I've been searching for a small (20 to 30mm Dia) disc shaped EM lock for a project I'm working on but can't find any. This type of lock's function, where when the EM is energized the magnet activates, attracting a pin or plate, is what I need it to do but I can't find them small and flat enough. I then found some 24V EM brakes for a "Duplicator" (copy machine?) where the size may be ok but if they were flatter it would be better. From what I understand these work the opposite way. The brake pad is normally engaged ("locked") to the hub by a spring, then when energized, the brake pad separates from the hub allowing it to rotate. Is this correct?

Would it be possible to convert the EM brake into an EM lock merely by reversing the wiring or would I need to reverse the direction of the winding? Would that work to then attract a plate when it is energized?

Also, how much could I reduce the voltage and have it still attract a metal plate with a decent pull strength - say from 1/4" away?

Thanks for you help!

  • \$\begingroup\$ There are magnetic locks for doors and gates. From your description, I can't tell if that is what you want. If you enter "magnetic lock" in a search engine, I think you will see some examples. They have two main parts, the electromagnet and the steel plate. When the electromagnet is energized, the steel plate is held against it. \$\endgroup\$ – mkeith Oct 25 '15 at 15:34
  • \$\begingroup\$ Yes, those are about the right size and function how I need them to but they are rectangular and I need the shape of a stack of three or four 1/2 dollar coins. I think what I will do is try to make a custom one by using the suggestions from you all or try to modify the duplicator I have. This should be interesting. I'll let you know what develops. \$\endgroup\$ – BretMan Oct 26 '15 at 19:43

The EM brakes are normally designed for spring-set, EM-release operation. With that design, the brake does not release if power is lost or the driver circuit fails. For most applications, that is the "safe" mod of operation. To convert such a brake to EM-set, spring-release operation, it would need to be mechanically altered so that the direction of the spring force and EM force would be interchanged with each other. That is not likely to be practicable.

Since EM-set brakes are rarely used, you may not be able to find one that is suitable. You might find an EM operated clutch that is suitable for installation as a brake.

  • \$\begingroup\$ Interesting, thanks. Well, my objective with the device is to have it lock momentarily and with much less EM force but the EM locks I'm finding are too thick due to the magnetic force they create. I need a thinner and flatter EM lock, which therefore will create less magnetic force. This will be fine for my purposes. Can you recommend a supplier of such small and flat EMs or the EM clutches you described? \$\endgroup\$ – BretMan Oct 25 '15 at 15:35
  • \$\begingroup\$ I assume that the brakes for a duplicator that you found stop a rotating shaft by friction. If that is not the action that you are looking for, you may need a solenoid rather than a brake. I am familiar with some clutch and brake products that are larger than you describe. Other suppliers probably make smaller products similar to what you found. You can regulate the force by regulating the current, but you will need to perform tests or get detailed information from the manufacturer. \$\endgroup\$ – Charles Cowie Oct 25 '15 at 18:05
  • \$\begingroup\$ I need the EM device to have a much higher width to height ratio and the height needs to be low - say similar to a stack of three or four 1/2 Dollar coins, so a solenoid would be tricky. As you say, I will need to do some tests on variations. \$\endgroup\$ – BretMan Oct 25 '15 at 19:01

Not clearly what you want. Do you want a device that, When the voltage is applied:
a) locks the motor or shaft -> EM brake
b) couples motor shaft with load -> EM clutch
c) unblocks the motor shaft -> safety brake

a and b variants are larger, meant to engage and disengage while motor/load is turning, meanwhile c type is small brake integrated on motor, it has to engage/disengage at standstil, only in emergency case can be switched in running condition.

The brand I know is Lenze: http://www.lenze-selection.com/en-gb/drive-components/electromagnetically-actuated-clutches-and-brakes/electromagnetic-clutches-and-brakes/

  • \$\begingroup\$ Thanks for the link. There is no motor involved. I believe it would be closest to an EM lock in function, where a disc is attracted to the EM. It's just the EM locks are too thick. As I mentioned above, it needs to be about the size of three or four stacked 1/2 Dollar coins. The brakes I found are about the right size, they just don't function, as brakes, the way I need them to. \$\endgroup\$ – BretMan Oct 25 '15 at 19:07
  • \$\begingroup\$ Maybe you should just make something. Wrap some magnet wire around a steel disk and play with it. Make sure you count the turns. Start with like 10 turns of large wire. Drive it with high current. And when you find a level of force that works for you, you can use more turns and less current, proportionally. \$\endgroup\$ – mkeith Oct 25 '15 at 19:52

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