    Science Advisor

    You do that. Good luck to you.
     
  8. 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 !
     
  9. Danger

    Danger 9,878
    Gold Member

    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.
     
  10. like ur style bro ... but im 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: Aug 4, 2009
  11. Danger

    Danger 9,878
    Gold Member

    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.
     
  12. 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?
     
  13. negitron

    negitron 842
    Science Advisor

    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.
     
  14. Danger

    Danger 9,878
    Gold Member

    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.
     
  15. berkeman

    Staff: Mentor

    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).
     
  16. OK guys ... i better tell ye all abt the whole project cuz 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 wont 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 ...
     
  17. eeeh .... i dont know who's ugly question was i answering ... i read the post again .. u guys were just refuting skeptics idea.... :confused:
     
  18. berkeman

    Staff: Mentor

    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 lets 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:)
     
  19. 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?imgurl=http://www.pt-hardware.com/ProductImages/300P%2520MAGNET.jpg&imgrefurl=http://www.pt-hardware.com/&usg=__CVBTOebrbvPQNZt5zO87ZFdejs0=&h=1010&w=714&sz=78&hl=en&start=10&um=1&tbnid=gZjipxD4wfmzPM:&tbnh=150&tbnw=106&prev=/images%3Fq%3Dmagnetic%2Block%26hl%3Den%26sa%3DN%26biw%3D1280%26um%3D1

    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 ?
     
  20. negitron

    negitron 842
    Science Advisor

    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.
     
  21. eerrr .... you talk about fire codes ....... we don't have fire alarms here ...
     
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