Powering 2 12V Electromagnets

Hi, perhaps this can help just a little.  First the ohms law stuff is P = I * E so you have power in watts is equal to current (I) in amps multiplied by voltage (E - electromotive force) in volts. Then the other part of the pie chart is E = I * R or voltage in volts is equal to current in amps times resistance in ohms.  The rest of the stuff are the factors of ten for milli, mega, nano, etc. Those pie charts usually have the equations for the different groupings added in as well, like  P = I^{2 *} R

Two 12v electromagnets are probably best connected in parallel, so the required voltage is delivered to both equally.  The factor that changes in this case is the required current is doubled because it needs to travel down two paths. This means you need a higher power output for your supply (remember P = I * E).  Remember have some resistance in the lines as well, or you could damage your power supply, a coil (which is the usual form for an electromagnet) acts as a resister only for a brief time in a DC circuit, then it becomes "saturated" and acts as just a plain wire after that, and will create an infinite current situation E = I * R or I = E / R when R == 0. Most often this is observed as thermal runaway (gets smokin' hot).

So to address the question, 12v supply for your power, and link the magnets in parallel.

Hope this helps,

Jack

ok, That makes sense, but before I explain a bit more, What is the difference in wiring something in parralel as opposed to wiring it in a series.  My idea is sort of a small electromagnetic lock, where I will have a small butt that will send a signal from an rf transmitter to an rf receiver to turn on one of the electromagnets sliding the iron bar to the right, unlocking the door, and then when i press the button again it sends a signal to the other magnet, moving the iron bar to the left, locking the door.  So the magnets will not be active at the same time, and they will not be active for very long.  I wan't to keep the project small, and if possible, keep it hidden, so what would be the best way of powering this, possibly something that will fit in the wall.  I have seen small power supplies surrounded by metal that look like this http://www.mouser.com/images/meanwell/lrg/rd50.jpg , that take mains and convert it to dc, but i don't know how efficient those are.  My guess is, that if i want to keep it contained within the wall, I will need to use some sort of AC to DC psu.  Ideas?

Just in response to your last entry Gabriel: What you're speaking of is a solenoid.  Energize a magnet, it pulls a rod up into the magnetic field, and holds it there until power is removed.  Rather than using two magnets on an electronic lock, a solenoid with a return spring is used.  Energized - The latch is pulled back into the body of the solenoid (open).  Remove power - The spring load on the latch pushes it back into place, and holds it.

If you rely solely on temporarily energizing magnets to pull the latch both ways it will never be secure.  Once the latch is engaged and the "locking magnet" is powered down the latch-rod is just resting in place.  I've seen a couple of projects like this: the first was defeated by using an external Neodymium magnet to move the rod out of the locked position.  The second just required banging with a hammer, until the vibration moved the latch-rod enough.

For your power you would normally use an AC-DC converter (yes, most electromagnets run off DC).  Pretty much all shapes and sizes; dependent upon what type of converter (full-wave, switching, etc.), what the max current output is, and power-factor correction.  For the solenoid system I mentioned above most are powered off the 120VAC doorbell circuit, in the U.S.

Amusing... Here is a clear case of getting the requirements established before deciding on a solution.  I think I am understanding the application you are attempting now.  My thinking, when you made your first statement, was that you needed both electromagnets operating at the same time, in which case they are connected in parallel. Instead, the application you described, the electromagnets operate independently.

Working toward the requirements, how big is this "iron bar", how far does it need to move, and how quickly does it need to get there.  This will establish how much power needs to be exerted by the electromagnet. When you determine how much power is required, then you can select a power source that matches the load. For a standard door type of deadbolt, mounted in a simple slide, you could probably get away with a basic wall plug type of supply.  The second part of the puzzle is the switching, to open and close the bolt. You could use a variety of switching components, like relays or transistors to rout the power to the correct electromagnet.

The other solution with a solenoid is also a good answer.

Jack

Amusing... Here is a clear case of getting the requirements established before deciding on a solution.  I think I am understanding the application you are attempting now.  My thinking, when you made your first statement, was that you needed both electromagnets operating at the same time, in which case they are connected in parallel. Instead, the application you described, the electromagnets operate independently.

Working toward the requirements, how big is this "iron bar", how far does it need to move, and how quickly does it need to get there.  This will establish how much power needs to be exerted by the electromagnet. When you determine how much power is required, then you can select a power source that matches the load. For a standard door type of deadbolt, mounted in a simple slide, you could probably get away with a basic wall plug type of supply.  The second part of the puzzle is the switching, to open and close the bolt. You could use a variety of switching components, like relays or transistors to rout the power to the correct electromagnet.

The other solution with a solenoid is also a good answer.

Jack