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I'm guessing these are designed for automatic release of locker doors like in the Amazon locker system. They operate at 12V and physically push the door open instantly when triggered.
The coils are only rated for brief pulses, and draw such a high current (2-4A) that any microcontroller based circuitry should be designed with separate tracks for the coils and logic from the PSU. To protect the switching transistor against the current spike caused by the collapsing magnetic field when turned off, a diode should be wired across the coil with the band pointing to the positive rail.
The keywords to find these on eBay are:-
electric magnetic door lock
Price will be around £$€7
Here's the manufacturer's website:-
https://www.doson.com.tw/index.php?mod=&lang=2
These could also be used as a controlled drop mechanism in some applications.
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These are electromagnetic locks, they're used for things like well a good example. The amazon lockers. Have you ever seen, amazon lockers that you order goods get it sent to the suitable amazon locker locally, and when you go up, you can scan your phone or type in a number and there's a click and uh the door of one of the lockers. Does this it basically unlocks and it pings open and that it physically spins open you can go and take your goods out, and then you close the door and it'll actually shut and that sugar, your goods, it's very good, it's a great way of picking stuff up.

If you you're not like to be at home, so this is the type of mechanism you'll find in these and they operate at 12 volts. But there's a few things you should know. This is a same mechanism, but this one has a spring plunger. The reason it's got a spring plunger is to push doors open and make sure they don't swing shut again, it's just a bit of extra oomph to get the doors to open, but it's the same principle there's a solenoid in the back and it pulls down and It kicks the the plate out and the door swings open.

Let me show you these operating electrical, and this is going to get very noisy, there's going to be very loud clicks because uh, it's quite spicy, so these ones operate at 12. Volts i've hooked up. Some leads temporarily, so i shall hook this up to here and it will eject as soon as i touch this on it'll eject the pin and it ejects it right across the the table. Both incidentally use the same pins.

Likewise quite connect this one up. It will fire the pin out and that's it unlocked it's worth mentioning that this one draws a lot more current, this little one they're very short duty cycle, solenoids they're, small solenoids - that punch quite a lot of force to actually unlock that reliably. This one draws about 3.5 amps at 12 volts, and this one draws about 2 amps at 12 volts when it's pulling its slightly bigger solenoid in um. It's also worth mentioning that you can't leave these energized for any length of time.

I'll show you, the circuitry that we used to drive them later on in the video, but uh they're, only rated for a 10 duty cycle, but in reality their operation would literally be once once or twice a day depending on the use of those lockers. It would just be a brief pulse, and that would be it that's how they're designed to be operated they're not designed for sustained current. So i can show you the rough interpretation of the mechanism here there is the swinging lock here now. If i can actually operate this, the screwdriver from down below, i can show you this going when the pin comes in.

Actually, you know what i'll just use the hasp that it's supposed to take when the pin comes in you'll, see that as it pushes that back a little lock comes up a little pin. It's basically an arrangement like this, where this is that hasp and as you push it in this pivots up and as it swings back if the blue chip blue, is the channel that that oh zoom down this is probably better you'll, see better. If the blue's the channel this slot that this goes into, that's what's out of sight inside the unit, there's the long arm, which is the locking arm and there's this one, which is the one that comes up and catches the pin and stops it being pulled open In its open state, that pin is free to move in and out, but when you push it in it pushes this back and then there's this arm on top, which you can see this metal plate, this pivot pivoting metal plate and it's got a little square cut Out this bit drops into that square cutout. So once it's pushed in that clicks that clicks down latches it and that's what stops it coming back out when you activate it, you can see the solenoid at the back here pulls down and it pivots that up and allows that to click back out.

This one is riveted together, the other one is held together with screws i'll show you the circuitry, that's like like to be used to draw these, and then i'm going to take this the screws out this and we'll see if we can open it without it, it Flying apart into millions of pieces, it might happen something really important. David blog mentioned this recently, the flyby protection diodes. I've mentioned a lot in other schematics as well, but really important for this one. Because of these high current coils, i've shown an order transistor here these days, you'd use a mosfet.

You could actually use something like a uln, 2803 style sort of pack of mosfets at darlington. Should i say, but these days it'd probably a mosfet, but i've just shown a generic transistor to fire control. This you'd basically send the signal to the transistor, but just very briefly, just to turn it on for as long as it takes to unlock the mechanism and fire open. But when it does so, this end starts off being positive.

It gets pulled down to negative and it builds a magnetic field in that direction. In the process of unlocking the diode is very important because when you turn it off again, this end will go positive. This end will go negative and it can create a massive because it's got no loading. It can create a really high voltage spike that can destroy the transistor.

So that's why this diode here the diode normally does nothing, because it's in the opposite polarity to the 12 volt supply. But when that magnetic field is collapsing, it takes a shortcut through that diode and that basically quenches that spike. It's a flyback, diode very important. Another thing that would be really useful to add here.

If you had a load of these solenoids on, say one common bus. It would be useful to add a ptc fuse in line rated for say just under the operated current of the calls, because they are operating very briefly. The ptc fuse would protect against the processor crashing or the transistor feeling and burning out the coil, because what would happen is that if it was just operated briefly, the ptc fuse wouldn't generate enough heat to actually go into its latching off state. But as if the coil jammed on this fuse would kick in and it would basically go high impedance and limit the current through until the whole system had been reset and the fault had gone, and then that would cool down and reset again just things worthy of Note in the past, i would also have used if i was using ordinary transistor, maybe a capacitor in series with a discharge resistor across a high value like 100k across that and say this would be say, 10 microfarad.

What that means is that, when this went positive, current would flow to charge that capacitor and it would it wouldn't be a nice square wave, but it would give a a controlled pulse to turn the transistor on. But then, after that, capacitor is charged. You'd only get a very small leakage through this resistor, so, basically speaking, the transistor would only be able to operate for a brief pulse. I used to do that.

I used to just play safe. I used to go too far, but that's better going too far than having terrible faults occur like a software update that results in all the solenoids burning out, people will have been there let's under some of these screws, let's use a smaller driver. What have i got here? That's too small. This one looks promising.

Is this going to ping apart? I do hope not, but then again it'll be a good exploration. If it does, the amazon lockers are great when you just can't get stuff delivered to home or work. It's nice if you're living or you have to pass through the city centre if you're commuting to a job, because you can't really drive to it in the case of some cities, it's useful to just order it and pick it up, particularly traveling away from home. This is promising there.

It is. Oh, i forgot to mention something this switch, and this is showing everything isn't it. This is showing absolutely everything and it needs brightened up. This is where it's going to be super bright, but i don't care it's fine.

That's going to be super bright, i'm going to look like mr or honky with his white fingers here. Here is the latching mechanism. This one doesn't have the hole through the plate, like the other one, i've just pinged this spring off. That's all right, and i can put that back out i'll, just leave that out at the moment.

So when this goes in, there's that switch there. The switch will, as this pushes back it lets go of that switch. Then this goes under the ramp and it clicks in and that's what holds it now, that switch because it's closed, because it's using the normally uh open contact and normally close contact, because it's now released that switch is now making. I can prove that i can prove that with the meter i shall bring the meter in, i shall set it to continuity, and i shall bring in the lead here that comes from that switch and i shall prove it and it will go beep, it's beeping and Then, when that solenoid activates, this is where it's going to get noisy hold on.

Let's see if i can get my probes back in here again, it's all the wires are quite stiff, they're they're, not playing ball at all. When i press this down - oh it pings out and because i've uh, because i've gone far too far and the switch has fallen out yeah. That was a very good demonstration, but this is what happens. Actuating, that, while it was open, was probably an absolutely terrible idea.

It's gone way too far: yeah! Oh, it's just little dimples down here. It really needs the case to be screwed up to actually hold that, and it's just blimey look. It's just dimples on both sides that hold that switch in, but nonetheless there it is. It would uh that's the position, it would be showing that the the door was closed and then, when this comes down it opens it.

This is a screw. I tried unscrewing it. It didn't unscrew, i didn't know what was inside. I do now there's a fairly powerful spring up there, and this one also has a very powerful spring, because it's the one that's designed to push that open and make it ping.

Would you like to see it activated electrically? Yes, you would right. Well, let's uh activate it electrically, pow very noisy, quite a loud click, i'm not sure how secure they are, but i will say that i got a big mofo, neodymium boron magnet and i just held it all around the case and it uh i'm going to tame This down again, i held it all around the case and i couldn't activate the solenoid with the magnet the magnets stuck to this steel case, but that was it uh. I just couldn't uh it's kind of shielded, they've, obviously thought of this people applying external magnets, but that's: what's in these they're quite interest they're quite nicely made, i shall provide links to the company involved. They have data sheets showing uh various things, including the duty cycle and the voltage rate in 12 or 24 volt optional and the current two amp.

It was uh two amp for this one, but uh 3.4 amp. That's absolutely right! That's exactly what i measured, because it's got a very low resistance, uh but interesting things well worth uh getting some of these and exploring them. I shall put links to the site, though, and i think these may have come from uh, banggood or ebay or something not really sure, but they weren't that expensive at the time, certainly they're quite a novel thing for say: secret, hatches and things like that for remote Control novel devices.

8 thoughts on “Inside an eBay electric lock mechanism”
  1. Avataaar/Circle Created with python_avatars Antoin Chamamyan says:

    It’s quite tricky for short powering pulse time that it doesn’t give you enough time to realise the latch, then push opening the door, at least, you need two – three seconds to complete the process, ( I usually set it to 5 sec with a buzzer as an indicator of activation), however, three seconds with 3.5 Amp needs to use quite thick power cables, that to avoid dropping voltage during distance , rather than this, you can improve the performance by powering it by using a 12 volt Ac transformer rated output power ( I’d assume 24VA) and a relay driver instead of an NPN transistor, it will be such a great solution as I do for all my installations.
    Cheers mate.
    Tony.

  2. Avataaar/Circle Created with python_avatars RV Sparky says:

    Reminds me of pin ball machines. Where like the flipper solenoids are really strong but would burn quickly. But they have a switch that changes from the (firing coil) to the hold coil since obviously much less energy needed to hold the solenoid once it's traveled all the way.

  3. Avataaar/Circle Created with python_avatars Jarkko Aitti says:

    I wonder if all that metal would stop a another coil energizing the solenoids coil. Could be a fast keyless way to open these 🙂 Anyway is that steel case magnetic? if not or weakly, one could be able to lure that probably more magnetic solenoid core in with sliding a strong magnet down besides it? In case of magnetic steel side panel, i wonder how the magnetic flux is directed in that (in case that could be used too)

  4. Avataaar/Circle Created with python_avatars EasilyFallsForClickbait says:

    Instead of a PTC, could a large capacitor be used to power each lock? First thing I though was if PTC resets then might have to wait a long time and would be annoying. With a capacitor per lock, the 12v supply could in a current limited way charge the cap, no need for a large 12v supply or heavy duty wires, and avoid the reset problem.

  5. Avataaar/Circle Created with python_avatars DoctorX17 says:

    Some of these can be forced open with enough pulling force, some you can pull the door and whack it with a hammer to make it jump open. But most lockers they don't give you anywhere to pull and get enough force for either method, so combined with the resistance to magnetic manipulation, they're fairly hard to force open — most thieves would probably just pry the door open with a crowbar and break it or otherwise smash their way in before they could really make one of these misfire or otherwise open.

  6. Avataaar/Circle Created with python_avatars DrHarryT says:

    Why put the screw into the latch arm??? Can't be to adjust tension because one end of the spring rests against the case and the other end hooks around the nose of the arm.
    Maybe to ease in assembly?
    If the switch was put in series with the coil it would not matter how long the pulse is as long as it is long enough to un-latch the system. That way the coil can only energize if the latch is hooked [door closed] then as soon as it is un-latched by the solenoid the current is interrupted immediately. With separate pigtail connections, the switch can register to a door control board as to whether the door is open or not. Maybe connect the 0V rail through the switch to the source pin of an N Channel MOSFET. This way a logic level signal could tell the door to open, which would only activate if the door is already shut.
    Fun contemplating potential engineering designs and reasons.

  7. Avataaar/Circle Created with python_avatars Jason Halverson says:

    wish we had those kind of lockers here for amazon. i've had several items stolen from outside my apartment, and it's not real convenient to have them deliver to my work either. and they always seem to show up when i'm not home

  8. Avataaar/Circle Created with python_avatars dizzygunner says:

    These remind me of the mag locks we have on the doors where i work (in a betting shop so we have a switch to lock the door from behind the counter, we just all it a mag lock, but the don't swing open like that) would be interesting to see what the differences are you you could get your hands on one of them.

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