Thread: Building an electromagnet...

Ok, First of all, this is my first post, i hope you will forgive me if this has already been done but i searched electromagnet and there were far too many results that were nowhere near relevant to building them.

Now that that is out of the way here is what i have to do.

I have been challenged to build an electro magnet and to obtain the best mass of device:mass lifted ratio. So please note THIS IS ABOUT EFFICIENCY NOT TOTAL AMOUNT LIFTED.

Specs:
The electromagnet and weight (not sure about the battery and holder) may not exceed a diameter of 100mm (5 cm radius if that helps) and may not exceed a length of 50 cm.

the entire device including weight may not exceed 5kg.

No permanent magnets are allowed anywhere in the weight or device (except the inevitable remnant magnetization)

must be powered exclusively by AAA, AA, C, or D size non-rechargeable batteries (no car batteries). they must be alkaline flashlight batteries and lithium, nickel-cadmium or nickel-metal-hydride may not be used, from any source. TOTAL VOLTAGE MAY NOT EXCEED 30 Volts.

also, no part may exceed a temperature of 50C during or after the 10 second run.


MY thoughts/ questions.

I know that the electromagnet would work best with the most current pumping through it, would anybody recommend the best combination of batteries? (i.e. 20 1.5V batteries in series, with some amount in parallel to increase amperage)

Also, I know the core would perform best if bent into a U shape.

As for the Core metal itself. Would you recommend a simple soft iron? or maybe a bar of Neodymium that was heated past the curie point (it's fairly cheap nowadays) ? what would you recommend?

obviously i want the thing to be efficient so what would be the best wire to use (it will have to be able to carry the current without heating over 50C)

That is my challenge. Does anyone have any input? ANYTHING would be appreciated.

Thanks,
Gmano

The magnetic flux in your electromagnet will be proportional to the current and the number of turns (ampere-turns). In order to maximize the number of turns in the limited space of your magnet, you will want to use magnet wire. This is the kind of wire in thngs like loudspeakers and such and has very thin varnish insulation.

With no limit on the number of batteries you can use, you can get a lot of current out of your battery pack, so you will eventually be limited by the temperature rise. During the 10 second run, there won't be much heat dissipated to the air, or probably even much into the core. so it will mostly go into heating up the copper windings. Yoo can get a good estimate by designing a core, figuring the current based of voltage and winding resistance, then calculate the heat (volts times current times 10 seconds.) Use the mass of copper and its heat capacity to calculate temperature rise. Work back and forth until you find the right combination of volts, wire gauge and number of turns, then buy your wire Are you allowed to put it in the freezer first?

OMG! THANK YOU your freezer idea is pure genius! (the rule book acknowledges that winning teams will often be the ones that stretch the rules, however direct violations will be disqualified), not only would it increase the conductive properties, but it would give me a ridiculous amount of leeway in terms of the temperature limit!

Also, now that I think of it, would you recommend, A: bending the core into a horseshoe? OR using a larger diameter?.

Also, due to the fact that there is a saturation point for the Core a, in order to maximize the efficiency one needs A) a core big enough so as not to waste the wire or B) a very, very ferromagnetic metal (please, can anyone advise me on either soft iron vs. neodymium?)

Originally Posted by Gmano

OMG! THANK YOU your freezer idea is pure genius! (the rule book acknowledges that winning teams will often be the ones that stretch the rules, however direct violations will be disqualified), not only would it increase the conductive properties, but it would give me a ridiculous amount of leeway in terms of the temperature limit!

Also, now that I think of it, would you recommend, A: bending the core into a horseshoe? OR using a larger diameter?.

Also, due to the fact that there is a saturation point for the Core a, in order to maximize the efficiency one needs A) a core big enough so as not to waste the wire or B) a very, very ferromagnetic metal (please, can anyone advise me on either soft iron vs. neodymium?)

You can also get copper ribbon magnet winding, mail order over the Internet, instead of round wire or square wire bar. Pretty tough to heat that up in ten seconds.

Or make your own with copper sheet purchased locally from a roofing supply, or lumber yard. You will want to silver solder copper bar onto the ends of the sheet or ribbon. Or TIG weld the copper bar onto the sheet.
And you will have to coat it with a dielectric that can withstand some heat and bending. You can get that mail order, or Internet too.

The ribbon and bar, can take amperage. If you could make a capacitor, and pulse into and out of the capacitor, you could really get some serious power out of it. It probably is not worth the work to find solenoids or SCR switching devices large enough to handle it though.

And of course if you mess up, you could start to magneform objects near you. Ha-ha. I have been in a magnetic field when a capacitor blew up in a five horse power 220 volt air compressor motor. The effect is not comforting. Ha-ha.

Sincerely,


William McCormick

Ok, so I am still wondering as to what the best possible core would be.

A rod-shaped neodymium magnet is really easy to de-magnetize, would it then function as a very powerful core?

It is cheap and simple to do, but i am wondering if it will yield the most power possible.

Originally Posted by Gmano

Ok, so I am still wondering as to what the best possible core would be.

A rod-shaped neodymium magnet is really easy to de-magnetize, would it then function as a very powerful core?

It is cheap and simple to do, but i am wondering if it will yield the most power possible.

I would think silicon steel, is cheap and easy to get, and fairly light. But there are some nickle alloys that are supposed to make wild electromagnets, and they can be very light. But probably out of this world in price.

I do not know that a permanent magnet material is going to give you the best, electromagnet effect. Usually for an electromagnet you want something that will create a magnetic field and let it go.



Sincerely,


William McCormick

I don't care about remnant megnetization, also the power is DC, not AC therefore I don't have to worry about eddy currents, do I?

I am going to try to make this small and efficient so i want whatever core will have the highest saturation point.

again, Remnant magnetization is not a problem, I am simply looking for the highest saturation point and/or the lowest weight for its saturation.

So far I have suggestions, 1. Soft iron 2. Neodymium 3. electrical steel (the iron/silicon alloy) 4. Magnetite.

I really, really want to figure out the best core.

also, does making the core hollow effect the magnet (not air, i mean a hollow pipe of the metal)

Any suggestions welcome, thanks

Gmano

Edit: also, what would be the best way to wire it, I only need it to run for 10 seconds, should I wire in series? or hook up things in parallel? or run a bunch of batteries on separate circuits?

Originally Posted by Gmano

I don't care about remnant megnetization, also the power is DC, not AC therefore I don't have to worry about eddy currents, do I?

I am going to try to make this small and efficient so i want whatever core will have the highest saturation point.

again, Remnant magnetization is not a problem, I am simply looking for the highest saturation point and/or the lowest weight for its saturation.

So far I have suggestions, 1. Soft iron 2. Neodymium 3. electrical steel (the iron/silicon alloy) 4. Magnetite.

I really, really want to figure out the best core.

also, does making the core hollow effect the magnet (not air, i mean a hollow pipe of the metal)

Any suggestions welcome, thanks

Gmano

Edit: also, what would be the best way to wire it, I only need it to run for 10 seconds, should I wire in series? or hook up things in parallel? or run a bunch of batteries on separate circuits?

Professional magnets for lifting are made of a steel core.

Sincerely,


William McCormick

Originally Posted by Gmano

So far I have suggestions, 1. Soft iron 2. Neodymium 3. electrical steel (the iron/silicon alloy) 4. Magnetite.

I really, really want to figure out the best core.

I don't really know but suspect you won't do much better than iron. A bit of research on the internet should turn up some useful info.

also, does making the core hollow effect the magnet (not air, i mean a hollow pipe of the metal)

Yes it will adversely affect the magnetic permeability if you make it hollow.

Edit: also, what would be the best way to wire it, I only need it to run for 10 seconds, should I wire in series? or hook up things in parallel? or run a bunch of batteries on separate circuits?

I think I'd use the maximum allowable voltage. You are trying to maximize the ampere-turns. For any given wire gauge and length of wire, more voltage will give more current. OTOH, this will be limited by the temperature limit. Pick a wire gauge, calculate how much of that wire will fit in the space, then determine the resistance of that length of wire and the current with a given voltage. Play around with it and see what works best.
Wire enough cells in parallel so that the battery will not be drained too much during the 10 second run.

ok, thanks, so a soft iron core would work best?

now, for wiring the batteries.

I am restricted to AAA,AA,C, or D size. (all yeild 1.5 volts)

AAA will yeild the best power:mass ratio.

now, i forget my wiring. if i wire 8 of these in series, to produce 12 volts and then, for maximum amperage can i wire 8 in parallel?

looking like

| -B-B-B-B-B-B-B-B
| B
| B
| B
| B
| B
| B
| B
|-----------MAGNET (then complete the circuit)

would this yeild 13.5 V while at the same time yeilding 8x the amps (how many amps can a AAA battery produce anyways?)

Also, what is the best shape, (i dont want a U for the reason that i have a size limitation on it) would a toroidal core be best?

What you would have to do is wire 8 in series, then wire another 8 in series and connect the two series combinations in parallel. Add more strings of 8 in parallel with those for more current if needed.

The cells will have a current rating. You can probably find typical values on the internet, if not on the battery packaging.

You might find tha one string of larger cells works better than parallel strings of AA.

A toroid would be good but it would have to have an opening in it where you would put the metal object you are trying to pick up. If the toroid is a continuous circle, no magnetic field gets outside the toroid, or very little.

Ok, so Ive gotten a hold of a variable power supply, wires of various gauges, and an amm/ohm/voltmeter.

Now i just need to find the best core.

I have decided that i want the highest saturation, permeability is a plus, if i am to be efficient, i want to keep the weight down and avoid excess wire weighing me down.

I bought a variety of core materials, a couple big, zinc coated (i think)iron or steel spikes of various sizes, an old electric motor i took apart yeilded quite a weak electromagnet, and a bunch of aluminum wire, it had a core of what i can only assume is soft iron and various other odds and ends.

a couple of questions,

1. would the hot-dip of zinc reduce the effectiveness of my core?

2. I have a bunch of steel knitting needles lying around, do you think those would give me more efficiency than the big spike? They would certainly be lighter.. but the battery and switch would have much more impact.

3. do you think the spike is soft iron? or some other form (or even iron at all)

This wouldn't happen to be for the 2009 UBC Physics olympics???

Your description of what you magnet needs to be like is that exact same as what those rules say...

Originally Posted by Gmano

Ok, so Ive gotten a hold of a variable power supply, wires of various gauges, and an amm/ohm/voltmeter.

Now i just need to find the best core.

I have decided that i want the highest saturation, permeability is a plus, if i am to be efficient, i want to keep the weight down and avoid excess wire weighing me down.

I bought a variety of core materials, a couple big, zinc coated (i think)iron or steel spikes of various sizes, an old electric motor i took apart yeilded quite a weak electromagnet, and a bunch of aluminum wire, it had a core of what i can only assume is soft iron and various other odds and ends.

a couple of questions,

1. would the hot-dip of zinc reduce the effectiveness of my core?

2. I have a bunch of steel knitting needles lying around, do you think those would give me more efficiency than the big spike? They would certainly be lighter.. but the battery and switch would have much more impact.

3. do you think the spike is soft iron? or some other form (or even iron at all)

This is the strongest, smallest craziest magnet I ever built or saw. It will pick up steel either AC or DC. It is a design from the early 1900's. They really built stuff back then.

With a twelve volt DC supply that you could probably run from a single set of double "A" batteries, you could pick up a metal bar weighing about four or five pounds, using 1.44 watts and .12 amps.


http://www.Rockwelder.com/WMV/AlumEl...tromagent.html

Here are the basic plans for it. It is well worth building. I had a couple hours one day. So I just rolled up some zinc coated sheet metal, into a multi layer core. I think I tack welded it together, to create the tubular outer core.
I cut some copper washers to separate outer core from the inner, and hold the inner core. And I used a solid carbon steel center punch, as the inner core. And it is still a wild magnet.





I actually made a couple different ones that afternoon. This thing will pick up aluminum. That is how strong it is. If you make it better or wind it with more fitting wire, you can get much better results. I wound it for house current. I have a lot of winding in there. It is small wire. But a lot of turns.

One note of caution. The book warns of electrocution. And very high voltages being created by electromagnets. I agree. So use caution.



Sincerely,


William McCormick,

omg, thats awesome, and its not too heavy?

lemme get this straight, i make 2 core, 1 solid center core, which i wrap like normal, copper washers around that, and another outer core, also wrapped like normal (in the same direction as the first)?

where would be the best place to get these materials (i have the wire already)
and do the washers have to be copper?

OMG McCormick (Better known for spices) actually posted a real example of some of his bullshit I'm impressed. If only you would continue to do so.

Originally Posted by Gmano

omg, thats awesome, and its not too heavy?

lemme get this straight, i make 2 core, 1 solid center core, which i wrap like normal, copper washers around that, and another outer core, also wrapped like normal (in the same direction as the first)?

where would be the best place to get these materials (i have the wire already)
and do the washers have to be copper?

Just saw this sorry.

You just wrap the outer core. Not the inner core. It is a serious magnet, no kidding.

The copper washer just separates the two cores. I used a solid core, because making and laminating a center core seemed like to much work. I had a couple of hours one day, and that was the only way it was going to get done.

The outer core, I just took a piece of zinc coated sheet metal, about two inches wide and about fifteen inches long. And rolled it over and over itself. Then I tack welded it.

Popped in my washers, and center core. Which was a center punch. A center punch is a tool, for aligning holes in a template to a fresh piece of metal to duplicate the template.

Then I just wound the magnet with rather small wire. I believe it was in the twenties. Pretty light stuff. A lot of wind went into that. It is like a ball of yarn.

I do not know that a larger size will make it stronger. It should. And I believe it would. But if you pick a size, I will roll and weld you an outer core, and cut the copper washers and give you a center core. I have some oil hardening round rod here, that will probably make a neat center core. Just let me know. I can send it on Saturday, you will have it by Tuesday, by priority mail. No charge.

I only have #39 angle hair wire in quantity here. And some #10 and #12 wire. I will look around though.

Let me know.

The magnet weighs about two pounds I would say maybe a bit more. It is rather light.


Sincerely,


William McCormick

I had this thing fired up one day. And the magnet was more then two feet from any other metal object.

I put a penny under the magnet about six inches from the magnet. And the magnet moved towards the penny. I mean I had to really compensate for the gain in weight of the magnet.

The only thing I could think of was that two feet below in the mobile workbench on wheels there are a lot of "C" clamps made of steel. Now if the penny somehow connected the magnet to the "C" clamps that might make sense.

But still that is a long distance for such a small magnet to effect or be effected.



Sincerely,


William McCormick

Here is the web address of the reprinter of the book. He is interested in anyone that is interested in the magnet, or uses its technology in manufacture.

http://www.engr.uark.edu/899.php


Sincerely,


William McCormick