Electromagnet help

[Njguy]

After an hour of number crunching I think I got it.

22 Gauge wire at 120 loops per layer with 20 layers, = 2,400 loops. 20 layers will give me .5 inch of copper surrounding the 2" iron core. 2,400 loops = 1,200 feet of wire @ 19 ohms. It would actually be more than 19 ohms because I was too lazy to take into account that core diameter increases with each added layer. So I would prob need roughly ~1500 feet of wire = 24 ohms.

How the hell can I possibly spin that?

Screw it maybe Ill just use 20 gauge wire and a resistor/ potentiometer/ PWM.

 

[giftiger_wunsch]

How the hell can I possibly spin that?

A considerable supply of patience.

 

[Roff]

Here's an Excel solenoid calculator that I created some time ago. It accounts for the increasing turns length for each layer.
Copy and paste the appropriate AWG data from the table on the right into row 5, cols. C, D, and E. Put your coil form diameter into 5F, and the length into 5G. Remember that if you have a 3 inch rod, you might only have 2.8" (or whatever) for the coil length.
The ampere turns column is probably the most useful when comparing wire sizes, but also watch coil diameter, etc.

I don't think it has errors, but I could be wrong. I was once before.

EDIT: A cylindrical electromagnet is a solenoid. It doesn't have to have a movable core (armature).

 

[Roff]

You konw it's aubot tmie to sotp dnrkinig wehn enthreivyg lkoos liek tihs...

I hda a cuopel of gni & tnoics, adn I cna nwo raed tihs. I tihkn is't tiem to spot.

 

[giftiger_wunsch]

Awww you didn't get it. It's the way the brain processes words rather than letters - you can understand words no matter how jumbled up they are, as long as the first and last letters are the same (and the other letters are present in the correct numbers).

 

[Roff]

Awww you didn't get it. It's the way the brain processes words rather than letters - you can understand words no matter how jumbled up they are, as long as the first and last letters are the same (and the other letters are present in the correct numbers).

Well, I have seen similar stuff, and I could read it just fine. I forgot about the last letter needing to be the same - besides, after tee martoonis, who remembers rules?

 

[Mr RB]

Awww you didn't get it. It's the way the brain processes words rather than letters - you can understand words no matter how jumbled up they are, as long as the first and last letters are the same (and the other letters are present in the correct numbers).

?? I didn't notice anything different about it. I thought you were saying we should stop drinking when everything looks smiley

Back on topic, coil circumference is linear to coil radius, so average per-coil wire length is equal to the middle of the range of coil radius.

And the next one i'm gonna guess; the magnet like-poles repulsion is equal to the weaker magnet repulsion MINUS the magnetic attraction of the strong magnet to the core material of the weaker magnet. Ie if the weaker magnet is weak enough it's actually attracted to the stronger magnet.

 

[Njguy]

?? I didn't notice anything different about it. I thought you were saying we should stop drinking when everything looks smiley

Back on topic, coil circumference is linear to coil radius, so average per-coil wire length is equal to the middle of the range of coil radius.

And the next one i'm gonna guess; the magnet like-poles repulsion is equal to the weaker magnet repulsion MINUS the magnetic attraction of the strong magnet to the core material of the weaker magnet. Ie if the weaker magnet is weak enough it's actually attracted to the stronger magnet.

That's what I figured, but the core also becomes a magnet in itself when its domains are re-arranged under current.

 

[Mr RB]

If the weak magnet is weak enough, its field will just be reversed by the field of the strong magnet and it will act like a simple metal core.

 

[ericgibbs]

I'm wondering how you figured 20 gauge wire? I believe, that I need 2,660 feet of 20 gauge wire to achieve 27ohms. A bit much no? Almost a half mile.

It came from your requirement to run from a 12V battery and have a like wattage rating to the types shown in your link.

For a nominal 5Watt magnet at 12V its 0.41A, which is about 29R.

A copper wire gauge of 20swg will safely carry 0.5A.

 

[ericgibbs]

That's what I figured, but the core also becomes a magnet in itself when its domains are re-arranged under current.

This is how permanent magnets are made!

 

[Njguy]

Ok, so I made my magnet. I used 21 gauge wire (fair compromise I think), I wrapped it with roughly 18 layers. This gave me .5 inch of copper going all the way around the 2" diameter iron rod.

Now at first I hooked it up to a 9 volt battery. Cold to the touch, small attraction.

Then I hooked it up to a 12 volt battery, mind you I hooked it straight up so it should have been at full power. It's an old battery which I am sure isn't fully charged, but it still gave a larger inductive spark. Magnet was a little bit stronger, but still cold to touch????? How can it be cold at 12V full power? As it stands the magnet isn't nearly strong enough.

The Neodymium mags overpower the electromagnet and stick to the iron rod. I don't have an ammeter at the moment, but I am hoping that my problem is the result of crap batteries not giving the amps necessary. But I may need smaller iron rods. Anyone know how to get smaller ferrite rods? Dura-bar was the best I could find and 2" is smallest diameter.

 

[giftiger_wunsch]

Ok, so I made my magnet. I used 21 gauge wire (fair compromise I think), I wrapped it with roughly 18 layers. This gave me .5 inch of copper going all the way around the 2" diameter iron rod.

Now at first I hooked it up to a 9 volt battery. Cold to the touch, small attraction.

Then I hooked it up to a 12 volt battery, mind you I hooked it straight up so it should have been at full power. It's an old battery which I am sure isn't fully charged, but it still gave a larger inductive spark. Magnet was a little bit stronger, but still cold to touch????? How can it be cold at 12V full power? As it stands the magnet isn't nearly strong enough.

How long was the power connected for? I don't know how much heat is meant to be produced, but it's likely that it will only heat up slowly, especially given the size of the core.

 

[Mr RB]

I don't know how much current you were putting into the coil (and neither do you ) but 18 "layers" of wire is not many turns, maybe a few hundred?

It's unlikely you are generating much magnetic field at all in such a massive 2" diameter core of iron.

Where's the pictures?