Hi guys

I've just been recently been experimenting with making my own powerful electromagnets and I can't figure why my electromagnet soft iron rod core is weak, it can barely lift up a paperclip and it does heat up a little so current is definitely flowing through the coil. But I thought it would be much more powerful considering these specs I'm using:

1. Geometry of Rod Cylinder: Length 15.24cm Diameter 1.27cm

2. Soft Iron Purity (according to buyer) 99.8% - 99.9% so relative permeability should be around 5 000% - 100 000% more than air.

3. Wire is 38 AWG enameled single film insulation (0.101mm in diameter)

4. There's about 1500 turns around the rod making 1 full layer of wire wrapping and I insured the wire did not overlap once and it was wounded anti-clock wise all the way through and the amount of current I use it up to 130 mili amps with about 16 - 17 volts as the resistance is about 125 - 127 ohms in the coil at room temperature.

5. The gap distance from the wire bare to core is about 0.0045mm as insulation is very small on this type of wire.

6. Inductance according to calculator is around 2269 uH due to number of turns

7. I did not use any insulation cover on rod as thought it wasn't needed as I'm using DC current so there wasn't going to be any eddy current problems.

With that all being said I have a gut feeling it is something I have overlooked in order for the electromagnet to be weaker than my fridge magnet as I already stated I have current flowing through coil but the problem is I'm hardly getting any strong flux density. Any help and suggestions out there is appreciated and I'll keep experimenting in the mean time to see if I can discover what the problem is.

Thank you

 

Rod electromagnetics are relatively not as powerful since there is a large air gap between the polls located at each end of the rod.
To make a strong magnet it should be U shaped so that the poles are close together such as below:

 

Rod electromagnetics are relatively not as powerful since there is a large air gap between the polls located at each end of the rod.
To make a strong magnet is should be U shaped so that the poles are close together such as below:

View attachment 162575

Thank you for the quick reply, okay I'll test out the horse shoe setup and I'll report back on the results soon, although I'm still a bit surprised considering how weak it is though even though it is a rod considering how many total amps I was using in the amount of turns on the rod core. Is there a formula out there explaining the pole gap distance/density ratio?

 

If you have no inulation between the iron rod and the wire then maybe some turns are being shorted by connection to the rod?

 

Yes maybe I thought of that too which is why I'm also going make an electromagnet with some insulation around the core (just like on transformers). The insulation on the wire however can handle a lot more than 16 - 17 volts but all it takes is a bit of insulation wear down especially on 38 awg wire as it is so easy to break and more sensitive to temperature, for those reasons I'm considering using 27 awg wire that I also have with me, only small downside though is it will be less efficient then the 38 wire, but it's better to have it working the way I want rather than nothing at all. Will be posting in hours to come to say what the results are so others can hopefully learn from my mistakes.

 

Back in elementary school we took small single stranded wire and a nail and wrapped the wire around the nail a few dozen times then connected it to a "Dry Cell" battery. Could pick up small steel bearings (we called them "Steeley marbles") Probably around 3/8 inch diameter. Maybe you have too many windings. I'm certainly not the expert on electro-magnetism.

Once I took two relay coils. Powered one and read the voltage on the other when stacked one on top of the other. There wasn't much impressive voltage, but then I stuck a screwdriver down through the center, acting like a core and the voltage jumped up quite a bit. Voi-la. My very own variable transformer. Horribly inefficient, but in concept - - - .

You said around 126 ohms? 16.5 volts? Yeah, I agree, 130 mA. 2160 mW (2.16 watts). That doesn't sound very strong to me. Even at 100% efficiency - 2 watts to pick up a pick-up truck? Not gonna happen. (made up the pick-up truck part)

 

The kind of dry cell battery I refer to:

 

The magnetic field produced is proportional to the number of turns (N) and the current (I). The resistance of your winding is so high that you are not getting sufficient current. Definitely go to a heavier wire, even if it requires multiple layers. In fact, you may want to try limiting the length of the wiring and using 4-5 layers instead of a single layer.

 

Shorted turns don't matter at DC unless there are so many it reduces the turns count significantly. I've hand wound many transformers and toroid inductors (which require rather brutal treatment of the wire) for use at high frequency and never had a problem with a shorted turn. Modern magnet wire insulation is pretty tough stuff and the chances of damaging it in making a simple solenoid winding are very small. Something that could cause grief is a turn near the start and another near the end of the winding shorting to the conductive core. This is easily checked with an ohmmeter.
I have seen the insulation just flake off of "old" magnet wire. Bring back double cotton covered! (welllll ... maybe not - I don't know if it is even made anymore; if it is it is probably hideously expensive)

If your inductance is correct, the AL is just a little over 1 nanohenry per turn squared, which is very low. Something is wrong in the calculation.

I think you can find some useful info on rod core inductors (though in ferrite) at the Fair-Rite website.

 

Shorted turns don't matter at DC unless there are so many it reduces the turns count significantly. I've hand wound many transformers and toroid inductors (which require rather brutal treatment of the wire) for use at high frequency and never had a problem with a shorted turn. Modern magnet wire insulation is pretty tough stuff and the chances of damaging it in making a simple solenoid winding are very small. Something that could cause grief is a turn near the start and another near the end of the winding shorting to the conductive core. This is easily checked with an ohmmeter.
I have seen the insulation just flake off of "old" magnet wire. Bring back double cotton covered! (welllll ... maybe not - I don't know if it is even made anymore; if it is it is probably hideously expensive)

If your inductance is correct, the AL is just a little over 1 nanohenry per turn squared, which is very low. Something is wrong in the calculation.

I think you can find some useful info on rod core inductors (though in ferrite) at the Fair-Rite website.

 

I did more research over the past day on both the formula's and experiments I've been using and I did more experimenting with shorter but wider soft iron rod (dimensions are 10cm in diameter and 5cm in legnth) I've got the materials to be able to build custom core shapes that I want and I put about 2 layers of 27 awg wire this time (about 260 turns) around this time on the cylinder rod and I can tell you it a lot stronger then the longer rod experiment, I'm using about 1 amp with about 12 - 13 volts which is 12 - 13 watts compared to just over 2 watts before so it does take more power but it works much better than before but my next step is to build another cylinder with the same dimensions over the next couple days (as I got busy work schedule ahead of me and I'm limited on free time) and I'm going to put the two rod cylinders connected to a horse show setup with the air gap gap less than 0.5mm between the two poles and I should get even more interesting results as 'crutschow' pointed out long rods are not good at producing strong magnetic fields as they have too much of an air gap.

Also I worked out a formula over the past day explaining how much less power there is on the air gap between poles I figured that whatever the diameter width of the magnet is (example 1cm wide in diameter) the flux loses about half if it's potential over 4cm away (1 in 4 ratio = 1/2 flux pontential) and then if you muiltiply the 4cm by 3/4 (0.75) you will get 2cm then add 4cm + 2cm = 6cm so now when you're 6cm away the flux will lose another half of it's potential strength and it goes on and on from there. If that formula was applied to my 15.24cm long rod with a width of 1.27cm then you can quickly figure out why my flux strength was poor as the air gap 15.24cm away which means there's little trace of the flux power. The formula also explaines why my ring neodymium magnet is about able to pull about 50kg which is strong enough to pull over 50 knifes and forks from my kitchen and the dimensions on it are 6.5cm in width and only 1.5cm long and 2cm hole diameter and yet I've seen much more expensive neodymium magnets rods that cost more than my ring magnent and you're lucky to get 25kg of pulling force.

I've only put together that formula together in the past day and it seems to make logic sense how it works but if there are any experts who has worked with magnetism longer feel free to correct or add things to it that I've missed so far, I've only been putting things together from my own learning the past few months with this kind of stuff. I'll keep all of you updated in time to come on this thread with the different results I get from my experiments whenever I get the free to put it together.

Also I appreciate all of your replies and suggestions on what I can do to experiment with too guys!

 

Inverse square law. Cut the distance in half and you quadruple the power of the magnetic field. This is why you can't get magnets very close without them touching (when you hold them). The closer you get the stronger the pull. Same is true in all forms of energy. Take radiation for instance: Your exposure is X at - lets say - 10 feet. At 20 feet your exposure is 1/4X. At 5 feet your exposure is 4X.

The volume of a stereo is the same. Twice as loud takes four times the energy. That's why there's a limit to how loud a concert can be. Power requirements go up exponentially.

 

Rod type electromagnets only use one of the two available poles of the magnet. That is why lifting or pulling magnets are made in the "pot" style. Look at the electromagnets on a scrap yard crane or the magnetic work holding chucks for machining.
https://science.howstuffworks.com/electromagnet.htm