Powering 2 12V Electromagnets

Give us an idea of the electromagnets you are powering.

It realy depends on the magnets, but it could be either way.

as for OHM's law It's not bad, If you have any 2 given points, you can find the other 1.

Watts is a combination of Amps*voltage. And so If you have resistance, and voltage, you can find out how many amps you use.

That will tell you the size of PSU you will need, or if you will need 2.

In the blue(amps*resistance=volts)

In green    (volts\amps=resistance)

In yellow  (volts\resistance=amps)

watts= amps*volts.

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

Jack Chaney wrote:

 

12v supply for your power, and link the magnets in parallel.

I would agree

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

Then for my project, a solenoid seems like the way to go, I am seeing lots of variations in the design, would something like this work http://www.onlinecomponents.com/johnson-electric-195205230.html?p=43844222&utm_source=google&utm_medium=cpc&utm_campaign… ?  I could figure out how to power it, I am just not 100% sure what type of solenoid i am looking for

Ok, first, here is an idea if you just wish for something ready-made for this.

http://goo.gl/BUOHls

Here is an Arduino option also. Unlock Your Front Door Without Keys Using This DIY Keyfob Entry System « Hacks, Mods & Circuitry

To answer your question for the  solenoid, it is a push solenoid, that is when you energized it is designed to extend out.

Then when you power it down, it will retract. I myself would not like it to be set up so you would need it to have its primary position as "out".

In other words, I would not have it powered 90% of the time than powered down for a minute, then powered up.

Personally, I would have it set up mechanically so it would be off most of the time, then when I need to access "the door" it will power on, let me in, then back off again.

On a larger scale, what are you using to drive this set up as far as a Microcontroller, or, and Arduino board, or do you have something already in place in mind?

In my thinking, If I wanted to automate a front door, with a latch, and build everything myself. This is what I would do.

Here is whatI would do.

https://sway.com/EM98djLYBMpg0167

the lock is for my bedroom door, it is mostly for when people knock, instead of getting up and opening it, i can just unlock it from my desk,  I will use some sort of microcontroller, probably the arduino pro mini, then send a signal via an rf transmitter and receiver to a mosfet to let power go through, though I am very new to mosfets, transistors, etc. so i am not sure what the best way to switch on and of the power would be

You should never have an automatic lock on your bedroom door (especially if under 90 years old) for the following reasons:

1) It puts off visitors

2) In case of fire you will not be rescued

3) Everyone will think you are up to something they should snoop on

MK