Multiple layer coil windings on an electromagnet

[EdFred]

I can't find a straight answer in any article on this so I'm asking here.

I've started construction of a pretty hefty electromagnet but it is not strong enough and the answer is more windings (already running off a 36V golf cart battery charger) on my coil by winding multiple layers. My core is about an 18" x 1.5" dia rod and I have turned one layer of wire on it and it works awesome, but not awesome enough. The first layer starts at the left end of the core and winds toward me at the bottom and away from me at the top and works its way to the right end where I have a tail to complete the circuit.

So my question is when I start my second layer do I:

Wind even layers from right to left and keep the winding toward me at the bottom and away from me at the top, and odd layers left to right or,

When I finish the each layer run the wire directly back to the left end (no winding) and then wind again left to right (like how a typewriter works: wind wind wind wind wind return wind wind wind wind return...), or

Use multiple individual wires with each layer being a single wire winding left to right and then solder the ends together.

Why am I making this? I had the materials laying around but also want to use it to to grab nails, screws, what not that end up in my fire pit because people dont listen and toss wood in there that has all this crap in it. Oh and really now its just to see how strong I can make it and at what distance I can get it to pull from.

It currently (get it?) will pull a box wrench from about 8" away.

 

[Doug Reid]

You can attach the coil form to a drill motor and wind enamel coated wire back and forth like a bobbin. I am not sure how many turns you will require...you can find more info online re: wire gage, resistance, current. Be careful.

 

[EdFred]

Thanks Doug it seemed like a bobbin style would be the way to go but nothing I found explicitly said that's how it should be done.

 

[Spring Ford]

You wind round and round and round until done. It doesn't matter if you lead the wire out to make a join and then back in. Wire parallel to the axis of the coil or normal (perpendicular) to the axis does not contribute the the magnetic field.

It is critical to wind in the same direction. Reverse winding will cancel out some of the forward winding. If you wind half one way and half the other you will get zero mag. field.

As i recall, the field depends on the current and the number of turns.

 

[EdFred]

36VDC at 60 or 100A. I forget the amperage, I just know it was way more than I thought it was going to be. Yeah, looking from the end of the core I will always wind it either CW or CCW, and the wire will just move towards or away from me. I've got a few hundred feet of wire. Will probably coil a few layers, test, splice, and coil some more.

 

[Crashnburn]

You wind round and round and round until done. It doesn't matter if you lead the wire out to make a join and then back in. Wire parallel to the axis of the coil or normal (perpendicular) to the axis does not contribute the the magnetic field.

It is critical to wind in the same direction. Reverse winding will cancel out some of the forward winding. If you wind half one way and half the other you will get zero mag. field.

As i recall, the field depends on the current and the number of turns.

Correct. Proportional to the current, and proportional to the square of the number of turns.

So, with the same voltage, if you double the number of turns, and thus resistance, you get half the current, but the turns squared factor will give you twice the original strength. If you double the voltage, to keep the current constant, you'll get 4X the original strength.

 

[EdFred]

I ended up winding down and back a few times, and this thing is pretty damn strong. Might go a few more turns because, well, I've got the wire.

 

[jsstevens]

I ended up winding down and back a few times, and this thing is pretty damn strong. Might go a few more turns because, well, I've got the wire.

Spoken like Tim the Tool Man Taylor.

 

[ElPaso Pilot]

I can't find a straight answer in any article on this so I'm asking here.

… Oh and really now its just to see how strong I can make it and at what distance I can get it to pull from.

It currently (get it?) will pull a box wrench from about 8" away.

Woo hoo!!

Working in Med Device, we had to be really careful with anything that could end up in the room with an MRI machine. Those magnets are incredible, and will suck O2 cylinders, floor buffers, chairs, and anything else ferrous across the room at huge velocities. Through anything and anyone in the way.

Plus, they don’t just turn off easily. Quenching the superconducting magnets is an expensive proposition.

http://www.simplyphysics.com/mri_safety.html