I have the electromagnetic fear...

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poutpout

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Hi!

I have bought two electromagnets 12V. I wanted to try them by connecting on a simple 9V battery. The guy who sold me the electromagnets wrote me " Don't forget the back emf diode". Now that I know what a back emf is, I'm afraid to try my electromagnets.

Can I plug the electromagnet directly to the battery without any damage for me and/or the battery or I need to make a circuit with a transistor and a diode?

Thanks!
poutpout
 
To connect to a battery directly you don't need anything, the diode is to protect a transistor if you use one to switch it.
 
Thanks for your reply!

So, it is not dangerous for me or for an example my computer? Because I've red that sometimes the power can be so high, it makes an arc. Does this happen with 12V electromagnets?

I really got the electromagnetic "fear"...
 

Just make sure you are not touching both ends of the coil when you make/break the circuit.

The back emf can be high and give an unpleasant shock.
 
Use the diode if you use a computer port to switch the magnets on/off. Better still use an opto coupler circuit.
 
Thanks a lot for your reply!

Ok, now. I have 9 electromagnets and I'd like to change polarity of them, like switching A-to-B_B-to-A and at a different speed for each electromagnet. What do you suggest? Where can I find a schematic somewhere?

Thanks again!
poutpout

btw: I don't understand why an optocoupler...
 

Hi,
I dont think you will find an existing schematic for that function, its a little unusual.

What is the purpose of switching the magnets in this way.?

I think the opto coupler was in cas you used a PIC pin to drive the coils [using a transistor]
 
What is the purpose of switching the magnets in this way.
Click to expand...

I will take paperclips for an example. What I want to do is moving paperclips up (vertival) and down (horizontal) and at a variable speed, kind of like "Push" "Pull" attraction/action. It is for a sound installation.
 
ericgibbs said:
Just make sure you are not touching both ends of the coil when you make/break the circuit.

The back emf can be high and give an unpleasant shock.
Click to expand...
Lol, I've done that before with home made electromagnets.

I imagine that a large electromagnet carrying a large current could even kill.
 
poutpout said:
Thanks a lot for your reply!

Ok, now. I have 9 electromagnets and I'd like to change polarity of them, like switching A-to-B_B-to-A and at a different speed for each electromagnet. What do you suggest? Where can I find a schematic somewhere?
Click to expand...

The circuit you would need is an H-Bridge. You would need one for each magnet. Unless every other magnet always had the same polarity as you switched, then you would need only two.

Ken
 
The circuit you would need is an H-Bridge. You would need one for each magnet
Click to expand...
Oh, thank you! I just did a reserach over the net and I have found a lot of H Bridge, do you have one in mind? One of course who have the diode protection...

Thanks!
 
poutpout said:
Oh, thank you! I just did a reserach over the net and I have found a lot of H Bridge, do you have one in mind? One of course who have the diode protection...

Thanks!
Click to expand...

You say they are 12Vdc, what is the resistance of the coil or the current rating.?
 
flat5 said:
Use the diode if you use a computer port to switch the magnets on/off. Better still use an opto coupler circuit.
Click to expand...

If you use an optocoupler, you will still need the diode to protect the optocoupler, unless you can verify that it has protection built in. Simple ones don't. (Note that I'm not positive that any optos have back EMF protection built in; I'm just guessing that there may be some out there which do.)


Torben
 
You say they are 12Vdc, what is the resistance of the coil or the current rating.?
Click to expand...
Sorry, I don't know. I don't have multimeter but I have the Data Sheet maybe it will help?
**broken link removed**
 
Those electromagnets are for DC and might not work with audio.
An H-bridge also is not for audio but might make a buzzing sound.
They draw a fairly high current and will kill a little 9V battery in a couple of minutes.
 
poutpout said:
... I have 9 electromagnets and I'd like to change polarity of them, like switching A-to-B_B-to-A and at a different speed for each electromagnet. ...
Click to expand...

poutpout,

If you're assuming that reversing the polarity on these electromagnets will change them from a pull movement to a push movement of the armature, you are mistaken. Either polarity will result in the armature being pulled into the magnet. They would only attract-vs-repel a PM magnet or another electromagnet. Or, am I missing your intended operation?

Ken
 
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I think the energy in an inductor is (1/2) L (I^2).
You need at least one joule to kill.
The trick may be measuring the inductance for this coil.
That's another post.
 
First, I want to thank you for keep going answering. I really really really appreciated it!

You are totally right! I've just tried with a DPDT switch and the armature is, either polarity, being pulled into the magnet. I am devastated!!!

Ok, I'll show where I take my inspiration. Of course, it is the first start of my idea. I have something else in my head.
[]
He wrote: Direction of currents for each magnets can be controlled individually from Pc. And magnetic field from electromagnets make paper clips move, and they create sound. When I play with this stuff, I control them randomly.

How does he do that?

Thanks!
 
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from the clip, it looks just like turning the magnets on and off, nothing else, when magnet is on the clip is attracted and "raise from surface" a bit, when he turn magnet off, the clip "fall down" on the surface .. if the clips get magnetised the reverse polarity of the magnet would repel them from the magnet and as you see on the video, they stay on same place...

if you want to attract / repel using different polarity, you will have to use permanent magnet as material for object you want to attract/repel.

The usual way push/pull movement is made (in locks for example) is that one force is doing the push and other one is doing the pull (for example, magnetic force produced by electro magnet is used to pull the piston and elastic force produced by spring is used to push the piston). This is exactly what this video shows, the one force is magnetic and the other one is gravity
 
Cute!

OK what you are see is:
1: paper clip pieces laying down (due to gravity) or standing up, aligning themselves with the magnetic field above the pulsing electromagnets.
2: paper clips pieces aligning themselves with the magnetic fields of adjacent, but opposite polarity electromagnets.
3: paper clip pieces, that over time may become permanently magnetized, and be attracted or repelled by the changing polarity of the fields of the electromagnets.

So, you are still on the right track for that display.

added...Looks like arhi beat me.

Ken
 
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