Electromagnet help

Njguy · Aug 30, 2009

Hey guys, I have a few iron rods two inches in diameter by 3 inches long and I glued large heat sinks with thermal grease on the backs. I was wondering what kind of wire I should use to make it as efficient as possible. Its kind of confusing because I have read that thin wire plus more turns equals stronger magnet, but too thin equals too much resistance. I want to use a 12 volt battery. Any suggestions? Basically I'm looking for wire gauge and number of layers.

I have no idea how electromagnets such as these can be so strong but so small.
**broken link removed**

giftiger_wunsch · Aug 30, 2009

Well for 12 volts you shouldn't need particularly thick wire. You could try salvaging the wire from the secondary coil of a 12V transformer? That should give you a good compromise on number of turns vs. resistance.

I don't know how powerful the magnet's likely to be using a 12V battery, however. Also bear in mind that if the current is too high you may simply end up damaging the battery. I'm sure someone knows how to approximate magnetic field strength from the power and number of turns, etc.

If you google it, you may be able to find a field strength calculator or something; I've found plenty of little gadgets like this written in javascript using google.

ericgibbs · Aug 30, 2009

Njguy said:
Hey guys, I have a few iron rods two inches in diameter by 3 inches long and I glued large heat sinks with thermal grease on the backs. I was wondering what kind of wire I should use to make it as efficient as possible. Its kind of confusing because I have read that thin wire plus more turns equals stronger magnet, but too thin equals too much resistance. I want to use a 12 volt battery. Any suggestions? Basically I'm looking for wire gauge and number of layers.

I have no idea how electromagnets such as these can be so strong but so small.
**broken link removed**

hi,
Looking at the chart on your link, say the EM-R2, thats rated at 5.2Watts, so for a 12V battery that would be 0.43Amps, giving a coil resistance of 12v/0.43A = 27ohms.

A copper wire gauge of 18swg or 20swg would carry 0.43Amps.

Its important to note that the magnets shown in the links are most likely using high grade ferro materials and that the coil is inside the core.
So when the magnet is in contact with a ferrous surface the magnetic path loop is closed.
Your magnet will be very inefficient compared to those in the link.

Njguy · Aug 30, 2009

ericgibbs said:
hi,
Looking at the chart on your link, say the EM-R2, thats rated at 5.2Watts, so for a 12V battery that would be 0.43Amps, giving a coil resistance of 12v/0.43A = 27ohms.

A copper wire gauge of 18swg or 20swg would carry 0.43Amps.

Its important to note that the magnets shown in the links are most likely using high grade ferro materials and that the coil is inside the core.
So when the magnet is in contact with a ferrous surface the magnetic path loop is closed.
Your magnet will be very inefficient compared to those in the link.

I'm using G1A dura-bar which is a ferrite matrix for my cores. Dura-Bar | Continuous Cast Iron Bar Stock Leader and Steel Alternative

I guess I'll stick with 20 gauge from this site. Thats about what I was predicting to use.
Magnet Wire - $0.00

ericgibbs · Aug 30, 2009

Njguy said:
I'm using G1A dura-bar which is a ferrite matrix for my cores. Dura-Bar | Continuous Cast Iron Bar Stock Leader and Steel Alternative

I guess I'll stick with 20 gauge from this site. Thats about what I was predicting to use.
Magnet Wire - $0.00

At 5watts or so it going to fairly hot.
Dont forget to put a layer of insulation between the coil and ferrous former.

The link materials look ok to me. You need a very smooth face on the end of the bar.

Njguy · Aug 30, 2009

ericgibbs said:
At 5watts or so it going to fairly hot.
Dont forget to put a layer of insulation between the coil and ferrous former.

The link materials look ok to me. You need a very smooth face on the end of the bar.

3 quick questions
So then would 18 gauge wire keep it cooler?

Also I really have no idea what kind of insulation to put between the wire and the bar.

How fast do you think it would drain your average 12 volt car battery?

I'm back and forth between 20 gauge and 18. Not sure which one I should go for. It's a balancing act.

giftiger_wunsch · Aug 30, 2009

Njguy said:
How fast do you think it would drain your average 12 volt car battery?

I believe a lot of car batteries are around 120AH, and this is 0.43A, so a car battery should be able to run it for at least a few days. I could be wrong about the capacity though so best to check the capacity of whatever you're planning on using.

I'd imagine the voltage will drop too low to be of use a considerable time before the entire capacity is used, also.

Mr RB · Aug 30, 2009

Have you got a complete magnetic path? Or as you just expecting something to stick hard to the end of your electromagnet rod??

ericgibbs · Aug 31, 2009

Njguy said:
3 quick questions
So then would 18 gauge wire keep it cooler?
If you wanted to have the 0.43A at 12V posted earlier, which is about 27R then using 18swg as opposed to 20swg would mean more turns to get the same resistance.

Also I really have no idea what kind of insulation to put between the wire and the bar.
Ideally it would be a plastic former, which could be prewind and then slipped over the core. A layer of thick paper would be better than having the enamelled copper wire wound directly on the core.

How fast do you think it would drain your average 12 volt car battery?
If you had a 60AHr battery in good condition and fully charged, a rough guide would be 60/0.43 = 130hrs,, say about 100 hours,

I'm back and forth between 20 gauge and 18. Not sure which one I should go for. It's a balancing act.

I would suggest 20swg and use a plastic former which fits tightly over the core.

Your magnet will be very inefficient compared to those in the link, as I understand it, yours is only a 'bar' magnet.!

What exactly are you planning to use this magnet for.??

Njguy · Aug 31, 2009

ericgibbs said:
I would suggest 20swg and use a plastic former which fits tightly over the core.

Your magnet will be very inefficient compared to those in the link, as I understand it, yours is only a 'bar' magnet.!

What exactly are you planning to use this magnet for.??

Well those magnets are bi-pole magnets. Mine is di-pole because I need it for repulsion.

giftiger_wunsch · Aug 31, 2009

I've found the best way to achieve repulsion is to stop showering for a while.

Sorry I couldn't resist that

Njguy · Aug 31, 2009

giftiger_wunsch said:
I've found the best way to achieve repulsion is to stop showering for a while.

Sorry I couldn't resist that

Shower bit aside, is there truth in that statement?

Njguy · Aug 31, 2009

Here is a serious question. Does magnetic repulsion equal the weakest magnet, or is it in combination of the two?

I have a 230 lb Neo-mag, and if I have an electromag that repulses around 5lbs at a 1 cm gab, would it only be a 5 lb repulsion against the Neo, or are they added or combine in some way?

ericgibbs · Aug 31, 2009

Njguy said:
Here is a serious question. Does magnetic repulsion equal the weakest magnet, or is it in combination of the two?

I have a 230 lb Neo-mag, and if I have an electromag that repulses around 5lbs at a 1 cm gab, would it only be a 5 lb repulsion against the Neo, or are they added or combine in some way?

hi,
For repulsion I would say it would be the sum of both magnets.
I'm assuming you are talking forcing the opposing poles towards each other.???

Im curious to know what you are going to do with the electromagnet, whats the purpose of the repulsion.?

Vizier87 · Aug 31, 2009

You want to build a magnetic-gun or what?
Okay... Last time I built a generator using neo-mags (out of hard-drives).. There are stator coils and the neo-mags turns, and a small supply of 3V on one of the coils made the armature turn real violent, at least for a few degrees of turn.

You can make your static magnets repulse the energized coil by stacking a waaaaay lot of those neo-mags and one small but efficient coil, I suppose.
~shrug~

Njguy · Aug 31, 2009

ericgibbs said:
hi,
Looking at the chart on your link, say the EM-R2, thats rated at 5.2Watts, so for a 12V battery that would be 0.43Amps, giving a coil resistance of 12v/0.43A = 27ohms.

A copper wire gauge of 18swg or 20swg would carry 0.43Amps.

Its important to note that the magnets shown in the links are most likely using high grade ferro materials and that the coil is inside the core.
So when the magnet is in contact with a ferrous surface the magnetic path loop is closed.
Your magnet will be very inefficient compared to those in the link.

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.

giftiger_wunsch · Aug 31, 2009

The more turns the better!

giftiger_wunsch · Aug 31, 2009

Vizier87 said:
You want to build a magnetic-gun or what?

I believe the correct term for such a device is a rail-gun, is it not?

Edit: Or a coilgun, depending on the design.

Njguy · Aug 31, 2009

giftiger_wunsch said:
I believe the correct term for such a device is a rail-gun, is it not?

Edit: Or a coilgun, depending on the design.

Its not anything exciting at the moment, I'm just trying to create the most efficient electromagnet I can. But seriously I think ill have to choose a higher gauge. 24 to 26 gauge.

giftiger_wunsch · Aug 31, 2009

Just make sure the wire can handle the power, and also remember that a lot of heat may be produced due to the resistive effects of thin wire. You probably won't have any problems with 24-26AWG wire though (I think?)

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